Preparation And Properties Of Zn-Sn High-temperature Lead-free Solder By Adding Third Alloy Elements And Nanoparticles

With the development of the electronics industry,there are some new functional materials,such as piezoelectric ceramic materials and shape memory alloys,which are sensitive to changes in temperature and composition,and have made severe demands on the connection process.Some mechanical properties and the use of the operating temperature can not meet the requirements.As the electronic products and microelectronic systems become more and more integrated,multifunctional and small,it makes a more severe application condition.There is the problem of step-assembly,the first part of the assembly to use a higher melting point of the solder.Thus in this context,the investigation of excellent reliability high-temperature solder was necessery.Zn-Sn solder alloy has good mechanical properties and excellent conductivity,thermal conductivity,and the cost is low,is regarded as a prospect of high-temperature lead-free solder.But the Zn has the low compactness,its strength and hardness is not high,so adding the third alloying elements and enhanced phase are the effective methods to improve the performance and reliability of Zn-Sn solder alloy.In the present paper,In,Ge alloy element and Ag₃Sn nanoparticles were mixed to Zn30Sn solder mechanically to form some new solder.This paper focuses on microstructure,wettability,melting point,hardness,shear test,and he interface growth behavior of intermetallic compounds?IMC?formed between solder and Cu pad was discussed.The result showed that adding of In and Ge alloy element significantly can lower the melting point of Zn-Sn solder alloy,and can increase the wettability of the solder alloy.Functioned as solid solution strengthening,adding of In and Ge alloy element increase the shear strength and hardness of the solder joint.And the adding of Ge alloy element has a more significant impact on Zn-Sn alloy solder.After reflow,the interfacial layer between solder and the Cu substrate were composed of two interfacial intermetallic compounds.Near the side of the solder is the CuZn₅ phase,and near the side of the Cu substrate exists Cu₅Zn₈ phase.During the isothermal aging?aging?process at 150?,with the increase of aging time,the thickness of the CuZn₅ layer gradually becoming bigger,the Cu₅Zn₈ layer gradually thickening.After aging for 360 h,the IMC composition at the interface becomes single Cu₅Zn₈ phase.After a certain aging process,the IMC at the interface between the solder and Cu substrate only exist Cu₅Zn₈ phase.The addition of In and Ge elements did not change the interface between the solder and Cu substrate,but also did not affect the phase transition of interface IMC,but only dissolved in the?-Sn phase of Zn30Sn solder.In the study of composite solder,Ag₃Sn nanoparticles were found to be dispersed in the solder matrix?-Zn phase and interface IMC layer after being added to the solder.The addition of Ag₃Sn nanoparticles will increase the melting point of the solder,but the range of variation is very small,and the addition of an appropriate amount of Ag₃Sn nanoparticles will improve the wettability of the solder.However,when the Ag₃Sn nanoparticles are added too much,the solder wettability decline.The addition of 0.4 wt.%Ag₃Sn nanoparticles inhibited the growth of interface IMC.After aging at 150?for different time,the thickness of IMC layer at the interface between composite solder and Cu was significantly increased,and the thickness of IMC layer in nanocomposite solder int erface increased obviously.Compared with the addition of Ag₃Sn nanoparticles,the growth rate of interface IMC was slowed down.The addition of Ag ₃Sn nanoparticles improved the shear strength of the solder joint and the hardness of the solder.When the addition of Ag₃Sn nanoparticles is 0.4 wt.%,the effect of strengthening is the best.It can be seen that the addition of Ag₃Sn nanoparticles can improve the reliability of the solder.