Compaq EXS Series manual Removal & Replacement Preliminaries, Electrostatic Discharge Information

chapter 3

REMOVAL & REPLACEMENT PRELIMINARIES

This chapter provides general service information for the computer. Adherence to the procedures and precautions described in this chapter is essential for proper service.

CAUTION: When the computer is plugged into an AC power source there is always voltage applied to the system board. You must disconnect the power cord from the power source before opening the computer to prevent system board or component damage.

3.1Electrostatic 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 be affected at all and can work perfectly throughout a normal cycle. The device may function normally for a while, then degrade 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.

3.1.1Generating Static

The following table shows that:

!Different activities generate different amounts of static electricity.

!Static electricity increases as humidity decreases.

	Relative Humidity
Event	55%		40%		10%
Walking across carpet	7,500	V	15,000	V	35,000	V
Walking across vinyl floor	3,000	V	5,000	V	12,000	V
Motions of bench worker	400	V	800	V	6,000	V
Removing DIPs* from plastic tube	400	V	700	V	2,000	V
Removing DIPs* from vinyl tray	2,000	V	4,000	V	11,500	V
Removing DIPs* from Styrofoam	3,500	V	5,000	V	14,500	V
Removing bubble pack from PCB	7,000	V	20,000	V	26,500	V
Packing PCBs in foam-lined box	5,000	V	11,000	V	21,000	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.

Compaq Deskpro EX and Deskpro EXS Series of Personal Computers 3-1