BTI’s Guide to Membrane Switch Design | Create Reliable Interfaces
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Aug 28, 2025
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About This Presentation
Discover key design practices for building durable, space-saving membrane switches that enhance usability and performance across multiple industries. From graphic overlays and tactile domes to waterproof sealing and advanced backlighting, this guide highlights everything you need to create reliable ...
Slide Content
The Ultimate
Membrane Switch
Design Guide
Membrane Switch
Design Guide
Table of Contents
2
Introduction 3
Butler Technologies, Inc. 3
What is a Membrane Switch? 3
Components of a Membrane Switch 4
Membrane Switch Layers 4
Layers: Graphic Overlay 5
Purpose 5
Material 5
Material Characteristics Table 6
Imaging & Decorating Options 7
Color Matching 8
Embossing & Forming of Features 9
Layers: Dome Retainer / Upper Circuit 13
Tactile vs. Non-Tactile Switches 13
Layers: Circuit Layer 16
Purpose 16
Types & Materials 16
Electrical Layout 17
Circuit Flex Tails 21
Terminations and Connections 22
Shielding 23
Surface Mounted Devices (SMD) 24
Lighting 24
Layers: Rear (Mounting) Adhesive 27
Adhesive 27
Water Tight Designs 28
Perimeter Seal 29
Back Panels 31
Membrane Switch Specifications 32
2
Introduction 3
Butler Technologies, Inc. 3
What is a Membrane Switch? 3
Components of a Membrane Switch 4
Membrane Switch Layers 4
Layers: Graphic Overlay 5
Purpose 5
Material 5
Material Characteristics Table 6
Imaging & Decorating Options 7
Color Matching 8
Embossing & Forming of Features 9
Layers: Dome Retainer / Upper Circuit 13
Tactile vs. Non-Tactile Switches 13
Layers: Circuit Layer 16
Purpose 16
Types & Materials 16
Electrical Layout 17
Circuit Flex Tails 21
Terminations and Connections 22
Shielding 23
Surface Mounted Devices (SMD) 24
Lighting 24
Layers: Rear (Mounting) Adhesive 27
Adhesive 27
Water Tight Designs 28
Perimeter Seal 29
Back Panels 31
Membrane Switch Specifications 32
Introduction
Butler Technologies, Inc.
Prototyping and full-scale manufacturing
Headquartered in Western Pennsylvania,
Butler Technologies, Inc. (BTI) was founded in
1990 as a human machine interface company
and has grown its product offerings to include
printed electronic products. As a manufactur-
ing facility, BTI plays a vital role as a develop-
er, helping clients turn ideas and needs into
functional product, with our proof-of-concept
development, prototyping and R&D activities.
Butler Technologies, Inc. is committed to
delivering the highest-quality membrane
switches on the market. If your company
requires a custom-designed membrane
switch, whether as a standalone product or
part of a larger concept, BTI has a solution for
you. If you would like to learn more about our
collaborative design process, rigorous quality
standards, and competitive pricing, give us a
call today.
We produce quality membrane switches and
keypads for a variety of industries including
home healthcare, medical devices, fire & safety
equipment, and industrial controls.
What is a Membrane Switch?
Membrane switches are a great option for
designers looking for a highly functional
and cost-effective means for a user to
interface with a device. Because they
typically incorporate screen printed circuitry
and low-profile components, membrane
switches are more economical and utilize
less design space than rigid circuit boards
and mechanical buttons. Membrane switches
can be designed for moisture, chemical, and
abrasion resistance making them easy to clean
and therefore ideal for medical devices and
industrial controls.
3
Butler Technologies, Inc.
Prototyping and full-scale manufacturing
Headquartered in Western Pennsylvania,
Butler Technologies, Inc. (BTI) was founded in
1990 as a human machine interface company
and has grown its product offerings to include
printed electronic products. As a manufactur-
ing facility, BTI plays a vital role as a develop-
er, helping clients turn ideas and needs into
functional product, with our proof-of-concept
development, prototyping and R&D activities.
Butler Technologies, Inc. is committed to
delivering the highest-quality membrane
switches on the market. If your company
requires a custom-designed membrane
switch, whether as a standalone product or
part of a larger concept, BTI has a solution for
you. If you would like to learn more about our
collaborative design process, rigorous quality
standards, and competitive pricing, give us a
call today.
We produce quality membrane switches and
keypads for a variety of industries including
home healthcare, medical devices, fire & safety
equipment, and industrial controls.
What is a Membrane Switch?
Membrane switches are a great option for
designers looking for a highly functional
and cost-effective means for a user to
interface with a device. Because they
typically incorporate screen printed circuitry
and low-profile components, membrane
switches are more economical and utilize
less design space than rigid circuit boards
and mechanical buttons. Membrane switches
can be designed for moisture, chemical, and
abrasion resistance making them easy to clean
and therefore ideal for medical devices and
industrial controls.
3
Components of a Membrane Switch
Membrane Switch Layers:
1. Graphic Overlay • This is the layer that the user interacts with
when pushing switches (buttons/keys), viewing indicator LEDs, or
when reading the display. Made of polyester or polycarbonate,
overlays can be screen or digitally printed to your graphical
specifications. Typically, the overlay consists of printed letters,
symbols, and icons to indicate areas of functionality. Embossed
features may be added to enhance tactile feel.
2. Graphic Adhesive • Usually fabricated from a pressure-sensitive
adhesive, this layer bonds the graphic overlay to the next layer.
3. Dome Retainer / Upper Circuit Layer • The dome retainer is
typically fabricated from thin, flexible polyester film and serves
to keep the metal domes in place in the Z-direction. The upper
circuit can function (1) as a shielding layer (Static / EMI / RFI) which
also holds the metal domes in place or (2) as the top circuit that
contains shorting pads and/or conductive traces. Typically, non-
tactile switch designs utilize an upper/top circuit while tactile
switch designs utilize the dome retainer.
4. Dome Spacer / Circuit Spacer Layer • The spacer adhesive layer
is used to keep the metal domes in place in the X and Y-directions
and to maintain separation between the upper and lower circuit
layers until the switch is depressed by the user.
5. Lower Circuit Layer • This layer contains the printed circuitry
and is the surface on which the metal domes rest and the surface
mount devices (LEDs, resistors, etc.) are attached. Typically, the
conductive circuitry is printed using silver, carbon, and dielectric
inks but can also be constructed from flexible or rigid copper
boards for more demanding applications.
6. Rear (Mounting) Adhesive Layer • A layer of acrylic-based
pressure sensitive adhesive that is used to bond the membrane
switch to the device or backer layer.
7. Rigid Backer • Fabricated from aluminum, steel, or plastic; this
layer provides support to the membrane switch and serves as a
method to bond the assembly to the customer’s device. In most
cases, this layer contains mounting hardware such as PEM® studs
or standoffs.
4
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2
3
4
5
6
7
Figure 1
Membrane Switch Layers:
1. Graphic Overlay • This is the layer that the user interacts with
when pushing switches (buttons/keys), viewing indicator LEDs, or
when reading the display. Made of polyester or polycarbonate,
overlays can be screen or digitally printed to your graphical
specifications. Typically, the overlay consists of printed letters,
symbols, and icons to indicate areas of functionality. Embossed
features may be added to enhance tactile feel.
2. Graphic Adhesive • Usually fabricated from a pressure-sensitive
adhesive, this layer bonds the graphic overlay to the next layer.
3. Dome Retainer / Upper Circuit Layer • The dome retainer is
typically fabricated from thin, flexible polyester film and serves
to keep the metal domes in place in the Z-direction. The upper
circuit can function (1) as a shielding layer (Static / EMI / RFI) which
also holds the metal domes in place or (2) as the top circuit that
contains shorting pads and/or conductive traces. Typically, non-
tactile switch designs utilize an upper/top circuit while tactile
switch designs utilize the dome retainer.
4. Dome Spacer / Circuit Spacer Layer • The spacer adhesive layer
is used to keep the metal domes in place in the X and Y-directions
and to maintain separation between the upper and lower circuit
layers until the switch is depressed by the user.
5. Lower Circuit Layer • This layer contains the printed circuitry
and is the surface on which the metal domes rest and the surface
mount devices (LEDs, resistors, etc.) are attached. Typically, the
conductive circuitry is printed using silver, carbon, and dielectric
inks but can also be constructed from flexible or rigid copper
boards for more demanding applications.
6. Rear (Mounting) Adhesive Layer • A layer of acrylic-based
pressure sensitive adhesive that is used to bond the membrane
switch to the device or backer layer.
7. Rigid Backer • Fabricated from aluminum, steel, or plastic; this
layer provides support to the membrane switch and serves as a
method to bond the assembly to the customer’s device. In most
cases, this layer contains mounting hardware such as PEM® studs
or standoffs.
4
1
2
3
4
5
6
7
Figure 1
Layers: Graphic Overlay
Purpose
In most cases, the layer of a membrane switch
that the operator interfaces with is the Graphic
Overlay, typically made from polyester or
polycarbonate film.
However, there are other options, most
notably, a silicone rubber keypad or a silicone
rubber keypad combined with a graphic
overlay.
In this section, the design options for both
graphic overlays and silicone rubber keypads
will be discussed.
Material
As noted above, the graphic overlay is
typically fabricated using polyester (PET)
or polycarbonate (PC) film, however, a
polycarbonate (PC) & Pocan (PBT) blended
material provides its own unique set of
characteristics borrowing traits from both PET
and PC films. Product designers can choose
from a variety of surface finishes, imaging
techniques, and embossed or thermoformed
features providing both aesthetic and
functional benefits.
Based on the typical qualities that make a good
overlay material (actuation life and chemical
& abrasion resistance), polyester is the ideal
substrate and is most commonly used on
membrane switches.
For good tactile feedback in your membrane
switch, the ideal graphic overlay material
thickness ranges from 0.006” (0.15mm) to
0.008” (0.20mm). However, 0.010” (0.25mm)
material is not uncommon for applications
with large, unsupported viewing windows or
where greater embossing height is required.
5
Purpose
In most cases, the layer of a membrane switch
that the operator interfaces with is the Graphic
Overlay, typically made from polyester or
polycarbonate film.
However, there are other options, most
notably, a silicone rubber keypad or a silicone
rubber keypad combined with a graphic
overlay.
In this section, the design options for both
graphic overlays and silicone rubber keypads
will be discussed.
Material
As noted above, the graphic overlay is
typically fabricated using polyester (PET)
or polycarbonate (PC) film, however, a
polycarbonate (PC) & Pocan (PBT) blended
material provides its own unique set of
characteristics borrowing traits from both PET
and PC films. Product designers can choose
from a variety of surface finishes, imaging
techniques, and embossed or thermoformed
features providing both aesthetic and
functional benefits.
