Study On Growth Behaviors Of Sn-Cu-Bi Lead-free Solder Interface IMCs

Intermetallic compounds?IMCs?produce from the reaction between the lead-free solder and substrate.The growth and evolution of IMCs has a great impact on the service life,reliability and quality of electronic packages.The biggest problem with lead-free solders currently used in electronic packaging is that the solder has a high melting point,which requires a higher heating temperature and holding time during the soldering process,thereby reducing the life and performance of electronic components.Aiming at the above problems:This topic using Sn-0.7Cu as matrix,adds Bi to reducing the melting point,and trace Ni and Co to improving the comprehensive mechanical properties of solder joints.In this paper,Sn-0.7Cu-10Bi-xNi/Co?SCB-xNi/Co,x=0,0.05,0.10,0.15,0.20 wt.%?composite lead-free solder was prepared by high-vacuum arc melting method to explore the role of trace Ni and Co in interface reactions and the growth and evolution of IMCs.The results show that the addition of Bi reduces the melting point of the solder alloy,and the effect of trace Ni and Co on the melting point is small.The addition of Ni and Co changed the morphology of the SCB-X/Cu interface IMCs layer from a scallop-like to a planar.The?Cu,Ni?₆Sn₅,CoSn₃ and?Cu,Co?₆Sn₅ phases were formed at interface,which can effectively prevent Cu atoms from diffusing from substrate side to solder/IMCs interface,Decreased Cu₆Sn₅ growth rate and reduced IMCs layer thickness.A porous structure CoSn₃ was formed at the SCB-0.15Co/Cu interface,and the growth rate was much faster than Cu₆Sn₅.Therefore,the morphology of the IMCs layer was planar and the thickness increased.Due to the porous structure of CoSn₃,the IMCs layer gradually dissolves during aging,and the thickness of the IMCs layer decreases.When Co is used as substrate,the content of Ni atoms in the IMCs layer determines the thermal stability of the IMCs layer.Ni atoms occupy the sublattice positions of Co atoms in the CoSn₃ phase,forming?Ni,Co?Sn₃ distributed in the IMCs layer,which improves the high temperature stability of the IMCs layer.Changes in the equilibrium of the Co atom concentration at the SCB-xCo/Co interface caused the IMCs layer to grow,delaminate,and dissolve.The free-state IMCs particles grew up under the action of adsorption force.