Meaning
Non-destructive testing methods utilize high-frequency sound waves to image internal structures and interfaces within solid materials. In the electronics industry, scanning acoustic microscopy operates as a primary tool for evaluating the integrity of package bonds and detecting internal delamination. The process provides detailed cross-sectional and three-dimensional images of the internal boundaries without damaging the device under test.
Acoustic Interaction
An acoustic transducer generates ultrasound pulses that travel through a coupling medium, typically deionized water, and penetrate the sample. As these waves encounter boundaries between different materials, such as the interface between the silicon die and the epoxy mold compound, a portion of the energy is reflected back. The amplitude and phase of these reflected signals depend on the density and elasticity of the materials, allowing the system to distinguish between solid bonds and air-filled gaps.
Defect Localization
Analyzing the return time of the reflected pulses allows the system to calculate the depth of each internal feature. By coordinating this timing data with the lateral position of the transducer, scanning acoustic microscopy maps the precise location of voids, cracks and delamination. These defects appear as areas of high contrast because the boundary between plastic and air reflects almost all the acoustic energy.
Production Integration
Quality engineers use this imaging technique during failure analysis and component qualification. The resulting reports help manufacturers refine their molding and bonding processes to prevent early field failures.