Based on the typical qualities that make a good
overlay material (actuation life and chemical
& abrasion resistance), polyester is the ideal
substrate and is most commonly used on
membrane switches.
For good tactile feedback in your membrane
switch, the ideal graphic overlay material
thickness ranges from 0.006” (0.15mm) to
0.008” (0.20mm). However, 0.010” (0.25mm)
material is not uncommon for applications
with large, unsupported viewing windows or
where greater embossing height is required.
5
Layer: Graphic Overlay
6
Materials Common
Gauges for
Graphic
OVerlays
Outdoor Use Applications
Chemical
Resistance
Abrasion
Resistance
Embossable
Topside
Selective
Texturable
Actuation Life
Velvet Texture
Polycarbonate
0.007” / 0.010” Poor* Very Good
•
Good
(50K+)
Fine-Velvet Texture Polycarbonate0.007” / 0.010” Poor* Very Good
•
Good
(50K+)
Gloss Hardcoat Polycarbonate 0.007” / 0.010” Very Good Very Good
• •
Good
(50K+)
Gloss Weatherable Hardcoat
Polycarbonate
0.007” / 0.010”
•
Very Good Very Good
Not Ideal
(LED Windows Only)
Good
(50K+)
Anti-Glare
Hardcoat Polycarbonate
0.007” / 0.010” Very Good Very Good
• •
Good
(50K+)
Matte
Hardcoat Polycarbonate
0.007” / 0.010” Very Good Very Good
• •
Good
(50K+)
Weatherable Matte
Hardcoat Polycarbonate
0.007” / 0.010”
•
Very Good Very Good
Not Ideal
(LED Windows Only)
Good
(50K+)
Velvet Texture
Hardcoat Polyester
0.006” / 0.008” /
0.010”
Excellent Excellent
•
Window Clearing
& Gloss Effects
Excellent
(1M+)
Weatherable Velvet Texture
Hardcoat Polyester
0.006” / 0.008”
•
Excellent Excellent
Not Ideal
(LED Windows Only)
Excellent
(1M+)
Fine-Velvet Texture
Hardcoat Polyester
0.006” / 0.007”
0.008” / 0.010”
Excellent Excellent
•
Window Clearing
& Gloss Effects
Excellent
(1M+)
Weatherable Fine-Velvet Texture
Hardcoat Polyester
0.008”
•
Excellent Excellent
Not Ideal
(LED Windows Only)
Excellent
(1M+)
Gloss
Hardcoat Polyester
0.007” / 0.010” Excellent Excellent
• •
Excellent
(1M+)
Weatherable Gloss
Hardcoat Polyester
0.007”
•
Excellent Excellent
Not Ideal
(LED Windows Only)
Excellent
(1M+)
Anti-Glare
Hardcoat Polyester
0.007” / 0.010” Excellent Excellent
• •
Excellent
(1M+)
Matte
Hardcoat Polyester
0.007” Excellent Excellent
• •
Excellent
(1M+)
Brushed (S.S.) Texture
Hardcoat Polyester
0.006” / 0.008” Excellent Excellent
•
Window Clearing
& Gloss Effects
Excellent
(1M+)
Fine Velvet Texture Blend 0.007” / 0.010” Good* Excellent
•
Very Good
(100K+)
Weatherable Velvet Texture Blend0.007” / 0.010”
•
Good** Very Good
•
Very Good
(100K+)
*Fair chemical resistance to
household cleaners
**Resistant to gasoline &
household cleaners
6
Materials Common
Gauges for
Graphic
OVerlays
Outdoor Use Applications
Chemical
Resistance
Abrasion
Resistance
Embossable
Topside
Selective
Texturable
Actuation Life
Velvet Texture
Polycarbonate
0.007” / 0.010” Poor* Very Good
•
Good
(50K+)
Fine-Velvet Texture Polycarbonate0.007” / 0.010” Poor* Very Good
•
Good
(50K+)
Gloss Hardcoat Polycarbonate 0.007” / 0.010” Very Good Very Good
• •
Good
(50K+)
Gloss Weatherable Hardcoat
Polycarbonate
0.007” / 0.010”
•
Very Good Very Good
Not Ideal
(LED Windows Only)
Good
(50K+)
Anti-Glare
Hardcoat Polycarbonate
0.007” / 0.010” Very Good Very Good
• •
Good
(50K+)
Matte
Hardcoat Polycarbonate
0.007” / 0.010” Very Good Very Good
• •
Good
(50K+)
Weatherable Matte
Hardcoat Polycarbonate
0.007” / 0.010”
•
Very Good Very Good
Not Ideal
(LED Windows Only)
Good
(50K+)
Velvet Texture
Hardcoat Polyester
0.006” / 0.008” /
0.010”
Excellent Excellent
•
Window Clearing
& Gloss Effects
Excellent
(1M+)
Weatherable Velvet Texture
Hardcoat Polyester
0.006” / 0.008”
•
Excellent Excellent
Not Ideal
(LED Windows Only)
Excellent
(1M+)
Fine-Velvet Texture
Hardcoat Polyester
0.006” / 0.007”
0.008” / 0.010”
Excellent Excellent
•
Window Clearing
& Gloss Effects
Excellent
(1M+)
Weatherable Fine-Velvet Texture
Hardcoat Polyester
0.008”
•
Excellent Excellent
Not Ideal
(LED Windows Only)
Excellent
(1M+)
Gloss
Hardcoat Polyester
0.007” / 0.010” Excellent Excellent
• •
Excellent
(1M+)
Weatherable Gloss
Hardcoat Polyester
0.007”
•
Excellent Excellent
Not Ideal
(LED Windows Only)
Excellent
(1M+)
Anti-Glare
Hardcoat Polyester
0.007” / 0.010” Excellent Excellent
• •
Excellent
(1M+)
Matte
Hardcoat Polyester
0.007” Excellent Excellent
• •
Excellent
(1M+)
Brushed (S.S.) Texture
Hardcoat Polyester
0.006” / 0.008” Excellent Excellent
•
Window Clearing
& Gloss Effects
Excellent
(1M+)
Fine Velvet Texture Blend 0.007” / 0.010” Good* Excellent
•
Very Good
(100K+)
Weatherable Velvet Texture Blend0.007” / 0.010”
•
Good** Very Good
•
Very Good
(100K+)
*Fair chemical resistance to
household cleaners
**Resistant to gasoline &
household cleaners
Layers: Graphic Overlay
Imaging & Decorating Options
The colored images and effects on the graphic overlay are
applied using either a screen or digital printing process, or
a combination of both. The graphics are printed on the sub-
surface (or 2nd surface) so the thickness of the material
protects the graphics from normal wear or damage.
Screen Printing vs. Digitally Printing
Screen printing (see Fig. 1) takes on a more industrial look
with areas of solid colors (PMS spot colors). Digital printing
(see Fig. 2) allows for photo-quality graphics.
Digital printing will also be utilized when an overlay requires
variable information or graphics (ex. serial numbers). When
true metallic colors are required, the overlays must be screen
printed. The digital printing of parts can result in reduced
costs and lead times due to multiple colors being applied at
one time. Screen printing is typically more cost-effective for
large production runs.
7
Tinted Display and LED Windows
Windows may be clear or printed with a transparent color to
help conceal the LCD/LED display or indicator LEDs when they
are not lit.
Windows can also be tinted to filter or allow certain
wavelengths of light to pass. LED windows can also be
deadfronted—icons that appear invisible until lit from behind
(ex. car’s turn signal icon).
Selective Texturing and Window Clearing
Screen-printed ultraviolet (UV) hardcoats can be selectively
applied to the top surface of the overlay to provide:
• A matte, textured background with gloss or anti-glare
windows.
• Contrasting matte/textured part background with high-gloss
graphical elements such as buttons, logos, etc.
When pre-textured material is used for the graphic overlay,
a window clearing agent can be applied to make the display
window transparent.
Fig. 1
Fig. 2
Imaging & Decorating Options
The colored images and effects on the graphic overlay are
applied using either a screen or digital printing process, or
a combination of both. The graphics are printed on the sub-
surface (or 2nd surface) so the thickness of the material
protects the graphics from normal wear or damage.
Screen Printing vs. Digitally Printing
Screen printing (see Fig. 1) takes on a more industrial look
with areas of solid colors (PMS spot colors). Digital printing
(see Fig. 2) allows for photo-quality graphics.
Digital printing will also be utilized when an overlay requires
variable information or graphics (ex. serial numbers). When
true metallic colors are required, the overlays must be screen
printed. The digital printing of parts can result in reduced
costs and lead times due to multiple colors being applied at
one time. Screen printing is typically more cost-effective for
large production runs.
7
Tinted Display and LED Windows
Windows may be clear or printed with a transparent color to
help conceal the LCD/LED display or indicator LEDs when they
are not lit.
Windows can also be tinted to filter or allow certain
wavelengths of light to pass. LED windows can also be
deadfronted—icons that appear invisible until lit from behind
(ex. car’s turn signal icon).
Selective Texturing and Window Clearing
Screen-printed ultraviolet (UV) hardcoats can be selectively
applied to the top surface of the overlay to provide:
• A matte, textured background with gloss or anti-glare
windows.
• Contrasting matte/textured part background with high-gloss
graphical elements such as buttons, logos, etc.
When pre-textured material is used for the graphic overlay,
a window clearing agent can be applied to make the display
window transparent.
Fig. 1
Fig. 2
Layers: Graphic Overlay
Color Matching
Within the printing industry, there are several color matching
systems used to communicate color requirements. However,
the most popular system in the membrane switch industry
is the Pantone Matching System (PMS). Pantone Formula
Guide and Pantone Color Bridge color swatch books are easily
accessible and affordable. These swatch books differ slightly
from book to book and fade with time, so they must be
replaced annually.
Colors are also matched using RGB values or other color
matching systems such as the Munsell Color System or
Federal Standard No. 595a.
Screen Printing Colors
The most common PMS color swatch book for matching
screen-printed colors is the Formula Guide – Solid Coated. The
color swatches in the book are designated with a numeric
value followed by a “C” to indicate the Solid Coated book (ex.
286 C).
8
Digital Printing Colors
For digital printing, the most common PMS color swatch
book is the Color Bridge – Coated. This swatch book shows the
screen-printed spot color side-by-side with the CMYK process/
digitally printed color. The process/digital color swatches in
this book are designated with a numeric value followed by a
“CP” to indicate coated & process color (ex. 354 CP).
You will notice that there is a difference between a screen-
printed spot color and its equivalent digitally printed CMYK/
process color. In the example to the left, PMS 354 C is
compared to PMS 354 CP.
NOTE: It is easier to color match a digitally printed color
with a screen-printed spot color than matching a screen-
printed color with a digitally printed CMYK/process color.
