Integration and packaging technology of MEMS-on-CMOS capacitive tactile sensor for robot application using thick BCB isolation layer and backside-grooved electrical connection

This paper describes a novel wafer-level integration and packaging technology for a chip-size-packaged integrated tactile sensor. A MEMS wafer and a CMOS wafer were bonded with a thick (50 μm thick) BCB (benzocyclobutene) adhesive layer, and a capacitance gap for capacitive force sensor is formed between the wafers. The large thickness of BCB is advantageous to capacitively isolate the CMOS circuit and the capacitance electrodes. The thick BCB layer was formed on the CMOS wafer and molded with a glass mold to make a flat surface and via holes simultaneously. For surface mounting, bond pads are located on the backside of the sensor chip by drawing electrical feed lines through the chip edge. To make the feed lines in wafer level, tapered grooves were fabricated along the scribe lines by TMAH (tetramethyl ammonium hydroxide) wet etching, and half dicing was done along the grooves to access electrodes on the BEOL (back end of line) layer of the CMOS. Finally, the tactile sensor was completed and preliminarily evaluated.