Appendix E - Electrostatic Discharge
Introduction
This appendix covers the proper methods for grounding and the use of
recommended materials and equipment for preventing damage from
electrostatic discharge (ESD).
A sudden discharge of static electricity from a finger or other conductor
can destroy static-sensitive devices or micro circuitry. Often the spark is
neither felt nor heard, but damage occurs. An electronic device exposed to
electrostatic discharge may not be affected at all and will work perfectly
throughout a normal cycle. Or it may function normally for a while, then
degrade in the internal layers, reducing its life expectancy.
Networks built into many integrated circuits provide some protection, but
in many cases, the discharge contains enough power to alter device
parameters or melt silicon junctions.
E.1 Generating Static
Table E-1 shows how different activities generate static electricity and at
different electrostatic voltage levels.
Table E-1. Typical Electrostatic Voltages
===========================================================================
Relative Humidity
Event 10% 40% 55%
===========================================================================
Walking across carpet 35,000V 15,000V 7,500V
Walking across vinyl floor 12,000V 5,000V 3,000V
Motions of bench worker 6,000V 800V 400V
Removing DIPS from plastic tubes 2,000V 700V 400V
Removing DIPS from vinyl trays 11,500V 4,000V 2,000V
Removing DIPS from Styrofoam 14,500V 5,000V 3,500V
Removing bubble pack from PCBs 26,000V 20,000V 7,000V
Packing PCBs in foam-lined box 21,000V 11,000V 5,000V
---------------------------------------------------------------------------
NOTE: 700 volts can degrade a product.
===========================================================================
E.2 Preventing Electrostatic Damage To Equipment
Many electronic components are sensitive to ESD. Circuitry design and
structure determine the degree of sensitivity. The following proper
packaging and grounding precautions are necessary to prevent damage:
To Next Page
Loading...
Need help?
General