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9.
A PRIMER ON ELECTRO-STATIC DISCHARGE
Teledyne Instruments 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
P
ROTONS
= 3
E
LECTRONS
= 3
N
ET
C
HARGE
= 0
P
ROTONS
= 3
E
LECTRONS
= 3
N
ET
C
HARGE
= 0
Materials
Separate
+
P
ROTONS
= 3
E
LECTRONS
= 2
N
ET
C
HARGE
= -1
+
P
ROTONS
= 3
E
LECTRONS
= 4
N
ET
C
HARGE
= +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
07272B DCN6552