A Novel Approach to Optimizing Solder Reflow Process in Assembling PQFN Packages

Solder void is a common defect during assembling Power Quad Flat No-lead (PQFN) packages. It is detrimental to the packages’ feature of good power management and reliability performance and needs to be controlled within certain specification. Reflow process is well considered as critical to the solder void formation for a given solder paste. The transport index of reflow oven, which determines how solder paste are reflowed through solder reflowing process within the reflow oven, has therefore been optimized by a novel approach in this study. The underlying principle of the optimization is to find such a transport index that solder paste have a best possibility to experience homogeneous heat transfer during reflow phase of the whole reflow process. Different from the traditionally experimental trial and error, the present approach first predicts the optimal transport index by calculating the relative locations of lead frame (solder paste are dispensed on it) to the heating blocks of the reflow oven and the amount of heat input at different locations on the lead frame during the reflow phase. Then only necessary experiments are conducted to validate the prediction. As the theoretic calculations already screen out part of experiments that have to be conducted in the traditional trial and error, the present approach saves time and cost in practice.