Soldering Technology And Joining Mechanism Of Bi_0.5Sb_1.5Te₃ And Cu

Bi₂Te₃-based thermoelectric materials have the highest thermoelectric value near room temperature,showing the best thermoelectric performance.In order to meet the needs of practical application,thermoelectric materials and electrodes should be connected to form thermoelectric devices.The thermoelectric conversion efficiency of thermoelectric devices is affected by the thermoelectric materials themselves and the quality of joints.The soldering technology and joining mechanism of Bi_0.5Sb_1.5Te₃ and Cu electrodes are studied in this paper.SnBi solder was used to realize the connection between Bi_0.5Sb_1.5Te and Cu.The typical interface structure of the soldered joint was Bi_0.5Sb_1.5Te₃/SnTe+SnSb/?-Sn+Bi-Rich/Cu₆Sn₅/Cu₃Sn/Cu.The variation of interfacial structure and mechanical properties of joints with process parameters was studied.With the increase of soldering temperature and the extension of holding time,the joint strength increases first and then decreases.The maximum strength of the joint is 7 MPa at 180?and holding time of 3 min.The fracture location of the joint is SnTe+SnSb reaction layer on Bi_0.5Sb_1.5Te₃ side.The surface barrier layer of Bi_0.5Sb_1.5Te₃ was prepared by electroplating method.The Ni coating can effectively inhibit the diffusion of Sn,Te and Sb elements.The optimum plating time is 10 min,the strength of the joint can reach 12 MPa,and the fracture position is on the base metal side of Bi_0.5Sb_1.5Te₃.At this time,the interface structure was Bi_0.5Sb_1.5Te₃/NiTe₂/Ni/?Ni,Cu?₃Sn₄/?Cu,Ni?₆Sn₅/?-Sn+Bi-Rich/Cu₆Sn₅/Cu₃Sn/Cu.The maximum strength of the joint is 12 MPa under the optimum solderng temperature 170?and holding time 3 min.In the process of service simulation,the single Ni coating will be consumed gradually,which will lead to failure.Therefore,the coating has been improved.The evaporated Ti test proves that Ti does not react with the elements in the soldering system and has a good barrier effect.The Ni/Ti/Ni composite coatings were prepared,which combined with the base metal on both sides and hindered the diffusion behavior of Sn,Te and Sb.The contact resistance of Bi_0.5Sb_1.5Te₃ is the highest and that of Bi_0.5Sb_1.5Te₃/Ni/SnBi is the lowest.However,due to the slow element diffusion and interface reaction after a long time of aging,the change range of the contact resistance of Bi_0.5Sb_1.5Te₃/Ni/Ti/Ni/SnBi is the smallest,while that of the other two kinds of joint structures is comparatively different.The results show that the Ni/Ti/Ni composite coating can effectively block the element diffusion and the mechanism of interface evolution was analyzed.In order to reduce the contact resistance of joints,graphene composite solder was prepared.The good conductivity of graphene reduced the joint resistance.The results showed that when the content of graphene was 0.2%,the interface bonding was good.The electrical properties showed that the contact resistance decreased by about 11%.