Design and performance of a thin, solid layer for high-resolution, dry-contact acoustic imaging

Compared to the usual water immersion case, more effective transmission and reception of high-frequency ultrasound through a thin, solid layer are reported. A theoretical model is presented to perform the signal amplification and the signal modulation toward the higher frequency components for getting the high-quality acoustic images without immersing the object to be imaged. Also, the thin, solid layers are designed from the theoretical model, and the transmission of high-frequency ultrasound is carried out through the layer/silicon interfaces with an applied pressure of about 0.1 MPa. The spectral intensity in the frequency range of 20 to 70 MHz remarkably improves compared with water immersion, and the peak frequencies of the spectra modulate the higher than water immersion. Furthermore, the solder joint inspection of a package is performed. The present dry-contact technique achieves the higher spatial resolution and the higher signal-to-noise ratio (SNR) than the usual water immersion technique, and clearly detects the defective joint without getting the package wet.