Navy Electricity and Electronics Training Series - Historic Naval ...

Table 3-2.—Typical Measured Statics Charges (in volts)RELATIVE HUMIDITYITEMLOW (10-20%) HIGH (65-90%)WALKING ACROSS CARPET 35,000 1,500WALKING OVER VINYL FLOOR 12,000 250WORKER AT BENCH 6,000 100VINYL ENVELOPES FOR WORK INSTRUCT. 7,000 600POLY BAG PICKED UP FROM BENCH 20,000 1,200WORK CHAIR PADDED WITH URETHANE FOAM 18,000 1,500Metal oxide semiconductor (MOS) devices are the most susceptible to damage from ESD. Forexample, an MOS field-effect transistor (MOSFET) can be damaged by a static voltage potential of aslittle as 35 volts. Commonly used discrete bipolar transistors and diodes (often used in ESD-protectivecircuits), although less susceptible to ESD, can be damaged by voltage potentials of less than 3,000electrostatic volts. Damage does not always result in sudden device failure but sometimes results indevice degradation and early failure. Table 3-2 clearly shows that electrostatic voltages well in excess of3,000 volts can be easily generated, especially under low-humidity conditions. ESD damage of ESDSparts or circuit assemblies is possible wherever two or more pins of any of these devices are electricallyexposed or have low impedance paths. Similarly, an ESDS device in a printed circuit board, or even inanother pcb that is electrically connected in a series can be damaged if it provides a path to ground.Electrostatic discharge damage can occur during the manufacture of equipment or during the servicing ofthe equipment. Damage can occur anytime devices or assemblies are handled, replaced, tested, or insertedinto a connector.Technicians should be aware of the many sources of static charge. Table 3-3 lists many commonsources of electrostatic charge. Although they are of little consequence during most daily activity, theybecome extremely important when you work with ESD material.3-39