| SAC solder has recently received a lot of attention because of its exceptional all-around performance,but its high cost limits its use in a wide range of industrial applications.Sn-0.7Cu,on the other hand,has gotten a lot of interest because of its inexpensive cost,high strength,and electrical conductivity.However,Sn-0.7Cu has a number of drawbacks,including a high melting point,poor mechanical qualities,and limited dependability,all of which limit its use.In this research,alloying and particle strengthening were used to make Sn-0.7Cu-xIn and Sn-0.7Cu-xMo solder,and the influence of particle strengthening on relative solder attributes was investigated.The macroscopic evolution mechanism of the interfacial IMC layer and the reinforcing phase interaction mechanism of the three types of brazed joints under high current density loading were explored using Sn-0.7Cu as a control in order to assess and study the EM failure mode of solder joints.The alloyed Sn-0.7Cu-xIn solder’s performance optimization method reveals that the alloyed element efficiently lowers the melting point of Sn-0.7Cu-xIn solder.Solder’s melting point drops as its In content rises,while its melting range grows.The In Sn4 phase was injected into the solder matrix,and it supplied a significant number of inhomogeneous nucleation spots for the growth of-Sn,which refined the solder matrix microstructure and increased microhardness.The electrical conductivity of the solder reduces with the addition of In,and the electrical conductivity of the solder decreases with the rise of In concentration.The wetting reaction and IMC development were aided by the addition of In.Welded joints’shear strength is also improved.The maximum shear load of a 10 wt%.In shear sample increases from 1.33 k N to 1.78 k N,and the maximum shear displacement increases from 2.14 mm to 4.27 mm when compared to Sn-0.7Cu.The performance optimization mechanism of Mo micron particles reinforced filler metal shows that Mo micron particles have little influence on the melting characteristics,electrical conductivity and wettability of the filler metal.The doping of Mo micron particles refines the matrix structure and improves the microhardness of the solder.The microhardness of the Sn-0.7Cu-0.25Mo matrix reaches 14.59 HV,30.24%higher than that of Sn-0.7Cu.Mo micron particles inhibit the growth of interfacial IMC and refine the IMC particle size.At the interface of Sn-0.7Cu-0.25Mo/Cu,the thickness and particle size of the IMC layer are 1.812μm and 1.359μm,respectively,which are significantly reduced compared with 3.389μm and 4.516μm of IMC layer at the interface of Sn-0.7Cu-0.25Mo/Cu.The doping of Mo micron particles improves the strength of the solder joint.The sn-0.7Cu-xMo composite solder bears the greater shear load and shear displacement than Sn-0.7Cu in the shear tensile test.At the current density of 2.0 x 10~3 A/cm~2,electromigration tests were performed on solder joints of three types of brazing materials.The results show that the electrical conductivity of Sn-0.7Cu-0.25Mo solder is relatively less affected by current.During the 384h electromigration test,the real-time resistance of the Cu/Sn-0.7Cu-0.25Mo/Cu solder joints increased by 0.64%,and the Cu/Sn-0.7Cu/Cu and Cu/Sn-0.7Cu-10In/Cu solder joints increased by 2.75%and 2.43%respectively under the same conditions.It was found that the cracks only appeared at the Cu/Sn-0.7Cu/Cu cathode side,and the IMC at the Cu/Sn-0.7Cu-0.25Mo/Cu electrode interface was relatively less affected by the current.The addition of In and Mo micron particles improves the reliability of solder joints under high electrical loads,but their mechanisms are different.The reverse diffusion of In atoms under the action of back stress supplemented the atom loss at the cathode side and inhibited the generation of cracks,while the Mo micron particles eliminated the original channel of rapid diffusion of Cu atoms by forming a planar IMC structure and delayed the change of IMC layer at the interface under the action of the current. |
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