Strength and reliability of ceramic modules soldered to flexible cables

A study of the strength and reliability of soldered interconnections between module pins and flexible cables is presented. A quantitative measure of the strength of the connection is developed. Individual pins were mechanically tested by measuring the force required to push them through the cable. Both force and failure mode were recorded. The push-through test was used to determine optimum solder volume for maximum initial strength and also to measure degradation following exposure to environmental stresses. The first reliability stress was to store units at constant elevated temperatures of 80, 100, and 125°C for up to 8500 h. Analysis of these results was done with a nonlinear regression model. Since multiple failure modes were present, the data was deconvolved by treating it as multiply censored and analyzing it using maximum-likelihood techniques. The temperature dependence of the degradation rate was assumed to be Arrhenius. For the dominant mode, the results of this model are shown. The results give an effective activation energy of 0.6 eV. The second reliability test was to thermally cycle units between -40 and +100°C for up to 1000 cycles. There was no degradation. A simple first-order estimate indicates that this is equivalent to about five lifetimes