HP COMPAQ DX2718 MT - Manual (Page 31)

Service Reference Guide 483941-001 5–3
Identifying the Chassis, Routine Care, and Disassembly Preparation
5.2 Electrostatic Discharge Information
A sudden discharge of static electricity from your 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 appear to be affected at
all and can work perfectly throughout a normal cycle. The device may function normally for a
while, but it has been degraded 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.
5.2.1 Generating Static
The following table shows that:
■ Different activities generate different amounts of static electricity.
■ Static electricity increases as humidity decreases.
✎
700 volts can degrade a product.
5.2.2 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 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.
Relative Humidity
Event 55% 40% 10%
Walking across carpet
Walking across vinyl floor
Motions of bench worker
7,500 V
3,000 V
400 V
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