One of the most straightforward approaches to fluxless solder bonding is using vacuum conditions to prevent further oxidation and, where needed, to reduce solder oxides by the use of molecular hydrogen (H-2).(1-3) This study On oxidation and reduction of solder oxides on SnPb (60/40) is aimed to provide a better understanding for fluxless solder bonding applications under controlled atmospheric conditions; By means of scanning Auger spectroscopy it is shown, that growth of oxide films on metallic SnPb above the eutectic temperature can be significantly reduced by decreasing the O-2 partial pressure up to similar to 10(-5) Pa. The native oxide, which was left on top of one part of the samples, prevented a further scale growth even during heating at temperatures above the melting point. The native oxide consists of SnO2, which has most likely an amorphous structure, whereas the oxide, grown at 200 and 250 degrees C is crystalline SnO. For sample preparation, the reduction of the native oxide on eutectic SnPb was carried out successfully using low temperature (250 degrees C) and short heating cycles (2 min). The effectiveness of H-2 to reduce SnO2 at typical soldering parameters (240 degrees C, <2 min) was furthermore proven by in situ Auger electron spectroscopy.
Journal of the Electrochemical Society, 1998, Vol 145, Issue 6, p. 2138-2142