The purpose of this paper is to examine the microstructure and evaluate the intermetallic compounds in the following lead‐free solder alloys: Sn98.5Ag1.0Cu0.5 (SAC105) Sn97.5Ag2.0Cu0.5 (SAC205) Sn96.5Ag3.0Cu0.5 (SAC305) and Sn95.5Ag4.0Cu0.5 (SAC405).
X‐ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to identify the main intermetallics formed during solidification. Differential scanning calorimetry (DSC) was used to investigate the undercooling properties of each of the alloys.
By using XRD analysis in addition to energy dispersive spectroscopy (EDS) it was found that the main intermetallics were Cu6Sn5 and Ag3Sn in a Sn matrix. Plate‐like ε‐Ag3Sn intermetallics were observed for all four alloys. Solder alloys SAC105, SAC205 and SAC305 showed a similar microstructure, while SAC405 displayed a fine microstructure with intermetallic phases dense within the Sn matrix.
Currently, low‐silver content SAC alloys are being investigated due to their lower cost, however, the overall reliability of an alloy can be greatly affected by the microstructure and this should be taken into consideration when choosing an alloy. The size and number of Ag3Sn plate‐like intermetallics can affect the reliability as they act as a site for crack propagation.
Reid, M., Punch, J., Collins, M. and Ryan, C. (2008), "Effect of Ag content on the microstructure of Sn‐Ag‐Cu based solder alloys", Soldering & Surface Mount Technology, Vol. 20 No. 4, pp. 3-8. https://doi.org/10.1108/09540910810902651
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