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A Primer on Electro-Static Discharge
311
9. A PRIMER ON ELECTRO-STATIC DISCHARGE
Teledyne API considers the prevention of damage caused by the discharge of static
electricity to be extremely important part of making sure that your analyzer continues to
provide reliable service for a long time. This section describes how static electricity
occurs, why it is so dangerous to electronic components and assemblies as well as how to
prevent that damage from occurring.
9.1. HOW STATIC CHARGES ARE CREATED
Modern electronic devices such as the types used in the various electronic assemblies of
your analyzer, are very small, require very little power and operate very quickly.
Unfortunately, the same characteristics that allow them to do these things also make them
very susceptible to damage from the discharge of static electricity. Controlling
electrostatic discharge begins with understanding how electro-static charges occur in the
first place.
Static electricity is the result of something called triboelectric charging which happens
whenever the atoms of the surface layers of two materials rub against each other. As the
atoms of the two surfaces move together and separate, some electrons from one surface
are retained by the other.
+
+
Materials
Makes
Contact
PROTONS = 3
E
LECTRONS = 3
N
ET CHARGE = 0
P
ROTONS = 3
E
LECTRONS = 3
N
ET CHARGE = 0
Materials
Separate
+
PROTONS = 3
E
LECTRONS = 2
N
ET CHARGE = -1
+
PROTONS = 3
E
LECTRONS = 4
N
ET CHARGE = +1
Figure 9-1: Triboelectric Charging
If one of the surfaces is a poor conductor or even a good conductor that is not grounded,
the resulting positive or negative charge cannot bleed off and becomes trapped in place,
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
07270B DCN6512