Moisture Determination in IC Packages by Conductance Technique

Abstract

An a.c. conductance technique using a lock-in-amplifier (LIA) is described. The conductance technique is a non-destructive technique and uses the die as a sensor. Our experiments and theoretical calculations revealed that the moisture-induced conductance variation is 10 to 400% whereas the moisture-induced capacitance variation is 0 to 20%. Hence, even though capacitance and conductance values were measured, only conductance variations are reported. A circuit model has been developed to explain the observed experimental behavior. This technique is thus superior to capacitance technique in deterining the low levels of moisture (<5000ppmu) in IC packages. The selective condensation problem experienced in the Harris or Al2O3 sensors is non existent in the conductance technique. Since the applied voltage in the conductance method is ~l00mV, there is no dissociation of water into hydrogen and oxygen, as is possible in the case of Harris sensors. Further, the moisture content determined by this non-destructive technique correlates well with the residual gas analysis (RGA) by the mass spectrometer. This technique is non-destructive, reliable, rapid and suitable for in-line testing.