Numerical and Experimental Study of Residual Stresses and Thermal Fatigue in Soldered Electronic Assemblies

摘要

The assembly examined consists of thin plates of alumina, Kovar, 410 stainless steel and 6061 aluminum bonded together using layers of three different solder alloys: 63% Sn - 37% Pb, 50% Pb - 50% In and 40% In - 40% Sn - 20% Pb. Numerical simulation of the fabrication process was performed using a simplified axisymmetric finite element ''microcell'' model of the actual assembly. The alumina, Kovar, 410 stainless steel and 6061 aluminum layers were modeled as temperature-dependent elastic-plastic materials while the solder alloys were treated as creeping solids following solidification. Experimental testing of the solder alloys was used to generate input for the finite element code constitutive models. The numerical results of this study have provided guidelines for the successful fabrication of the subject assembly. In particular, slower cooling rates following solidification of the solders have been shown to dramatically lower bending stresses generated in the alumina plate. The experimental portion of the program has provided data on the degration of solder bond integrity used to thermal cycling and has identified possible important factors in the mechanical response of thin solder layers. (ERA citation 11:028044)