A nonlinear thermal stress analysis of surface mount solder joints

A set of nonlinear finite-element (FE) cyclic thermal stress analyses of leaded ceramic chip carriers (LCCC) was performed. The FE models included the geometric and elastic compliance effects associated with the LCCC cavity, Kovar lid, copper solder pads and thermal joints, the orthotropic printed wiring board (PWB), and a constraining thermal core. The effect of nonlinear and rate-dependent constitutive characteristics of the solder alloy on the distribution of cyclic stress, strain, and energy-dissipation behavior was studied. It is shown that the inclusion of rate effects in the material behavior has a paramount effect on the stress, strain, and energy-dissipation predictions. The difference is due to the creep relaxation leading to redistribution of the load, which was not predicted by an elastic-plastic material model alone. Acceleration factors were calculated from the results of analyses performed for an accelerated thermal test cycle case and a specific real-life thermal cycle case