Metallising of Circuit Boards Using Mixed SnCl2 / PdCl2 Catalysts

Mixed SnCl2/PdCl2 catalyst solutions are often used to catalyse the board surface prior to metallising by electroless deposition. An accelerator is also required in the catalysing sequence in order to boost the catalytic activity of the surface. Skip plating is a prime source of unreliability and can often be traced to low catalytic activity. Processing variables directly affecting catalytic activity are discussed. These include surface roughness, type of accelerator employed and its operating conditions, and the efficiency of rinsing as well as the composition of the catalyst solution. The mechanism of catalysis is also discussed, involving theories of the colloidal and complex nature of the catalyst solution.