Wetting of Al pads by Sn, Sn8.8Zn (wt.%) eutectic alloy, and ternary Sn-Zn-In and Sn-Zn-Ag alloys containing 1.5 wt.% of In and Ag, respectively, were studied with the sessile drop method. The wetting tests were carried out at 523 K, in the presence of Amasan ALU33® flux, for 5, 15, 30 and 60 min., respectively,. The tests were carried out in a setup allowing fast transfer of the sample to and from the furnace heated to the test temperature. It was found that the studied alloys wet Al pads nearly completely as the wetting angles of alloys, determined after cleaning the flux residue from solidified alloy-substrate couples, were lower than 15 degrees. There are no significant differences between different compositions and time of wetting does not affect the wetting angles values.
Solidified alloy-substrate couples were cross-sectioned, mounted in conductive resin and after polishing were examined with scanning electron microscopy coupled with electron dispersive X-ray analysis. The results of microstructure analysis indicated similarity of the solder substrate interface of all of the samples, in particular there are no interlayers present at the interface. Instead, the surface of the substrate is jagged and the solders penetrate and dissolve the substrate along Al-grain boundaries. Dissolution of Al in solders was confirmed by EDS analysis. In the case of Sn8.7Zn1.5Ag/Al couples, precipitates containing Zn and Ag are observed near the interface in the vicinity of dissolved grain boundaries. Some of these precipitates are in contact while others are detached from the substrate.
Acknowledgement. This work is a part (task 4.3) of the project “POIG.01.01.02-00-015/09 – Advanced materials and technologies of their production – ZAMAT”. The project is funded by the European Regional Development Fund (ERDF) under the framework of Innovative Economy Program, in the years 2010-2013.