Thermal simulation for predicting substrate temperature during reflow soldering process

Widespread use of lead-free solders requires precise control of the temperature on a substrate during reflow soldering, because the margin between the higher melting temperatures of lead-free solders and the heat-resistant temperatures of electronic components becomes narrow. For this purpose, the thermal simulation method has been developed for predicting the temperature on a substrate and optimizing the temperature profile during the reflow soldering process. Most reflow furnaces have two heating systems: forced convection by hot gas and radiation by infrared rays. Heat transfer by convection can be calculated with the experimental equation for multiple impinging jets without any fluid analysis. Heat transfer by radiation was calculated with a mechanical solver, taking into account the shape factor between the moving substrate on a conveyer and the heater. The predicted temperatures obtained by the simulation method showed good agreement with measured temperatures using a test substrate. Then, this simulation method was applied to mobile phone substrate in order to optimize the reflow process.