Reflow profile simulation by finite element method for a BGA package

During reflow process, solder ball temperature profile is a concern, but it is difficult to direct measure the temperature. In this study, a forced convective airflow reflow furnace was analyzed. Measured profiles from two typical BGA packages were simulated successfully. Temperature profile of package surface has been compared with that of solder balls. Temperature distribution among solder ball array has been observed and analyzed. It has been found that impinging jet airflow model provides appropriate convective heat transfer coefficient that can be applied to profile simulation successfully. Dominant heat transfer mechanism is vertical thermal conduction from package top surface to solder ball, while other heat transfer mechanism also have notable effects on solder ball temperature. Solder ball array layout has a significant effect on temperature uniformity of solder balls. A uniform distribution can be obtained when all the balls are located under chip area.