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- Title
Microstructures and mechanical properties of ultrasonic-welded Cu–Cu joints for power module terminals in electric vehicles.
- Authors
Kim, Hyeon-Tae; Yoon, Jeong-Won
- Abstract
Power modules play a vital role in electric vehicles (EVs), and various bonding methods, including reflow soldering, wire bonding and ultrasonic welding, are employed to establish connections between substrates and power terminals. In this study, ultrasonic welding and reflow soldering were used as terminal bonding processes for EV power modules. While pressure and welding time were used as parameters in the ultrasonic welding process to bond the terminals, reflow soldering was performed using Sn-3.5 wt% Ag solder for comparison with ultrasonic welding. The bonding process resulted in an increase in terminal deformation with higher pressure and longer welding time in the case of ultrasonic welding. Conversely, reflow soldering process oxidized both the substrate and terminal. Electron backscattered diffraction analysis indicated the presence of fine equiaxed grains, at the bonded interface, formed through dynamic recrystallization; moreover, these grains grew and elongated with increasing ultrasonic energy. In reflow soldering, fine Ag3Sn was dispersed in the solder matrix, and Cu6Sn5 was formed at the upper and lower interfaces. Under a pressure of 0.18 MPa, the shear strength increased linearly from 54.4 to 76.1 MPa as the welding time increased, reaching a value similar to that of reflow soldering at 0.5 s. Under a pressure of 0.36 MPa, the shear strength rapidly increased from 90.6 to 130.3 MPa as the welding time increased, gradually reaching 134.7 MPa at 0.7 s. However, high ultrasonic energy caused deformation of the Cu terminal. Considering the mechanical properties and deformation of Cu terminals, the optimal ultrasonic conditions are 0.36 MPa and 0.5 s. Consequently, ultrasonic welding can form Cu–Cu joints with excellent bonding strengths under appropriate conditions.
- Publication
Journal of Materials Science: Materials in Electronics, 2023, Vol 34, Issue 29, p1
- ISSN
0957-4522
- Publication type
Article
- DOI
10.1007/s10854-023-11432-4