Temperature distribution in solder joints during melting and solidification

The most vulnerable components of electronic circuits (PCA - Printed Circuit Assembly) are the solder joints. During the soldering process different anomalies may occur (changes in the reflow temperature profile, different cooling rates) leading to the inception of some defects, as excessive voids inside the solder, brittle phase formation, concentration gradients of elements or metallurgical composition etc. To avoid this, it is mandatory to follow the parameter values of the reflow process (speed, temperature values etc.). Temperature computing model for two PCA samples during the reflow soldering process, by using Comsol Multiphysics software (heat transfer 3 D module) is presented in this paper. PCA samples with and without resistor contains substrate with two soldering pads together with lead free solder. To carry out the computations, the latent heat of fusion/solidification and the variation with the temperature of the alloy parameters were considered. The results show that the presence of the resistor leads to the decrease of the temperature in the alloy during melting and its increase during solidification.