General Site Preparation Guidelines
Environmental Elements
Chapter 2
30
Electrostatic Discharge (ESD) Prevention
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
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 laying tiles)
•
Use conductive wax if waxed floors are necessary
•
Ensure that all equipment and flooring are properly grounded and are at the same ground potential
•
Use conductive tables and chairs
•
Use a grounded wrist strap (or other grounding method) when handling circuit boards
•
Store spare electronic modules in antistatic containers
Acoustics
Computer equipment and air conditioning blowers cause computer rooms to be noisy. Ambient noise level in a
computer room can be reduced as follows:
•
Dropped ceiling—Cover with a commercial grade of fire-resistant, acoustic rated, fiberglass ceiling tile
•
Sound deadening—Cover the walls with curtains or other sound deadening material
•
Removable partitions—Use foam rubber models for most effectiveness
Table 2-1
Effect of Humidity on ESD Charge Levels
Personnel Activity
a
a. Source: B.A. Unger, Electrostatic Discharge Failures of Semiconductor Devices (Bell Laboratories,
1981).
Humidity
b
and Charge Levels (voltages)
c
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.
26%
32%
40%
50%
Person walking across a linoleum floor
6,150V
5,750V
4,625V
3,700V
Person walking across a carpeted floor
18,450V
17,250V
13,875V
11,100V
Person getting up from a plastic chair
24,600V
23,000V
18,500V
14,800V
