Glass-to-Glass Anodic Bonding with Liquid Tin Based Fillers: A Mechanistic Study

Abstract

A new variant of solid state anodic bonding termed activated liquid tin solder anodic bonding (ALTSAB) was recently developed. Here, we report the systematic investigation of bonding parameters temperature, bonding voltage and the alloy composition in a sandwich type configuration with soda-lime glass. Of the five different alloys tested (Sn, SnAl0.6, SnMg0.6, SnLi0.02 and SnLi0.06), SnAl shows the best mechanical integrity of the glass-metal-glass bonds and the lowest current density values during bonding. SnLi alloys entail very high bonding current densities up to 4 mA cm−2 at 270°C and 800 V but poor mechanical performance due to alkali corrosion of the glass at the bonding interface. Supported by the large drift currents in the case of Li containing alloys, it is believed that the overall ALTSAB process is anode limited. With SnAl0.6 alloys, bonds with a shear strength >35 MPa can be produced in less than 7 minutes at a mere 270°C. From temperature dependent data, apparent activation energies in the 70–100 kJ mol−1 range were extracted for all alloys, as it is expected for ion transport processes in soda lime glass. Compared to conventional anodic bonding, ALTSAB offers improved mechanical strength at far lower process temperature and voltage.