Maintenance &
Service Guide
Presario 1600 Series Portable Computers
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Electrostatic Discharge
This chapter provides general service
information for the Compaq Presario Series of portable computers. Adherence to the
procedures and precautions described in this chapter is essential for proper
service. The topics covered include Electrostatic
Discharge and its effects, a table of activities that Generate Static and the potential voltages, ways of Preventing Electrostatic
Damage to Equipment, and Preventing
Damage to the Drive, Grounding Methods, Grounding Work Areas, and Recommended Materials and Equipment
to use in the service area. Return to Removal & Replacement
Procedures.
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.
The table below shows how different activities generate static
electricity and at different electrostatic 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. |
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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 avoid hand contact, transport products in the static-safe
containers such as tubes, bags, or boxes.
- 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 anti-static belts and
metal roller bushings. Mechanized equipment used for moving materials must be wired to
ground and proper materials selected to avoid static charging. When grounding is not
possible, use an ionizer to dissipate electric charges.
To prevent static damage to hard drive and diskette drive, use the
following precautions:
- Handle drive gently, using static-guarding techniques.
- Store drive in the original shipping containers.
- Avoid dropping drive from any height onto any surface.
- Handle drive on surfaces that have at least one inch of
shock-proof foam.
- Always place drive PCB assembly side down on the foam.
The method for grounding must include a wrist strap or a foot step
at a grounded work area. 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 |
Anti-static
Plastic |
1,500 |
Carbon-Loaded
Plastic |
7,500 |
Metallized
Laminate |
15,000 |
To prevent static damage at the work area, use the following
precautions:
- Cover the work area 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 work areas.
- 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, 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.
Use the following equipment to prevent static
electricity damage to the equipment:
Wrist-straps are flexible straps with a minimum of 1
megohm +/- 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
work areas 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.
Other materials and equipment that are recommended for use in
preventing static electricity include:
- Anti-static tape
- Anti-static smocks, aprons, or sleeve protectors
- Conductive bins, and other assembly or soldering aids
- Conductive foam
- Conductive tabletop work areas 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 megohm +/- 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
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