During reflow process, it is the temperature of solder balls that is the most concerned. However, it is difficult to directly measure its temperature and reflow profile is obtained by measuring the package surface temperature. Based on our previous study of reflow profile simulation [1], a comprehensive finite element model (FEM) has been built for precisely simulating reflow profile of solder balls in a forced convective airflow reflow furnace. It is found that impinging jet airflow model provides appropriate estimation of convective heat transfer coefficient as a boundary condition for FEM. Phase transition effect of solder balls has been successfully included and evident influence on solder ball's temperature has been observed. Length of Cu metallization which connects solder balls to outside power/signal sources is found to influence temperature of specific solder balls. Size of printing circuit board (PCB) on which package located is also found to considerably affect reflow profile around its peak temperature.
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