Compaq Deskpro 4000N - Desktop PC, Maintenance & Service Manual

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4-2 Removal and Replacement Preliminaries
4.1.1 Generating Static
Table 4-1 shows how different activities generate static electricity at different electrostatic voltage
levels.
Table 4-1
Typical Electrostatic Voltages
Relative Humidity
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 tube 2,000 V 700 V 400 V
Removing DIPs* from vinyl tray 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 PCB 26,500 V 20,000 V 7,000 V
Packing PCBs in foam-lined box 21,000 V 11,000 V 5,000 V
* Dual Inline Packaging (DIP) is the packaging around individual microcircuitry. These are then multi-packaged inside plastic
tubes, trays, or Styrofoam.
✎ ✎
700 volts can degrade a product.
4.1.2 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 to electric components and accessories.
■
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
foam.