Study On Low Temperature Diffusion Bonding Of AlCu0.5/6061Al Alloy And Phase Transformation Behavior At Interface

Aluminum alloys have become an important raw material for integrated circuit interconnects due to their high electrical conductivity,strong electrochemical corrosion resistance,easy processing,deposition and lithography,and easy formation of good ohmic contact with the underlying semiconductor.The high-purity aluminum alloy target,as an important supporting material for the aluminum interconnection,is mainly divided into a functional target blank and a structural backplate,and the connection between the target blank and the backplate becomes an important part of the target manufacturing process.As a solid-phase connection method,diffusion bonding has the characteristics of high bonding accuracy and good bonding quality,which makes it unique in the connection of target,and the realization of low-temperature diffusion bonding of high-purity Aluminum alloy is conducive to ensuring the functionality of the target.In this work,AlCu0.5 alloy and 6061A1 alloy are used as the research objects,and the electroplated Ni layer and the electroplated Ag layer are used as the intermediate layer to carry out the low temperature diffusion welding process test.The bonding strength of the bonded joints is required to be above 20 MPa.The ultrasonic C-scan,optical microscope(OM),scanning electron microscope(SEM),Energy Dispersive Spectroscopy(EDS)and Backscatter Diffraction(EBSD)were used to observe the grain size of AlCu0.5 alloy,microstructure evolution and element diffusion,and the mechanical properties of the bonded joints were tested.The influence of different bonding temperature and holding time on bonded joints was analyzed.Bonding temperature and holding time have significant effects on the grain size of AlCu0.5 alloy after welding.Under the process conditions of P=120 MPa,t=4 h,the average grain size of AlCu0.5 alloy is about 33?m at T=250??280?.Compared with the grain size before bonding,there are no significant changes.However,when the temperature increases to 295?,the average grain size increase to 46 ?m,and abnormally coarse grains appeare.The grain size uniformity become significantly worse.Under the conditions of T=280? and P=120 MPa,the effect of holding time on the grain size showes the same trend.When the holding time is extended to 12 h,the grains begin to grow significantly,and the average grain size increases to 42 ?m.When the electroplated Ni layer is used as the intermediate layer,there are no intermetallic compounds and no diffusion reaction layers at the interface.As the bonding temperature increases,the residual Ni layer at the interface gradually becomes thinner with the diffusion deepening,and there are always unbonded gaps at the connection interface.The bonding rate is low and the strength of the welded joint is also low.At the conditons of T=310?,P=120 MPa,t=4 h,the tensile strength of the joint is only 1 MPa and the bonding rate is 73.4%.When electroplating Ag is used as the intermediate layer,under different bonding temperatures and holding times,there is no obvious diffusion reaction layer at the interface except for the residual intermediate layer.As the bonding temperature increases,the thickness of the intermediate layer gradually decreases,and the bonding rate and mechanical properties also gradually increase.At the conditions of T=310?,P=120 MPa,t--4 h,the bonding rate of the bonded joint reaches 98.7%,and the tensile strength of the joint is 26.7 MPa.With the prolongation of holding time,the mechanical properties of bonded joints shows a trend of increasing first.At T=280?,P=120 MPa,and t=10 h,the bonding strength which reaches 22.3 MPa is the largest.With the holding time is further prolonged,Kirkendall voids will appear at the Ag/Ni interface which results in a decrease of mechanical properties of bonding joint.