Electroless Copper Plating

In electroless copper plating solution, the reaction among copper sulfate, Rochelle salt, and sodium hydroxide is shown by the following equation:Reaction of deposition of copper is shown by the following equation:When this solution is settled for a time, sodium hydroxide is decomposed by the reactions shown in the following two equations:NaOH+CO2→NaHCO3…… (3)NaOH+2HCHO→HCOONa+CH3OH…… (4)It is derived from the four equations mentioned above that 4 mol or more of sodium hydroxide, 1 mol or more of Rochelle salt, and 2 mol or more of formalin are required for the deposition of 1 mol of copper.Rate of deposition of copper is proportional to the temperature and the amounts of copper sulfate and sodium hydroxide in plating solution. However, self-decomposition of the solution will take place with the increase of the above amounts or temperature rise. The rate is promoted by mechanical stirring of the plating solution, which will prevent self-decomposition.For preventing self-decomposition in the solution of high concentration, it is effective to add 1-3g/l of potassium cyanide to the solution. However, as the effects of the addition, the rate of deposition is lower and blackish brown deposit in initial stage has much less adhesive power.