Table 5-1 Static electricity
Relative humidity
Event 55% 40% 10%
Walking across carpet
Walking across vinyl floor
Motions of bench worker
7,500V
3,000V
400V
15,000V
5,000V
800V
35,000V
12,000V
6,000V
Removing bubble pack from PCB
Packing PCBs in foam-lined box
7,000V
5,000V
20,000V
11,000V
26,500V
21,000V
CAUTION: 700 volts can degrade a product.
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
electric components and accessories:
●
Transport products in static-safe containers such as tubes, bags, or boxes, to avoid hand contact.
●
Protect all 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 their containers.
●
When handling or touching a sensitive component or assembly, ground yourself by touching the
chassis.
●
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 to equipment:
●
Wrist straps—flexible 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 fit snugly into the banana plug connector on the grounding mat or workstation.
●
Heel straps, toe straps, and boot straps—can be used at standing workstations and are
compatible with most types of shoes or boots. On conductive floors or dissipative floor mats, use
them on both feet with a maximum of one megohm ± 10% resistance between the operator and
ground.
Table 5-2 Static shielding protection levels
Method Voltage
Antistatic plastic
Carbon-loaded plastic
Metallized laminate
1,500V
7,500V
15,000V
ENWW Service considerations 53
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