BGA PAD CRATERING AND PEELING DURING SMT REFLOW

摘要

The industry is moving toward ultra-low loss Printed Circuit Board (PCB) laminate material with increasingly higher thermal glass transition temperature (T_g) for high speed routing and route length requirements. Traditionally pad cratering and pad peeling failure mechanisms are generally observed post mechanical stressing or post reliability testing. This paper shows that these failures can happen during the Surface Mount Technology (SMT) reflow process. During product development, two products requiring the latest generation of ultra low loss materials with different board thickness and BGA package sizes were found to exhibit these failures immediately after exiting SMT reflow. The commonality was high T_g PCB material and Via in Pad Plated Over (VIPPO) structures. Multiple Design of Experiments (DOEs) were performed, including the use of various PCB laminate materials, to understand the factors and interactions that contribute to this type of failure. Based on lab scale testing and analysis results it was concluded the best possible mitigation was to use hybrid stackups with lower T_g material on the outer layers to overcome this failure. Further testing is planned to identify a better method to predict this failure.