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

Chip carrier/printed wiring board joints have been tested isothermally, at 35 degrees 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/sub 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.<
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