Solder wetting measurement of back contact paste using a wetting balance

As a paste supplier, Heraeus works to improve the cell-tabbing joint quality. Contact paste is not only required for this bond, but its chemistry is one of a few variables that influence the reliability of the connection. We investigate new ways to quantify joint quality. In this paper a wetting balance technique, used by the Surface Mount Technology, SMT, industry, is considered as a means to evaluate solder wetting as a function of paste chemistry. We focus on the solder/back-contact-paste/cell system, as it relates to crystalline silicon solar cells and modules. Prior work is reviewed to outlines the significance of solder wetting to the cell-tabbing joint quality. The commercially available Heraeus back contact paste SOL230 is tested alongside a Ag paste commonly used in industry. The wetting balance test clearly shows the influence of paste chemistry on wetting. We find that solder wets the SOL230 better than the Reference paste.