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ELECTROSTATIC DISCHARGE
SERVICE
CONSIDERATIONS
PREPARATION
FOR DISASSEMBLY
SERIAL
NUMBER
SIDE
ACCESS PANEL
GRAPHICS
CARD
EXPANSION
CARD
(Modem or Network Card)
SOUND
CARD
1394
CARD
MEMORY
MODULE
HARD
DRIVE
DISK
DRIVE
REMOVING
THE TOP DOOR
REMOVING
THE CD STORAGE DOOR
(Lower Front Panel - Open the CD Storage Door)
OPTICAL
AND MASS STORAGE DEVICES
(CD, CD-RW and/or DVD Drive, Hard Drive, Disk Drive)
FAN
ASSEMBLY
POWER
SUPPLY ASSEMBLY
FRONT
I/O BOARD
SYSTEM
BOARD COMPONENTS
(RTC Battery, Microprocessor/Heatsink Assembly) |
Electrostatic Discharge
A sudden discharge of static electricity
from a finger or a 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.
Generating Static
The table below shows the different
amounts of static electricity generated by different activities.
| 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 |
400V |
| 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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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 electrostatic-sensitive
parts from assemblies in protective packaging or conductive foam.
Use transporters and conveyors made of
antistatic belts and metal roller bushings. To avoid static charging,
mechanized equipment used for moving materials must be wired to ground.
When grounding is not possible, use an ionizer to dissipate electric
charges.
Preventing Damage to Drives
To prevent static 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 shock-proof foam.
- Always place drives PCB assembly side
down on the foam.
Grounding Methods
The method for ground 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.
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Static-Shielding
Protection Levels
|
| Method |
Antistatic Plastic |
Carbon-Loaded Plastic |
Metallized Laminate |
| Voltages |
1,500 |
7,500 |
15,000 |
Grounding Workstations
To provent 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 contact dissipative surfaces directly.
- 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.
Ground Equipment
Use the following equipment to prevent
static electricity damage to the equipment:
Wrist Straps are flexible straps
with a minimum of 1 megohm plus or minus 10% resistance to the ground
cords. To provide proper ground, a strap must be worn snugly against
the skin. On grounded mats without banana-plug connectors, connect a
wrist strap to the mat with alligator clips.
Heelstraps/Toestraps/Bootstraps
can be used at standing workstations and are compatible with most types
of boots and shoes. On conductive fllors 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 a hard tie to ground
- Field service kits
- Static awareness labels
- Wrist straps and footwear straps providing
1 megohm plus or minus 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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