http://h18000.www1.hp.com/athome/support/msgs/2000/esd.html
United States December 10, 2002
Maintenance & Service Guide
Presario 2250 Series
2510, 2410 ES & 4240 ES Personal Computers
|
|
Electrostatic Discharge
ESD
A sudden discharge of static electricity from a finger or other
conductor can destroy static-sensitive devices or microcircuitry.
Often the spark is neither felt nor heard, but damage occurs.
An electronic device exposed to electrostatic discharge (ESD)
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.
Click on the topics below for additional ESD information.
Preventing
Electrostatic
Damage to
Equipment
Generating Static
The following table shows how different activities generate static electricity
and and at different electrostaic voltage levels.
Typical Electrostatic Voltages
Relative Humidity
Event
10%
40%
55%
Walking across carpet
35,000 V
15,000 V
7,500 V
Walking across vinyl floor
12,000 V
5,000 V
3,000 V
Motions of bench worker
6,000 V
800 V
400 V
Removing DIPS from plastic
tubes
2,000 V
700 V
400 V
Removing DIPS from vinyl trays 11,500 V
4,000 V
2,000 V
Removing DIPS from Styrofoam 14,500 V
5,000 V
3,500 V
Removing bubble pack from
PCBs
26,000 V
20,000 V
7,000 V
Packing PCBs in foam-lined box 21,000 V
11,000 V
5,000 V
NOTE:
700 volts can degrade a product.
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:
■
Protect all electrostatic parts and assemblies with conductive or
approved
containers or packaging.
■
Keep electrostatic sensitive parts in their containers until they arrive at
static-free stations.
■
Place items on a grounded surface before removing them from their
container.
■
Always be properly grounded when touching a sensitive component or
assembly.
■
Place reusable electronic-sensitive parts from assemblies in protective
packaging or conductive foam.
Use transporters and conveyors made of antistatic belts and metal roller
bushings. Mechanized equipment used for moving materials must be wired to
be grounded, and proper materials must be selected to avoid static charging.
When grounding is not possible, use an ionizer to dissipate electric charges.
Preventing Damage to Drives
To prevent damage to hard drives, use the following precautions:
■
Handle drives gently, using static-guarding techniques.
■
Store drives in the original shipping containers.
■
Avoid dropping drives from any height onto any surface.
■
Handle drives on surfaces that have at least one inch of shockproof
foam.
■
Always place drives PCB assembly side down on the foam.
Grounding Methods
The method for grounding must include a wrist strap or a foot strap at a
grounded workstation. When seated, wear a wrist strap connected to a
grounded system. When standing, use footstraps and a grounded floor mat.
Static-Shielding Protection Levels
Method
Voltages
Antistatic Plastic
1,500
Carbon-Loaded Plastic
7,500
Metallized Laminate
15,000
Grounding Workstations
To prevent static damage at the workstation, use the following precautions:
■
Cover the workstation with approved static-dissipative material. Provide
a
wrist strap connected to the work surface and properly grounded tools
and
equipment.
■
Use static-dissipative mats, heel straps, or air ionizers to give added
protection.
■
Handle electrostatic-sensitive components, parts, and assemblies by the
case or
PCB laminate. Handle them only at static-free workstations.
■
Avoid contact with pins, leads, or circuitry.
■
Turn off power and input signals before inserting and removing
connectors or test equipment.
■
Use fixtures made of static-safe materials when fixtures must directly
contact dissipative surfaces.
■
Keep work area free of nonconductive materials such as ordinary plastic
assembly aids and Styrofoam.
■
Use field service tools, such as cutters, screwdrivers, and vacuums, that
are conductive.
■
Use a portable field service kit with a static dissipative vinyl pouch that
folds out of a work mat. Also use a wrist strap and a ground cord for the
work surface. Ground the cord to the chassis of the equipment
undergoing test or repair.
Grounding Equipment
Use the following equipment to prevent static electricity damage to the unit:
Wrist Straps
are flexible straps with a minimum of 1 /- 10%
resistance
to the ground cords. To provide proper ground, a strap must be worn snug
against the skin. On grounded mats without banana-plug connectors, connect
a wrist strap with alligator clips.
Heelstraps/Toestraps/Bootstraps
can be used at standing workstations
and are compatible with most types of boots and shoes. On conductive floors
or dissipative floor mats, use them on both feet with a minimum of 1
megohm resistance between operator and ground. To be effective, the
conductive strips must be worn in contact with the skin.
Recommended Materials and Equipment
Other materials and equipment that are recommended for use in preventing
static electricity include:
■
Antistatic tape
■
Antistatic smocks, aprons, or sleeve protectors
■
Conductive bins, and other assembly or soldering aids
■
Conductive foam
■
Conductive tabletop workstations with ground cord of 1 megohm
of resistance
■
Static dissipative table or floor mats with hard tie to ground
■
Field service kits
■
Static awareness labels
■
Wrist straps and footwear straps providing 1 /- 10%
resistance
■
Material handling packages
■
Conductive plastic bags
■
Conductive plastic tubes
■
Conductive tote boxes
■
Metal tote boxes
■
Opaque shielding bags
■
Transparent metallized shielding bags
■
Transparent shielding tubes
privacy statement
legal notices
http://h18000.www1.hp.com/athome/support/msgs/2000/esd.html [12/10/2002 8:59:39 AM]
