Geometry Influence on Fracture Behavior of Lap-Shear Solder Joints

Abstract

Single lap-shear (SLS) specimens of 63Sn37Pb solder joints were prepared with three different adherend thicknesses at three varying joint lengths. The fracture force was measured at a shear strain rate of 0.01 s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> for different geometries. The elastic–plastic fracture mechanics (EPFM) theory was used to find the energy dissipated in each case using a finite element model (FEM), and the fracture energy was obtained by cohesive zone modeling (CZM). Both 2-D and 3-D models were used to explain the variations in fracture energy by the level of constraint on the joint. Also, the plastic zone area and stress distribution along the solder layer were calculated at the moment of fracture. A phase angle definition was proposed and compared in different solder lengths to show its influence on fracture energy. It was concluded that the fracture energy was influenced by the local phase angle and plastic zone area at the moment of fracture. The effect of adherend thickness on fracture load was significant especially for long joints (i.e., lengths of 6.35 and 12.7 mm). The observations on the crack path showed that the crack was initiated near one of the adherends and tended to propagate within the intermetallic compound (IMC) layer. Also, the planar fracture surface was observed in all the specimens except for the short solder joints (i.e., with the length of 2.54 mm).