Glass-Cu joining by anodic bonding and soldering with eutectic Sn-9Zn solder

A new coupling technique for glass-metal joining was presented in this paper. Firstly, the glass and Al were successfully bonded by anodic bonding process, then the joining between Al and Cu was achieved by soldering with eutectic Sn-9Zn solder. The microstructures of glass/Al interface and solder joint were investigated by using scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), and the interface evolution mechanism as well as the correlation between the glass/Cu joining strength and the interface morphology were discussed. The results showed that a sodium-depleted layer with a thickness of 546 nm was formed on the glass/Al interface at 400 °C/1000 V. 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 10 min, micro grooves on Al foil were observed, and CuZn5 IMCs spalled off and dispersed into liquid solder, which deteriorated the joint strength. During the soldering process, the whole interface evolution could be divided into four stages and was analyzed explicitly. Shear tests indicated the fracture mainly occurred at solder/Cu interface and a small amount of Al foil was torn off the glass substrate when soldering time exceeded 5 min. The shear strength increased at first and then reduced with the prolongation of soldering time, and the maximum strength was 12.7 MPa when the joint was achieved at 240 °C for 5 min.