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11.2. 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 12-1 with the those shown in the Table 12-2, 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 11-2: Sensitivity of Electronic Devices to Damage by ESD
DEVICE
DAMAGE SUSCEPTIBILITY VOLTAGE
RANGE
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
Potentially damaging electro-static discharges can occur:
Any time a charged surface (including the human body) discharges to a device. Even simple
contact of a finger to the leads of a sensitive device or assembly can allow enough discharge to
cause damage. A similar discharge can occur from a charged conductive object, such as a
metallic tool or fixture.
When static charges accumulated on a sensitive device discharges from the device to another
surface such as packaging materials, work surfaces, machine surfaces or other device. In some
cases, charged device discharges can be the most destructive.
A typical example of this is the simple act of installing an electronic assembly into the connector
or wiring harness of the equipment in which it is to function. If the assembly is carrying a static
charge, as it is connected to ground a discharge will occur.