Compaq Deskpro 2000 - Manual (Page 94)

Compaq Deskpro 2000 Series of Personal Computers 4-1
chapter 4
R
EMOVAL AND
R
EPLACEMENT
P
RELIMINARIES
This chapter provides general service information for the computer. Adherence to the procedures and
precautions described in this chapter is essential for proper service.
4.1 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 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.
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.