Impact of Zn Content on Cu/Al Joints with (Cu+Zn+Al) Mixed Particles

In this study, 1-μm Zn particles were mixed with 28-μm Cu particles and 28-μm Al particles as solder to scrutinize the influence of varied Zn content on Cu/Al interconnects. The interconnection of Cu/Al heterogeneous metals is achieved with the use of ultrasonic-assisted. A relationship has been observed between the Zn content and shear strength of joints. Initially, with an increase in Zn content, there is a positive effect on the shear strength; however, after reaching an optimum value, further increases in Zn content leads to a subsequent decline in shear strength. The maximum shear strength of joints was found to be 23.34 MPa at a Zn content of 70%. Due to the increase of Zn content, a more complete and continuous Cu
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Zn
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compound can be formed at the Cu-side interface, and more Al-Zn solid solution can also be formed at the Al-side, allowing the solder particles to achieve a tight connection. However, too much Zn can lead to the aggregation of Zn particles after the reaction of Zn particles with Cu and Al in the solder, which fails to generate compounds with Cu and solid solutions with Al, and leads to the loss of strength.