Microstructure evolution and thermostability of bondline based on Cu@Sn core-shell structured microparticles under high-temperature conditions

Cu@Sn core-shell structured particles with different coating layer thicknesses were fabricated and used as bonding materials. The microstructure evolution and thermostability of the bondline were studied under high-temperature conditions; the minimum thickness of the Sn coating layer required to consume all the inner Cu cores when forming epsilon-Cu3Sn was determined; and the accompanying volume shrinkage was verified. The phase transformation pathway for particles with a thin Sn coating layer was Cu6Sn5 -> epsilon-Cu3Sn -> delta-Cu41Sn11 -> gamma-phase -> beta-phase upon heating to 600 degrees C. Thermal instability occurs at 520 degrees C and 586 degrees C due to the formation of the Cu-rich phases. High-temperature shearing tests were conducted at 500 degrees C and 550 degrees C to verify the existence of a critical point for brittle rupture and tough rupture at approximately 520 degrees C. For particles with a thick Sn coating layer, the outer Sn shell completely consumes the inner Cu core when forming a epsilon-Cu3Sn intermetallic phase, and no other Cu-rich phases formed when heating to 600 degrees C.