Intermetallic compound layer development during the solid state thermal aging of 63Sn-37Pb solder/Au-Pt-Pd thick film couples

A study was performed which examined the solid state, intermetallic compound layer growth kinetics between 63Sn-37Pb solder and a 76Au-21Pt-3Pd (wt.%) thick film conductor on 96% alumina substrates. A linear, multivariable regression analysis was used to assess the experimental data according to the following empirical relationship: x-x0=Atⁿ exp(-ΔH/RT). A time exponent of n=0.78±0.08 was observed, suggesting that a combination of bulk diffusion and interface reaction mechanisms were responsible for layer growth. The apparent activation energy, ΔH, was 106⩾8 kJ/mol. Parallel aging experiments were performed on diffusion couples fabricated between 63Sn-37Pb solder and bulk alloy stock having the same Au-Pt-Pd composition as the thick film. Similar growth kinetic parameters were computed. Intermetallic compound layer growth was accelerated under thermal cycling and thermal shock conditions due to residual stresses generated by the thermal expansion mismatch between the solder and the ceramic substrate