Low cycle fatigue of surface mounted chip carrier/printed wiring board joints

Chip-barrier/printed-wiring-board joints have been tested isothermally, at 35°C, in shear. The joints were subjected to fully reversed cycling with fixed plastic displacement limit. The fatigue life was correlated with this displacement by a pseudo Coffin-Manson law. The fatigue life was defined in terms of 25%, 50%, 90%, and 100% drop in the load required to produce a given displacement. The resistance of each of 22 joints was also measured and the fatigue life, N_f, defined in terms of the first joint to increase by 0.02%, 0.05%, 0.1%, 1%, 10%, 100%, and 10×. The results were found to be in general agreement with those obtained previously on single, larger, solder joints. Some variations were noted in the Coffin-Manson exponent, depending on how the displacement and fatigue lives were defined. This is discussed along with a model describing the process of joint failure. A set of displacement versus fatigue life curves which can be used to estimate the joint life on the basis of a variety of criteria is provided