Thermal cycle performance of Ag-bearing thick film conductors for automotive applications

The reliability of several soldered thick film Ag/Pd and Ag/Pt conductors under thermal cycle conditions is reported. Evaluations were made of the thermal cycled adhesion by wire peel tests, as well as the electrical reliability of soldered components. In some cases, the failure modes with the mounted components were at the conductor/substrate or conductorlsolder interfaces, and agreed generally with peel test results. However, when components were soldered to Pd/Ag conductors, vertical cracks were often observed through the conductor at the edge of the solder fillet. These cracks did not agree with failure modes from peel tests. The tendency for vertical and interface cracks was significantly reduced with the use of a high adhesion, dense firing Pd/Ag composition. The use of severe shock thermal cycle profiles tended to generate more vertical cracks as well as conductor/substrate cracks compared to slower thermal cycle profiles. No vertical cracks or conductorlsubstrate cracks were observed with the PVAg conductor because of the much slower rate of Sn intermetallic formation compared with Pd/Ag conductors. Failure modes with the PVAg conductor were often in the solder near the conductor/solder interface.