Spalling behavior of interfacial intermetallic compounds in Pb-free solder joints subjected to temperature cycling loading

Morphological evolution of interfacial intermetallic compounds (IMC) subjected to thermal cycling loading was studied numerically and experimentally. In this study, the microstructure of Sn3.5Ag0.7Cu solder joint and its interfacial IMCs were investigated using Tape Ball Grid Array assemblies. Needle-type and hemispherical-type morphologies of interfacial IMCs were formed after reflow. During temperature cycling, the IMC grains ripened into large hemispherical-type and spheroidal-type morphologies and spalled into the solder joint. Finite element analysis showed that the spalling behavior was promoted by the geometrical changes of the IMC structure and the induced cyclic shear stresses during temperature cycling loading. For needle-type grains, the stress was concentrated at the tip of the IMCs, while the maximum shear stress was redistributed to the roots of the spheroidal-type grains.