Electrostatic discharge (ESD) information
Generating static Dierent activities generate dierent amounts of static electricity through electrostatic discharge (ESD).
Static electricity increases as humidity decreases.
CAUTION: Static electricity in the amount of 700 volts might degrade a product.
Event
Relative humidity
55% 40% 10%
Walking across carpet
Walking across vinyl oor
Motions of bench worker
7,500 V
3,000 V
400V
15,000 V
5,000 V
800 V
35,000 V
12,000 V
6,000 V
Removing bubble pack from PCB
Packing PCBs in foam-lined box
7,000 V
5,000 V
20,000 V
11,000 V
26,500 V
21,000 V
Preventing ESD
equipment damage
Many electronic components are sensitive to ESD. Circuitry design and structure determine the degree of
sensitivity. The following packaging and grounding precautions are necessary to prevent damage to
electronic components and accessories:
●
Transport products in static-safe containers such as tubes, bags, or boxes, to avoid hand contact.
●
Protect electrostatic parts and assemblies with nonconductive 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 containers.
●
Before handling or touching a sensitive component or assembly, ground yourself by touching a
grounded metal object.
●
Avoid contact with pins, leads, or circuitry.
●
Place reusable electrostatic-sensitive parts from assemblies in protective packaging or
nonconductive foam.
Personal grounding
methods and
equipment
Use the following items to help prevent ESD damage:
●
Wrist straps — These are exible straps with a maximum of one megohm ± 10% resistance in the
ground cords. To provide a proper ground, wear the strap against bare skin. The ground cord must
be connected and t snugly into the banana plug connector on the grounding mat or computer.
●
Heel straps, toe straps, and boot straps — These can be used at standing computers and are
compatible with most types of shoes or boots. On conductive oors or dissipative oor mats, use
them on both feet with a maximum of one megohm ± 10% resistance between the operator and
ground.
Static shielding
materials
Static shielding materials provide the following levels of protection.
Method
Antistatic plastic
Carbon-loaded plastic
Metalized laminate
Voltage
1,500 V
7,500 V
15,000 V
Grounding the work
area to prevent static
damage
●
Cover the work surface with approved
static-dissipative material. Use a wrist strap
connected to the work surface, and properly
grounded tools and equipment.
●
Use static-dissipative mats, foot straps, or
air ionizers to give added protection.
●
Disconnect power and input signals before
inserting and removing connectors or test
equipment.
●
Use xtures made of static-safe materials
when xtures must directly contact dissipative
surfaces.
Service considerations 43
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