Butler Technologies matches colors within the acceptable
industry standard Delta-E measurements using a
spectrophotometer and computerized color-matching system
that includes an ink recipe archive.
Color Matching
Within the printing industry, there are several color matching
systems used to communicate color requirements. However,
the most popular system in the membrane switch industry
is the Pantone Matching System (PMS). Pantone Formula
Guide and Pantone Color Bridge color swatch books are easily
accessible and affordable. These swatch books differ slightly
from book to book and fade with time, so they must be
replaced annually.
Colors are also matched using RGB values or other color
matching systems such as the Munsell Color System or
Federal Standard No. 595a.
Screen Printing Colors
The most common PMS color swatch book for matching
screen-printed colors is the Formula Guide – Solid Coated. The
color swatches in the book are designated with a numeric
value followed by a “C” to indicate the Solid Coated book (ex.
286 C).
8
Digital Printing Colors
For digital printing, the most common PMS color swatch
book is the Color Bridge – Coated. This swatch book shows the
screen-printed spot color side-by-side with the CMYK process/
digitally printed color. The process/digital color swatches in
this book are designated with a numeric value followed by a
“CP” to indicate coated & process color (ex. 354 CP).
You will notice that there is a difference between a screen-
printed spot color and its equivalent digitally printed CMYK/
process color. In the example to the left, PMS 354 C is
compared to PMS 354 CP.
NOTE: It is easier to color match a digitally printed color
with a screen-printed spot color than matching a screen-
printed color with a digitally printed CMYK/process color.
Butler Technologies matches colors within the acceptable
industry standard Delta-E measurements using a
spectrophotometer and computerized color-matching system
that includes an ink recipe archive.
Layers: Graphic Overlay
Embossing & Forming of Features
Graphical elements on the surface of the overlay (such as buttons, LEDs windows, and logos) can
be embossed or formed to produce three-dimensional features that enhance the aesthetics and
function of the membrane switch. In this section, the different types of embossing & forming will
be discussed.
Embossing of Buttons
There are three basic styles of embossing for membrane switch buttons: Pillow, Rim, and Dome.
• Pillow (a.k.a. plateau or pad emboss): The entire shape of the key is raised and the top is flat.
• Rim (a.k.a. rail or perimeter emboss): A raised border around the perimeter of the button.
• Dome: The entire button is raised in a spherical shape. NOTE: This will require a more costly
emboss tool.
Design Factors for Embossing
Height: Typical emboss height of a button is 1.0x material thickness for a PET overlay and 1.5x
for a PC overlay.
Width: The recommended width of a rim emboss is between 0.040” and 0.050” depending on
material thickness.
Radius: The recommended minimum corner radius is 0.032”. Square corners will crack the
overlay material.
Spacing: Minimum spacing of 0.187” between an embossed button/feature and (a) another
embossed button/feature, (b) an internal cutout, or (c) the edge of the membrane switch overlay.
9
Pillow Emboss Rim Emboss Dome Emboss
Embossing & Forming of Features
Graphical elements on the surface of the overlay (such as buttons, LEDs windows, and logos) can
be embossed or formed to produce three-dimensional features that enhance the aesthetics and
function of the membrane switch. In this section, the different types of embossing & forming will
be discussed.
Embossing of Buttons
There are three basic styles of embossing for membrane switch buttons: Pillow, Rim, and Dome.
• Pillow (a.k.a. plateau or pad emboss): The entire shape of the key is raised and the top is flat.
• Rim (a.k.a. rail or perimeter emboss): A raised border around the perimeter of the button.
• Dome: The entire button is raised in a spherical shape. NOTE: This will require a more costly
emboss tool.
Design Factors for Embossing
Height: Typical emboss height of a button is 1.0x material thickness for a PET overlay and 1.5x
for a PC overlay.
Width: The recommended width of a rim emboss is between 0.040” and 0.050” depending on
material thickness.
Radius: The recommended minimum corner radius is 0.032”. Square corners will crack the
overlay material.
Spacing: Minimum spacing of 0.187” between an embossed button/feature and (a) another
embossed button/feature, (b) an internal cutout, or (c) the edge of the membrane switch overlay.
9
Pillow Emboss Rim Emboss Dome Emboss
Layers: Graphic Overlay
Design Notes for Embossing
Greater emboss heights, than listed above, can be achieved
but are not recommended for membrane switch buttons.
Excessive emboss heights increase the risk of material failure
and the cracking or discoloration of the hardcoat.
If button heights need to be greater than listed above, a
thermoforming or hydroforming process will need to be
utilized, which has higher processing and tooling costs.
Embossed areas that are backlit must be taken into
consideration during the design phase due to the thinning
of material or ink that is not normally visible with non-backlit
applications.
Emboss widths or spacings less than stated above are
possible but this tends to distort the surrounding material
and excessively stresses the material, which could result in
fracture.
The minimum spacing between embossed buttons allows for
an adequate amount of graphic adhesive and space between
the dome cavities in the underlying spacer layer.
10
Embossing of LED Windows
Typically, LED windows need to be embossed in the graphic
overlay to account for the height of the LEDs mounted to the
circuit layer underneath.
The embossed windows will have a similar profile as the pillow
embossed button but with a greater height. LED windows can
be embossed to a height of 2.5x material thickness due to lack
of flexing like buttons.
Design Notes for Embossing
Greater emboss heights, than listed above, can be achieved
but are not recommended for membrane switch buttons.
Excessive emboss heights increase the risk of material failure
and the cracking or discoloration of the hardcoat.
If button heights need to be greater than listed above, a
thermoforming or hydroforming process will need to be
utilized, which has higher processing and tooling costs.
Embossed areas that are backlit must be taken into
consideration during the design phase due to the thinning
of material or ink that is not normally visible with non-backlit
applications.
Emboss widths or spacings less than stated above are
possible but this tends to distort the surrounding material
and excessively stresses the material, which could result in
fracture.
The minimum spacing between embossed buttons allows for
an adequate amount of graphic adhesive and space between
the dome cavities in the underlying spacer layer.
10
Embossing of LED Windows
Typically, LED windows need to be embossed in the graphic
overlay to account for the height of the LEDs mounted to the
circuit layer underneath.
The embossed windows will have a similar profile as the pillow
embossed button but with a greater height. LED windows can
be embossed to a height of 2.5x material thickness due to lack
of flexing like buttons.
Layers: Graphic Overlay
Hydroforming & Thermoforming
of Buttons & Features
Both hydroforming and thermoforming are
different methods that can be used to produce
more complex and higher (2x to 3x material
thickness) shapes and dome-shaped buttons in
the graphic overlay. Tooling for these processes is
more costly than standard embossing. Examples
of formed features include multi-level buttons,
buttons with braille, raised logos, and dome-
shaped buttons with tactile feedback.
11
Overlay
Materials
0.006” PET0.007” PET0.008” PET0.010” PET0.007” PC0.010” PC
Max Dome ø 0.488” 0.488” 0.488” 0.488” 0.423” 0.480”
Max Dome
Height
0.031” 0.033” 0.030” 0.032” 0.024” 0.032”
Min Dome ø 0.340” 0.340” 0.340” 0.340” 0.340” 0.340”
Min Dome
Height
0.016” 0.016” 0.013” 0.015” 0.015” 0.015”
Typical Sizes of Hydroformed Buttons in Graphic Overlays
Multi-Layer Emboss
Hydroforming & Thermoforming
of Buttons & Features
Both hydroforming and thermoforming are
different methods that can be used to produce
more complex and higher (2x to 3x material
thickness) shapes and dome-shaped buttons in
the graphic overlay. Tooling for these processes is
more costly than standard embossing. Examples
of formed features include multi-level buttons,
buttons with braille, raised logos, and dome-
shaped buttons with tactile feedback.
11
Overlay
Materials
0.006” PET0.007” PET0.008” PET0.010” PET0.007” PC0.010” PC
Max Dome ø 0.488” 0.488” 0.488” 0.488” 0.423” 0.480”
Max Dome
Height
0.031” 0.033” 0.030” 0.032” 0.024” 0.032”
Min Dome ø 0.340” 0.340” 0.340” 0.340” 0.340” 0.340”
Min Dome
Height
0.016” 0.016” 0.013” 0.015” 0.015” 0.015”
Typical Sizes of Hydroformed Buttons in Graphic Overlays
Multi-Layer Emboss
Layers: Graphic Overlay
Silicone Rubber Keypads
As an alternative to a PET or PC graphic overlay, a
silicone rubber keypad can be used as the interface to
a membrane switch.
The fact that silicone rubber keypads are three-
dimensional makes them an ideal way to upgrade the
appeal of the user interface, especially when used in
combination with a graphic overlay.
Silicone rubber keypads can be enhanced with
features such as:
• Coatings to improve abrasion resistance and
lifetime of keytop graphics.
• Injection molded plastic keycaps
• Surface finish (glossy or matte)
• Multi-color and durometer silicone rubbers and
printed graphics
• Translucent button graphics for backlighting and
lightpipes for LEDs
12
Silicone Rubber Keypads
with Graphic Overlays
As previously mentioned, a silicone rubber keypad
can be used in combination with a graphic overlay.
The picture to the left is the same silicone keypad
shown above but with a digitally-printed graphic
overlay added.
Because the graphic overlay can be printed with
either a screen or digital print processes, the
level of decoration on a keypad can greatly be
increased over traditional keypad decorating
methods.
For more information on keypad design, please
reference Butler Technologies’ Silicone Rubber
Keypad Design Guide.
Silicone Rubber Keypads
As an alternative to a PET or PC graphic overlay, a
silicone rubber keypad can be used as the interface to
a membrane switch.
The fact that silicone rubber keypads are three-
dimensional makes them an ideal way to upgrade the
appeal of the user interface, especially when used in
combination with a graphic overlay.
Silicone rubber keypads can be enhanced with
features such as:
• Coatings to improve abrasion resistance and
lifetime of keytop graphics.
• Injection molded plastic keycaps
• Surface finish (glossy or matte)
• Multi-color and durometer silicone rubbers and
printed graphics
• Translucent button graphics for backlighting and
lightpipes for LEDs
12
Silicone Rubber Keypads
with Graphic Overlays
As previously mentioned, a silicone rubber keypad
can be used in combination with a graphic overlay.
The picture to the left is the same silicone keypad
shown above but with a digitally-printed graphic
overlay added.
Because the graphic overlay can be printed with
either a screen or digital print processes, the
level of decoration on a keypad can greatly be
increased over traditional keypad decorating
methods.
For more information on keypad design, please
reference Butler Technologies’ Silicone Rubber
Keypad Design Guide.
Layers: Dome Retainer / Upper Circuit
Tactile vs. Non-Tactile Switches
When considering the tactile/haptic, and sometimes audible,
response of a membrane switch, there are two basic
constructions: tactile and non-tactile. In either case, they
contain momentary switches that are normally open.
