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This paper aims to investigate the effects of different ultrasonic-assisted loading degrees on the microstructure, mechanical properties and the fracture morphology of Cu/Zn+15%SAC0307+15%Cu/Al solder joints.

A new method in which 45 μm Zn particles were mixed with 15% 500 nm Cu particles and 15% 500 nm SAC0307 particles as solders (SACZ) and five different ultrasonic loading degrees were applied for realizing the soldering between Cu and Al at 240 °C and 8 MPa. Then, SEM was used to observe and analyze the soldering seam, interface microstructure and fracture morphology; the structural composition was determined by EDS; the phase of the soldering seam was characterized by XRD; and a PTR-1102 bonding tester was adopted to test the average shear strength.

The results manifest that Al–Zn solid solution is formed on the Al side of the Cu/SACZ/Al joints, while the interface IMC (Cu₅Zn₈) is formed on the Cu side of the Cu/SACZ/Al joints. When single ultrasonic was used in soldering, the interface IMC (Cu₅Zn₈) gradually thickens with the increase of ultrasonic degree. It is observed that the proportion of Zn or ZnO areas in solders decreases, and the proportion of Cu–Zn compound areas increases with the variation of ultrasonic degree. The maximum shear strength of joint reaches 46.01 MPa when the dual ultrasonic degree is 60°. The fracture position of the joint gradually shifts from the Al side interface to the solders and then to the Cu side interface.

The mechanism of ultrasonic action on micro-nanoparticles is further studied. By using different ultrasonic loading degrees to realize Cu/Al soldering, it is believed that the understandings gained in this study may offer some new insights for the development of low-temperature soldering methodology for heterogeneous materials.

The purpose of this study was to investigate the effects of aging time on the microstructure, mechanical properties and fracture morphology of Cu/Zn160%SAC0307/Al solder joints produced through solid-state bonding.

Zn particles with a size of 1 µm and Sn-0.3Ag-0.7Cu (SAC0307) particles ranging from 20 to 38 µm were used to achieve Cu/Al micro-connections using ultrasonic assistance at a temperature of 180 °C, followed by aging treatment at 150 °C to enhance the quality of Cu/Al joints. Scanning electron microscopy was used for observing and analyzing the solder seam, interface microstructure, and fracture morphology. The structural composition was determined using energy dispersive spectroscopy, while a PTR-1102 bonding tester was used to measure the average shear strength.

The results indicated that the intermetallic compounds formed at the interface between Cu substrates and solder metal primarily consisted of smooth Cu5Zn8. The Al-side interface mainly comprises an Al-Sn-Zn solid solution, with Zn-Sn-Cu phases forming between SAC0307 particles at 180 °C. During the aging process, atomic diffusion was accelerated, leading to improved connection quality. The shear strength of the joints initially increased before decreasing as aging time progressed; it peaked at 32.92 MPa after 24 h – an increase of 76.8% compared to as-received joints. After reaching stability at 96 h, there was still a notable increase in shear strength by 48.4% relative to as-received joints.

This study further explores the strengthening mechanisms associated with solid-state bonded Cu/SACZ/Al joints through aging processes. Joints created via solid-state bonding demonstrate superior reliability compared to traditional soldered connections. It is anticipated that insights gained from this research will contribute valuable knowledge toward developing low-temperature soldering methodologies for heterogeneous materials.