Ultrasonic interference spectroscopy for plastic IC packages

Electronic IC (integrated circuits) packages are routinely inspected for delaminations, voids, cracks, and corrosion using the C-mode acoustic microscopy. Plastic IC packages are hygroscopic and can absorb moisture subjected to environmental cycling depending on the quality of the plastic mold compound used to encapsulate the IC chip. The advanced ultrasonic interference spectroscopy (UIS) technique that was used successfully to detect presence of moisture in adhesively bonded joints is applied to analyze the plastic IC packages. Manually fabricated (simulated) plastic packages with thin water film trapped between two layers of plastic material (Lexan) and the silicon wafer were used to evaluate the technique. The technique successfully detected the presence of an extra water layer in the assembly inspected and estimated its thickness. At present the technique is under development for detection of water films thinner than 0.1 mm in actual plastic IC packages.