A Simple Method of using the Die of an Integrated Circuit to Measure the Relative Humidity Inside its Encapsulation

Abstract

A technique (the capacitance-ratio test) is described for assessing the water content of hermetic packages containing an integrated circuit die. It is based on a theoretical analysis which shows that the frequency dependence of the capacitance between a selected pair of IC metallisation tracks can be used to derive the moisture induced component of this capacitance. A measurement on an encapsulated integrated circuit die, held at a constant temperature, is used to determine the ratio of the moisture induced capacitance and the intrinsic capacitance between metallisation tracks. By comparing this ratio with that obtained from a sample of integrated circuits exposed to a known relative humidity, the test can indicate whether the relative humidity in the package is greater or less than a specified value. The accuracy of the test is comparable with that of other moisture sensing methods for encapsulations, and its sensitivity is adequate for the control of known moisture-related failure mechanisms in integrated circuits.