In this section, the differences between the two types
of constructions will be reviewed, including the typical
performance specifications of each.
Non-Tactile Membrane Switch
Non-tactile membrane switches do not provide a tactile or
audible response from the switch itself, but can be designed
to have a broad range of button actuation forces, typically
between 2 to 10 ounces. Non-tactile membrane switches
are commonly used in applications where light-to-medium
actuation forces are desired or where other forms of feedback
are provided (visual cues or audible beeps).
Some common devices where non-tactile membrane
switches are utilized include keypads for microwave ovens,
vending machines, medical devices, high-speed data entry
interfaces, and military applications where audible feedback is
sometimes undesired.
13
The actuation force of a non-tactile membrane switch is defined by the thickness of the dome/
circuit spacer layer and the diameter of the hole (for the electrical contacts) in the spacer layer.
For example, a membrane switch with a thick spacer and small diameter spacer hole will have a
greater actuation force than one with a thin spacer and larger hole diameter.
In addition, the thickness of the graphic overlay material plays a part in the actuation force. A
0.010” thick graphic overlay contributes to a higher actuation force as compared to a 0.007”
graphic overlay material.
Graphic Overlay
Graphic Adhesive
Upper Circuit
Circuit Spacer
Lower Circuit
Rear Adhesive
Typical Non-Tactile Membrane Switch Stack-up
Tactile vs. Non-Tactile Switches
When considering the tactile/haptic, and sometimes audible,
response of a membrane switch, there are two basic
constructions: tactile and non-tactile. In either case, they
contain momentary switches that are normally open.
In this section, the differences between the two types
of constructions will be reviewed, including the typical
performance specifications of each.
Non-Tactile Membrane Switch
Non-tactile membrane switches do not provide a tactile or
audible response from the switch itself, but can be designed
to have a broad range of button actuation forces, typically
between 2 to 10 ounces. Non-tactile membrane switches
are commonly used in applications where light-to-medium
actuation forces are desired or where other forms of feedback
are provided (visual cues or audible beeps).
Some common devices where non-tactile membrane
switches are utilized include keypads for microwave ovens,
vending machines, medical devices, high-speed data entry
interfaces, and military applications where audible feedback is
sometimes undesired.
13
The actuation force of a non-tactile membrane switch is defined by the thickness of the dome/
circuit spacer layer and the diameter of the hole (for the electrical contacts) in the spacer layer.
For example, a membrane switch with a thick spacer and small diameter spacer hole will have a
greater actuation force than one with a thin spacer and larger hole diameter.
In addition, the thickness of the graphic overlay material plays a part in the actuation force. A
0.010” thick graphic overlay contributes to a higher actuation force as compared to a 0.007”
graphic overlay material.
Graphic Overlay
Graphic Adhesive
Upper Circuit
Circuit Spacer
Lower Circuit
Rear Adhesive
Typical Non-Tactile Membrane Switch Stack-up
Layers: Dome Retainer / Upper Circuit
Higher actuation force applications
include industrial controls and other
cases where operators may be using
heavy gloves or where accidental
button pushes are undesired.
Stainless steel domes are the most
common type used in membrane
switches due to cost and versatility. By
using different styles, sizes, and forces,
stainless steel domes are able to meet
most actuation force requirements.
14
Below is a list of the common stainless steel domes and their corresponding specifications. At
BTI, the most widely used dome is the 12mm x 16 oz. actuation force, four-leg, square type. In
general, BTI selects the proper dome based on customer performance and design specifications.
BTI can assist the customer in specifying the proper dome for their application.
Tactile Membrane Switch
Tactile membrane switches provide haptic and often audible feedback in the form of a clicking
sound when a button is pushed. The feedback is accomplished through use of stainless steel
or polyester domes (Polydomes®) and, in cases where a rubber keypad is used, the button’s
webbing provides the feedback (reference BTI’s Silicone Rubber Keypad Design Guide).
Stainless steel and polyester domes are typically used in applications requiring medium (8 to 14
ounce) or high (16+ ounces) actuation force. Many applications require the medium actuation
force domes, including medical devices, test and laboratory equipment, and OEM devices.
Dome Size (ø) Actuation Force Dome Height
6mm 3 to 6oz (85 to 180g) 0.30 to 0.33mm
7mm 3 to 11oz (85 to 320g) 0.30 to 0.48mm
8.4 / 8.5mm 6 to 14oz (150 to 400g) 0.43 to 0.61mm
10mm 7 to 16oz (200 to 450g) 0.51 to 0.64mm
12 / 12.2mm 7 to 16oz (200 to 450g) 0.58 to 0.76mm
14mm 14 to 24oz (400 to 700g) 0.81 to 0.97mm
16mm 14 to 23oz (400 to 650g) 0.86 to 1.00mm
20mm 14 to 80oz (400 to 2,250g) 1.17 to 1.45mm
Typical Sizes of Stainless Steel Four-Leg, Square Domes
The actuation forces listed for the dome itself. Other factors, including material type
& thickness and embossing will influence the actuation force and tactile feedback.
Graphic Overlay
Graphic Adhesive
Dome Retainer
S.S. Dome / Spacer
Circuit layer
Rear Adhesive
Typical Tactile Membrane Switch Stack-up
Higher actuation force applications
include industrial controls and other
cases where operators may be using
heavy gloves or where accidental
button pushes are undesired.
Stainless steel domes are the most
common type used in membrane
switches due to cost and versatility. By
using different styles, sizes, and forces,
stainless steel domes are able to meet
most actuation force requirements.
14
Below is a list of the common stainless steel domes and their corresponding specifications. At
BTI, the most widely used dome is the 12mm x 16 oz. actuation force, four-leg, square type. In
general, BTI selects the proper dome based on customer performance and design specifications.
BTI can assist the customer in specifying the proper dome for their application.
Tactile Membrane Switch
Tactile membrane switches provide haptic and often audible feedback in the form of a clicking
sound when a button is pushed. The feedback is accomplished through use of stainless steel
or polyester domes (Polydomes®) and, in cases where a rubber keypad is used, the button’s
webbing provides the feedback (reference BTI’s Silicone Rubber Keypad Design Guide).
Stainless steel and polyester domes are typically used in applications requiring medium (8 to 14
ounce) or high (16+ ounces) actuation force. Many applications require the medium actuation
force domes, including medical devices, test and laboratory equipment, and OEM devices.
Dome Size (ø) Actuation Force Dome Height
6mm 3 to 6oz (85 to 180g) 0.30 to 0.33mm
7mm 3 to 11oz (85 to 320g) 0.30 to 0.48mm
8.4 / 8.5mm 6 to 14oz (150 to 400g) 0.43 to 0.61mm
10mm 7 to 16oz (200 to 450g) 0.51 to 0.64mm
12 / 12.2mm 7 to 16oz (200 to 450g) 0.58 to 0.76mm
14mm 14 to 24oz (400 to 700g) 0.81 to 0.97mm
16mm 14 to 23oz (400 to 650g) 0.86 to 1.00mm
20mm 14 to 80oz (400 to 2,250g) 1.17 to 1.45mm
Typical Sizes of Stainless Steel Four-Leg, Square Domes
The actuation forces listed for the dome itself. Other factors, including material type
& thickness and embossing will influence the actuation force and tactile feedback.
Graphic Overlay
Graphic Adhesive
Dome Retainer
S.S. Dome / Spacer
Circuit layer
Rear Adhesive
Typical Tactile Membrane Switch Stack-up
Layers: Dome Retainer / Upper Circuit
Polyester Domes (or Polydomes®) are generally thermoformed into 0.005” thick sheets of
polyester film after conductive silver or carbon shorting pads have been screen printed.
Polydomes® are not as common as the stainless steel domes due to increased processing costs,
lead-times, and tooling charges. However, they are often preferred when significant numbers of
stainless steel domes are required in a membrane switch design such as a QWERTY keypad and
when the production volumes are high enough to offset the cost of the tooling.
Polydome® size ranges from: Ø 6mm x 0.50mm at the smallest to Ø 12.7mm x 0.96mm at the
largest. Polydomes® typically fall within the low-to-medium actuation force range (3 to 14 oz).
Actuation forces in Polydomes® can be difficult to match to stainless steel domes due to
thermoforming’s sensitivity to process variation and material tolerances. Other factors such
as membrane switch design and material thickness will affect the overall actuation force of
Polydomes®.
15
There are some differences between the mechanical and electrical performance of tactile and
non-tactile membrane switches (with graphic overlays). Below is a comparison chart.
Charateristic Type Typical Value Comments
Life Expectancy
Tactile 1,000,000 actuations
Value will vary depending on switch construction,
materials/dome type, and operating environment.
Non-Tactile 5,000,000 actuations
Actuation Force
(most common)
Tactile 6 to 16 oz
Non-Tactile 2 to 10 oz
Switch Travel
(most common)
Tactile 0.6 to 1.5mm
Non-Tactile 0.13 to 0.5mm
Overall Thickness
(min.)
Tactile 0.84mm
Many factors can influence switch thickness including:
large dome sizes, adding backlighting or shielding, etc.
Non-Tactile 0.55mm
Contact Bounce
Tactile < 5ms
Non-Tactile < 20ms
Performance Specifications of Tactile vs. Non-tactile Membrane Switches
Graphic Overlay
Graphic Adhesive
Dome Retainer
S.S. Dome / Spacer
Circuit Layer
Rear Adhesive
Typical Tactile Membrane Switch Stack-up
Polyester Domes (or Polydomes®) are generally thermoformed into 0.005” thick sheets of
polyester film after conductive silver or carbon shorting pads have been screen printed.
Polydomes® are not as common as the stainless steel domes due to increased processing costs,
lead-times, and tooling charges. However, they are often preferred when significant numbers of
stainless steel domes are required in a membrane switch design such as a QWERTY keypad and
when the production volumes are high enough to offset the cost of the tooling.
Polydome® size ranges from: Ø 6mm x 0.50mm at the smallest to Ø 12.7mm x 0.96mm at the
largest. Polydomes® typically fall within the low-to-medium actuation force range (3 to 14 oz).
Actuation forces in Polydomes® can be difficult to match to stainless steel domes due to
thermoforming’s sensitivity to process variation and material tolerances. Other factors such
as membrane switch design and material thickness will affect the overall actuation force of
Polydomes®.
15
There are some differences between the mechanical and electrical performance of tactile and
non-tactile membrane switches (with graphic overlays). Below is a comparison chart.
Charateristic Type Typical Value Comments
Life Expectancy
Tactile 1,000,000 actuations
Value will vary depending on switch construction,
materials/dome type, and operating environment.
