Selection of a solid layer for high-resolution acoustic imaging of IC packaging defects under dry-contact conditions

This paper describes a way to select a solid layer for performing the high-resolution acoustic imaging of integrated circuit (IC) packaging defects under the dry-contact conditions. High frequency ultrasound exited with the 100 MHz focused ultrasonic transducer is transmitted into a sample through a solid layer. The use of two polymer films and two rubber membranes as a solid layer are examined by conducting ultrasonic testing of the acrylic resin plate and the silicon chip sample. The transmission efficiency and the lateral resolution in the cases of polymer-contacts and rubber-contacts are determined, and the selection of a solid layer for clearly visualizing the IC packaging defects by means of the dry-contact technique is discussed. We demonstrate the acoustic imaging of an encapsulated package and a bare chip package via the selected layers. The delamination parts and the debondings in the IC packages are clearly visualized under dry-contact conditions as if the acoustic imaging is performed under water immersion.