HP Labs Technical Reports

A Demountable 50 x 50 Pad Grid Array Interconnect System

Daane, Larry; Greenstein, Michael

HPL-97-26

Keyword(s): ultrasound; medical; array; transducer; interconnect; PGA; interconnection

Abstract: Interconnecting a microminiature coaxial cable to a fully populated two-dimensional transducer array for diagnostic ultrasound is a significant challenge due to high element counts and termination densities. Pad Grid Array (PGA) structures allow inline interconnect to array contacts, but have not been previously demonstrated to allow elements to be interconnected at spacing matching the pitch of transducer arrays typical of 2.5 to 7.5 Mhz diagnostic imaging (300 to 100 mm). PGAs provide a capable platform for experimentation and to allow transducer replacement because they are demountable. This paper reports on such a structure to allow a cabled 50 x 50 contact PGA to be connected by means of an anisotropic elastomeric anisotropic material to a 50 x 50 element transducer backing structure at 300 micron pitch, the acoustic half-wavelength normally used for 2.5 MHz imaging. Multiple flexible printed circuits provide the interconnect between coaxial cabling and a precision-drilled monolithic alumina substrate. The substrate is finished to provide a planar array of contact pads, each of which is used to contact gold wires embedded in a silicon medium which in turn connect to the backing electrodes of the transducer module. Using this approach, 97% of targeted interconnects were successfully accomplished. Acceptable pulse echo performance was demonstrated, suitable for diagnostic imaging.

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