Electrostatic
Discharge
Service
Considerations
Preparation for
Disassembly
Serial Number
Side Access
Panel
Expansion Card
(Modem or Network 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, Diskette Drive)
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 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 |
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 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 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 |
Antistatic Plastic |
Carbon-Loaded Plastic |
Metallized Laminate |
Voltages |
1,500 |
7,500 |
15,000 |
Grounding Workstations
To prevent static damage at the workstation, use the
following precautions:
- Cover the workstation with an approved static-dissipative
material. Provide a wrist strap connected to the work surface and use 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
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
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