Non-Tactile 5,000,000 actuations
Actuation Force
(most common)
Tactile 6 to 16 oz
Non-Tactile 2 to 10 oz
Switch Travel
(most common)
Tactile 0.6 to 1.5mm
Non-Tactile 0.13 to 0.5mm
Overall Thickness
(min.)
Tactile 0.84mm
Many factors can influence switch thickness including:
large dome sizes, adding backlighting or shielding, etc.
Non-Tactile 0.55mm
Contact Bounce
Tactile < 5ms
Non-Tactile < 20ms
Performance Specifications of Tactile vs. Non-tactile Membrane Switches
Graphic Overlay
Graphic Adhesive
Dome Retainer
S.S. Dome / Spacer
Circuit Layer
Rear Adhesive
Typical Tactile Membrane Switch Stack-up
Layers: Circuit Layer
Purpose
The next important layer in a membrane switch is the circuit
layer. Depending on the design of the membrane switch,
there can be multiple circuit layers such as the shielding layer,
upper circuit layer, and the lower circuit layer.
The circuit layer is usually the most complex layer to design.
Typically, the circuit design starts with the electrical schematic
or pinout. Butler Technologies can use the customer-supplied
schematic/pinout to design the circuit or our engineers can
develop the pinout and circuit design. BTI provides a design
approval drawing to the customer for review and sign-off.
Types & Materials
16
Polyester film with printed conductive silver circuitry
Polyester film with printed conductive silver circuitry is the most common type of circuit used in
membrane switches. These types of circuits are typically constructed of 0.005” heat-stabilized
polyester film with screen-printed circuitry consisting of conductive silver and carbon inks as
well as an insulating UV dieletric ink. Any surface mount components, such as LEDs, are attached
using conductive epoxy. Multi-layer, two-sided circuits are possible for high trace density
applications.
Polyimide film with etched copper circuitry
Polyimide (PI) film with etched copper circuity is another popular type of circuit used in
membrane switches. Sometimes referred to as flexible boards or flexible printed circuitry
(FPC), they are more costly than their screen printed counterparts. Because of the nature of
the materials and processes used to make copper etched circuitry, they are a better choice for
demanding applications due to their durability and ease of producing fine trace pitch and two-
sided, multi-layer constructions. Surface mount devices are typically soldered to the circuity
making the bond much more robust than the epoxied components. Thickness for etched copper
circuits typically ranges from 0.008” to 0.012” (one-sided or two-sided with PI coverlay insulation).
Printed Circuit Board (PCB)
Printed Circuit Boards (PCBs) offer similar benefits to the etched copper circuits except they
are made from rigid material (ex. FR4) and typically range in thickness from 0.031” (0.78mm)
to 0.062” (1.57mm). The advantage of using PCBs as the circuit layer is that any mounting
hardware, such as PEM® studs and standoffs, can be easily installed in PCBs. One disadvantage
of using printed circuit boards is that if a copper flex tail is required, it needs to be fabricated
separately and then soldered to the PCB. In contrast, various types of thru hole and surface
mount connectors such as ZIFs or male headers can easily be integrated (soldered) into the PCB
design.
Purpose
The next important layer in a membrane switch is the circuit
layer. Depending on the design of the membrane switch,
there can be multiple circuit layers such as the shielding layer,
upper circuit layer, and the lower circuit layer.
The circuit layer is usually the most complex layer to design.
Typically, the circuit design starts with the electrical schematic
or pinout. Butler Technologies can use the customer-supplied
schematic/pinout to design the circuit or our engineers can
develop the pinout and circuit design. BTI provides a design
approval drawing to the customer for review and sign-off.
Types & Materials
16
Polyester film with printed conductive silver circuitry
Polyester film with printed conductive silver circuitry is the most common type of circuit used in
membrane switches. These types of circuits are typically constructed of 0.005” heat-stabilized
polyester film with screen-printed circuitry consisting of conductive silver and carbon inks as
well as an insulating UV dieletric ink. Any surface mount components, such as LEDs, are attached
using conductive epoxy. Multi-layer, two-sided circuits are possible for high trace density
applications.
Polyimide film with etched copper circuitry
Polyimide (PI) film with etched copper circuity is another popular type of circuit used in
membrane switches. Sometimes referred to as flexible boards or flexible printed circuitry
(FPC), they are more costly than their screen printed counterparts. Because of the nature of
the materials and processes used to make copper etched circuitry, they are a better choice for
demanding applications due to their durability and ease of producing fine trace pitch and two-
sided, multi-layer constructions. Surface mount devices are typically soldered to the circuity
making the bond much more robust than the epoxied components. Thickness for etched copper
circuits typically ranges from 0.008” to 0.012” (one-sided or two-sided with PI coverlay insulation).
Printed Circuit Board (PCB)
Printed Circuit Boards (PCBs) offer similar benefits to the etched copper circuits except they
are made from rigid material (ex. FR4) and typically range in thickness from 0.031” (0.78mm)
to 0.062” (1.57mm). The advantage of using PCBs as the circuit layer is that any mounting
hardware, such as PEM® studs and standoffs, can be easily installed in PCBs. One disadvantage
of using printed circuit boards is that if a copper flex tail is required, it needs to be fabricated
separately and then soldered to the PCB. In contrast, various types of thru hole and surface
mount connectors such as ZIFs or male headers can easily be integrated (soldered) into the PCB
design.
Layers: Circuit Layer
Electrical Layout
Common Bus
The common bus configuration shown is comprised of separate traces for each of the four
switches and one common (or ground) trace. Hence, the membrane switch’s termination will
have five traces.
17
X-Y Matrix (Rows & Columns)
The 2x2 matrix configuration shown below is comprised of two rows and two columns. Matrix
circuit layouts are desirable for membrane switches with high numbers of keys to reduce the
number of traces required and to simplify the interconnect. Unlike the four-switch common bus
design, which requires a five-position connector, the four-switch (2x2) matrix design requires
only a four-position connector.
Connector
SW1
SW3
SW2
SW4
Common Bus Schematic and Pinout
1
2
4
5
3
PINOUT
Pin
Key12345
(GND)
SW1
SW2
SW3
SW4
2
1
SW1 SW2
SW3 SW4
Connector
2 x 2 Matrix Schematic and Pinout
3
4
PINOUT
Pin
Key1234
SW1
SW2
SW3
SW4
Electrical Layout
Common Bus
The common bus configuration shown is comprised of separate traces for each of the four
switches and one common (or ground) trace. Hence, the membrane switch’s termination will
have five traces.
17
X-Y Matrix (Rows & Columns)
The 2x2 matrix configuration shown below is comprised of two rows and two columns. Matrix
circuit layouts are desirable for membrane switches with high numbers of keys to reduce the
number of traces required and to simplify the interconnect. Unlike the four-switch common bus
design, which requires a five-position connector, the four-switch (2x2) matrix design requires
only a four-position connector.
Connector
SW1
SW3
SW2
SW4
Common Bus Schematic and Pinout
1
2
4
5
3
PINOUT
Pin
Key12345
(GND)
SW1
SW2
SW3
SW4
2
1
SW1 SW2
SW3 SW4
Connector
2 x 2 Matrix Schematic and Pinout
3
4
PINOUT
Pin
Key1234
SW1
SW2
SW3
SW4
Layers: Circuit Layer
Electrical Layout Assistance
If needed, Butler Technologies has on-site engineers that can layout your circuit for you. To
accomplish this, BTI needs a copy of your electrical schematic and/or pinout. If you do not have
either of these, BTI can develop the circuit layout (with pinout) and forward a copy to you for
approval.
Unless you have prior experience, it is typically faster and more cost-effective to have BTI
develop the membrane switch circuit layout for you.
Circuit Routing
Depending on the size, shape, and circuit density of your part, one or more methods of
circuit routing may be utilized on your circuit. Techniques such as using conductive jumpers
(or “bridging”), through-hole printing, or multiple circuit layers are used to accommodate the
functionality required.
18
BTI’s experienced engineers will layout your circuit while taking several factors into consideration
including efficient material & process utilization, durability, and Design for Manufacture (DFM)
which all contribute to reduced costs and lead-times.
Traces Needing
Jumped
Through-Holes (Vias)
are Laser Cut into
PET Film
Side View
Side View
Dielectric (Insulative)
Layers are Printed
(green)
Conductive Traces
are Printed on A-side
of PET Film (ink
partially fills Vias)
Conductive Jumper is
Printed to Complete
the Electrical
Connection
Conductive Jumper
is Printed on the
B-side of the PET film
and Fills the Vias to
Complete the Electrical
Connection to the
A-side Traces
Electrical Layout Assistance
If needed, Butler Technologies has on-site engineers that can layout your circuit for you. To
accomplish this, BTI needs a copy of your electrical schematic and/or pinout. If you do not have
either of these, BTI can develop the circuit layout (with pinout) and forward a copy to you for
approval.
Unless you have prior experience, it is typically faster and more cost-effective to have BTI
develop the membrane switch circuit layout for you.
Circuit Routing
Depending on the size, shape, and circuit density of your part, one or more methods of
circuit routing may be utilized on your circuit. Techniques such as using conductive jumpers
(or “bridging”), through-hole printing, or multiple circuit layers are used to accommodate the
functionality required.
18
BTI’s experienced engineers will layout your circuit while taking several factors into consideration
including efficient material & process utilization, durability, and Design for Manufacture (DFM)
which all contribute to reduced costs and lead-times.
Traces Needing
Jumped
Through-Holes (Vias)
are Laser Cut into
PET Film
Side View
Side View
Dielectric (Insulative)
Layers are Printed
(green)
Conductive Traces
are Printed on A-side
of PET Film (ink
partially fills Vias)
Conductive Jumper is
Printed to Complete
the Electrical
Connection
Conductive Jumper
is Printed on the
B-side of the PET film
and Fills the Vias to
Complete the Electrical
Connection to the
A-side Traces
Layers: Circuit Layer
Contact Pad Design
There are several options to consider when designing the switch elements of the circuit. The
switches in a membrane wwitch assembly are momentary, single pole/single throw. There are
contact pad designs for both tactile and non-tactile switches.
Tactile Switch
Probably the most common type of tactile switching device used in a membrane switch is the
square, four-leg metal dome. The design for its contact pad typically looks like one of the two
shown in the left diagram below. The diagram at the bottom of the page demonstrates how the
metal dome interfaces with the contact pad.
19
Corresponding designs for the various sizes of metal domes can be obtained from BTI or from
metal dome manufactures/suppliers such as Snaptron or Odorfer & Associates Corp.
Metal Dome
Contact Pad
Typical Metal Dome Contact Pad Designs
Contact Pad Design
There are several options to consider when designing the switch elements of the circuit. The
switches in a membrane wwitch assembly are momentary, single pole/single throw. There are
contact pad designs for both tactile and non-tactile switches.
