Study On Microstructure And Mechanical Properties Of Sn-1.0Ag-0.5Cu-xBi Soldered Joint

In the world,for the protection of human health and environmental protection requirements,electronic products lead-free has entered the stage of implementation.Sn-Ag-Cu is considered to be the most potential lead-free solder due to its excellent performance,and the mechanical properties of solder joints with Ag content 3%are excellent,but the cost is relatively high.This paper presents a new type of low silver lead-free solder The Sn-Ag-Cu-xBi,and studies the effect of different Bi content?0,1,3,4.5wt.%?on melting temperature,wettability and microstructure of the solder alloy.The results show that with the addition of Bi elements,the effect of fine grain strengthening,the melting point of the solder,the wetting,and the excessive bi can lead to the coarsening of the microstructure.The Sn-Ag-Cu-xBi filler metal is spread on Ni,Cu and Co substrates,then the interfacial liquid aging is studied,and the influence of the microstructure of the solder/substrate interface on the evolution of the liquid aging and the shear strength is investigated.Ni substrate Interface Generation?Cu,Ni?₆Sn₅ and?Ni,Cu?₃Sn₄ two intermetallic compounds,which were initially generated by IMC in the interface?Cu,Ni?₆Sn₅.With the increase of aging time,the size of IMC particles increases and the thickness of IMC layer becomes thicker.Bi Atomic energy can effectively reduce the diffusion rate of sn-ni substrates in brazing alloys.The shear strength increases with the addition of the Bi element,the 3%Bi strength of the solder alloy is the highest when adding the 4.5%Bi,and the shear strength of the filler metal decreases sharply when the liquid aging is added.As the Cu₆Sn₅ of the interface of Cu substrate,the formation of Cu₃Sn,Bi on the substrate near the base plate inhibited the thickening of IMC as the liquid aging.The growth rate of IMC is the fastest in the Co substrate and IMC is CoSn₃.The interface of CoSn3 and solder joint will produce crack with liquid aging.Sn-Ag-Cu-xBi/Cu solder joints under 150?respectively aging 120h,240h,360h,480h,720h.The sawtooth-like IMC obviously thickened with the aging time and became a stable mountain shape.When the Bi content is 4.5%and 1%,the interface IMC has a lot of protruding parts and the IMC layer is relatively flat when the Bi content is 3%.The shear strength of solder joint is higher than that of 3%Bi with the increase of Bi content,when the Bi content is added to 3%,the shear strength is the highest,and the shear strength of solder joint decreases greatly when added to 4.5%Bi.