Moisture determination in hermetic IC packages by the dew point method using AC capacitance and conductance measurement

The dew point in ceramic packages is shown to be observable by ac phase-sensitive measurement of the real and imaginary parts of the dielectric constant of an air gap capacitor. Only the package surface directly under the sensor is cooled, enhancing the sensitivity by preferential condensation. The dew point response peak is followed by a sharp drop due to interface freezing phenomena. Milligrams of liquid water had to be placed in the packages before sealing with epoxy at 175°C for dew points above -20°C to been seen. Large amounts of water were thus eliminated even at this moderate temperature.