The Research On Dissolution Behavior And Interfacial Reaction Of Cu-Sn System With Ultrasonic

So far,Sn-based lead-free solders and Cu substrate have been widely used in the connection of electronic devices.The main problem of Cu-Sn soldering joint was that interfacial intermetallic compounds（IMC）easily formed in the soldering process,an excessively thick compound layer would weaken the mechanical properties of the brazed joint.As a promising brazing method,ultrasonic assisted soldering（UAS）has been widely used in the connection of various electronic components with its excellent performance and improvement of traditional brazing technology since the1970s.The studies mainly focused on breaking oxide film with ultrasonic cavitation and promoting interface wetting behavior,etc.,but the mechanism of dissolution and metallurgical reaction has not been systematically studied by the ultrasonic assisted brazing.According to the analysis,pure Sn solder was used,ultrasonic assisted soldering（UAS）was employed to investigate the dissolution behavior of Cu base metaland the evolution of Cu/Sn interfacial IMC layer with and without ultrasonic wave.The study was to reveal the mechanism that how to improve the reliability of the brazed joint and construct the dissolution mechanism of the base metal and interfacial reaction behavior of Cu-Sn joints by ultrasound-assisted soldering.The dissolution behavior of Cu-Sn system at 573K and 523K was investigated in this work.In the process of heat preservation,the diffusion rate of Cu base metal in Sn liquid at 573 K was higher than that at 523 K at the same time,it gradually decreased with the increasing of reaction time,a Cu-Sn IMC layer formed at the Cu/Sn solid-liquid interface.The dissolution of Cu base metal in Sn liquid was controlled by the diffusion mechanism without ultrasonic wave,but that was mainly controlled by reaction mechanism with ultrasonic wave.After applying for ultrasonic,IMCs at the Cu/Sn solid–liquid interface were broken,which would further promote the dissolution rate of Cu atoms into Sn liquid.Then,the evolution and formation of Cu-Sn brazed joins was investigated at 573K with or without ultrasonic.The results indicated that the morphology of interfacial Cu-Sn intermetallic compounds（IMCs）were gradually transformed from planar shape to scallop-like shape a period of heat preservation,in which the formation of Cu₆Sn₅was mainly controlled by diffusion mechanism,and the formation of Cu₃Sn layer was controlled by the reaction mechanism.The Cu₆Sn₅ phase precipitated in the Sn solder was being regular hexagonal columnar.After applying for ultrasonic,IMCs at the Cu/Sn solid-liquid interface were continuously broken,and dissolved,which occurred successively in the Cu₆Sn₅ and Cu₃Sn layers.Furthermore,it was found that the Cu₆Sn₅ grains in the Sn solder was in regular hexagonal columnar without ultrasonic,but that transformed into a facet-shaped geometry with ultrasonic.What’s more,the relationship between the thickness of the IMC layer and ultrasonic action time in Cu-Sn samples were identified.The thickness of the interfacial IMC was controlled by changing the ultrasonic time,which was expected to improve the performance of the brazed joint.The effect of ultrasonic waves increased the shear strength of the Cu-Sn joints.The maximum shear strength of the Cu-Sn soldering joint was about 30MPa without ultrasonic action.However,it could reach 50MPa when the ultrasonic action time was30s,the shear strength of the brazed joint firstly increased and then decreased with the increasing of the ultrasonic action time.