Study on Flux and Alloy of Lead Free Solder with Mitigation Effect and Consideration for Acceleration Test Method

Abstract

We previously researched whisker growth from solder, and reported that whiskers occurred from a non-corroded tin layer that was sandwiched between the non-uniform progressed corroded tin layers in a high-temperature and high-humidity atmosphere.Here, we report further on the results obtained from the EPMA analysis and the electrochemical properties. First, it was ascertained that the corrosion of tin was promoted as bromine in the ux invaded the solder. Furthermore, in addition to the high-temperature and high-humidity environment, oxygen was found to be indispensable for the generation of whiskers, and to nally change into tin oxide through tin hydroxide.In addition, from an experiment that varied the temperature while maintaining a uniform relative humidity, it is understood that the activation energy was 0.84 eV when whiskers were generated from the solder. Also, an experiment that changed the relative humidity while maintaining a uniform temperature revealed that a plot of the whisker-generating time forms a straight line on a semi-log plot for the reciprocal number of the relative humidity.

Board Reflow Processes and their Effect on Tin Whisker Growth

“…Tsukui et al [7] investigated the effect of different flux activators on tin whisker growth on Sn3Ag0.5Cu soldered pads. The flux activators tested included diethyl amine HBr salt (2 wt% and 4 wt% concentrations), 1.9 wt% adipic acid, and 2.41 wt% lauryl amine.…”