Signal Loss
Wave energy reduction as ultrasound propagates through board materials limits the depth and resolution of acoustic microscopy inspections. Ultrasonic attenuation refers to the combined effects of absorption and scattering that weaken the acoustic signal as it travels through a medium. This reduction in signal amplitude is particularly severe in composite and highly heterogeneous materials.
Damping Factor
Material density, elastic properties, and internal structures like glass fibers or filler particles govern the rate of energy dissipation. Epoxy resins and woven fiberglass scatter and absorb acoustic energy much faster than silicon, copper, or ceramics. This high rate of decay limits the effectiveness of high-frequency inspection methods when checking thick multi-layer boards or complex molded modules.
Compensation Technique
Advanced acoustic systems use automatic gain control and distance-amplitude correction to compensate for this loss of signal strength. If the system does not adjust for the loss, deeper features will appear artificially faint, which might be mistaken for a material defect or a void. Applying these signal processing methods ensures that the system maintains uniform sensitivity throughout the entire thickness of the inspected component.
By equalizing the response from all depths, inspectors can quickly spot genuine delaminations and cracks without being misled by the natural decrease in signal strength caused by the material itself.
