EVALUATION OF THE EFFECTS OF PROCESSING CONDITIONS ON SHEAR STRENGTH AND MICROSTRUCTURE IN PB-FREE SURFACE MOUNT ASSEMBLY

摘要

Under a three-year long National Science Foundation (NSF) grant, we are investigating factors contributing to Pb-free material adoption. Specifically, we are trying to determine the effect of processing conditions (namely, reflow processing) on the microstructure and shear-test strength of Pb-free solder joints. Presented here are some of the initial findings of a study of the shear strength of these joints. The composition and microstructure of solder joints is characterized as a function of solder joint metallurgy and heat treatment, including reflow schedule and environment, and subsequent annealing treatments. Solder joints evaluated are constructed in ball-on-substrate geometries. The evolution of the microstructure of solder joints is being determined by optical microscopy and scanning electron microscopy. This data will be correlated with measurements of the mechanical properties of solder joints, namely, the shear strength studies. The need to perform microstructural studies, and to correlate these studies with manufacturability and reliability, has been clearly articulated by many researchers from different organizations (notably, by NEMI). This work directly addresses this need.