Pulse Reflection
Ultrasound imaging techniques provide high resolution visualization of internal material interfaces. Integrating c-sam acoustic microscopy into the failure analysis workflow allows for the identification of sub-surface gaps without destroying the sample. An acoustic transducer emits high frequency sound waves into a coupling medium to penetrate the component.
These waves encounter boundaries between materials of different densities and return a signal to the sensor.
Bond Assessment
Analysis of the reflected signal polarity identifies air gaps between the molding compound and the silicon die. When c-sam acoustic microscopy encounters a solid to gas interface, the phase of the sound wave flips by 180 degrees. This phase shift creates a bright white area in the resulting image.
Delamination or voiding in the die attach layer becomes visible through these distinct color contrasts. Gray areas typically indicate a healthy bond where the signal passes through without a major phase change.
Detection Limit
Resolving power depends on the frequency of the transducer where higher frequencies detect smaller defects but offer less penetration depth. Standard inspection for plastic encapsulated microcircuits often utilizes transducers between 15 and 230 megahertz. Surface roughness on the package exterior can scatter the sound and reduce the clarity of the internal scan.
