What problems are usually encountered when PCB nickel plating solution is used

On PCBs, nickel is used as a substrate coating for precious and base metals. PCB‍Low stress nickel deposition layer is usually plated with a modified Watt nickel bath and some sulfamate nickel baths with stress-reducing additives.

1. Temperature - Different nickel processes use different bath temperatures. In the nickel plating solution with higher temperature, the obtained nickel coating has low internal stress and good ductility. The general operating temperature is maintained at 55 to 60 degrees. If the temperature is too high, the hydrolysis of the nickel salt will occur, causing pinholes in the coating and reducing cathodic polarization.

2. PH value - The PH value of the nickel plating electrolyte has a great influence on the performance of the coating and the electrolyte. Generally, the pH value of PCB nickel plating electrolyte is maintained between 3 and 4. Nickel baths with higher pH have higher dispersion power and higher cathode current efficiency. However, if the pH is too high, due to the continuous evolution of hydrogen from the cathode during the electroplating process, when it is greater than 6, pinholes will appear in the coating. The nickel plating solution with lower pH has better anode dissolution, which can increase the content of nickel salt in the electrolyte. However, if the pH is too low, the temperature range for obtaining bright coatings will be narrowed. Adding nickel carbonate or basic nickel carbonate, the pH value increases; adding sulfamic acid or sulfuric acid, the pH value decreases, check and adjust the pH value every four hours during the working process.

3. Anode - The conventional nickel plating of PCBs that can be seen at present all use soluble anodes, and it is quite common to use titanium baskets as anodes with built-in nickel corners. The titanium basket should be put into an anode bag made of polypropylene material to prevent the anode slime from falling into the plating solution, and should be cleaned and checked regularly to see if the holes are unobstructed.

4. Purification - When there is organic pollution in the plating solution, it should be treated with activated carbon. However, this method usually removes a portion of the stress reliever (additive), which must be replenished.

5. Analysis - The plating solution should use the key points of the process regulations specified by the process control, regularly analyze the plating solution components and the Hull cell test, and guide the production department to adjust the parameters of the plating solution according to the obtained parameters.

6. Stirring - the nickel plating process is the same as other electroplating processes. The purpose of stirring is to accelerate the mass transfer process to reduce the concentration change and increase the upper limit of the allowable current density. Stirring the plating solution also has a very important role in reducing or preventing pinholes in the nickel plating layer. Compressed air, cathode movement and forced circulation (combined with carbon core and cotton core filtration) are commonly used for stirring.

7. Cathode current density - Cathode current density has an effect on cathode current efficiency, deposition rate and coating quality. When using the electrolyte with lower pH for nickel plating, in the low current density region, the cathode current efficiency increases with the increase of the current density; in the high current density region, the cathode current efficiency has nothing to do with the current density, and when using a higher pH The cathodic current efficiency has little to do with the current density when electroplating nickel solution. Like other plating species, the range of cathode current density selected for nickel plating should also depend on the composition, temperature and stirring conditions of the electroplating solution.