5. Maintenance of Plating Solution

a) Temperature

– Different nickel processes require different bath temperatures.

– Higher temperature results in low internal stress and good ductility of nickel coating.

– Internal stress of the coating stabilizes at 50°C.

– General operating temperature is maintained at 55–60 degrees C.

– Excessive temperature can lead to hydrolysis of nickel salt, causing pinholes in the coating and reducing cathodic polarization.

– It is essential to control and maintain the working temperature within the specified range by using a normal temperature controller.

b) PH value

– PH value of the nickel plating electrolyte significantly affects the coating and electrolyte performance.

– Maintenance of PCB nickel plating electrolyte PH value between 3-4 is crucial.

– Higher PH values result in better dispersion power and cathode current efficiency, but excessive PH levels can lead to the appearance of pinholes and increased brittleness in the coating.

– Regular PH value checks and adjustments are necessary during the working process.

c) Anode

– Conventional nickel plating of PCBs often uses soluble anodes, typically titanium baskets with nickel corners inside.

– Anode maintenance involves placing the titanium basket in a polypropylene anode bag to prevent anode slime from contaminating plating solution.

– Regular cleaning and checks of the anode holes are needed.

d) Purification

– Organic contamination in the bath should be treated with activated carbon, but this often removes a portion of the stress reliever (additive) that must be replenished.

– Several steps, including heating, aeration, and use of filter powder, are involved in the purification process.

– Anode hanger cleaning, cathode plating, and other maintenance procedures are also necessary.

e) Analysis

– Regular analysis of the plating solution components and Hull cell testing are essential to guide production department adjustments.

f) Stirring

– Stirring accelerates the mass transfer process, reduces concentration changes, and increases the allowable current density.

– It plays a critical role in reducing or preventing pinholes in the nickel plating layer.

– Various methods such as compressed air, cathode movement, and forced circulation can be used for stirring.

g) Cathode Current Density

– Cathode current density has a direct impact on cathodic current efficiency, deposition rate, and coating quality.

– Selection of cathode current density should depend on composition, temperature, and stirring conditions of the electroplating solution.

– Due to the large area of the PCB board, the current density in high and low current areas is reduced, generally being around 2A/dm2.