Anodic bonding of activated tin solder alloys in the liquid state: A novel large-area hermetic glass sealing method

A new variant of the anodic bonding technique (ALTSAB: Activated Liquid Tin Solder Anodic Bonding) is described, which offers a number of advantages for direct glass to metal sealing over conventional methods. It employs a tin solder alloy containing an activating metal which is anodically bonded to alkali rich glass substrates in the liquid state. Two different test specimens were fabricated and characterized under vacuum at a pressure of 5×10−4 mbar and a bonding temperature of 300 °C and compared with standard Al/glass anodic bonds. The ability to fabricate dual interface bonds of good quality and high shear strength >16 MPa by the ALTSAB method was demonstrated. With the sealant metal in the liquid state, this methodology promises superior surface adaptation and therefore joint performance when compared with the standard anodic bonding. More importantly, there is no need for premetallization or surface pretreatment of the glass substrates, and unlike in conventional anodic bonding, there is no need for mechanically loading the joining assembly. Wetting of the float glass substrates by the activated solder alloy SnAl0.6 after successful anodic bonding was confirmed by optical microscopy. The enrichment of the activating element Al at the bonding interface was confirmed by SEM and EDS element mapping. The methodology presented here shows great promise for various large-area sealing applications, particularly vacuum glazing, thin film and organic PV and OLED technology.

► A new glass–metal sealing method using liquid phase anodic bonding of tin alloys is presented.
► The method is high-vacuum compatible and produces strong, large-area hermetic seals.
► The applied E-field promotes glass wetting, yielding an ideal interfacial load distribution.
► The method offers great potential for vacuum glazing, solar cell and collector module sealing.
► It uses inexpensive raw materials and is well suited for large-scale industrial production.