Page
8
C2670M
‐
C
ELECTROSTATIC DISCHARGE PREVENTION
Electrostatic
discharge
(ESD)
occurs
when
objects
are
separated
or
rubbed
together.
The
voltage
level
of
a
static
charge
is
determined
by
the
following
factors:
•
Type
of
materials
•
Relative
humidity
•
Rate
of
change
or
separation
Refer
to
Table
B
for
sample
data
on
the
effect
of
humidity
on
charge
levels.
Table
B.
Effect
of
Humidity
on
ESD
Charge
Levels
Humidity†
and
Charge
Levels
(voltages)‡
Personnel
Activity*
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
*Source:
B.A.
Unger,
Electrostatic
Discharge
Failures
of
Semiconductor
Devices
(Bell
Laboratories,
1981).
†For
the
same
relative
humidity
level,
a
high
rate
of
airflow
produces
higher
static
charges
than
a
low
airflow
rate.
‡Some
data
in
this
table
has
been
extrapolated.
Static
Protection
Measures
Observe
the
following
precautions
to
minimize
possible
ESD
‐
induced
failures
in
the
server
room:
•
Maintain
the
recommended
humidity
level
and
airflow
rates
in
the
server
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.
