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A Primer on Electro-Static Discharge Teledyne API – Model T300/T300M CO Analyzer
326
or static. The most common example of triboelectric charging happens when someone
wearing leather or rubber soled shoes walks across a nylon carpet or linoleum tiled floor.
With each step, electrons change places and the resulting electro-static charge builds up,
quickly reaching significant levels. Pushing an epoxy printed circuit board across a
workbench, using a plastic handled screwdriver or even the constant jostling of
Styrofoam
TM
pellets during shipment can also build hefty static charges.
Table 14-1: Static Generation Voltages for Typical Activities
MEANS OF GENERATION 65-90% RH 10-25% RH
Walking across nylon carpet 1,500V 35,000V
Walking across vinyl tile 250V 12,000V
Worker at bench 100V 6,000V
Poly bag picked up from bench 1,200V 20,000V
Moving around in a chair padded
with urethane foam
1,500V 18,000V
14.2. HOW ELECTRO-STATIC CHARGES CAUSE DAMAGE
Damage to components occurs when these static charges come into contact with an
electronic device. Current flows as the charge moves along the conductive circuitry of
the device and the typically very high voltage levels of the charge overheat the delicate
traces of the integrated circuits, melting them or even vaporizing parts of them. When
examined by microscope the damage caused by electro-static discharge looks a lot like
tiny bomb craters littered across the landscape of the component’s circuitry.
A quick comparison of the values in Table 14-1 with the those shown in the Table 14-2,
listing device susceptibility levels, shows why
Semiconductor Reliability News estimates
that approximately 60% of device failures are the result of damage due to electro-static
discharge.
Table 14-2: Sensitivity of Electronic Devices to Damage by ESD
DAMAGE SUSCEPTIBILITY VOLTAGE
RANGE
DEVICE
DAMAGE BEGINS
OCCURRING AT
CATASTROPHIC
DAMAGE AT
MOSFET 10 100
VMOS 30 1800
NMOS 60 100
GaAsFET 60 2000
EPROM 100 100
JFET 140 7000
SAW 150 500
Op-AMP 190 2500
CMOS 200 3000
Schottky Diodes 300 2500
Film Resistors 300 3000
This Film Resistors 300 7000
ECL 500 500
SCR 500 1000
Schottky TTL 500 2500
06864B DCN6314