Real time thickness measurement based on terahertz time-domain spectroscopy for chip-top epoxy molding compound in semiconductor package

The refractive index and thickness of EMC were measured non-destructively using the terahertz time-domain spectroscopy (THz-TDS) system. A theoretical model was developed using an analysis of time response on transmission and reflection THz signals. Using this developed theoretical model, the refractive index of EMC was measured within 1% of the error range. Simultaneously, the thickness of EMC was calculated through the measured refractive index and induced time delay. As a result, the refractive index and thickness of EMC was measured within the error range of 0.9% and 3.0%, respectively.