摘要
Abstract
The copper indium micro nano layer with pine like morphology and ultrasonic energy are used to realize bonding interconnection at low temperature.The work aims to ensure the reliability of interconnection,and solve the problem of high thermal stress and signal delay caused by high temperature of traditional reflow soldering process.The surface of the substrate coated with pine like secondary copper indium micro nano layer was used as one end of the bonding couple,and the other end was lead-free solder.A monolayer of conformal graphene was added between the bonding couples as a barrier layer.At low temperature(120℃),the transient solid state bonding of copper indium substrate and lead-free solder could be realized by applying ultrasonic energy and certain pressure to the bonding contact area.A scanning electron microscope,a transmission electron microscope,an X-ray diffraction(XRD)and a welding strength tester were used to analyze the microstructure,intermetallic compound and shear strength at the bonding interface.The copper micro layer had a conical convex surface structure,which was coated with nano indium layer.The indium nano layer protected the conical copper array structure from air oxidation.The pine like copper indium secondary micro nano structure formed had a huge surface area.Under the condition of ultrasound,low pressure and low temperature,due to the nano size effect,the surface of pine like indium layer was highly meltable.The copper indium pine like array structure was inserted into the soft tin based solder to form a stable physical barrier structure,which could realize the welding interconnection with the surrounding lead-free solder.The thin indium layer at the bonding interface was rapidly diffused into intermetallic compounds(Cu6Sn5,Cu2In)under the action of ultrasonic energy.Cu2In was a high-quality phase with good mechanical properties,which was conducive to improving the interconnection strength.When the thickness of indium layer at the bonding interface was 300 nm,the bonding temperature was 120℃,the bonding pressure was 0.6 MPa,and the bonding time was 2.5 s,the optimal bonding quality was obtained,and the bonding interface pores disappeared.The average shear strength of the bonding interface was about 36 MPa,which was still a gap compared with the reflow soldering process,which could reach 43 MPa.If the bonding pressure was too small or the ultrasonic time was too long,linear holes or cracks would be generated at the bonding interface.These holes or cracks could not disappear through heat treatment.The monolayer conformal graphene barrier layer avoided direct contact between tin solder and copper substrate with rough surface.The copper tin reaction was slowed down and excessive growth of brittle intermetallic compounds was prevented.After aging at 160℃for 100 h,the microstructure of the bonding interface had no obvious change.The interface composition was stable and no new holes were generated.As the graphene interlayer prevents dislocation expansion,the average shear strength of the bonding interface increased to 40 MPa.It was predicted that the long-term use process could maintain high reliability.The graphene interlayer can avoid the aging of the structure and improve the life of the bonding interface.Due to the special morphology of copper indium pine wood like array structure and the introduction of ultrasonic energy,the bonding can be completed in an instant and at low temperature.The bonding quality is good,and smaller bonding size can be obtained.关键词
超声波键合/Sn-Ag-Cu/石墨烯/界面反应/扩散Key words
ultrasonic bonding/Sn-Ag-Cu/graphene/interfacial reaction/diffusion分类
通用工业技术
