Investigation of the effect of indium addition on wettability of Sn-Ag-Cu solders

Purpose - The purpose of this paper is to investigate the influence of In additions on the wetting properties of the Sn2.86Ag0.40Cu (in wt%) eutectic-based alloys, on a copper substrate, in the presence of a flux. The main goal was to find correlations between the results of the wetting balance (WB) and the sessile drop (SD) method, in relation to the contact angles. Design/methodology/approach - The WB method was applied for the wetting measurements, at 250 degrees C, in an air atmosphere and in the presence of a flux. The SD measurements were conducted at the same temperature, in the presence of the same flux, but in an Ar atmosphere, while the maximum bubble pressure (MBP) and dilatometric measurements were conducted in an Ar + H-2 atmosphere. The density data from the dilatometric method were used for the determination of the surface tension by means of MBP, and the WB method was used to determine the surface and interfacial tension. Next, the surface tension data from these two methods were compared. The WB data were used to calculate the contact angles and the obtained indirect data were compared with the results of the direct SD measurements of the contact angle. Findings - A higher In content in the alloy resulted in a lower contact angle on the copper, and the WB results agreed well with the results of the SD experiments. It was confirmed that, in liquid In-Sn and the alloys containing In and Sn (Ag-In-Sn, Sn-Ag-Cu-In, Sn-Zn-In), the improvement of the wettability was indicated only by the increase of the contact angle with the increasing In content. Research limitations/implications - Further studies are necessary for the confirmation of practical application, but they should be directed to the soldering of high indium alloys on printed circuit boards, with different finishes and qualities of the solder joint performance. Practical implications - Taking into account the contact angle data from the WB and SD methods, the best results of the SAC-In alloy on copper were obtained for the alloy of the highest In content. It was found that the contact angles from SD after 4s were higher (non-equilibrium conditions) than the values calculated from WB after 3s. In contrast, the contact angles from SD after 10 min (equilibrium conditions) were lower than those from WB after 3s. The comparison suggests that the contact angles from WB are situated within the data from SD, showing the same lowering tendency with the increasing content of In, and they may be well accepted for practical purposes. On the other hand, the sample of the solder in the SD method, after a prolonged time in order to get the equilibrium contact angle may be used to study the interfacial phenomena with the Cu substrate. The differential thermal analysis results indicate that the melting temperature decreases with increasing tin concentration. Taking into account the results of this study and the available literature data, alloys containing 8-10 wt% of In can be recommended for practical application. Originality/value - The WB and SD methods were used for the contact angle determination of a wide range of solder compositions, in the same temperature and flux conditions. Also, the surface tensions for these alloys were determined with the use of two independent methods: the MBP and the WB methods. The results obtained made it possible to draw conclusions regarding the correlation between the output of different methods and the conditions in which a comparison of the results can be made. It is supposed that these observations apply to many other alloy systems.