Study of the Optimal Cu Core Size Based on Surface Evolver for Solder Bridge and HiP Free of Large PBGA Package

Although the demand for large body size packages such as AI accelerators is increasing, the surface mount technology (SMT) challenge and solution due to the increase in package size and weight vary from each company. SMT which determines product success become competitive in large package. This paper recently analyzed the deterioration of the SMT environment of customers employing large package and the resulting SMT risk, and defined that there is a limit to the traditional method of responding only with package warpage control. The self-developed ‘Effective Warpage Calculator’ and ‘SMT Simulation Tool’ predicted all solder joint shapes in the entire reflow high temperature section to predict solder bridge and head-in-pillow(HiP) defects during reflow soldering process. And to predict the optimal copper core solder ball(CCSB) size, we derived the optimal core size by reflecting the abnormal solder compression phenomenon caused by the solder joint structure (ball pitch and package/board pad structure, solder volume, etc.) and excessive warpage. Samples were produced based on the predicted results and the surface mounting evaluation was conducted. When ‘optimal core’ was applied in the mounting evaluation, the solder bridge defect rate decreased to zero, and the HiP free effect was also confirmed. Based on these technologies, it is judged that it will be competitive in the large packaging market such as AI/Automotive/Server scent in the future, and is also expected to be applicable to Fine-pitch BGA package products with high mounting risk.