On reflow soldering process and reflow profile

In order to obtain good welding quality, some influencing factors of reflow soldering process were studied in this research. A series of welding experiments were conducted in a small reflow soldering oven. Oxidation and surface treatment of soldering materials are important factors in the welding process. Temperature curve of reflow soldering has a great influence on the welding quality, and the welding effects under temperature profile of the ramp-soak-spike (RSS) and ramp-to-spike (RTS) were compared. The microstructure of the solder joints and the intermetallic compound were observed by electron microscopy. The tensile tests were used to measure the mechanical properties of solder joints. A SAM machine was used to evaluate the voiding ratio of welding interface layer. Some results were obtained. Some expired solders and oxidized copper were used for comparison study. There were gas cavities existing in the inner metal interface layer, and the gas cavities were hard to be eliminated by the common reflow soldering. It was also found that the reflow of solder paste was not very good under the RTS curve, comparing to the typical temperature curve. All these welding experiments demonstrated that the reflow soldering process and reflow profile have a relatively large impact on welded results.