Modelling thermal behavior of surface mounted components during reflow soldering

Nowadays reflow soldering is the most widespread technology used for electrical and mechanical attachment of surface mount devices (SMDs) to printed wiring boards (PWBs). In recent reflow ovens the required temperature to remelt the solder was typically achieved by forced convection. Nevertheless the thermal conduction is also important for the exact description of the soldering process because the heat spreads inside the components and within the PWB. Despite of the thermal profile optimization of the oven, inhomogeneous thermal distribution can form in the PWB and in the large-size SMD components. This effect could generate unexpected reflow soldering failures. With the aim of proper thermal modelling these failures can be eliminated. Thermal investigation of components during reflow soldering is very special problem. This objective demands to apply special conditions in the thermal models, which highly differ from the common ones. Hence we have decided to develop a special thermal modelling tool. The model designing aspects which defined the way of development are presented in the paper. The mathematical description and formalism of the modelling tool are presented in the paper as well.