Rubber-coupled acoustic microscopy for dry inspections of industrial products

This paper describes the transduction of high-frequency ultrasound via rubber membranes. Four kinds of rubber membranes with Young's moduli of 0.91-9.59 MPa and thickness of 0.2 mm are prepared, and the ultrasound exited with the 50 MHz focused ultrasonic transducer is transmitted into the acrylic resin targets with various surface roughness through the membrane/target interfaces with an applied pressure of about 0.1 MPa. The rubber membrane with low Young's modulus realizes small coupling loss at the membrane/target interfaces, and the lateral resolution of the rubber-coupled acoustic microscopy is found to be governed by ultrasonic attenuation in the membrane. Finally, we repeatedly demonstrate the acoustic imaging of a semiconductor package in a dry environment via the selected membrane.