| The effect of cold work on the wettability of copper substrates by Sn-3.5Ag, Sn-37Pb, Sn-9Zn, and Sn-0.7Cu solders was investigated using a wetting force balance. Copper substrates were cold worked between 0% and 50% reduction in thickness and the wetting force measured at 245°C and Tm + 62°C. In general, the wetting force was found to be directly related to the extent of cold work. The other factors found to affect wetting force were the solder bath temperature and the type of flux, either aqueous or no-clean, used. The wetting forces were found to be higher at the solder bath temperature of Tm + 62°C as compared to 245°C. Use of an aqueous flux resulted in higher wetting forces, compared to the no-clean flux. The combination of high degree of cold work (greater than 40%), test temperature (Tm + 62°C) and aqueous flux resulted in the highest wetting forces. Of the three lead free solders tested Sn-3.5Ag exhibited the highest wetting force. |
