Preparation And Characterization Of Cu@Sn Core-shell Nanoparticles

In recent years, with the rapid development of the electronics industry, the performance of electronic products has gradually increased and evolved into miniaturization and integration. At present, the main methods of die attachment are nano-paste sintering, transient liquid phase bonding and high temperature alloy soldering, etc, but each of them has its drawbacks. Nano-silver sintering method has good thermal and electrical properties, but the cost of nano-silver paste is extremely high, which means it can not be used in large-scale production. Transient liquid phase bonding is low-cost, but needs much longer reaction time and tends to result in incomplete reaction, which can cause reliability problems. Therefore, this study aimed to explore a possible new solder material which is low-cost but can achieve interconnection under low temperature(300?) and work at high temperatures(above250?).Based on the size effect of nano materials, nanoparticles have obvious advantages. In addition to silver nanoparticles, Cu has better cost advantage but easy oxidation. So the presented paper proposed a kind of core-shell structure metal powder as the soldering material. This kind of powder has the structure of Sn outer layer and Cu core. When reflowed at 250?, outer Sn are melted and react with the Cu core to form the intermetallic bonding. The solder joint with a structure of Cu particles dispersed in IMC has high melting point, leading to the capability of high temperature service.The core-shell metal powder mentioned in this paper was prepared using the chemical method. The preparation of Cu nanoparticles in diethylene glycol is performed via the following displacement reaction: PVP, CTAB and NaH2PO2·H2O are mixed into DEG under vigorous stirring at room temperature under ambient condition. By changing key parameters such as the concentration of reductant,reaction temperature, reaction time, the concentration of dispersant and the concentration of precursors, the optimal conditions to synthesize Cu nanoparticles were obtained. After completing the preparation of Cu nanoparticles, then prepare the Cu@Sn core-shell nanoparticles. Due to the reaction between Cu and complexing agent, the electrode potential of Cu2+/Cu was reduced. Thus, the nobler Cu can replace Sn2+. Then obtain the the optimal conditions to synthesize Cu@Sn core-shell nanoparticles.Cu@Sn core-shell nanoparticles synthesized by using optimal processing parameters were pressed into block with a pressure of 30 MPa and sintered at 200?,250? and 300?. The morphology of the sintered nanoparticles was identified by observing SEM images and the formation of sintering neck was found. At the sametime, the performance of block after sintering is tested. By comparing we found the best performance of sintering was the block under 250?, the elastic modulus is 17.58 GPa, current resistivity is 23.67×10-6 ?·m, and the porosity is 7.67%.The metal powder and commercially available rosin-based flux were uniformly mixed, then sintering with copper under 200?, 250? and 300?. By comparing the SEM microstructure of joint, the best sintering temperature is 250?. Then sintering30 min, 60 min and 90 min respectively under the temperature of 250 ?. By comparing the SEM microstructure of joint, the best sintering time is 60 min.