Quantitative Evaluation of Moisture in Encapsulant Resin of IC Packages by Microwaves

摘要

A method to measure moisture in encapsulant resin of IC packages by microwaves was demonstrated, which can determine moisture directly without drying and weighing the packages. An coaxial line sensor acts both as a source and receiver of microwave signal that is transmitted into and reflected from the package. A frequency of 100 GHz was used to increase the measurement sensitivity. The relationship between the measured amplitude of the reflection coefficient and the moisture content in the packages was found to be linear. The amplitude difference, which is corresponding to the attenuation of microwave, in the cases of packages with and without moisture content, increases linearly with the increase of the thickness of the resin above the chip pad. For any kinds of packages, if the thickness of the packages is the same, the moisture content can be determined by the microwave amplitude measurement after testing two reference packages; if the thickness of the packages is known, the proposed method can be used directly after measuring a dry package.