A non-isothermal technique for rapid characterization of moisture diffusion in molding compounds of plastic encapsulated microcircuits (PEMs) is suggested.  The technique is based on measurements of the weight losses during heating in dry conditions of a polymer sample or plastic package pre-saturated with moisture.  It allows calculation of the moisture diffusion coefficients and the activation energy of diffusion.  The duration of this test does not exceed a few hours, and the necessary calculations can be performed easily in an MS Excel spreadsheet.  The test can be performed directly on PEMs using a thermogravimetric analyzer (TGA) or a simple balance with 0.1 mg accuracy and a regular thermal chamber, which is capable of providing a linear temperature increase, fast heating to a pre-set temperature and cooling down to room temperature.

The results obtained by the non-isothermal desorption technique are shown to agree with the results of the diffusion coefficient measurements obtained by conventional isothermal sorption/desorption techniques.

The effect of lead frames on measurement results is discussed.  It has been demonstrated that the probability of moisture leakage along the molding compound/lead frame interface can be estimated by comparing diffusion coefficients measured on the molding compound and on the plastic package.

Temperature dependencies of moisture diffusion coefficients of molding compounds used in different types of PEMs (QFP, DIP, and PLCC packages) manufactured by different vendors have been characterized.