| This thesis describes the development of a model of the reflow process of actual solder pastes as used in Surface Mount Technology (SMT) lines. Solder paste is a mixture consisting of three functional components: solder powder, flux, and solvent. The model considers the coupled heat transfer process between the solder and the flux including changes in solder paste properties. Specifically, the model considers the loss of solvents in the vehicle system of the flux, melting, solidification and further single phase cooling. The model clearly shows the effect that the oven temperatures and conveyor speeds may have in accelerating/decelerating the loss of weight, melting and solidification processes.;Experiments were conducted with the objective of validating the temperature profiles and the loss of weight due to flux solvent evaporation predictions. Results are shown for typical eutectic paste 63%Sn-37%Pb and experimental data is in good agreement with the numerical model. The model predicts the thermal behavior of any eutectic solder paste system, and as an example a simulation using the lead-free solder paste system 96.5%Sn-3.5%Ag is reported. Finally, the model is capable of predicting the temperature profiles of, the multi-layer printed circuit boards (PCB's), the solder pads, and components of a SMT assembly during the reflow process with reasonable accuracy. |
