Numerical investigations on the effects of different cooling periods in reflow-soldering process

Cooling periods in the reflow soldering process significantly influence heat transfer coefficient and temperature distribution on solder joints, which constituently contribute to soldering defects. The domain of a desktop lead-free reflow oven was built based on the actual dimensions of a sample in GAMBIT 2.3.16. The model was exported to FLUENT 6.3.26 for further parametric study. After grid independency test, simulation results were validated by experimental data according to the American Society of Mechanical Engineers standard for computational fluid dynamics and heat transfer. Next, a simulation model was used to analyze the correlation between temperatures, heat transfer coefficient, and heat flux against reflow cooling durations. Results revealed that a very high radiation heat flux (122.760 W/m 2 ) in a short cooling duration result in unmelted solder powders, which contribute to poor wetting. However, the reduced heat flux of 9.262 W/m 2 affects the mechanical properties of solder balls with its continued cooling. Temperature variation and heat transfer coefficient on different points of the substrate are attributed to the non-uniform airflow distribution during the cooling stage. To sum up, the numerical investigation correlates temperature, heat transfer coefficient, and heat flux distribution on different reflow cooling periods to determine their effect on soldering quality.