Table 4-1 Static electricity occurrence based on activity and humidity (continued)
Relative humidity
Event 55% 40% 10%
Walking across vinyl oor
Motions of bench worker
Removing DIPs (dual in-line packages) from plastic tube
3,000 V
400 V
400 V
5,000 V
800 V
700 V
12,000 V
6,000 V
2,000 V
Removing DIPs from vinyl tray
Removing DIPs from polystyrene foam
Removing bubble pack from PCB (printed circuit board)
Packing PCBs in foam-lined box
2,000 V
3,500 V
7,000 V
5,000 V
4,000 V
5,000 V
20,000 V
11,000 V
11,500 V
14,500 V
26,500 V
21,000 V
Multiple electric components can be packaged together in plastic tubes, trays, or polystyrene foam.
NOTE: As little as 700 V 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 packaging and grounding precautions are necessary to prevent static electricity
damage to electronic components.
● To avoid hand contact, transport products in 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.
● Avoid contact with pins, leads, or circuitry.
● Place reusable electrostatic-sensitive parts from assemblies in protective packaging or conductive
f
oam.
Personal grounding methods and equipment
Using certain equipment can prevent static electricity damage to electronic components.
● Wrist straps
are exible straps with a maximum of 1 MΩ ±10% resistance in the ground cords. To
provide proper ground, a strap must be worn snug against bare skin. The ground cord must be
connected and t snugly into the banana plug connector on the grounding mat or workstation.
● Heel straps/Toe straps/Boot straps
can be used at standing workstations 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 1 MΩ ±10% resistance between the operator and ground.
24 Chapter 4 Removal and replacement procedures preliminary requirements
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