Tactile Switch
Probably the most common type of tactile switching device used in a membrane switch is the
square, four-leg metal dome. The design for its contact pad typically looks like one of the two
shown in the left diagram below. The diagram at the bottom of the page demonstrates how the
metal dome interfaces with the contact pad.
19
Corresponding designs for the various sizes of metal domes can be obtained from BTI or from
metal dome manufactures/suppliers such as Snaptron or Odorfer & Associates Corp.
Metal Dome
Contact Pad
Typical Metal Dome Contact Pad Designs
Layers: Circuit Layer
Non-tactile Switch Options
In many applications, the device operator user will receive feedback by means other than the
snap of a metal dome (ex. audible beeps, visual cues, etc.). In such cases, the circuitry can
be designed for on-tactile switches. Shown below are two of the non-tactile switch options,
including the layer stack-up of each construction.
20
NOTE: If the applications warrants a matrix circuit layer and a tactile snap is desired, a metal
dome can be placed in between the top circuit and bottom circuit shorting pads as shown in the
picture below.
Inter-digitated
Finger Silver
Trace Pattern
Shorting Pad/
Traces for Rows
(Matrix)
Shorting Pad/
Traces for
Columns (Matrix)
Matrix Grid
Shorting Pad
Silver or Carbon
Two Layers
Overlayed
Non-tactile Switch Options
In many applications, the device operator user will receive feedback by means other than the
snap of a metal dome (ex. audible beeps, visual cues, etc.). In such cases, the circuitry can
be designed for on-tactile switches. Shown below are two of the non-tactile switch options,
including the layer stack-up of each construction.
20
NOTE: If the applications warrants a matrix circuit layer and a tactile snap is desired, a metal
dome can be placed in between the top circuit and bottom circuit shorting pads as shown in the
picture below.
Inter-digitated
Finger Silver
Trace Pattern
Shorting Pad/
Traces for Rows
(Matrix)
Shorting Pad/
Traces for
Columns (Matrix)
Matrix Grid
Shorting Pad
Silver or Carbon
Two Layers
Overlayed
Layers: Circuit Layer
Circuit Flex Tails
The function of circuit flex tails is to connect the membrane switch to the printed circuit board.
Tails can be designed to almost any length and include both straight and angled sections needed
to make the assembly with the PCB easier for the operator.
• As the overall length of the flex tail increases, more material and ink is required, thus
increasing cost.
• Less-costly extension cables can be produced to provide the necessary length rather than
designing a long tail.
• The conductive traces on flex tails are typically protected with insulative ink (UV-cured
dielectric ink) but can also be protected/insulated with polyester or polyimide film for more
demanding applications.
• Tail insulation is required to protect the printed traces from such conditions as: silver
migration, shorting with components inside the device, abrasive environments, and damage
when threading the tail during assembly.
• For more demanding applications (extreme creasing, temperatures, etc.; tails can be
designed as part of an etched copper flex circuit.
• Whether the circuit is made from printed PET or etched copper flex, the tail can have traces
and/or terminations on one or both sides through use of through-hole technology. It is much
easier and more durable to have two-sided circuits made from etched copper on polyimide.
Once the tail design is figured out, the next step is to determine how it will be terminated and
connected to the circuit board.
21
Circuit Flex Tails
The function of circuit flex tails is to connect the membrane switch to the printed circuit board.
Tails can be designed to almost any length and include both straight and angled sections needed
to make the assembly with the PCB easier for the operator.
• As the overall length of the flex tail increases, more material and ink is required, thus
increasing cost.
• Less-costly extension cables can be produced to provide the necessary length rather than
designing a long tail.
• The conductive traces on flex tails are typically protected with insulative ink (UV-cured
dielectric ink) but can also be protected/insulated with polyester or polyimide film for more
demanding applications.
• Tail insulation is required to protect the printed traces from such conditions as: silver
migration, shorting with components inside the device, abrasive environments, and damage
when threading the tail during assembly.
• For more demanding applications (extreme creasing, temperatures, etc.; tails can be
designed as part of an etched copper flex circuit.
• Whether the circuit is made from printed PET or etched copper flex, the tail can have traces
and/or terminations on one or both sides through use of through-hole technology. It is much
easier and more durable to have two-sided circuits made from etched copper on polyimide.
Once the tail design is figured out, the next step is to determine how it will be terminated and
connected to the circuit board.
21
Layers: Circuit Layer
Terminations and Connections
Once the tail design is figured out, the next step is to determine how it will be terminated and
connected to the circuit board. The most common type of tail terminations and connectors are
shown below.
22
.5mm Pitch
Zero Insertion Force (ZIF)
1mm Pitch
Zero Insertion Force (ZIF)
1.27mm Pitch
Female Pins + Housing
2.54mm Pitch
Female Pins + Housing
2.54mm Pitch
Male Solder Tabs
2.54mm Pitch
Amphenol FCI Berg Male Pins
0.5mm and 1.0mm Pitch ZIF terminations
have a stiffener opposite the traces (total
termination thickness = 0.30mm nominal)
1.27mm Pitch Female Pins + Housing
• Mates with 0.38 to 0.45mm round or
square pin headers
• Latching/Locking and Dual-Row housing
available
2.54mm Pitch Female Pins + Housing
• Mates with 0.635mm round or square pin
headers
• Latching, Semi-Lock, and Dual-Row
housings available
• Berg-FCI-Amphenol connector options
available
In addition to the ZIF and female pin
terminations, 2.54mm pitch male Solder Tab
and Pin options are available as shown in the
examples to the right.
Terminations and Connections
Once the tail design is figured out, the next step is to determine how it will be terminated and
connected to the circuit board. The most common type of tail terminations and connectors are
shown below.
22
.5mm Pitch
Zero Insertion Force (ZIF)
1mm Pitch
Zero Insertion Force (ZIF)
1.27mm Pitch
Female Pins + Housing
2.54mm Pitch
Female Pins + Housing
2.54mm Pitch
Male Solder Tabs
2.54mm Pitch
Amphenol FCI Berg Male Pins
0.5mm and 1.0mm Pitch ZIF terminations
have a stiffener opposite the traces (total
termination thickness = 0.30mm nominal)
1.27mm Pitch Female Pins + Housing
• Mates with 0.38 to 0.45mm round or
square pin headers
• Latching/Locking and Dual-Row housing
available
2.54mm Pitch Female Pins + Housing
• Mates with 0.635mm round or square pin
headers
• Latching, Semi-Lock, and Dual-Row
housings available
• Berg-FCI-Amphenol connector options
available
In addition to the ZIF and female pin
terminations, 2.54mm pitch male Solder Tab
and Pin options are available as shown in the
examples to the right.
Layers: Circuit Layer
Shielding
Shielding can be incorporated into a membrane switch to protect
devices from electrostatic discharge (ESD) and electromagnetic
interference (EMI). There are several types of shielding options and
methods to terminate them.
Shielding Types:
• Printed - Screen printed (silver or carbon ink) solid/full-coating,
busbar, or grid pattern options.
• Foil - Aluminum foil or aluminum foil & polyester laminate.
• Transparent Film - Transparent conductive films, such as ITO
coated PET, for shielding display windows.
Termination Methods:
• Tail / Tab - A flexible tail/tab exiting from the edge of the switch
assembly can be attached with to a stand-off on the back panel
or to the metal enclosure via conductive adhesive or mechanical
fastener.
• Connector - The shield can be terminated into its own
connector or within one or more pins of the primary membrane
switch connector.
• Wrap-around - The conductive shield layer can wrap around
the edges of a membrane switch so the backside can ground
to the device’s chassis. If required, conductive adhesive can be
utilized to electrically bond the shield layer to the metal chassis.
23
Shielding
Shielding can be incorporated into a membrane switch to protect
devices from electrostatic discharge (ESD) and electromagnetic
interference (EMI). There are several types of shielding options and
methods to terminate them.
Shielding Types:
• Printed - Screen printed (silver or carbon ink) solid/full-coating,
busbar, or grid pattern options.
• Foil - Aluminum foil or aluminum foil & polyester laminate.
• Transparent Film - Transparent conductive films, such as ITO
coated PET, for shielding display windows.
Termination Methods:
• Tail / Tab - A flexible tail/tab exiting from the edge of the switch
assembly can be attached with to a stand-off on the back panel
or to the metal enclosure via conductive adhesive or mechanical
fastener.
• Connector - The shield can be terminated into its own
connector or within one or more pins of the primary membrane
switch connector.
• Wrap-around - The conductive shield layer can wrap around
the edges of a membrane switch so the backside can ground
to the device’s chassis. If required, conductive adhesive can be
utilized to electrically bond the shield layer to the metal chassis.
23
Layers: Circuit Layer
Surface Mounted Devices (SMD)
Butler Technologies can surface mount various devices to
the circuit layer using conductive epoxy, underfill adhesive
and/or encapsulant for mechanical strength.
Surface Mount Devices include but are not limited to:
• LEDs (and other diodes)
• Capacitors
• Resistors (can be printed too!)
• Ambient Light Sensors
• Integrated Circuit (IC) “Chips”
24
Lighting
Adding lighting to your membrane switch can be as simple as embedding indicator LEDs to
provide feedback to the user or through use of more sophisticated technologies that provide
backlighting to graphics and buttons. In this section, the various options will be discussed.
Indicator LEDs
Indicator LEDs are used to indicate a particular function is engaged (ex. Power On), status, or
warnings. Top-fire LEDs are mounted to the circuit layer and direct their output upwards (90⁰
to the circuit layer). The internal membrane switch layers have corresponding openings to
For prototypes and small production runs, SMDs can be mounted by hand using analog fluid
dispensing equipment. When high volumes or technically demanding designs are required,
SMDs can be attached using precision digital dispensing and pick & place equipment.
For copper flex circuits, the SMDs can be soldered in place for added durability.
permit the light to pass upwards to the graphic
overlay. The graphic overlay would have clear,
textured, tinted or translucent colored windows
(flat or embossed) to make the LED output visible.
Options for indicator LEDs include mono-color,
bi-color, RGB, and several others. Typical indicator
LEDs are yellow/amber, red, or green in color,
however, blue and white are also common. LED
windows that are embossed provide a wider
viewing area of a lit indicator LED.
Surface Mounted Devices (SMD)
Butler Technologies can surface mount various devices to
the circuit layer using conductive epoxy, underfill adhesive
and/or encapsulant for mechanical strength.
Surface Mount Devices include but are not limited to:
• LEDs (and other diodes)
• Capacitors
• Resistors (can be printed too!)
• Ambient Light Sensors
• Integrated Circuit (IC) “Chips”
24
Lighting
Adding lighting to your membrane switch can be as simple as embedding indicator LEDs to
provide feedback to the user or through use of more sophisticated technologies that provide
backlighting to graphics and buttons. In this section, the various options will be discussed.
