Shear deformation of indium solder joints

Indium solder joint deformation has been investigated under conditions of shear loading and stress relaxation at room temperature. The deformation behavior was characterized as a function of strain, strain rate, joint thickness, and hold time. Implications of the results are discussed relative to thermal stresses and solder joint reliability in an electronic package. Work hardening during loading was found to increase with strain rate and volume fraction of intermetallics. The behavior was also dependent on the amount of work hardening and recovery that occurred in the prior stress relaxation cycle. The stress-strain rate characteristics during relaxation were found to be a function of the initial strain level and the spring constant of the assembly. It is shown how a material constitutive relation can be used with the assembly spring constant to calculate stress reduction over time. This procedure can be applied to any electronic assembly which undergoes stress relaxation during a constant temperature hold.<
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