Effect of Cu₆Sn₅ nanoparticles size on the properties of Sn0.3Ag0.7Cu nano-composite solders and joints

The effect of different-sized Cu₆Sn₅ nanoparticles on thermal behavior and interfacial reaction with Cu substrate of Sn–0.3Ag–0.7Cu solder was evaluated. The results showed that 30 nm and 70 nm Cu₆Sn₅ nanoparticles were successfully synthesized by using the method of different reductants, attributed to the difference of reductive ability. Under condition of the same heating parameters, 30 nm Cu₆Sn₅ nanoparticle owned lower sintering temperature than that of 70 nm Cu₆Sn₅ nanoparticle. The thermal behavior was revealed that the composite solders with the addition of different-sized Cu₆Sn₅ nanoparticles had slightly lower melting point and higher undercooling value, compared with original Sn–0.3Ag–0.7Cu solder alloy. The highest undercooling value occurred with 30 nm Cu₆Sn₅ nanoparticle addition. Moreover, the interfacial reactions between Cu substrate and Sn–0.3Ag–0.7Cu solders mixed with different-sized Cu₆Sn₅ nanoparticles have produced after reflowing at 250 °C and aging at 150 °C for different interval time. It was clearly found that comparing to the initial Sn–0.3Ag–0.7Cu/Cu solder joint, the thickness of interfacial intermetallic compound (IMC) layer on solder joint with adding nanoparticle was thinner and the growth rate was slower. The growth of interfacial IMC was suppressed with the addition of Cu₆Sn₅ nanoparticle, and 30 nm Cu₆Sn₅ nanoparticle had the strongest inhibition effect on the growth of IMC, as well as the growth of IMC grains.