Influence of latent heat released from solder joints on the reflow temperature profile

The reflow process of SAC305 solder paste was investigated by differential scanning calorimetry (DSC) and measurement of the temperature profiles in a real continual convection reflow furnace. Melting and solidification processes of two solder joints were investigated by both methods to determine the influence of latent heat on the surrounding temperature. While one peak was present during melting in DSC, two peaks were present during solidification of two joints connected by a resistor. The released latent heat from one joint increased the temperature of the surroundings and delayed the solidification process of the second joint. Analysis of the temperature profiles obtained during the reflow processes in a real furnace shows that latent heat influences the surrounding temperature not only during the phase transformation, but also during the whole following passage of the sample in the furnace. The maximum temperature increase of the joint is substantial: 25 mg of the solder paste increases the joint temperature by about 15 °C. When two joints are placed on the sample the temperature increase is close to 20 °C.