CFD Modeling the Cooling Stage of Reflow Soldering Process

Abstract

Reflow soldering is one of the most widespread soldering technologies used in the electronics industry. It is a method of attaching surface components to a circuit board with solder paste. The goal of the reflow process is to melt the solder and heat the adjoining surfaces, without overheating and damaging the electrical components. In the present study, computational fluid dynamics (CFD) was used to investigate the convection flow field during the cooling reflow process stage. The convection heat-transfer coefficient and temperature distribution within the board level were also studied. The analysis comprises three main objectives: (1) the simulation of the cooling process of a PCB in the final section of the reflow oven; (2) the calculation of the heat transfer from the PCB to the air as the PCB moves throughout the woven; and (3) use a “dummy” PCB with two generic components with different dimensions and analyze the heat dissipation. The geometry definition, the mesh generation, as well as the numerical simulations were carried out using the Workbench™ platform from ANSYS® 15. It was programmed an UDF to represent the relative motion between the PCB and the cooling air flow. Results shown that, during the cooling process, there is a gradient over the PCB board. It is also observed that there is a small differentiation in the temperatures' profile along the board length probably because of the formation of recirculation areas inside the oven. Thus, nozzle spacing has a great impact in the formation of those recirculation areas, and consequently in heat dissipation.