19
Determine the ESD Requirements
Static charges (voltage levels) occur when objects are separated or
rubbed together. The voltage level of a static charge is determined by the
following factors:
•Types of materials
• Relative humidity
• Rate of change or separation
Effect of humidity on ESD charge levels
The table following lists charge levels based on personnel activities and
humidity levels.
Static protection measures
Follow these precautions to minimize possible ESD-induced failures in
the computer room:
• Maintain recommended humidity level and airflow rates in
the computer room.
• Install conductive flooring (conductive adhesive must be used when
Table 4
Personnel activity
a
Humidity
b
and charge levels (voltages)
c
26% 32% 40% 50%
Person walking across a linoleum floor 6,150 V 5,750 V 4,625 V 3,700 V
Person walking across a carpeted floor 18,450 V 17,250 V 13,875 V 11,100 V
Person getting up from a plastic chair 24,600 V 23,000 V 18,500 V 14,800 V
a. Source: B.A. Unger, Electrostatic Discharge Failures of Semiconductor Devices (Bell
Laboratories, 1981)
b. For the same relative humidity level, a high rate of airflow produces higher static charges
than a low airflow rate.
c. Some data in this table has been extrapolated.
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