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

Chip-barrier/printed-wiring-board joints have been tested isothermally, at 35 degrees 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/sub 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.<<ETX>>