On PCBs, nickel is used as a substrate plating for precious and base metals. The deposited layer of PCB low-stress nickel is usually plated with a modified Watts nickel plating solution and some sulfamate nickel plating solutions with stress-reducing additives. The following is an analysis of what problems you usually encounter when using PCB nickel plating solution?
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 55-60 degrees. If the temperature is too high, hydrolysis of the nickel salt will occur, causing pinholes in the plating, and also reducing the 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 performance of the electrolyte. Generally, the pH value of the PCB nickel plating electrolyte is maintained between 3 and 4. The nickel plating solution with higher pH value has higher dispersion force and higher cathodic current efficiency. However, if the pH is too high, because the cathode continuously precipitates hydrogen 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 a bright coating will be narrowed. Add nickel carbonate or basic nickel carbonate, the pH value will increase; add sulfamic acid or sulfuric acid, the pH value will decrease, 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 nickel angles inside. The titanium basket should be put into an anode bag made of polypropylene material to prevent the anode mud from falling into the plating solution, and should be cleaned regularly and checked whether the holes are unblocked.
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 main points of the process regulations stipulated in the process control, regularly analyze the components of the plating solution 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, reduce the concentration change, and increase the upper limit of the allowable current density. Stirring the plating solution also has a very important effect, which is to reduce or prevent pinholes in the nickel plating layer. Commonly used compressed air, cathode movement and forced circulation (combined with carbon core and cotton core filter) stirring.
7. Cathode current density—the cathode current density has an impact on the cathode current efficiency, deposition rate and coating quality. When electrolytic nickel plating with a lower pH is used, in the low current density area, the cathode current efficiency increases with the increase of the current density; in the high current density area, the cathode current efficiency has nothing to do with the current density, and when a higher PH is used When electroplating liquid nickel, the relationship between cathode current efficiency and current density is not great. Like other plating types, the range of cathode current density selected for nickel plating should also depend on the composition, temperature and stirring conditions of the plating solution.
