Effect of temperature and storage environment on the preservation of copper surfaces for fluxless soldering

Self-assembled monolayers of alkanethiols have been demonstrated to preserve copper surfaces for fluxless soldering. However, the performance of these coatings for electronics manufacturing will be strongly influenced by their thermal stability. For example, printed circuit boards (PCBs) may be subjected to several high temperature excursions including multiple reflows and adhesive cure. Consequently this study systematically investigates the fluxless solderability of alkanethiol coated copper after storage at a range of temperatures. It was found that while storage at elevated temperatures does reduce the coatings´ preservative properties, this effect can be reduced by decreasing the oxygen content in the surrounding atmosphere. In addition, a quantitative relationship between loss of solderability and temperature was found to exist, providing evidence for the mechanism of the loss of coating preservative properties