Mechanism Of Interfacial Formation And Progress Of Ultrasonic Aided Soldering Of Sapphire

As a kind of optical material, sapphire is widely used in optical devices andsemiconductor devices with merits of being resistant to abrasion, corrosion,radiation and so on. Considering the problems, hard to reaction and wetting, largeresidual stress, etc., in sapphire connection, a method of welding sapphire assistedby ultrasonic with Sn-based solder containing aluminum at a low temperature wasproposed. The bonding mechanism of sapphire/solder interface with the action ofultrasonic, joint microstructure and fracture characteristics were analyzed, a suitableprocess of cryogenic sapphire soldering was researched.According to the study, with the action of ultrasonic at230℃, a reliablecombination of SnZnAl and sapphire was obtained. SEM analysis showed that alayer of compound at the interface between SnZnAl/sapphire was formed. TEManalysis showed that this compound was nano-crystalline-Al2O3layer (NCAL),The compound layer thickness was about100nm when ultrasonic acting last for1000s. It is found that the ultrasound promoted rapid oxidation reaction ofaluminum and a NCAL was generated.At the temperature of270℃, ultrasonic-assisted soldering sapphire withSnAgCuAl, a layer of Al2O3, as a transition layer, also formed at the sapphire/solder interface. With the extension of ultrasonic duration, the interface reactionproducts gathered more and thicker, meanwhile, the ultrasonic also promoted Aldiffusion at the interface. In the weld, the Al content of solder near the interface washigher than that away from the interface. Shear fracture analysis found thatcombination of sapphire and Al2O3was stronger than that of Al2O3and solder,fracture occured at the joint of Al2O3and solder. Mechanical test results showed thatwith the extension of ultrasound duration, the joint shear strength increased, themaximum strength was57MPa.At the temperature of180℃, with the solder SnBiAl, a sapphire connectionwith the shear strength up to28MPa was achieved. By increasing Ultrasoundduration, Al oxidation near the interface increased, and more generated Al2O3deposed at the interface, leading to the increasing of the roughness of the interface,and improving the mechanical properties of the joint. The fracture analysis foundthat fracture also occured at the interface of Al2O3and solder. With the increasing ofultrasound duration there was more residual Bi in the fracture on the side of sapphire, proving that the extension of ultrasound duration contributes to the bettercombination of sapphire and solder, improvement of strength.