Dry acoustic microscopy for non-destructive evaluation of electronic materials (selection of a solid layer for high-resolution inspection)

This paper describes a way to select a solid layer for performing the high-resolution acoustic imaging of electronic materials under the dry environment. A dry acoustic microscopy performs the transduction of broadband, high-frequency ultrasound via a solid layer inserted between water and a sample. Firstly, the acoustic impedance matching between water, the layer and the sample is considered, and an equation for predicting the frequency response of inserted layer is shown. The transmission of broadband ultrasound into an acrylic resin sample is performed with the layers made of two polymers and two elastomers and without the layer, and the efficiency of dry ultrasonic transmission is determined. Based on the theoretical consideration and the experimental results, a solid layer for clearly visualizing the defects in electronic materials by means of the present dry manner is discussed. Furthermore, we demonstrate the acoustic imaging of an encapsulated package and a Si/Si bonding sample via the selected layers. The present acoustic microscope promises the realization of high-resolution acoustic imaging of the delamination of the encapsulated package and the nanometer gaps in the Si/Si bonding sample without having to immerse the samples in water.