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Analysis of Thermomechanical Strains in Solder Joints of Surface-Mount Assemblies

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The mechanical response of solder joints during thermal cycling is a complex phenomenon. In addition to pure shear due to the mismatch between the coefficients of thermal expansion (CTEs) of the package and that of the substrate, [1] and bending of the whole assembly by bimetallic strip effect, [2] the CTE mismatches at the solder joint/package and solder joint/substrate interfaces are additional sources of shear in the solder joint.