SOLDER PASTE: FUNDAMENTAL MATERIAL PROPERTY / SMT PERFORMANCE CORRELATION

摘要

Aggressive form factors, reducing pitch, thinner packages, and larger die to package ratios are leading to higher package warpage during SMT reflow. It is getting more challenging to mitigate warpage driven SMT defects viz. non-wet open (NWO), head-on-pillow (HoP) and solder bridging (SB). We studied multiple paste formulations using SMT hammer tests. Lab level characterizations were also used to establish a correlation between SMT performance and fundamental properties ofsolder pastes. We found that NWO and HoP compete with each other while having a correlation with flux activity to clean OSP on the Cu surface. SB risk showed a correlation with high temperature viscosity, indicating a rheology driven defect. Printability performance also showed a good correlation with the thixotropic index. These learnings will be extremely useful to develop next generation solder pastes to mitigate warpage driven defects.