THE IMPROVEMENT OF ENCAPSULATING FOAMS AND QUALITY ASSURANCE OF POTTING PLASTIC.
JOHNS HOPKINS UNIV SILVER SPRING MD APPLIED PHYSICS LAB
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Plastic foams used for encapsulating electronic circuits may, during their formation, exert sufficient pressures to damage components and connective wiring. This probably caused by the increasing viscosity of the plastic while gas is still being generated. The danger may be alleviated by altering the formulation chemically so that gas generation is completed before the plastic begins to harden. The consequences which would result from the use of a mislabelled or substandard can of potting plastic in flight hardware are so serious that each can must be individually tested to eliminate that possibility. This may readily be accomplished by casting a test disk and then measuring its dielectric constant, volume resistivity, surface resistivity and density. The electrical testing can be performed in less than ten minutes and is, therefore, feasible as a standard quality assurance procedure. Author