Mathematical modeling for the solidification heat-transfer phenomena during the reflow process of lead-tin alloy solder joint in electronics packaging

摘要

In electronic packaging lead-tin alloy is frequently used to joint electronic components. For the formation of solder joint, lead-tin alloy usually undergoes a reflow process which includes spreading, re-melting, and then solidification of the alloy. Therefore, the properties of lead-tin alloy solder joint and in turn the success of electronic packaging will be significantly affected by the reflow process. In this study, solidification heat-transfer analysis is conducted for a auto-rectifier to obtain the temperature distribution and variation of the lead-tin alloy as well as the whole electronic part during the reflow process. Explicit finite difference method is employed to conduct the solidification simulation for the reflow process. First a solid model for analysis is constructed based on the actual shape and size of the electronic component including the solder joints. Then the model is meshed for the subsequent numerical analysis. The next step is to investigate all possible heat-transfer mechanisms. All the heats to be extracted and relevant heat-transfer mechanisms are considered in the solidification model to calculate for the temperature distribution and variation of the lead-tin alloy solder joints during the reflow process. Temperature measurement at one particular location of the auto-rectifier is conducted during the whole reflow process in an actual pro-duction line. The calculated temperature for the same position is then compared to the measurement and satisfactory consistency is found. Then a shrinkage criterion is also used to quantitatively predict the extent of shrinkage formation in the solder joints.