Cu/Al Dissimilar Interconnection With Tin Ball By Dual Ultrasonic Excitation

With the development of 5G technology and the continued demand for tiny and thin electronic products,the direct low-temperature interconnection homogeneous and heterogeneous material of heat-free chip aluminum electrodes,heat-sink-free ceramic etc.This will become an important research direction in the future.In this paper,a uniquely designed dual-ultrasonic welding process and 40%Zn+60%SAC0307 solder were used to achieve Cu/Al interconnections at low-temperature.We researched the gain effect of dual-ultrasonic,the turn-on sequence for dual-ultrasonic soldering,and the power of ultrasonic on the quality of Cu/Cu(Al)interconnections,and initially explored the mechanism of dual-ultrasonic interconnections.The following conclusions were drawn.(1)Based on the excitation and resonance effects of ultrasonic,the gain effect of dual-ultrasonic is significant.In homogeneous interconnections,the effect of simultaneous opening of dual-ultrasonic is more significant;in heterogeneous interconnections,the effect of simultaneous loading of thermal ultrasonic on the aluminum side is more significant.The quality of solder seam of Cu/Cu joints after double ultrasonic action is excellent,and the IMC of both upper and lower interfaces is CuZn₄+Cu₅Zn₈,and the shear strength of solder joints can reach 45.43 MPa,which is 1.5 times of the single ultrasonic solder joints at the same power.Cu/Al solder joints with dual-ultrasonic interconnection,there were CuZn₄and Cu₅Zn₈on the Cu side,Al-Zn solid solution on the Al side,the shear strength(aluminum underneath)is 26.99 MPa,which is about 40%improvement over single ultrasonic joints at the same power.(2)At a soldering temperature of 200°C,the Cu/Cu solder joints reached the maximum shear strength of 47.69 MPa by using the dual-ultrasonic process of upper 800W and lower 400 W.The solder joints all fractured in the solder layer and had a large number of parabolic tough nests in the fracture.The shear strength of Cu/Al solder joints reached the maximum of 34.49 by using the dual-ultrasonic process of upper 800 W and lower 300 W at a soldering temperature of 220?.The positions of fracture were located at the solder layer,and the number of tough nests on the fracture surface was more and more uniformly distributed.(3)There were five types solders of 4#SAC0307+1?m Zn,4#SAC0307+45?m Zn,5?m SAC0307+1?m Zn,500nm SAC0307+1?m Zn,500nm SAC0307+100nm Zn.And at a soldering temperature of 200°C,the Cu/Cu dual-ultrasonic joint shear strength with4#SAC0307+45?m Zn reached the maximum of 50.99 MPa by using the dual-ultrasonic process of 800 W for upper sonication and 400 W for lower sonication.At a soldering temperature of 220°C,the shear strength of Cu/Al solder joints with 4#SAC0307+45?m Zn reached the maximum of 38.79 MPa by using the dual-ultrasonic process of 800 W for upper sonication and 300 W for lower sonication,.