Development of a numerical simulation model for predicting the temperature of a flip-chip package during the laser-assisted bonding (LAB) process

The Laser-assisted bonding (LAB) method has recently been developed as a next-generation technology. It is a very important factor for the quality of bonding whether the temperature of solder rises above the melting point and maintains enough to melt. However, by the existing measurement method, only the temperature of the silicon chip can be measured so the temperature of solder is still unclear. Therefore, to predict the temperature of the whole flip-chip package including the solder bumps during the LAB process, a numerical simulation model is developed. Governing equations for transient heat conduction are solved using the Finite Volume Method(FVM). The absorbed laser in each layer is analyzed based on the optical characteristics of the laser, which contributes to the heat generation rate of governing equation. Based on the increasing contact area of solder bump during the melting process, point-contact to area-contact, the melting process of solder bumps is replaced by introducing the effective thermal conductivity according to the contact area between solder bump and substrate. Through the simulation model developed in this study, the transient temperature profile during the LAB process is obtained. The temperature of the silicon chip obtained by the simulation model is compared to that measured by IR thermometry to validate the simulation model. It is confirmed that the melting process is well reflected through the fact that inflection points of temperature profile are shown in both simulation results and IR thermometry. Furthermore, it is expected that the warpage problem and optimized process conditions can be analyzed using the numerical simulation developed in this study.