Dr.RGH_CLASShhhhhhhhhhhhhhhhhh PPT_3.pptx

pcb

1. Introduction to PCB Design Manufacturing

2. What is PCB Printed Circuit Board Electronic Board that connects circuit components PCB populated with electronic components is a printed circuit assembly (PCA) PCBs are rugged, inexpensive, and can be highly reliable Mass manufacturing Professional

3. Materials of PCB Conducting layers are typically made of thin copper foil. The board is typically coated with a solder mask that is green in color. Other colors that are normally available are blue and red. Unwanted copper is removed from the substrate after etching leaving only the desired copper traces or pathways

4. Parts of a PCB Components Pads Traces Vias Top Metal Layer Bottom Metal Layer

5. Components Components are the actual devices used in the circuit. This includes input/output connections. I/O ports, including power supply connections, are also important in the PCB design.

6. Pads Location that components connect to. You will solder components to the pads on the PCB. Pads will connect to traces. Pads have an inner diameter and outer diameter.

7. Traces Traces connect pads together. Traces are essentially the wiring of the PCB. Equivalent to wire for conducting signals Traces sometimes connect to vias. High current traces should be wide. Signal traces usually narrower than power or ground traces

8. Vias Pad with a plated hole connecting traces from one layer of board to other layers. Attempt to minimize via use in your PCBs. Some component leads can be used as vias.

9. Top Metal Layer Most of the components reside on the top layer Fewer traces on the top layer Components are soldered to the pads on the top layer of PCB Higher circuit densities

10. Bottom Metal Layer Few components on this layer. Many traces on this layer. Most soldering done on this layer.

11. Jumpers Often, many signal wires need to exist in too small of a space and must overlap. Running traces on different PCB layers is an option. Multilayer PCBs are often expensive. Solution: use jumpers

12. Solder Mask Protect copper traces on outer layers from corrosion Areas that shouldn't be soldered may be covered with polymer resist solder mask coating Designed to keep solder only in certain areas Prevents solder form binding between conductors and thereby creating short circuits

13. Silkscreen Printing on the solder mask to designate component locations Readable information about component part numbers and placement. Helpful in assembling, testing and servicing the circuit board.

14. Multilayer PCBs More then a top and bottom layer. Typically there will be a power plane, ground plane, top layer, and bottom layer. Sometimes signal layers are added as needed. Sometimes RF planes made of more expensive materials are added.

15. Parts of a PCB The assembly consists the following parts. Components – Actual devices in the board. PCB components can be categorized as active and passive. Active components include: Diode – Allows current to flow in one direction. Transistor – Amplifies and switches electrical power and electronic signals. Integrated Circuits (ICs) – Responsible for several signal processing functions. Passive components include: Capacitor – Stores and discharge electricity. Resistor – Limits the power of electrical current. Inductor – Responsible for creating magnetic field.

16. Parts of a PCB Pads – Location where components connect/solder to. Traces – Connect pads together. Vias – Responsible for making electrical connection between the layers of PCB. Top metal layer – The layer where most of the components are assembled. Fewer traces in this top metal layer. Bottom metal layer – Fewer components in bottom layer and many traces.

17. Package Types PCB components can be mounted onto the board in two ways. Surface Mount – PCB components are mounted directly onto the board. Through-Hole – Components with leads are inserted through mounting holes, hence the name through hole.

18. PCB Material Options When it come to manufacturing PCBs, there are several material options available. Substrate Material Epoxy imprinted fiberglass Polyester (PET) Polyimide Conductor Materiel Electro-deposited copper foil Rolled copper foil Adhesives Polyimide Adhesives Polyester Adhesives Acrylic Adhesives Epoxies Protective Coating Polyimide Adhesives Cover Lays - Polyester or polyimide is combined with a suitable adhesive. Cover Coat - A thin coating of liquid acrylated epoxy and acrylated polyurethane.

19. PCB Material Options

20. Physical Design Issues Component Size Heat Dissipation Input and Output Mounting Points

21. Component Size Make sure components will actually fit. This especially applies for circuits that require high component densities. Some components come in multiple sizes. SMT vs Through Hole Sometimes you can get tall and narrow caps or short and wide capacitors.

22. Heat Dissipation-Heat Sinks Heat sink dissipates heat off the component Doesn’t remove the heat just moves it Some components may get hot. Make sure you get a large enough heat sink. Data sheets specify the size of the heat sink A short circuit may result when two devices share the same heat sink

23. Mounting Points The PCB needs to be mechanically secured to something. Could be the chassis-consist of metal frame on which the circuit boards and other electronic components are mounted. Could be another PCB/socket on PCB. Could be attachments to a heatsink.

24. Parasitics High frequency circuits Series Inductance Shunt Capacitance Inductive Coupling Capacitive Coupling

25. Series Inductance Not an issue for low frequency circuits(<10 Mhz ) The inductance of a trace may be signifigant . For power connections, a shunt capacitor is added to counter the series inductance of a long trace. A capacitor has a low AC impedance A 100nF capacitor is often used along with a larger capacitor. 100 nF ceramics have very low impedance at higher frequencies.

