Moisture diffusion in molding compounds in PEMs might cause problems during the ground phase period of integration and testing of flight hardware.  Highly accelerated stress testing (HAST) is widely used to assure robustness of PEMs in moisture environments.  This testing often results in failures due to extremely harsh environments, which are not only inadequate for the space conditions, but are much more severe than typical conditions during the ground phase period as well.

In this work an approach to the moisture prevention strategy and adequate accelerated testing is suggested.  The moisture prevention strategy can be implemented by reinforcement of the requirements for handling and storage of PEMs and PEM-containing assemblies, virtual evaluation of moisture content during storage and testing of the parts and assemblies, and calculations of the bake-out conditions. 

JEDEC recommendations for bake-out conditions, accelerated factors of standard HAST testing, and the relevance of HAST conditions to typical ground phase environment have been analyzed.  A possible alternative to HAST to assure quality of PEMs for space applications is discussed.

A simple method for in-situ measurements of temperature dependence of moisture diffusion characteristics of MC in PEMs is described.  Results of these measurements can be used to calculate moisture distribution in plastic packages, estimate bake-out conditions, and develop an adequate accelerated stress testing.