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Abstract: The morphology and phase transformation of the intermetallic compounds (IMCs) formed at the Sn–9Zn–3.5Ag/Cu interface in a solid-state reaction have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron diffraction (ED), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The monoclinic η′-Cu6Sn5 transforms to the hexagonal η-Cu6Sn5 and the orthorhombic Cu5Zn8 transforms to the body-centered cubic (bcc) γ-Cu5Zn8 as aged at 180°C. The scallop-shaped Cu6Sn5 layer is retained after aging at 180°C for 1000h. In the solid-state reaction, Ag is repelled from η′-Cu6Sn5 and reacts with Sn to form Ag3Sn, and the Cu5Zn8 layer decomposes. Kirkendall voids are not observed at the Sn–9Zn–3.5Ag/Cu interface even after aging at 180°C for 1000h. [Copyright &y& Elsevier]

Abstract: The growth and morphology of the intermetallic compounds formed at the solder joint between the Sn–9Zn–2.5Ag lead-free solder and the Cu substrate have been investigated in this study. The planar Cu6Sn5 formed after soldering transforms to a scalloped Cu5Zn8 after aging at 180°C for 250h. However, the Cu5Zn8 decomposes and the scalloped Cu6Sn5 reforms at the interface close to the solder alloy after aging for 400h. The η′-Cu6Sn5 transforms to the η-Cu6Sn5 as aged at 180°C. The interdiffusion coefficient of Cu and Sn in the Cu6Sn5 is determined as 2.58×10−13 cm2 s−1, and that of Cu and Zn in the Cu5Zn8 layers is determined as 3.36×10−14 cm2 s−1 at 180°C, from the estimated thickness of the intermetallic compound (IMC). On the other hand, they are determined as 3.43×10−13 and 2.36×10−14 cm2 s−1, respectively, from the microbeam EDS analysis. [Copyright &y& Elsevier]

The enhancement of the wettability and solder joint reliability at the Sn–9Zn–0.5Ag solder alloy–Cu interface by Ag precoating has been investigated. The wettability of the Sn–9Zn–0.5Ag solder alloy–Cu interface has been improved by Ag precoating. The adhesion strength of the solder alloy–Ag precoated Cu interface increases from 4.11±0.56 to 6.92±0.85 MPa as dipped at 250 °C for 10 s. When the dipping time is prolonged from 10 to 30 s, the interfacial adhesion strength increases from 6.92±0.85 to 13.62±0.73 MPa. The interfacial adhesion strength is enhanced by the rod-like Cu–Zn intermetallic compound (IMC) formed close to the interface. The diffusion coefficients of Sn and Zn in the IMC layer are determined as 5.76×10−10 and 9.50×10−11 cm2/s at the Sn–9Zn–0.5Ag–Cu and Sn–9Zn–0.5Ag–Ag precoated Cu interfaces, respectively. [Copyright &y& Elsevier]

The kinetics of intermetallic compounds (IMCs) formation at the 91Sn–8.55Zn–0.45Al lead-free solder alloy/Cu substrate interface during soldering and subsequent aging have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), transmission electron microscopy (TEM) and electron diffraction (ED). From the XRD results, γ-Cu5Zn8 and Cu6Sn5 are found in the eutectic 91Sn–8.55Zn–0.45Al solder alloy/copper interface, but no γ′-Cu9Al4 is formed in the wetted samples aged at 423 K for 250 h. However, by TEM observation and ED analysis, γ′-Cu9Al4 is found at the interface of the solder alloy and the Cu substrate, and the IMC growth can be expressed as X = (Dt)1/2. The activation energy of the γ-Cu5Zn8 layer growth in 91Sn–8.55Zn–0.45Al solder alloy/Cu interface is determined as 53.77 kJ/mol. [Copyright &y& Elsevier]