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Chapter 4. Removal and Replacement Preliminaries
Chapter 4.0 Introduction
This chapter provides general service information for the computer.
Adherence to the procedures and precautions described in this chapter is
essential for proper service.
Chapter 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. Or it 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 and
at different electrostatic voltage levels.
Table 4-1. Typical Electrostatic Voltages
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-- Relative Humidity --
Event 10% 40% 55%
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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
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NOTE: 700 volts can degrade a product.
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4.1.2 Preventing Electrostatic Damage to Equipment