Understanding the Sintering Mechanism of Cu@Ag Nanoparticles for Power Device Packaging

Due to the small size effect, nano-metal paste is regarded as the famous die-attach material. Nano metal paste has excellent thermal conductivity, which could be used to prepare high-temperature resistant interconnect joints at low temperatures. Unfortunately, during the sintering process, nano-silver paste has a high porosity and is prone to electromigration. Nano-Cu paste is prone to oxidation, which is not conducive to the mechanical properties of interconnect structures. The nanocomposite paste of Cu and Ag has gradually gained widespread attention, such as Cu-Ag mixed structure and Cu@Ag coating structure. These can effectively hinder the oxidation of Cu nanoparticles and the electromigration of Ag nanoparticles, which is beneficial for improving the service characteristics of power devices. However, the sintering mechanism of composite nanoparticles has not been revealed, and the industrial application of composite paste lacks theoretical analysis. In this paper, molecular dynamics (MD) is used to describe the sintering behavior of Cu@Ag composite nanoparticles. The effects of Ag surface coating thickness and sintering heating speed on sintering properties were investigated. The MD results show thinner Ag shells and slower heating rates are beneficial for atomic diffusion and improve the reliability of nanoparticle sintering. The degree of sintering is closely related to atomic motion and energy conversion. The phase transition form of nanoparticles is affected by the heating rate.