Study Of Cu₆Sn₅ Nanoparticle On Lead-Free Solder Alloy And Interfacial Structure Of Solder Joint

In electronic packaging industries,the addition of Cu₆Sn₅ nanoparticle as the reinforcing agent into lead-free tin-based solders can effectively improve the thermal properties of solder alloys and affect interfacial reaction of solder joints.In this paper,Cu₆Sn₅ nanoparticle was prepared by using reduction precipitation method.The effects of Cu₆Sn₅ nanoparticle on SAC305 alloy and SAC305/Cu solder joint were investigated.Meanwhile,the mechanisms of different sized Cu₆Sn₅ nanoparticles on Sn0.3Ag0.7Cu alloy and Sn0.3Ag0.7Cu/Cu solder joint were explained.Cu₆Sn₅ nanoparticle with a diameter of 30-40 nm was prepared by using SnCl₄·5H₂O,CuCl₂ oxidant,NaBH₄ reducing agent and sodium citrate dispersant.SAC305-xCu₆Sn₅?x=0,0.05,0.1 and 0.2 wt.%?composite solder alloys were prepared by using remelting method at 400 ^oC.The XRD results showed that the diffraction peak of Cu₆Sn₅ was more obvious after adding Cu₆Sn₅ nanoparticle.The DSC curve analysis showed that the addition of Cu₆Sn₅ nanoparticle slightly reduced the solidus temperature of composite alloys,obviously increased the degree of undercooling of composite alloys.Nanoindentation analysis showed that the addition of Cu₆Sn₅ nanoparticle effectively improved the hardness and elastic modulus of composite solders.The experiment was prepared that Cu substrate was dropped in molten SAC305-xCu₆Sn₅?x=0,0.05,0.1 and 0.2 wt.%?composite solder for 1 minute,then aged at 250 ^oC for 24 h,120 h,240 h and 360 h,respectively.The results showed that the growth of interfacial IMC on SAC305/Cu solder joint was significantly inhibited by adding different mass fractions of Cu₆Sn₅ nanoparticle.The most effective inhibition occurred when 0.1 wt.%Cu₆Sn₅ nanoparticle was added into the composite solder.The inhibition effect was weakened with the excess addition of Cu₆Sn₅nanoparticles.In addition,the nanoparticle effectively refined the IMC grains,the refining effect was most obvious with the addition of 0.1 wt.%of the Cu₆Sn₅nanoparticle.Cu₆Sn₅ nanoparticles of 30 nm and 70 nm were successfully prepared by SnCl₂,CuCl₂·2H₂O oxidant,sodium hexametaphosphate dispersant,NaBH₄ and Zn powder reducing agent.According to analysis of DSC curves,the 30 nm Cu₆Sn₅ nanoparticle had a lower sintering temperature than that of 70 nm Cu₆Sn₅ nanoparticle.The experimental analysis showed that 0.1 wt.%of 30 nm and 70 nm Cu₆Sn₅nanoparticles were added to the Sn-0.3Ag-0.7Cu solder alloy,the melting point of composite solder alloys decreased and the degree of undercooling improved.Solder alloy with 30 nm Cu₆Sn₅ nanoparticles had the highest undercooling value of 12.6 ^oC.0.1wt.%of the two kinds of nanoparticle powders were uniformly mixed with Sn-0.3Ag-0.7Cu solder powder,then reflowed at 250 ^oC with flux and subsequently aged at 150 ^oC for 24 h,72 h,120 h and 240 h,respectively.The experimental results showed that comparing to the initial Sn-0.3Ag-0.7Cu/Cu joint,the thickness of interfacial IMC on Sn-0.3Ag-0.7Cu/Cu solder joint with adding two kinds of Cu₆Sn₅nanoparticle was thinner and the growth rate was slower.Cu₆Sn₅ nanoparticle had an inhibition effect on the growth of interfacial IMC,and 30 nm Cu₆Sn₅ nanoparticle had the strongest inhibition effect on the growth of IMC and most obvious refining effect on IMC grains.