Towards a nondestructive procedure for characterization of molding compounds

The applicability of using ultrasonics for characterizing and fingerprinting molding compounds is investigated in this study. The goal is to compile a database of ultrasonic parameters for several commercial molding compound and investigate if different molding compounds have distinct “signatures”. The suitability of using ultrasonic parameters to estimate the void fraction is also investigated using calibration specimens with varying amounts of voids (simulated with 100 μm glass spheres). Results presented demonstrate that different classes of molding compounds can be distinguished from each other from their frequency dependent attenuation curves and acoustic impedance. In general, the biphenyl resins exhibit a lower attenuation, higher velocity and higher impedance than the creosol-novolac resin. Post-mold cure (PMC) does not change the attenuation curves significantly, and the molding compounds retain distinctly different behaviors. The attenuation measured for even the least attenuative molding compound (MP7320) at 30 MHz is significantly higher (~10 dB) than that at 10 MHz. The slope of the frequency dependent scattering loss correlated well with the volume fraction of the simulated voids. Thus, ultrasonics is demonstrated to be an attractive technique to monitor the material parameters of molding compounds nondestructively and over a small area