Wettability of rapid thermal firing silver-pastes

Photovoltaic technology is evolving rapidly with new concepts and ideas to systematically improve module efficiency. Cell metallizations based on thick film pastes have to be fired less than one minute. It has already been shown that the solder interconnection of these rapid thermal firing pastes is critical in terms of wettability [1]. Main problems are solder leaching of commercially available pastes and paste adhesion to the silicon substrate. The correlation between paste composition and solder wettability has not been investigated yet. The aim of this work is to evaluate the wettability of rapid thermal firing pastes in dependence on paste composition and firing temperature. Pastes with spherical silver particles and lead free glass composition have been developed and fired with an industrial standard rapid thermal firing profile between (760...840) °C. Thick film surfaces and cross sections have been inspected. Solder wettability was evaluated with solder dip and solder reflow tests. Correlations between resulting thick films and their wetting or leaching characteristics have been investigated to improve the solder interconnection for rapid thermal firing solar cell metallizations.