Anthony Thomas

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Electrical insulators are used in many applications in industry, education and the home environment. They work by keeping electricity contained. They are not however perfect and under stress can become ineffective. Every insulator has a dielectric strength, a measurement of how much electrical stress it can withstand. If the material is stressed beyond that strength the material will breakdown. Electrostatic breakdown is defined as “the abrupt irreversible drop in resistivity at high fields, often accompanied by destruction of the material” (See Fig. 1) [McGraw-Hill]. The point at which the material breaks down is called the electrostatic discharge breakdown voltage, or ESD voltage, measured in volts (V). Breakdown voltages are measured by sandwiching a sample between two plates and increasing the voltage of one plate while the other is grounded (See Fig. 2). The sample then acts like a dielectric in a common capacitor, keeping the circuit from being complete. When the potential is stronger than the dielectric strength breakdown occurs. The electrostatic breakdown field strength of a material, EESD measured in mega-volts per meter (MV/m), has been shown to be related to the thickness of the material [ASTM D 3755-97]; the thinner the sample the easier it is to breakdown. The ESD field strength then becomes a function of thickness.

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