On the Influence of Internal Void Size on the Fracture Stress of Constrained Solder Joints

The fracture strengths of thin solder joints were investigated experimentally and with Finite Element Analysis. Due to a constraining effect, thin solder joints can carry loads which are much higher than the ultimate tensile strength of bulk solder material. On the other hand, thin solder joints show a tendency of being brittle. In fact, the tensile properties show a dependence on the quality of the intermetallic compound at the interface to the base material. Consequently, the size of microscopic defects in the intermetallic compound has a dominant influence on the fracture stress. This behavior could nicely be explained with Finite Element simulations based on strain gradient elasticity.