Techniques for wirebond free interconnection of piezoelectric ultrasound arrays operating above 50 MHz

Interconnects between high frequency ultrasound (HFUS) arrays and external circuitry may be difficult and expensive because of the small element pitch, as low as 15 ¿m, and the large number of piezoelectric elements, up to 256. The wire bonding commonly used can be time consuming and difficult to achieve on piezocomposite material because of the relatively soft filler material. Moreover, the minimum pitch is limited by the footprint requirement for the bonding head. This requires the creation of an electrical fan-out, in turn increasing the size of the array package; this interconnect technology is disadvantageous for medical applications such as ophthalmology and dermatology. This paper proposes a wirebond free bonding process for HFUS piezocomposite arrays operating at frequencies above 30 MHz. The suggested process is integration of ultrasound ¿chips¿ with a silicon (Si) wafer using state-of-the-art fabrication techniques and materials including anisotropic conductive film, through silicon vias, powder blasting and laser machining.