Research On Composition Design And Properties Of Multi-component Sn-based High Temperature Solder Alloys

The functional diversification of the electronic components and the complexity of the use environment have put forward higher requirements for the long-term stability of the solder alloy materials.The traditional high-temperature solders have high lead content.Although the application of lead-containing solders and other harmful substances in microelectronics and other fields have been legislated to restrict in recent years,the performance and reliability of the current high-temperature lead-free solders are far inferior to traditional solders alloys,due to the poor mechanical properties,inappropriate melting point,high cost price and poor brazing performance.Therefore,it is crucial to find a material that can replace traditional hightemperature solder materials.In this paper,the Sn-based multicomponent lead-free high-temperature solder(the alloy systems are Sn-Cu-Co-Ni-Bi,Sn-Cu-Co-Ni-Zn,Sn-Cu-Ni-Sb-Bi and Sn-Cu-Co-Sb-Bi).It has been developed based on the principles of high-entropy alloy,the microstructure,mechanical properties and brazing properties of solder alloys with different components were investigated,including microstructure,mechanical properties,melting properties,corrosion resistance and resistivity,etc.The results provide a theoretical basis and experimental guidance for improving the comprehensive properties of solder alloys.The main conclusions are as follows:(1)The microstructure of the solder alloy is composed of solid solution and precipitation phase.In alloys containing Bi,since Bi has a low solid solubility in other elements,the Bi phase exists in the grain boundary in the form of a simple substance,with the increase of mixing entropy value,the content of solid solution in the alloy structure of the alloys gradually increases,and the content of Sn matrix gradually decreases.(2)For the solder alloy with the same alloy system,the hardness value increases with the increase of alloy mixing entropy.The maximum Vickers hardness is 410 HV0 5,The maximum Brinell hardness value is 160 HB.The compressive strength of solder alloys increases gradually with the increase of alloy mixing entropy,with the maximum value of 266 MPa and the minimum value of 55 MPa;The tensile strength increases first and then decreases,with the maximum value of 84.3 MPa and the minimum value of 11 MPa.The tensile fracture mode of solder alloys is brittle fracture.(3)For the solder alloy with the same alloy system,the melting point increases first and then decreases with the increase of mixing entropy.The melting point ranges of Sn-Cu-Co-NiBi,Sn-Cu-Co-Ni-Zn,Sn-Cu-Ni-Sb-Bi,Sn-Cu-Co-Sb-Bi re138-269 ℃,180-350 ℃,141-251 ℃,and 140-243 ℃,respectively.The melting point of Sn-Cu-Co-Ni-Bi and Sn-Cu-Co-Ni-Zn alloys are higher than the melting point of traditional Sn-90 Pb solder with melting point of268 ℃.It shows that the multi-element Sn based alloy can be used as alternative material of high temperature solder.(4)For the solder alloy with the same alloy system,the corrosion resistance increases gradually with the increase of alloy mixing entropy.At the same time,the resistivity range of the alloys is 0.101-0.87 μΩ·m.Although showing a gradual increasing trend,resistivity range of the multi-element Sn based alloys is still comparable with the resistivity of Sn-90 Pb solder(0.194 μΩ·m).