Process And Mechanism Of Low Temperature Soldering Of Sapphire With Sn-based Solder

Sapphire has excellent high-frequency characteristics and optical properties,moreover the linear expansion coefficient is very similar with that of electronic components,so it is widely used as packaging substrate materials now.In the field of electronic packaging,low-temperature soldering is the main connection technology out of the temperature requirements.However,due to its high chemical stability,sapphire is very hard to be wetted by solders.This paper improve d the wettability by using Sn-based active solder adding active element Ti and Al and introducing the assistance of ultrasound to realize the connection of sapphire in the atmospheric and the connection mechanism was studied.Soldering of sapphire with Sn3.5Ag4Ti solder,which added the active element Ti was studied.It was proved that the solder had good wettability to sapphire.Direct ultrasonic soldering and ultrasonic soldering after ultrasonic dipping could both form a good connection of sapphire.When the ultrasonic dipping time was 10 s,a joint could achieve a stable strength of 33 MPa,continued extension of ultrasonic time didn't affect the joint strength.The connection mechanism is Ti with high activity in solder spread to interface,then react with Al₂O₃ on the surface of sapphire and O in the air to form Ti₂O₃ layer.Under the assistance of ultrasound,we also studied soldering of sapphire with SnAg-based activated solder Sn3.5Ag4Al added the active element Al.The wetting of this solder was relatively poor.Direct ultrasonic soldering could't connect sapphire.Only after ultrasonic dipping to improve wetting could form a good conntion between sapphire.The shear strength increased with the prolongation of ultrasonic dipping time,and the maximum strength reached 36 MPa.The interfacial bonding mechanism is that the Al and Al compounds in solder dissolve and diffuse to interface,then react with O to form Al₂O₃.TEM proves that Al₂O₃ amorphous layer and Ag enrichment on the interface can strengthen bonding.However,both the active elements Ti and Al in the above-mentioned two kinds of solders were present in the form of compounds and could not easily dissolved,and both of them contained high cost metal Ag.Therefore,low cost Sn9Zn2Al solder was proposed,and the solder had ternary eutectic phase Sn Zn Al with low melting point and was more soluble.It was proved that ultrasonic soldering with or without ultrasonic dipping could both form a good connection of sapphire.With the prolongation of ultrasonic time,the shear strength was divided into 2 stage of rapid rise for 20s⁵0s and slow rise for 50s²000s.The connection mechanism is similar to that of Sn3.5Ag4Al.Al₂O₃ amorphous layer and Zn enrichment on the interface are main reason for connection.Direct ultrasonic soldering of sapphire with Snx Zn2Al?x = 9,25,45?of different Zn content could form a good connection of sapphire.The strength of the joint raised with the increase of the Zn content.The maximum strength of joint formed with Sn45Zn2 Al reached 32 MPa.We achieved the connection of sapphire with high strength in short time through increasing the content of Zn in solder.