Investigation of the vapour phase soldering process

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Dr. Illyefalvi-Vitéz Zsolt
Department of Electronics Technology

The Vapour Phase Soldering (VPS) technology is a newly applied reflow soldering method. In the seventies machines using this principle had a wide application, but because of the harmful effect on the environment, the application of the liquid (the soldering medium) was limited by strict regulations. It was in the last decade, when a medium was developed, which meets all the environmental requirements as well. As it can be derived from the wide variety of the VPS machines on the market, vapour phase soldering has again a good chance to compete with the conventional methods. Because the method was out of use for many long years, vapour phase soldering cannot be considered a matured technology. However, there are lots of questions, which could not be answered on the basis of the literature. I tried to find solutions for some of these problems with my experiments. I realized an experimental VPS system, and in this machine I investigated the vapour blanket generated over a low boiling point Galden type liquid. My experiments proved that the vapour blanket really exists over the liquid, but its density and temperature are not homogeneous, both quantities are decreasing in the direction of the water cooled lid and the cooler walls of the chamber. The temperature of the vapour never exceeds the boiling point of the liquid, therefore overheating is physically impossible. The upward decreasing temperature gradient of the vapour was used to set up required thermal profiles. I realized the thermal profile, described by the manufacturer for the NC-SMQ®8 type solder paste of Indium Corporation, by placing the test board into a vapour region of proper temperature for a defined time period. I made several solder joints on test boards using this thermal profile. The quality control of the solder joints proved the applicability of vapour phase soldering and my thermal profiling method.


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