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

Chip carrier/printed wiring board joints have been tested isothermally, at 35°C, in shear. The joints were subjected to fully reversed ramp cycling with fixed plastic displacement limits. The fatigue life was correlated to this displacement by a pseudo Coffin-Manson law. The fatigue life was defined in terms of a 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 N_f defined in terms of the first joint to increase by 0.02%, 0.05%, 0.1% 1%, 10%, and 100% as well as 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 that can be used to estimate the joint life on the basis of a variety of criteria is provided