Intermetallic growth between lead-free solders and palladium

Intermetallic growth between Pd and the lead-free solders Sn-Ag and Sn-AgCu has been studied. Diffusion couples were prepared by reflowing the solders on Pd and then aging the couples at 156 degreesC, 175 degreesC, 195 degreesC, and 210 degreesC. At the higher temperatures of 175 degreesC, 195 degreesC, and 210 degreesC, PdSn4 made up most of the layer that grew between the solders and the Pd, although small regions of second phases were always found in the PdSn4 matrix, and it was sometimes possible to identify discontinuous regions of PdSn3 next to the Pd. The thickness of the intermetallic layer increased with the square root of time, consistent with diffusion-controlled growth. In couples annealed at 156 degreesC, the morphology of the PdSn3 phase and growth kinetics differed depending on the composition of the solder.