The effect of ultrasonic processing on the microstructure and mechanical properties of (SnBiInZn)_99.5Ga_0.5 high entropy alloy/Cu solder joint

Abstract

Ga, valued for its low melting point, was introduced into the SnBiInZn alloy to develop a high-entropy solder with a reduced melting temperature of 82° C. This study examined the effect of ultrasonic assistance on the interfacial reaction between (SnBiInZn)_99.5Ga_0.5 HEA and a Cu substrate. With increasing ultrasonic time, the spreading area expanded to 82.3 mm², and the microstructure was refined. Following 15 s of ultrasonic treatment, a stable bilayer structure composed of β-Sn and InBi phases was formed. The interfacial intermetallic compound (IMC) transformed into a mixed structure of Cu₉Ga₄ and Cu₆Sn₅. Prolonged ultrasonication promoted Cu₉Ga₄ growth, which suppressed Cu₆Sn₅ thickening. The shear strength initially increased, peaking at 30.5 MPa (a 46.6 % improvement) at 15 s, and then declined due to excessive brittle IMC formation, increasing joint brittleness, and reducing reliability.

Keywords

high entropy alloys / solder joints / microstructure / ultrasonic / shear strength

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