Deformation analysis of lap-shear testing of solder joints

A combined numerical and experimental study of lap-shear testing of solder joints was carried out. The primary objective was to provide a quantitative evaluation of shear deformation experienced by the solder. The numerical analysis was based on finite element modeling of deformation in the substrate-solder assembly. The calculated shear response, utilizing both the commonly adopted far-field measurements and the actual shear strain in solder, was found to differ significantly. The geometric and material parameters during lap shear were explored to provide physical insight into the problem. The nature of deformation of the substrate was seen to greatly influence the shear behavior of the solder. The "transmission" of shear strain into the solder is very ineffective when the solder is in the elastic state, resulting in smaller shear strains in the solder than the nominal values. This effect is also true even when the solder is deforming plastically. Experimental measurements of solder shear using direct optical measurements confirmed the numerical findings. Subtraction of the average deformation of the Cu substrate provides a reasonable, albeit not complete, approximation of the solder strain.