Size effects in small scaled lead-free solder joints

Due to the ongoing miniaturization in modern microelectronics reliability and quality control of microelectronics devices will also depend on a detailed understanding of the complex mechanical and thermal of solder joints. Therefore the question of the occurrence of size effects or dimensionally induced constraints, which could change the mechanical properties of solder joints in small dimensions dramatically, came into focus of investigation. Tensile tests were performed to investigate the influence of joint size on the tensile strength and fracture strain. Strains across the solder joint were measured using a non-contacting laser speckle sensor. Scanning electron microscopy (SEM) was used to analyze the complex modes of fracture and crack propagation in the solder interconnect. The variation of the gap size influenced also the crack growth behavior. The observed behavior can be interpreted in terms of an existing theory for brazed joints to complement Finite Element Analysis that is usually used for a description of these phenomena.