Analysis of Mechanism of Corrosion Fracture of Gold Plated Kovar Transistor Leads

After analyzing the factors such as the presence of the contaminants containing free chloride, the presence of the stresses, the incomplete Au-plating on the Kovar and the entrance of hydrogen into the Kovar, it is found that the discontinuity of cathodic plating is bound to create the galvanic corrosion in the presence of the appropriate electrolyte, and the extent of corrosion of substrate Kovar exposed at such discontinuities depends on Cl-concentration and pH, etc. Especially when the pores in the plating exceed a certain critical diametre, it is possible to form constantly growing pitting, which is the most harmful. Thus in the presence of applied stress, remained stress or wedging action of corrosion product it can lead to scc.
The mechanism of corrosion fracture of Au-plated Kovar transistor leads caused by the coordinated actions of galvanic corrosion, pitting (or crevice corrosion) and scc can better explain the facts observed in the practice. The ways to improve the resistance to corrosion of Au-plated Kovar transistor leads are also proposed.