The fabrication mechanism and sintering behaviour of Cu@Ag micro-nano mixed particles solder paste for power electronics packaging

Nano-solder pastes have been proven to be used as a bonding material for power electronics packaging. Especially, the Ag-coated Cu nanoparticles (Cu@Ag NPs) solder paste is gradually becoming a potential candidate. Herein, the innovative structure of Cu@Ag micro-nano mixed particles (Cu@Ag MNPs) is fabricated in the same reaction system. It is found that the nanoparticle and microparticle sizes are dominated by the interaction of multiple parameters. The PVP molecular weight (MW) can mainly control the nanoparticle size by the steric hindrance effect. The reaction time ( t ) can mainly regulate the microparticle size by the particle growth time. The reaction temperature ( T ) can mainly control the microparticle size by the nucleation rate. Besides, based on the observation of in-situ TEM, the sintering behaviour of the Cu@Ag MNPs mainly includes particle connection, void evolution, coarsening, and smoothness in this work. The sintering mechanism includes the atom flow on the surface of the particle, grain boundary diffusion, and Ostwald ripening. Consequently, Cu@Ag MNPs solder paste obtained the lowest porosity and the highest shear strength of Cu-Cu joints compared to the Ag NPs and Cu MPs solder paste at 250 °C and 300 °C without pressure in the air condition. Accordingly, this work clarifies the fabrication mechanism and sintering behaviour of the Cu@Ag particles, which provides a facile strategy and theoretical basis for the development of power electronics packaging.