Acoustic Microscopy Protocols for High Density Interconnect Substrate Defects
Acoustic microscopy detects sub-micron HDI substrate delamination using phase-inversion gating at frequencies between 100 MHz and 300 MHz.
Cross-Sectional B-Scan
Depth Slicing
Non-destructive physical analysis workflows use linear scanning passes to generate two-dimensional depth slice images of internal structures. A cross-sectional b-scan displays acoustic reflection data gathered along a single axis scan line across a printed circuit board or semiconductor package. The vertical axis represents signal time of flight converted to depth, while the horizontal axis tracks mechanical transducer position.
Variations in echo intensity appear as brightness variations, highlighting internal delaminations and substrate warpage along the scanned plane.
Scan Generation
Sequential ultrasonic pulses are emitted and recorded as the transducer traverses a linear axis above the target sample. Time-gated reception captures internal reflections at varying depths, compiling multiple individual a-scans into a continuous cross-sectional image. Internal voids appear as distinct high-amplitude bands due to complete acoustic reflection at air-gap boundaries.
Software algorithms correct for sound velocity changes across heterogeneous material layers, such as silicon and mold compound, to prevent vertical image distortion. Delamination tilt across a large die bond line becomes immediately apparent without sectioning the physical component.
Thickness Boundary
Vertical resolution depends on acoustic pulse duration and transducer center frequency during linear cross-sectioning. A cross-sectional b-scan cannot resolve internal defects when layer thicknesses drop below half the acoustic wavelength. Sound attenuation in thick plastic encapsulants limits penetration depth, restricting high-frequency b-scan imaging to shallow package interfaces.