冷卻速率對 Sn-Ag-Cu 無鉛銲料 Ag3Sn 形貌及拉伸強度之研究

Abstract

Effect of the different cooling rate (from 0.008 to 100°C/s) on the morphological evolution of the Ag3Sn, Cu6Sn5 and β-Sn formed during the solidification of Sn-3Ag-0.5Cu (SAC305) and Sn-3.8Ag-0.7Cu (SAC387) solder was investigated. The tensile tests and high temperature storage tests were also used to estimate the tensile strength and thermal influence of microstructure under different cooling rates. Experimental results showed that cooling rate has a significant effect on the solidification time, and therefore influences both the size and the morphology of the eutectic Ag3Sn compound. Specifically, as the cooling rate is reduced, the Ag3Sn compound exhibits a coarsening evolution: particle-like → needle-like → plate-like. The Ag3Sn particles have average diameters of about 0.2µm by fast cooling. The tensile strength is reduced by the coarsening of Ag3Sn. The tensile strength for SAC305 tensile specimens decreased from 60.8MPa to 39.5MPa. SAC387 solder possesses more additional Ag and Cu than SAC305, and its tensile strength is degraded seriously due to the formation of coarse primary Ag3Sn compounds. SAC387 under slower cooling, cracks tend to occur at plate-like primary Ag3Sn compound and extend into the matrix. As a result, such a large and brittle primary compound precipitation is harmful to strength and ductility of solders. In summary, Ag content and cooling rates have influences on morphological evolution of Ag3Sn compound where faster cooling and/or less Ag addition seem to have beneficial effect on morphological evolution of Ag3Sn and mechanical properties as well.