Energy Loss
An acoustic propagation characteristic measures the rate of wave energy loss per unit distance as sound travels through a composite material matrix. During acoustic microscopy of printed circuit board laminates and encapsulated IC packages, matrix attenuation quantifies how resin layers and filler particles absorb and scatter high frequency ultrasonic waves. This attenuation behavior stops governing signal strength once acoustic waves enter non-attenuating uniform liquids or homogeneous single-crystal metals.
Dispersion Mechanism
Ultrasonic energy decreases exponentially as sound waves propagate through heterogeneous structural materials. Viscoelastic absorption converts acoustic energy into thermal energy within the polymer binder of circuit board substrates. Microstructural scattering occurs when sound waves hit filler particles or void boundaries whose dimensions match the acoustic wavelength.
Higher signal frequencies experience steeper attenuation rates, limiting the effective penetration depth of acoustic inspection beams. Inspection equipment must apply time-gated gain controls to amplify weak echo signals returning from deeply buried substrate interfaces. Failure to account for material absorption leads to misinterpreting weak reflections as material voids or delaminations.
Calibration blocks matching the target substrate density and filler loading allow operators to adjust receiver sensitivity across varying material thicknesses.
Signal Compensation
High matrix attenuation reduces echo amplitude from deep die attach interfaces in thick power packages. Compensating receiver gain maintains image clarity across varying acoustic penetration depths.
