Surface treatment plating process

Discusses the electroplating process details and associated criticalities

1. PLATING-PROCESS CRITICALITIES 1 [email protected]

2. Sequence What & Why of Elctroplating Factors Influencing Electro Deposition Current density Cathode Efficiency Agitation Bath composition & Solution concentration Water Requirement The presence of impurities & Filtration Hydrogen Embrittlement and its Effects

3. What is Electroplating Electroplating is often called "electro deposition", and the two terms are used interchangeably. As a matter of fact, "electroplating" can be considered to occur by the process of electro deposition. Electro deposition is the process of producing a coating, usually metallic, on a surface by the action of electric current.

4. What is Electroplating The deposition of a metallic coating onto an object is achieved by putting a negative charge on the object to be coated and immersing it into a solution which contains a salt of the metal to be deposited (in other words, the object to be plated is made the cathode of an electrolytic cell)

5. What is Electroplating The metallic ions of the salt carry a positive charge and are thus attracted to the object When they reach the negatively charged object (that is to be electroplated), it provides electrons to reduce the positively charged ions to metallic form.

6. Why Electroplating Electroplating is a surface coating method that forms an adherent layer of one metal on another To achieve the desired electrical and corrosion resistance, reduce wear & friction, improve heat tolerance and for decoration purposes

7. Requisites of Electroplating Clean substrates, solutions, and containers, etc. Even low impurity levels would result in poor-quality films Good resist adhesion on the substrate is required The plating solution must have easy access to recesses, and be compatible with the resist and substrate materials Uniform current distribution on the substrate surface

8. Factors Influencing Electro Deposition Current density Cathode Efficiency Agitation Bath composition and Solution concentration Water Requirement The presence of impurities (from poor cleaning, poor anodes, water contaminants, poor water rinse before plating bath etc) & Filtration

9. Factors Influencing Electro Deposition Current Density It is the application of current (Amperes) per unit area Current density for a particular bath are defined on the basis of bath composition and required deposition thickness and deposition rates Selection of current density is critical as poor selection will result in defects in deposition quality like porosity, poor deposition thickness Areas of the parts to be plated, must carefully be calculated and current densities be selected accordingly

10. Factors Influencing Electro Deposition Cathode Efficiency The ratio of the weight of metal actually deposited to the weight that would have resulted if all the current had been used for depositing it is called the cathode efficiency Cathode efficiency in plating depends on : Electrolyte or bath Concentration of chemical composition pH and agitation Current density

11. Factors Influencing Electro Deposition Cathode Efficiency Effects of poor Cathode Efficiency If any of the depending factors are disturbed then cathode efficiency will adversely suffer and result in: Poor deposition Process will be less cot effective in terms of electricity consumption, solution composition and early anode dissolution

12. Factors Influencing Electro Deposition Agitation In a plating solution near the cathode, as metal is depleted, the solution becomes less dense and tends to rise along the face of cathode Opposite occurs at the face of anode: solution tends to stream down The solution is required to be agitated for homoginaty This problem, if not catered (through agitation) wherever required, will cause non-uniform deposition of metal on the substrate Cathode efficiency will greatly suffer

13. Factors Influencing Electro Deposition Bath Composition and Solution Concentration Metal Ions Electrolytes Organic Additives Brighteners Levelers Structure Modifiers Wetting Agents

14. Factors Influencing Electro Deposition Bath Composition and Solution Concentration 1. Metal Ions The metal ions to be plated are present in solution 2. Electrolytes Electrolytes give conductivity to the bath and high concentration of the electrolyte ensures max conductivity Electrolytes control the bath PH value which if higher than required level, will lead to deposition of Metal Hydroxyl ions (not desired) Conductivity of electrolyte effects “Throwing Power” (ability of the bath to give even deposit) of the bath

15. Factors Influencing Electro Deposition Bath Composition and Solution Concentration 3. Organic Additives Brighteners To cause an even, fine grained deposit Levelers To produce a level deposit where otherwise there would be rapid deposition of metal Structure Modifiers To optimize particular deposit properties e.g hardness etc Wetting Agents To accelerate the release of hydrogen gas bubbles from solution surface

16. Factors Influencing Electro Deposition Water Requirement Water is the main ingredient in all of the baths used and its quality will effect the various operations Impurities present in most water supplies may include dissolved mineral salts; organic compounds; suspended solids and microorganisms De-ionized water requirement is critical Final rinse before Plating bath to avoid bath contamination Plating bath to avoid contamination Final rinse before dispatch to avoid stains caused by Ca, Mg salts present in non treated water

17. Factors Influencing Electro Deposition Presence of Impurities and Filtration Water is the main ingredient in all of the baths used and falk;sjdkjfalkjd

18. Hydrogen Embrittlement Hydrogen embrittlement is a generic term used to describe a variety of fracture phenomena having a common relationship to the presence of hydrogen in the metal as a solute or in the atmosphere as a gas In general any process producing atomic H at a metal surface will induce considerable hydrogen absorption in that metal (Electroplating, Electroless plating, Acid Pickling, Electrolytic cleaning) Hydrogen embrittlement alters the Fatigue limit characteristics of the metal

19. Effects of Hydrogen Embrittlement Corrosion reactions can generate Hydrogen, and choosing proper coating to prevent corrosion is important Problems as a result of H embrittlement/ hydriding : • Failure of aircraft components • Blisters in Cu, Al, and Steel components • Reductions in mechanical properties of materials