Indicator LEDs
Indicator LEDs are used to indicate a particular function is engaged (ex. Power On), status, or
warnings. Top-fire LEDs are mounted to the circuit layer and direct their output upwards (90⁰
to the circuit layer). The internal membrane switch layers have corresponding openings to
For prototypes and small production runs, SMDs can be mounted by hand using analog fluid
dispensing equipment. When high volumes or technically demanding designs are required,
SMDs can be attached using precision digital dispensing and pick & place equipment.
For copper flex circuits, the SMDs can be soldered in place for added durability.
permit the light to pass upwards to the graphic
overlay. The graphic overlay would have clear,
textured, tinted or translucent colored windows
(flat or embossed) to make the LED output visible.
Options for indicator LEDs include mono-color,
bi-color, RGB, and several others. Typical indicator
LEDs are yellow/amber, red, or green in color,
however, blue and white are also common. LED
windows that are embossed provide a wider
viewing area of a lit indicator LED.
Layers: Circuit Layer
Metal Domes for Backlighting
Metal domes have been developed with the holes in the center to permit the passage of light
from the circuit- mounted LEDs. Using metal domes in this configuration generally allows for
crisp tactile feedback.
One disadvantage of this technique is the hotspot created in the backlit image (as shown
below in the green backlit power button). If the membrane switch design permits, the distance
between the backlit graphic and the LED can be increased to diminish or eliminate the severity
of the hotspot.
25
Light Guide Film (LGF) Technology
Another common method for backlighting graphics and buttons is through the use of Light
Guide Film (LGF) technology. In this method, backlighting is generated through use of side-
fire LEDs (typically white) and an optical film that has been patterned by various methods. The
pattern gathers the light that is traveling horizontally through the optical film and directs it
upwards through translucent graphics.
Circuit layer with the embedded side-fire
white LEDs and patterned Light Guide Film
panels.
Powered circuit with illuminated Light
Guide Film. Patterned “dots” are visible
and directing light towards the viewer.
Backlit graphic overlay. Notice the patterned
LGF “dots” are visible in the rim embossed
POWER button and the non-embossed
LASER button because there is minimal
space between the button graphics and
LGF. The ARROW buttons are pillow
embossed that allows for space between
the graphics and LGF.
Metal Domes for Backlighting
Metal domes have been developed with the holes in the center to permit the passage of light
from the circuit- mounted LEDs. Using metal domes in this configuration generally allows for
crisp tactile feedback.
One disadvantage of this technique is the hotspot created in the backlit image (as shown
below in the green backlit power button). If the membrane switch design permits, the distance
between the backlit graphic and the LED can be increased to diminish or eliminate the severity
of the hotspot.
25
Light Guide Film (LGF) Technology
Another common method for backlighting graphics and buttons is through the use of Light
Guide Film (LGF) technology. In this method, backlighting is generated through use of side-
fire LEDs (typically white) and an optical film that has been patterned by various methods. The
pattern gathers the light that is traveling horizontally through the optical film and directs it
upwards through translucent graphics.
Circuit layer with the embedded side-fire
white LEDs and patterned Light Guide Film
panels.
Powered circuit with illuminated Light
Guide Film. Patterned “dots” are visible
and directing light towards the viewer.
Backlit graphic overlay. Notice the patterned
LGF “dots” are visible in the rim embossed
POWER button and the non-embossed
LASER button because there is minimal
space between the button graphics and
LGF. The ARROW buttons are pillow
embossed that allows for space between
the graphics and LGF.
Layers: Circuit Layer
Lighting
Fiber Optics
Fiber optic panels are ideal for applications that require
uniform lighting over large areas. In recent years, Light Guide
Film Technology has superseded fiber optics as the primary
choice for backlighting. However, fiber optic technology still
has its place in membrane switch constructions. Besides
offering uniform lighting, fiber optic technology offers several
other advantages including a low-profile construction,
long life (10K to 100K hours), and the ability to operate in a
wide range of environmental conditions. Depending on the
overall construction, fiber optic panels can reduce the tactile
feedback response of a membrane switch.
EL Lamps
Electroluminescent (EL) lamps are another solution for
applications that require uniform lighting over large areas.
EL lamps generate light when the printed phosphor inks are
excited by AC current. Therefore, they require an alternating
current source or a DC to AC power inverter so they are not
appropriate for all membrane switch applications.
26
Lighting
Fiber Optics
Fiber optic panels are ideal for applications that require
uniform lighting over large areas. In recent years, Light Guide
Film Technology has superseded fiber optics as the primary
choice for backlighting. However, fiber optic technology still
has its place in membrane switch constructions. Besides
offering uniform lighting, fiber optic technology offers several
other advantages including a low-profile construction,
long life (10K to 100K hours), and the ability to operate in a
wide range of environmental conditions. Depending on the
overall construction, fiber optic panels can reduce the tactile
feedback response of a membrane switch.
EL Lamps
Electroluminescent (EL) lamps are another solution for
applications that require uniform lighting over large areas.
EL lamps generate light when the printed phosphor inks are
excited by AC current. Therefore, they require an alternating
current source or a DC to AC power inverter so they are not
appropriate for all membrane switch applications.
26
Layers: Rear (Mounting) Adhesive
Adhesive
One of the most important and often overlooked requirement is the mounting adhesive used
to bond the membrane switch to the device. If not properly specified, the adhesive bond will
fail and the membrane switch will separate from the device allowing unwanted debris and/or
moisture to reach the internal components. It is critical for the designer to know the material
and surface finish of the area to which the membrane switch will be mounted. Different types
of materials (HSE or LSE plastics, glass, metals) and finishes (painted, plated, etc.) have varying
levels of surface energy that require the appropriate adhesive type for proper adhesive.
27
Metal and Glass High Surface Energy (HSE) Plastics Low Surface Energy (LSE) Plastics
Substrate Dynes/cm Substrate Dynes/cm Substrate Dynes/cm
Copper 1103 Kapton
®
[polyimide (PI)] 50 Polyvinyl Acetate (PVA) 37
Stainless Steel 700-1100Phenolic 47 Polystyrene (PS) 36
Aluminum 840 Nylon [polyamide (PA)] 46 Acetal (or polyacetal) 36
Zinc 753 Alkyd Enamel (oil-based paint) 45 Delrin 36
Tin 526 Polyester (PET) 43 Powder Coat Paints 36
*
Lead 458 Epoxy Paint 43 Ethylene Vinyl Acetate (EVA) 33
Glass 250-500 Polyurethane (PU) / PU Paint 43 Polyethylene (PE) 31
ABS (acrylonitrite butadiene styrene) 42 Polypropylene (PP) 29
Polycarbonate (PC) 42 Tedlar 28
Polyvinyl Chloride (PVC) 39 Teflon 18
Noryl
®
38
Acrylic [polymethyl methacrylate (PMMA)] 38
Polane
®
Paint (PU-based) 38
*Typical value for powder coat paint. In general, powder coat paints have a broad range of surface energy, usually in the LSE range.
NOTE: The surface energy values are provided as a guide only. The values may vary depending on the substrate formulation.
Adhesive Selector
Metal and Glass High Surface Energy (HSE) Plastics Low Surface Energy (LSE) Plastics
Gauge Adhesive TypeGauge Adhesive TypeGauge Adhesive Type
.002"3M 200MP series.002" 3M 200MP series.002" 3M 300LSE series
.005"3M 200MP series.005" 3M 200MP series.0035" 3M 300LSE series
NOTE: Equivalent adhesives can be substituted .005" 3M 300 High Strength series
Adhesive
One of the most important and often overlooked requirement is the mounting adhesive used
to bond the membrane switch to the device. If not properly specified, the adhesive bond will
fail and the membrane switch will separate from the device allowing unwanted debris and/or
moisture to reach the internal components. It is critical for the designer to know the material
and surface finish of the area to which the membrane switch will be mounted. Different types
of materials (HSE or LSE plastics, glass, metals) and finishes (painted, plated, etc.) have varying
levels of surface energy that require the appropriate adhesive type for proper adhesive.
27
Metal and Glass High Surface Energy (HSE) Plastics Low Surface Energy (LSE) Plastics
Substrate Dynes/cm Substrate Dynes/cm Substrate Dynes/cm
Copper 1103 Kapton
®
[polyimide (PI)] 50 Polyvinyl Acetate (PVA) 37
Stainless Steel 700-1100Phenolic 47 Polystyrene (PS) 36
Aluminum 840 Nylon [polyamide (PA)] 46 Acetal (or polyacetal) 36
Zinc 753 Alkyd Enamel (oil-based paint) 45 Delrin 36
Tin 526 Polyester (PET) 43 Powder Coat Paints 36
*
Lead 458 Epoxy Paint 43 Ethylene Vinyl Acetate (EVA) 33
Glass 250-500 Polyurethane (PU) / PU Paint 43 Polyethylene (PE) 31
ABS (acrylonitrite butadiene styrene) 42 Polypropylene (PP) 29
Polycarbonate (PC) 42 Tedlar 28
Polyvinyl Chloride (PVC) 39 Teflon 18
Noryl
®
38
Acrylic [polymethyl methacrylate (PMMA)] 38
Polane
®
Paint (PU-based) 38
*Typical value for powder coat paint. In general, powder coat paints have a broad range of surface energy, usually in the LSE range.
NOTE: The surface energy values are provided as a guide only. The values may vary depending on the substrate formulation.
Adhesive Selector
Metal and Glass High Surface Energy (HSE) Plastics Low Surface Energy (LSE) Plastics
Gauge Adhesive TypeGauge Adhesive TypeGauge Adhesive Type
.002"3M 200MP series.002" 3M 200MP series.002" 3M 300LSE series
.005"3M 200MP series.005" 3M 200MP series.0035" 3M 300LSE series
NOTE: Equivalent adhesives can be substituted .005" 3M 300 High Strength series
Water Tight Designs
Water-Tight Designs
In many applications, membrane switches need to be protected from moisture and/or dust
ingress. Butler Technologies is experienced in designing membrane switches that meet IP and
NEMA ratings.
The IP and NEMA ratings most requested of Butler Technologies are IP66, IP67, and NEMA4x.
Please note that the combination of the membrane switch construction and how it is affixed to
the device’s enclosure helps determine what rating the device will meet. Moisture and dust may
not ingress into a properly constructed membrane switch, however, if it is not properly bonded
to its mounting surface, moisture and dust can ingress through the flex tail cutout other cutouts
in the enclosure. Below are tables detailing the IP and NEMA ratings.
