Study On Reliability Of SAC305/Cu Solder Joints

In recent years,with the advancement of global lead-free,Sn-3.0Ag-0.5Cu(SAC305)solder has become one of the alternatives to traditional Sn-37Pb materials due to its good overall performance.However,there are still many deficiencies in the use of SAC305 solder,such as the intermetallic compound(IMC)growing too fast during service,which impairs the performance of the solder joint.Therefore,in order to solve the above problems,this work used the double-roll rapid solidification technology to improve the performance of SAC305 solder,and added Bi element on the basis of it to study the effect of welding process,isothermal aging and electromigration on the interface IMC layer.The research shows that the solder joints prepared by rapid solidification SAC305(Rapid Solidification,RS)gradually increase the thickness of the IMC layer at the interface of the solder joint with the extension of the welding time.In the end,there is a tendency to transform into a flat layer.It is found that the more suitable brazing time is 20s.Compared with the casting and rolling SAC305(Casting and Rolling,CR),the IMC layer morphology of the rapidly solidified SAC305/Cu solder joint interface is more uniform and flat,and the thickness is thinner;After adding Bi element to the rapidly solidified SAC305 solder,the thickness is further reduced,and the growth is significantly inhibited.It is found that with the increase of effective temperature,the growth rate of the IMC layer is accelerated,the thickness of the interface IMC layer is increased,and the Cu₃Sn compound is formed earlier in the interface IMC layer.When the aging temperature is fixed,the thickness of the IMC layer gradually increases with the extension of the aging time,and the growth rate gradually decreases and tends to be stable.The morphology of the interface IMC layer changes from scallop to plane,which consists of the Cu₆Sn₅ intermetallic compound layer Converted to(Cu₆Sn₅+Cu₃Sn)composite layer.The diffusion coefficients of common SAC305/Cu solder joints at different aging temperatures are D_CR1=5.81×10^-20m²/s,D_CR2=9.37×10^-19m²/s,D_CR3=8.31×10^-17m²/s.With the increase of aging temperature,the rapid solidification SAC305/Cu solder joints have diffusion coefficients of D_RS1=4.67×10^-19m²/s,D_RS2=5.76×10^-19 m²/s,and D_RS3=5.66×10^-17m²/s.After adding Bi element to the rapidly solidified SAC305 solder,the diffusion coefficients are DBi1=1.24×10-21m2/s,DBi2=9.73×10-20m2/s,DBi3=2.28×10-18m2/s,and the addition of Bi further Reduce the diffusion rate of atoms.The dynamic index n of the three solder joint IMC layers is close to 0.5,and the growth of the IMC layer is controlled by volume diffusion.Compared with ordinary SAC305/Cu solder joints,the growth activation energy of the IMC layer at the interface of the rapidly solidified SAC305/Cu solder joints increased from 15.56KJ/mol to 19.01KJ/mol.After the addition of Bi in the solder,the activation energy of the IMC layer increased to 24.33KJ/mol.The rapid solidification technology and the addition of Bi elements can effectively suppress the growth of the interface IMC layer during the aging process and increase the reliability of the solder joints.The study found that the common SAC305/Cu solder joints with the electromigration,the thickness of the IMC layer at the anode side interface increases,the thickness of the IMC layer at the cathode side interface decreases,the thickness of the IMC layer at the bipolar interface is getting larger and larger,and obvious polarity appears effect.Also,as Cu atoms accumulate on the anode,bumps appear on the anode side solder matrix.Compared with ordinary SAC305/Cu solder joints,the thickness of the IMC layer at the interface of the rapidly solidified cathode side increases first and then decreases,but the thickness of the IMC layer at the anode side interface grows faster than that of ordinary solder joints.Although the rapid solidification technology eases the dissolution of the IMC layer on the cathode side of the solder joint,it makes the thickness of the IMC layer on the anode side interface increase too fast,which has an adverse effect on the solder joint.The growth of the IMC layer on the anode side of the solder joint conforms to the parabolic law,and the growth process is controlled by volume diffusion.After adding Bi element,it was found that the growth rate of the IMC layer on the anode side of the solder joint was slower,and the dissolution of the IMC layer on the cathode side interface was also alleviated.The addition of Bi element can inhibit the electromigration behavior of solder joints.