26. Shunt Capacitance Result of wide wires over a ground plane. Limits speed of circuits, including digital circuits Typically insignificant for low performance circuits. To minimize place a capacitor from voltage to ground

27. Inductive Coupling Transfer of energy from one circuit component to another through shared magnetic field Change in current flow through one device induces current flow in other device Current flow in one trace induces current in another trace Minimize the long parallel runs of traces Run traces perpendicular to each other

28. Capacitive Coupling Transfer of energy in electrical n/w due to capacitance between circuit nodes Minimizing long traces on adjacent layers will reduce capacitive coupling Ground planes are run between the signals that might affect each other.

29. Pre-work Thoroughly simulate your circuit-make sure the circuit worked in simulations Thoroughly test the prototype-make sure the circuit worked on the bread board Have all the data sheets handy for every components Play around with the placement of the components

30. Simulations Important to simulate the circuits before building them Allow margin for component tolerances Avoid using precise components. e.g a PWM controller that requires exact 10 V DC to work and will fail if there is 10.01V High performance circuits or SMT devices require PCBs and should be simulated extensively first.

31. Manufacturing/Assembly Steps Following are the step involved in PCB manufacturing. PCB Manufacturing Steps Following are the steps involved in PCB fabrication. Base Material Preparation – Clean the laminate, containing copper foil. Cutting the Base Material – Post the cleaning process, cut the laminate to required specifications. Apply Adhesive on the Laminate - Choose between epoxy or acrylic adhesives to get the job done. Generate Circuit Pattern –Desired circuit patterns can be generated by screen printing or photo imaging. Etch the Circuit Pattern – Etch the copper laminate containing the circuit pattern. Drilling – Drill holes, pads, and vias by using high speed drilling tools. Through-Hole Plating – Deposit the holes with copper and must be chemically plated. Apply Cover lay – Protect the top and bottom side of the board by applying suitable cover lay. Cutting Flex - Cut individual flex from the production panel.

32. Manufacturing/Assembly Steps 11. Cleaning – Clean flux residues that are left behind during the manufacturing process. Use water solution or active cleaning agents to get the job done. 12. Testing – This Includes Automated Optical Inspection (AOI), flying probe test, functional test, and burn-in test. 13. Rework – Rework may be done on the PCB in case of: 14. Component missing 15. Component replacement 16. Trace or pad repair 17. Cuts and Jumps

33. PCB FLOW

34. LIBRARY CREATION OF COMPONENTS IN ORCAD We have to create each and every component in library .

35. PCB DESIGNING PROCESS Step by step: Schematic design: It is a circuit diagram. It uses agreed symbols to represent components and show how they area electrically connected.

36. ENTERING PCB FOOTPRINT FILE & CREATE NETLIST

37. ROUTING & LENGTH MATCHING In electronic design, wire routing, commonly called simply routing, is a step in the design of printed circuit board and integrated circuit.

38. GERBER FILE The gerber format is an open ASCII vector format for 2D binary image. It is used to describe the printed circuit board images: copper layer solder mask.

39. POST FABRICATION The gerber format is loaded to different machine (Re-flow Soldering/Wave Soldering Machine) to fabricate the final physical PCB board.

40. Ten Rules for Components Placement on PCB Design 1. Start placement of big/main/critical components( this could be MCU,DSP,FPGA,DDR, clock devices) and then place support component like resistors, capacitors around them. 2. Use 50 or 100mm as component grid to place these big components ( QFP, BGA, SOP, SOIC, or through hole connectors). Use 25mm as component gird for these SMT resistors/capacitors or other small passive components. 3. Isolate the analog, digital and power supply section. 4. Clock driver/synchronizer should be located close to clock oscillator. 5. Arrange components in rows and columns, and oriented uniformly for ease of installation, inspection and rework. When possible, all polarized components such as tantrum capacitor and diodes in the same direction. Polarity of these components should be indicated on the silkscreen.

41. 6. Keep at least 40mmspace between components and 100mm space from component to board edge. Locate connectors on one edge or one corner of the board. 7. Try to place all components on the top side only. If not possible, only these low profile, small size and low thermal dissipation component (like SMD passive parts) can be on bottom side. 8. Place decoupling capacitors close as much as possible to VCC pin on active components. 9. Keep at least 200mm clearance from transformer to electrolytic capacitor. 10. Locate indication LEDs, test points, switches, jumpers and adjustable components for easy access. One more rule, it’s always good to double check analog, high frequency, RF, high voltage, high profile, heavy or high heat components before starting trace routing .

42. Introduction to Design Rules There are four types of design rules: - Electrical Constraints: Performance characteristics - Physical Constraints: Line (Trace) width, via selection, and layer restriction - Spacing Constraints: Clearances between lines,pads, vias,and copper - Same Net Spacing constraints: Clearances between lines pads vias, and copper areas (shape) on the same net.

43. Steps in PCB design Film Generation 2. Shear Raw Material 3. Drill Holes Industry standard 0.059" thick, copper clad, two sides

44. Steps in PCB design 4. Electrolus copper Apply copper in hole barrels 5. Apply Image Apply Photosensitive Material to develop selected areas from panel

45. Steps in PCB Design 6. Strip and Etch Remove dryfilm, then etch exposed copper Tin protects the copper circuitry from being etched 7. Solder Mask Apply solder mask area to entire board with the exception of solder pads

46. Steps in PCB Design 8. Solder Coat 9. Silkscreen Apply white letter marking using screen printing process Apply solder to pads