Evaluation of electrical material properties: Embedment stress testing on electrical encapsulation resins

The embedment stress of a variety of encapsulation resins including HTPB (hydroxyl terminated polybutadiene) based polyurethanes, epoxies, and silicone is addressed. The embedment stress method followed is ASTM F135-76. The test determines the embedment stress of a rigid system with a peak cure exotherm under 200° F. The data reflect the stress exerted on a glass encased encapsulated component by measuring the stress exerted on a glass encased encapsulated component by measuring the stress exerted on a thermometer bulb below the peak exotherm of the system. In this test, a thermometer and a thermocouple are embedded in the various encapsulation systems. The test samples are subjected to a range of temperatures. Temperature readings are taken from both the thermometer and thermocouple. The relative embedment stress is calculated from the differences between the two temperature readings