Of Sn-ag-bi-cu-in Solder Alloys

Sn-Pb solder is widely applied in surface mount and packaging in electronics. However, due to the toxic impact of toxic substrate-Pb on the environment, as well as the increasing demands of the reliability of solder, it is necessary to study and develop Pb-free solder.In this paper, by adding elements of Ag,Bi,Cu,In to Sn, new lead-free solder of Sn-Ag-Bi-Cu-In system was designed at the basis of element table and relation of phase diagram. At first, taking melting temperature as an evaluation standard, the optimal composition of lead-free solder of Sn-Ag-Bi-Cu-In system through orthogonal experiment method were studied. Physical chemistry solder alloys properties of density, conductance, mechanics, the capability of welding and erodibility were analyzed, and so on, compared with properties of Sn₆₄Pb₃₇ solder. In addition, the figures of the solder microstructure were observed. And the reason of diversification of properties of solder alloy were explained through observing fabric of the solder microstructure. At last, the interface reaction of Sn-Ag-Bi-Cu-In/Cu was analyzed. And the configuration of Sn-Ag-Bi-Cu-In/Cu was explained. It was investigated that the interface intermetallic compound(IMC) growth behavior and element diffusion path off our solder joints during aging.The results show that, melting temperature of Sn-Ag-Bi-Cu-In lead-free solders and Sn₆₃Pb₃₇ solder are very close, and melting range is small. The density of Sn-Ag-Bi-Cu-In lead-free solders are about 87percent of traditional Sn₆₃Pb₃₇. Conductance and heat conducting rate of solders are larger than that of traditional Sn₆₃Pb₃₇ .The spread area of samples correspond with the spread area of Sn₆₃Pb₃₇ solder. The shear strength and tensile strength is much higher than that of traditional Sn₆₃Pb₃₇. And the tensile strength is twice as high as traditional Sn₆₃Pb₃₇. But plasticity of solders are less than that of traditional Sn₆₃Pb₃₇. And the fracture surface of solder is around grain boundary. The erodibility of Sn-Ag-Bi-Cu-In lead-free solders are better than that of traditional Sn₆₃Pb₃₇. The morphology of intermetallic compound (IMC) at the interface of Sn-Ag-Bi-Cu-In/Cu exhibits a scallop structure after soldering. But the IMC morphology of the sawtooth structure can develop into a planar structure. Decisive factor of this development is mostly dG/dt. The growth kinetic of IMC layer during aging versus t^1/2 shows a linear dependence, and it is diffusion mechanism. The growth velocity constant K of IMC is 0.12μm²/h.