28
1st
Digit
Protection From
Foreign Body and
Particulate Ingress
2nd
Digit
Protection from moisture
ingress
0No Protection 0No Protection
1
Protected from
solid objects over
50mm
1
Protected from vertical falling
drops of water
2
Protected from
solid objects over
12mm
2
Protected from direct sprays of
water 15º off vertical
3
Protected from
solid objects over
2.5mm
3
Protected from direct sprays of
water 60º off vertical
4
Protected from
solid objects over
1mm
4
Protected from direct sprays
of water from all directions -
limited ingress permitted
5
Protected from
limited dust ingress
5
Protected from low pressure
jets of water from all directions
- limited ingress permitted
6
Totally protected
from dust ingress
6
Protected from strong jets
of water from all directions -
limited ingress permitted
7
Protected from temporary
water immersion up to 1m
deep
8
Protected from long periods of
immersion under pressure
Nema IP
1 10
2 11
3 54
3r 14
3s 54
4 and 4x 55
5 52
6 and 6p 67
12 and 12k 52
13 54
NOTE: There is no direct correlation
between NEMA ratings and IP ratings as
the two systems are based on different
variables. However, the table aboves
shows an approximate cross-reference.
Summary Table of IP Rating Numbers Nema vs. IP Ratings Table
Water-Tight Designs
In many applications, membrane switches need to be protected from moisture and/or dust
ingress. Butler Technologies is experienced in designing membrane switches that meet IP and
NEMA ratings.
The IP and NEMA ratings most requested of Butler Technologies are IP66, IP67, and NEMA4x.
Please note that the combination of the membrane switch construction and how it is affixed to
the device’s enclosure helps determine what rating the device will meet. Moisture and dust may
not ingress into a properly constructed membrane switch, however, if it is not properly bonded
to its mounting surface, moisture and dust can ingress through the flex tail cutout other cutouts
in the enclosure. Below are tables detailing the IP and NEMA ratings.
28
1st
Digit
Protection From
Foreign Body and
Particulate Ingress
2nd
Digit
Protection from moisture
ingress
0No Protection 0No Protection
1
Protected from
solid objects over
50mm
1
Protected from vertical falling
drops of water
2
Protected from
solid objects over
12mm
2
Protected from direct sprays of
water 15º off vertical
3
Protected from
solid objects over
2.5mm
3
Protected from direct sprays of
water 60º off vertical
4
Protected from
solid objects over
1mm
4
Protected from direct sprays
of water from all directions -
limited ingress permitted
5
Protected from
limited dust ingress
5
Protected from low pressure
jets of water from all directions
- limited ingress permitted
6
Totally protected
from dust ingress
6
Protected from strong jets
of water from all directions -
limited ingress permitted
7
Protected from temporary
water immersion up to 1m
deep
8
Protected from long periods of
immersion under pressure
Nema IP
1 10
2 11
3 54
3r 14
3s 54
4 and 4x 55
5 52
6 and 6p 67
12 and 12k 52
13 54
NOTE: There is no direct correlation
between NEMA ratings and IP ratings as
the two systems are based on different
variables. However, the table aboves
shows an approximate cross-reference.
Summary Table of IP Rating Numbers Nema vs. IP Ratings Table
Water Tight Designs
Perimeter Seal
One of the most effective methods constructing a membrane switch to meet the IP and NEMA
ratings is to design a perimeter seal as shown in the cut-away view and example photos below.
The width of a perimeter seal may vary depending on the combination of mounting surface and
desired ingress rating. For demanding applications, a perimeter seal made from a very high
bond foam adhesive may be required.
29
Graphic Adhesive
PC, PET, PMMA Spacer
Rear Adhesive
Perimeter Seal
Circuit Tail
Common Perimeter Seal width:
3mm (0.12”) min.
Membrane Switch Assembly
with Perimeter Seal
Membrane Switch
Sub-Assembly
Graphic Overlay +
Perimeter Seal
Perimeter Seal
One of the most effective methods constructing a membrane switch to meet the IP and NEMA
ratings is to design a perimeter seal as shown in the cut-away view and example photos below.
The width of a perimeter seal may vary depending on the combination of mounting surface and
desired ingress rating. For demanding applications, a perimeter seal made from a very high
bond foam adhesive may be required.
29
Graphic Adhesive
PC, PET, PMMA Spacer
Rear Adhesive
Perimeter Seal
Circuit Tail
Common Perimeter Seal width:
3mm (0.12”) min.
Membrane Switch Assembly
with Perimeter Seal
Membrane Switch
Sub-Assembly
Graphic Overlay +
Perimeter Seal
Water Tight Designs
Perimeter Seal Continued
Another variation of the perimeter seal is shown below. This particular constructions adds a
solid backer of adhesive with the tail exiting internally. Advantages of this variation include the
need to peel only one adhesive liner before applying the membrane switch as well as a more
robust sealing solution for irregular mounting surfaces.
30
Graphic Adhesive
PC, PET, PMMA Spacer
Rear Adhesive
Membrane Switch Sub-Assembly
NOTE: The tail exits the switch assembly inside the perimeter
seal and within the perimeter of the solid adhesive backer.
Example based on the cut-
away view above. Again, the
tail exist within the perimeter
of the solid adhesive backer
PC, PET, PMMA Spacer
Rear Adhesive
Perimeter Seal
Solid Adhesive Backer
Perimeter Seal Continued
Another variation of the perimeter seal is shown below. This particular constructions adds a
solid backer of adhesive with the tail exiting internally. Advantages of this variation include the
need to peel only one adhesive liner before applying the membrane switch as well as a more
robust sealing solution for irregular mounting surfaces.
30
Graphic Adhesive
PC, PET, PMMA Spacer
Rear Adhesive
Membrane Switch Sub-Assembly
NOTE: The tail exits the switch assembly inside the perimeter
seal and within the perimeter of the solid adhesive backer.
Example based on the cut-
away view above. Again, the
tail exist within the perimeter
of the solid adhesive backer
PC, PET, PMMA Spacer
Rear Adhesive
Perimeter Seal
Solid Adhesive Backer
Back Panels
Back Panels
If the assembly requires, Butler Technologies can source and apply a membrane switch to a
rigid metal or plastic back panel (a.k.a. sub-panel). Back panels are typically fabricated from
aluminum and can include a variety of mounting hardware. The aluminum can be left unfinished
or produced with an anodized or painted finish. Back panels can also be fabricated from acrylic
or polycarbonate sheet but do not have mounting hardware but can include holes for mounting
hardware.
Back panels serve several functions:
• Act as a rigid backing for actuating switches if the device’s enclosure is not rigid.
• Allow the user interface sub-assembly to be mounted to the device’s chassis.
• Provide a mounting system for internal components such as circuit boards and LCD or LED
displays.
31
Back Panels
If the assembly requires, Butler Technologies can source and apply a membrane switch to a
rigid metal or plastic back panel (a.k.a. sub-panel). Back panels are typically fabricated from
aluminum and can include a variety of mounting hardware. The aluminum can be left unfinished
or produced with an anodized or painted finish. Back panels can also be fabricated from acrylic
or polycarbonate sheet but do not have mounting hardware but can include holes for mounting
hardware.
Back panels serve several functions:
• Act as a rigid backing for actuating switches if the device’s enclosure is not rigid.
• Allow the user interface sub-assembly to be mounted to the device’s chassis.
• Provide a mounting system for internal components such as circuit boards and LCD or LED
displays.
31
Membrane Switch Specifications
Generic Membrane Switch Specifications
Mechanical Characteristics
Life Expectancy: Tactile Type = 1,000,000 actuations
Non-tactile Type = 5,000,000 actuations
NOTE: Life expectancy depends on key design, materials used,
and environment
Actuation Force: 180 to 450g (6 to 16 oz.) for Tactile Type (most common range)
55 to 285g (2 to 10 oz.) for Non-Tactile Type (most common
range)
Switch Stroke: 0.6 to 1.5mm (.023” to .060”) for Tactile Type
0.13 to 0.5mm (.005” to .020”) for Non-Tactile Type
Bend Radius of Tail: 3.2 to 25.4mm (0.125” to 1.00”) typical.
NOTE: Over-flexing the body of the membrane switch may
result in dome failure and/or damage to surface mount
components.
Electrical Characteristics
Maximum Circuit Rating: 30V DC, 100mA, 1 watt
Closed Circuit Resistance: < 100Ω (closed circuit resistance)
Contact Bounce: < 5 milliseconds for Tactile Type
< 20 milliseconds for Non-Tactile Type
Insulation Resistance: 100MΩ at 100V DC
Dielectric Strength: 250VRMS (50-60Hz, 1 min.)
Environmental Characteristics
Operating Temperature: -40° to +80°C (-40° to +176° F)
Chemical Resistance: Excellent chemical resistance when a hardcoated or polyester
graphic overlay is used.
Weatherability: Outdoor polycarbonates and polyesters available for graphic
overlays.
Moisture Resistance: Water-tight constructions available NEMA and IP-rated
assemblies.
NOTICE: The performance specification data listed above is typical to the average membrane switch construction and can vary
dependent on the actual switch construction (layers, materials, components, etc.). The data shall be used only as a reference
guide for product design or selection with the actual performance evaluated through customer validation testing.
32
Generic Membrane Switch Specifications
Mechanical Characteristics
Life Expectancy: Tactile Type = 1,000,000 actuations
Non-tactile Type = 5,000,000 actuations
NOTE: Life expectancy depends on key design, materials used,
and environment
Actuation Force: 180 to 450g (6 to 16 oz.) for Tactile Type (most common range)
55 to 285g (2 to 10 oz.) for Non-Tactile Type (most common
range)
Switch Stroke: 0.6 to 1.5mm (.023” to .060”) for Tactile Type
0.13 to 0.5mm (.005” to .020”) for Non-Tactile Type
Bend Radius of Tail: 3.2 to 25.4mm (0.125” to 1.00”) typical.
NOTE: Over-flexing the body of the membrane switch may
result in dome failure and/or damage to surface mount
components.
Electrical Characteristics
Maximum Circuit Rating: 30V DC, 100mA, 1 watt
Closed Circuit Resistance: < 100Ω (closed circuit resistance)
Contact Bounce: < 5 milliseconds for Tactile Type
< 20 milliseconds for Non-Tactile Type
Insulation Resistance: 100MΩ at 100V DC
Dielectric Strength: 250VRMS (50-60Hz, 1 min.)
Environmental Characteristics
Operating Temperature: -40° to +80°C (-40° to +176° F)
Chemical Resistance: Excellent chemical resistance when a hardcoated or polyester
graphic overlay is used.
Weatherability: Outdoor polycarbonates and polyesters available for graphic
overlays.
Moisture Resistance: Water-tight constructions available NEMA and IP-rated
assemblies.
NOTICE: The performance specification data listed above is typical to the average membrane switch construction and can vary
dependent on the actual switch construction (layers, materials, components, etc.). The data shall be used only as a reference
guide for product design or selection with the actual performance evaluated through customer validation testing.
32
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