Capacitive micromachined ultrasonic transducer packaging for forward-looking ultrasonic endoscope using low temperature co-fired ceramic side via

This paper reports part of a novel packaging method for a capacitive micromachined ultrasonic transducer (CMUT) base ultrasonic endoscope using low temperature co-fired ceramic (LTCC) side via architecture. An annular ring array CMUT devic is designed and fabricated for packaging. LTCC is used as a prime wafer for CMUT fabrication and LTCC side via structure i achieved by hexagonal shape dicing of the fabricated CMUT device. A hexagonal shaped polyimide substrate mounted at th backside of the CMUT is used as a base layer for IC integration (flip-chip bonding) and also provides mechanical support to th CMUT. Cr/Au electrodes were patterned on the LTCC side via and polyimide substrate to achieve electrical connection betwee CMUT arrays and IC circuits. Au bonding pads were successfully completed on the polyimide substrate by electroplating fo flip-chip bonding. Flip-chip mounting on the polyimide substrate is described and the electrical resistance of bumps is measure using the 4-probe method. The difference between the measured and calculated resistance is discussed. This method with th indirect connection of CMUT arrays and IC circuits has flexibility for high performance tube-shaped CMUT packaging wit small diameters for intravascular imaging.