Low Cycle Fatigue of Surface Mounted Chip Carrier/Printed Wiring Board Joints

摘要

Chip carrier/printer wiring board joints have been tested isothermally, at 35 C, in shear. The joints were subjected to fully reversed 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 Nf defined in terms of the first joint to increase by 0.02%,0.05%,0.1%,10%,100%, and 10X. 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 was discussed along with a descriptive model describing the process of joint fatigue. A set of displacement vs. fatigue life curves is provided, which can be used to determine the joint life based upon a variety of criteria. Keywords: Surface mount technology, Chip carrier, PWB, Low cycle fatigue joint cracking. (sdw)