Aerospace electronic and photonic packaging: Predicted thermal stresses in Bi- and tri-material assemblies

Simple, easy-to-use and physically meaningful analytical predictive models are developed for the evaluation of thermal stresses in bi- and tri-material bodies employed in various aerospace electronic and photonic packaging designs. The numerical examples are carried out for a bi-material assembly comprised of a silicon IC and a ceramic substrate, and for 2) a tri-material body obtained as a result of soldering the above assembly onto a copper heat sink. In both cases the solder layer is viewed as the weakest element in the structure. The developed models can be used in physical design and reliability evaluations of assemblies of the type in question. It is suggested that analytical models of the type considered in this paper always precedes FEA simulations and experimentations, especially when there is a need to understand and to explain the physics of the observed or anticipated failure.