Papers by Keyword: Sn-Ag-Cu Alloy

Abstract: In the present contribution, atomised Sn-3.0Ag-0.7Cu powder alloy with a size of less than 250 μm was first compacted and then microwave and conventionally sintered at 175 °C for 15 and 120 minutes, respectively. Despite the very different processing times applied, the degree of porosity was very similar, i.e., around 7%. The as-atomized microstructure of the conventionally sintered samples was barely altered with β-Sn dendritic matrix comprising Cu₆Sn₅ and Ag₃Sn intermetallic particles. The microwave sintered Sn-3.0Ag-0.7Cu sample exhibited a combination of fine and very coarse intermetallic particles, with the presence of well-developed needle-like Ag₃Sn, and its dendritic pattern disappeared completely. The Vickers hardness of both samples was measured and found to be consistent with their microstructures.

Abstract: Sn-Ag-Cu alloys are considered one of the most favorable lead-free solder systems. In slowly-cooled eutectic Sn-Ag-Cu alloys, sometimes large primary Ag3Sn or Cu6Sn5 intermetallic compounds (IMCs) form. These IMCs may affect the mechanical properties of solders. However, explanations for the formation of these IMCs are still not clear. This study deals with interrupted tests in order to clarify the nucleation of IMCs in the liquid phase. In this study, Sn-4.41Ag-0.63Cu and Sn-3.30Ag-1.47Cu alloys were prepared. According to the thermodynamic calculation, Pandat, the equilibrium solidification paths are described as follows: Sn-4.41Ag-0.63Cu :L → primary Ag3Sn → binary eutectic (Ag3Sn +Sn) → ternary eutectic; Sn-3.30Ag-1.47Cu :L → primary Cu6Sn5 → binary eutectic (Cu6Sn5 + Sn)→ ternary eutectic. The actual solidification process was different from the estimation from the equilibrium phase diagram. In the case of Sn-4.41Ag-0.63Cu, only Ag3Sn grew as a primary phase in the liquid, while in the case of Sn-3.30Ag-1.47Cu, not only primary Cu6Sn5 but also pseudo-primary Ag3Sn grew in the liquid. Ag3Sn may nucleate easily in the liquid phase, but Cu6Sn5 would not nucleate in the liquid.