Abstract
An alternative lead-free solder alloy In–48 at%Sn with a melting point of 120 °C and its implementation to bond Cu substrates in a diffusion soldering joining method are presented. According to the EPMA, TEM/EDX and electron diffraction analyses, two different behaviors were observed in the interconnection zone depending on the temperature range: (i) a single layer consisting of η phase below 200 °C; (ii) a Cu-poor region consisting of η phase and a Cu-rich layer formed by a mixture of thin alternate regions of ζ-Cu 10Sn 3 and δ-Cu 7In 3 phases perpendicular to the interconnection plane above 200 °C. The η layer shows two morphologies: large grains and fine grains at the η/In–48Sn (liquid) and at the η/Cu-rich interfaces, respectively. Additionally, the η region shows a gradual change in composition, suggesting a change from the Cu 6Sn 5 to the Cu 2In structures. Thermal stability tests indicate that the thermal resistance of the bonds is about 750 °C.
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