Comparison of Wax and Wax-free Mounting of Irregular Piezocomposite Materials for Thinning for High-frequency Medical Devices

Ultrasound is used in more than 20% of biomedical imaging scans. Several clinical applications would benefit significantly from the higher spatial resolution offered by higher frequency operation than is presently common. A key issue in the development of ultrasound imaging arrays to operate at frequencies above 30 MHz is the need for photolithographic patterning of array electrodes. To achieve this directly on the surface of the piezoceramic-polymer composite material requires planar, parallel and smooth surfaces. An investigation of the surface finishing of piezocomposite material by mechanical lapping and/polishing has recently demonstrated that excellent surface flatness can be obtained. However, the use of wax mounting during the surface processing causes problems because of the required temperatures and the need to remove wax from the very fragile substrates after finishing. Conventional tape mounting cannot withstand the high lateral forces generated by the irregularly shaped samples presently produced by the composite development process. Wax-free mounting has been developed as an alternative, utilising a porous ceramic vacuum chuck incorporated within otherwise standard mechanical lapping/polishing equipment. High frequency array elements have been successfully fabricated on composite surfaces and good electrode edge definition and electrical contact to the composite have been obtained. It is expected that the use of the wax-free equipment and techniques will reduce the eventual cost and increase the yield of such components when they reach production.