Silicon liquid flow sensor encapsulation using metal to glass anodic bonding

This paper reports on the encapsulation of a piezoresistive Silicon/Pyrex liquid flow sensor using metal to glass anodic bonding. The bonding technique allowed integrating robust metallic microfluidic interconnects and eliminating the use of glue and Orings. The bonding parameters of a Silicon/Pyrex/Metal triple stack were optimised to minimise the residual stress and to obtain a strong and liquid tight bonding interface. The flow sensor was successfully bonded to metallic plates of Kovar and Alloy 42, on which tubes were fixed and a PCB integrated. The encapsulated liquid flow sensor characteristics, such as the temperature coefficient of sensitivity, fulfilled the specifications. Wafer level packaging using metal to glass anodic bonding was considered to reduce the packaging size and cost.