SOLDER FLOW ON NARROW COPPER STRIPS

Various solderability tests have been developed over the years to quan tify the wetting behavior of solder on metallic surfaces. None offer a n exact measure of capillary flow normally associated with conventiona l plated-through-hole and surface mount soldering. With shrinking pack age designs, increasing reliability requirements, and the emergence of new soldering technologies, there is a growing need to better underst and and predict the flow of solder on printed wiring board (PWB) surfa ces. Sandia National Laboratories has developed a capillary flow solde rability test, through a joint effort with the National Center for Man ufacturing Sciences, that considers this fundamental wetting issue for surface mount technology. The test geometry consists of a metal strip (width, delta) connected to a circular metal pad (radius, r(c)). Sold er flow from the pad onto the strip depends on the geometric relations hip between delta and r(c). Test methodology, experimental results, an d validation of a flow model are presented in this paper.