PACKAGING HIGH DENSITY CAPACTIVE MICRO-MACHINED ULTRASONIC TRANSDUCER (cMUT) SENSOR ARRAYS USING HYPERBGA TECHNOLOGY
Authors: Charles G. Woychik, et al. Company: GE Global Research and Endicott Interconnect Technologies, Inc. Date Published: 10/4/2009
Abstract: Piezoelectric transducers have long dominated ultrasonic transducer technology, but capacitive micro-machined ultrasound transducers (cMUTs) have emerged as an alternative. Features of cMUT devices are wide signal bandwidth, ability to use MEMs (Micro Electro-Mechanical Systems) silicon fabrication methods to produce large arrays and potential for integration with supporting electronic circuits. cMUT technology can potentially produce the type of integrated sensor array to enable advanced 3-D imaging. A major challenge to achieve this goal is how to package these cMUT devices such that one can produce a large sensor array for imaging. We have used a high-density Teflon interposer, HyperBGA technology, produced by Endicott Interconnect to design a modular package in which the sensor cMUT array is on the topside and the supporting electronics on the backside. The cMUT devices are flip chip attached to the interposer and are spaced 100um between adjacent die. A 40 mm module size was designed having a 4x12 array of cMUT devices in the center region of the module that are flip chip attach to the topside of the interposer. Each cMUT device is 3 mm in size with an element pitch of 185 um and having a 16x16 element array. On the backside are three 10mm x 11mm dummy ASIC die having a pad pitch of 150um, each die having about 4100 I/O pads. In addition, there are about 648 BGA pads with a 1.0 mm pitch on the backside for attach to a 2.85 mm board. The packaging challenges to design and build this type of advanced sensor array will be presented.