| This thesis presents the development of a numerical model to predict the thermal behavior during the surface mount technology reflow process. The reflow process is a heating process in which the solder paste is melted and then solidified on printed circuit boards (PCBs). Various assumptions were used during the development of the model to simplify the different heat transfer modes present in the problem, including negligible temperature gradient in the vertical direction. The final numerical model was able to predict the temperature profile for an ideal PCB. The ideal PCB consisted of a solid copper plate 0.3048 m by 0.2413 m with a 0.0635 m thickness, dimensions similar to many actual motherboards. Experiments were designed and executed with the objective of gathering data for model calibration. Temperature distributions inside an actual reflow oven were collected simultaneously with temperature measurements along a test board. The reflow oven consisted of twenty heating panels symmetrically distributed below and above the PCB conveyor, as used in actual manufacturing applications. Two oven temperature conditions were considered, namely, ideal and actual set-points, and two conveyor speeds, 1.27 cm/s and 1.905 cm/s. Ideal set-points consisted of uniform temperatures throughout the panels. Comparisons between the numerical and experimental solutions show that the proposed model predicts transient, multi-dimensional heat transfer trends in reflow processes reasonably well. Results indicate that ideal set-point conditions are better predicted by the model, with an average temperature difference of 5.10$spcirc$C. Actual set-point conditions are approximated by the model within an average temperature difference of 9.51$spcirc$C. Major differences between the model and the experimental data were found in the cooling section of the oven. (Abstract shortened by UMI.). |
