A simplified model of the reflow soldering process

Previous models of the reflow soldering process have used commercial finite difference (FD) or computational fluid dynamics simulation software to create detailed representations of the product and/or the reflow furnace. Such models have been shown to be highly accurate at predicting the temperatures a PCB design will achieve during the reflow process. These models are however complex to generate and analysis times are long, even using modem high performance workstations. With the move to adopt lead free soldering technology, and the consequently higher reflow process temperatures, optimisation of the reflow profile is gaining a renewed emphasis. This paper describes a less complex approach to modelling of the process, which uses simplified representations of both the product and the process, together with a FD solver developed specifically for this application, and which achieves an accuracy comparable with more detailed models. In order to establish an accurate representation of the specific reflow furnace being simulated, a reflow logger is used to make measurements of the temperature and level of thermal convection at each point along the length of the furnace for a small number of carefully chosen reflow profiles. The temperatures for any other reflow profile can then be predicted from these measurements.