Composition design and properties of low melting point (SnBiInZn)100-Ga high entropy alloy for electronic packaging

Low-temperature solders are critical in electronic packaging to reduce thermal damage and improve solder quality. In this paper, (SnBiInZn) 100- x Ga x ( x = 0.5, 1, 2, 4, at.%) high-entropy alloys (HEAs) were prepared, and the effects of adding different contents of Ga on the thermal properties, microstructures, and interfacial morphology of the isotropic-ratio SnBiInZn low-melting-point (LMP) HEAs were investigated. Since Ga has a low melting point, its addition significantly reduced the melting temperature of the HEA. Adding 4 at.% Ga lowered the HEA's liquidus temperature to 76.3 °C, enabling soldering at 100 °C, 130 °C, and 160 °C. Higher temperatures improved wettability, with the best results at 160 °C (83.6 mm 2 spreading area at 1 at.% Ga). The microstructure also refined, changing the Zn phase from rod-like to needle-like. At the interface, a bilayer IMC structure formed: first CuZn 5 near the microstructure, then Cu 5 Zn 8 next to the Cu substrate as higher temperatures and longer reaction times boosted Zn diffusion. Ga partially dissolved into the CuZn 5 IMC, slowing Zn diffusion and thinning the Cu 5 Zn 8 layer. At 160 °C, the (SnBiInZn) 99 Ga 1 /Cu joint reached peak shear strength, 26.6 MPa, with a ductile fracture mode characterized by a fracture surface exhibiting numerous honeycomb-like dimples.