Strength and reliability of ceramic modules soldered to flexible cables

The strength and reliability of soldered interconnections between module pins and flexible cables are discussed. A quantitative measure of the strength of the connection is described. Individual pins were mechanically tested by measuring the force required to push them through the cable, and force and failure mode were recorded. The push-through test was used to determine optimum solder volume for maximum initial strength and to measure degradation following exposure to environmental stresses. The first reliability stress was to store units at constant elevated temperature of 80, 100, and 125 degrees C for up to 8500 h. Analysis of these results was done with a nonlinear regression model. For the dominant mode, the results of this model are: PS/sub i/(t,T)=3.05-58*exp(-2629/T)*t/sup 0.38/+ epsilon /sub i/, where PS(t,T) is the push-through strength as a function of time, t, and Kelvin temperature, T. epsilon /sub i/ represents the random part and is distributed normally with 0 mean. These results give an effective activation energy of 0.6 eV. The second reliability test was to thermally cycle units between -40 and +100 degrees C for up to 1000 cycles. There was no degradation. A simple first-order estimate indicates that this is equivalent to about five lifetimes.<>