TO 1-1-700 - Robins Air Force Base
TO 1-1-700 - Robins Air Force Base
TO 1-1-700 - Robins Air Force Base
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<strong>TO</strong> 1-1-<strong>700</strong><br />
10.20 ELECTROSTATIC DISCHARGE (ESD) COMPO-<br />
NENTS.<br />
Figure 10-14. Magnesium Corrosion Products<br />
Figure 10-15. EMI Bonding Washers for Electronics<br />
Corrosion can degrade the electrical and mechanical properties<br />
of ESD protection systems. The exposure of ESD devices/<br />
ESD protection systems to various environmental conditions<br />
can significantly increase their susceptibility to damage from<br />
the discharge of static electricity. Under field service conditions,<br />
military avionics experience corrosion between metal<br />
surfaces such as electrical bonding/grounding connections.<br />
This problem is two-fold. First, corrosion between metal surfaces<br />
in avionics creates structural weaknesses that undermine<br />
its effectiveness to shield ESDS components from induced<br />
potentials. Second, the corrosive process creates nonconductive<br />
products that decrease the paths of conduction of static<br />
charge away from the device or assembly (see Figure 10-16).<br />
Although no valid method of evaluating the effect of corrosion<br />
on ESD sensitivity exists presently, certain trends can be identified.<br />
The performance of ESD protection for enclosed avionic<br />
equipment can degrade over time. This occurs often after<br />
only 3 or 4 months of exposure to the field environment and<br />
normal use. Galvanic corrosion is usually the principal form of<br />
attack. This type of corrosion can rapidly destroy a bonding<br />
connection if suitable precautions are not observed (refer to<br />
Chapter 7 of <strong>TO</strong> 1-1-689-3 and Chapter 8 of this manual).<br />
Damage to bonding/grounding hardware can cause the buildup<br />
of static potentials that could result in a spark discharge. Without<br />
regular maintenance, the buildup of metal oxides,<br />
absorbed atmospheric pollutants, dust, and field debris will<br />
also contribute to ESD shielding degradation of the avionic<br />
enclosure. This buildup introduces a nonconductive film<br />
between electrical contact materials which can often severely<br />
degrade ESD protection. See Chapter 9 of <strong>TO</strong> 1-1-689-3 and<br />
Chapters 3 and 8 of this manual for the corrosion effects on<br />
ESD and the corrosion prevention, treatment, and control for<br />
ESD.<br />
10-16