Electrostatic Discharge Information; Generating Static - HP xw4000 Service & Reference Manual

Identifying the Chassis, Routine Care, and Disassembly Preparation
7.2

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.

7.2.1 Generating Static

The following table shows that:
Different activities generate different amounts of static electricity.
Static electricity increases as humidity decreases.
Walking across carpet
Walking across vinyl floor
Motions of bench worker
Removing DIPs* from plastic tube
Removing DIPs* from vinyl tray
Removing DIPs* from Styrofoam
Removing bubble pack from PCB
Packing PCBs in foam-lined box
*These are then multi-packaged inside plastic tubes, trays, or Styrofoam.
700 volts can degrade a product.
7–2
Event
Relative Humidity
55% 40%
7,500 V 15,000 V
3,000 V 5,000 V
400 V 800 V
400 V 700 V
2,000 V 4,000 V
3,500 V 5,000 V
7,000 V 20,000 V
5,000 V 11,000 V
Service Reference Guide
10%
35,000 V
12,000 V
6,000 V
2,000 V
11,500 V
14,500 V
26,500 V
21,000 V