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Packaging and modular assembly of large-area and fine-pitch 2-D ultrasonic transducer arrays

: Lin, D.-S.; Wodnicki, R.; Zhuang, X.; Woychik, C.; Thomenius, K.E.; Fisher, R.A.; Mills, D.M.; Byun, A.J.; Burdick, W.; Khuri-Yakub, P.; Bonitz, B.; Davies, T.; Thomas, G.; Otto, B.; Töpper, M.; Fritzsch, T.; Ehrmann, O.


IEEE transactions on ultrasonics, ferroelectrics and frequency control 60 (2013), No.7, pp.1356-1375
ISSN: 0885-3010
ISSN: 0018-9537
Journal Article
Fraunhofer IZM ()

A promising transducer architecture for largearea arrays employs 2-D capacitive micromachined ultrasound transducer (CMUT) devices with backside trench-frame pillar interconnects. Reconfigurable array (RA) application-specified integrated circuits (ASICs) can provide efficient interfacing between these high-element-count transducer arrays and standard ultrasound systems. Standard electronic assembly techniques such as flip-chip and ball grid array (BGA) attachment, along with organic laminate substrate carriers, can be leveraged to create large-area arrays composed of tiled modules of CMUT chips and interface ASICs. A large-scale, fully populated and integrated 2-D CMUT array with 32 by 192 elements was developed and demonstrates the feasibility of these techniques to yield future large-area arrays. This study demonstrates a flexible and reliable integration approach by successfully combining a simple under-bump metallization (UBM) process and a stacked CMUT/interposer/ ASIC module architecture. The results show high shear strength of the UBM (26.5 g for 70-¿m balls), high interconnect yield, and excellent CMUT resonance uniformity (s = 0.02 MHz). A multi-row linear array was constructed using the new CMUT/interposer/ASIC process using acoustically active trench-frame CMUT devices and mechanical/ nonfunctional Si backside ASICs. Imaging results with the completed probe assembly demonstrate a functioning device based on the modular assembly architecture.