Analyzing the mechanical strength of SMT attached solder joints

Analytic approaches to the pull strength and shear strength of SMT (surface mount technology) attached solder joints have been studied by mathematical models. The predicted pull/shear strength of leaded ceramic quad packages correlated with the experimentally measured data quite well. Lead/pad design is shown to have the most significant impact on the solder joint strength. The design rules for butt leaded and land patterns have been developed. The predictive models have been used for defining the design guidelines for selecting the optimum lead/pad configurations, the minimum solder volume, and the maximum component misalignment for fine pitch SMT assemblies. The SPC (statistical process control) limits established through destructive mechanical testing can be used as online monitors for checking the short-term reliability of solder joints. The short-term reliability data generated by conducting destructive mechanical testing are complementary to the long-term reliability test.<
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