Experimental Investigation On Phase Equilibria Of The Partial Sn-based Lead-Free Solder Systems

Tin-lead(Sn-Pb)solders were widely used in the electronics industry during past decades because of its good joining performance and low price.In recent years,as people pay more attention to health and environmental problems,as well as the implementation of RoHS and WEEE directives,it has become an inevitable trend in the electronic industry to fully realize lead-free.The development of new lead-free solder has become an urgent demand in the field of electronic packaging.As a powerful tool for material design,the phase diagram can provide theoretical guidance for the composition,melting point and preparation process of the alloy,and can predict the solidification structure of the alloy effectively.It plays an important role in the study of the welding interface reaction.In this study,the phase equilibrium of Sn-Sb-Cu,Ni-Al-Sn and Co-Cu-Zn ternary systems were measured by the alloy method,and some important phase transformation processes were analyzed and discussed.The main research results of this paper are as follows:(1)The isothermal phase diagram of Sn-Sb-Cu ternary system at 400 and 500℃were determined by meams of electron probe microanalysis(EPMA),X-ray diffraction(XRD),and differential scanning calorimetry(DSC).At the 400℃ isothermal section,the δ-Cu4Sb phase is unstable,and the Cu11Sb3 phase take the place of it.At the same time,the high temperature stabilized Cu6(Sn,Sb)5 and γ-Cu11(Sb,Sn)2 phases were obtained at 400℃ and 500℃ respectively.(2)The martensite transformation process in the Sn-Sb-Cu ternary system was studied by meams of DSC and HTXRD.The results showed that the parent phase of martensite was β-Cu3Sb,the martensite was unstable during the heating process,and the eutectoid decomposition reaction(M →ε-Cu3Sn + η-Cu2Sb)occurred.(3)The phase equilibria of Ni-Al-Sn ternary system at 800 and 1000℃ were determined by meams of EPMA,XRD,and DSC.The solubility of Sn in Ni3Al was about 14.7 at.%at 800℃,and it decreases to 8.0 at.%at 1000℃.(4)The phase equilibria of Cu-Co-Zn ternary system at 800 and 1000℃ were determined by meams of EPMA and XRD.The solubility of Co in β-CuZn is 32.36 at.%at 800℃,and Cu in β1-CoZn is 5.28 at.%。The γ-Co5Zn21 and γ-Cu5Zn8 have the same crystal structure;therefore,an extensive region of mutual solubility was observed in the Co-Cu-Zn ternary system,and labeled as γ.