Study On The Interface Behavior And Mechanical Properties Of Glass-Metal Joining Based On Anodic Bonding

Originally developed in the late 1960s,anodic bonding,also known as electrostatic bonding or field-assisted bonding,has become one of the most important technologies for glass-metal joining in the packaging and manufacturing of micro electro mechanical systems?MEMS?.The joining between glass and metal has been widely used in the fields of electronics,aviation,aerospace and so on.However,owing to the big difference between glass and metal in physical and chemical properties,an excellent joint is difficult to achieve.With the development of the integration of MEMS devices and the extension of the application area,it is an urgent problem to realize multiple-stack anodic bonding and expand the types of bonding metals.Si-glass-Al was successfully bonded together through a two-step anodic bonding process.The focus was on the current variation in bonding process.Based on that,a new coupling technique for glass-metal joining was presented.Firstly,the glass and Al were successfully bonded by anodic bonding process,then the joining between Al and Cu was achieved by soldering with Sn-Zn solder.A glass-Cu interface evolution model was established.The effects of soldering time and Zn content in Sn-Zn solder on the interface microstructure and mechanical properties were studied.The results indicate that,for the Si-glass-Al joint,the current variation of two bonding process was similar.The peak current of the second step bonding was always larger than the first step,which indicated resistance produced by incomplete contact between bonding materials had a significant effect on peak current.A Na⁺depletion layer was formed at Si/glass and glass/Al interface respectively,and its thickness increased with the increase of voltage.In tensile test,fracture always occurred near the second step bonding interface or the glass substrate.For the glass-Cu joint,typical interface structure of the glass/Cu joint can be expressed as glass/Al/Al-Sn-Zn solid solution/?Al?'phase+?Al?"phase/CuZn₅/Cu₅Zn₈/Cu when eutectic Sn-9Zn solder was used.In the process of anodic bonding,the thickness of Na⁺depletion layer at the glass/Al interface was 300nm at 450?/600V.While in the soldering process,Al-Sn-Zn solid solution,Cu₅Zn₈ and CuZn₅ reaction layers were detected on Al/solder interface and Cu/solder interface respectively.As the soldering time increased,needle-like?Al?'phases and round?Al?"phases were observed in sequence near Al/solder interface;at the same time,the thickness of Cu₅Zn₈ and CuZn₅ layers increased accordingly.When the soldering time was 10min,micro grooves on Al foil were observed,and CuZn₅ IMCs spalled off and dispersed into liquid solder.The shear strength increased at first and then reduced with the prolongation of soldering time,and the maximum strength was 12.7MPa when the joint was achieved at 240?for 5min.In shear test,the joint presented a typical ductile fracture mode.Fracture mainly occurred at solder/Cu interface and a small amount of Al foil was torn off the glass substrate when soldering time exceeded5min.The content of Zn in Sn-Zn solder had a great influence on the soldering performance of metallized glass and copper.With the increase of Zn content,the dissolution rate of Al foil at Al/solder interface decreased,and the transition from Cu-Sn IMCs to Cu-Zn IMCs at solder/Cu interface occurred.The total thickness of intermetallic compound layers increased.The shear strength of the specimens increased with the increase of Zn content.When the content of Zn was 20wt%,the shear strength was 15.5MPa.When the content of Zn in the filler metal was 0-9wt%,fracture occurred along the solder/Cu interface,while fracture was near at the glass/Al interface when the content of Zn was 9-20wt%.