Interfacial intermetallic compounds (IMCs) help determine the reliability of soldered joints; thus, it is necessary to understand their formation and evolution. This study focus on Cu-Sn IMCs formed in ultrasonic-assisted soldering (UAS), wherein the formation of IMCs at the Sn/Cu interface is controlled by changing the ultrasonic action time. After being subjected to ultrasonic vibration, the IMCs at the Cu/Sn solid–liquid interface are continuously crushed, dissolved, and formed, which occurs successively in the Cu6Sn5 and Cu3Sn layers. The relationship between the thickness of the IMC layer and ultrasonic action time in Cu-Sn samples was identified. Simultaneously, the growth pattern of Cu6Sn5 grains in the Sn solder is transformed, and the tin solder (Sn solder) is kept in a dynamic non-equilibrium state with IMCs at the Sn/Cu interface through UAS. More Cu6Sn5 grains formed and were evenly distributed in the joint after cooling, which improves the performance of the joints.
Ultrasonic-assisted soldering interfacial intermetallic compounds microstructure tin solder
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