Grounding guidelines

Electrostatic discharge damage

Electronic components are sensitive to electrostatic discharge (ESD). Circuitry design and structure determine the degree of sensitivity. Networks built into many integrated circuits provide some protection, but in many cases, ESD contains enough power to alter device parameters or melt silicon junctions.

A discharge of static electricity from a finger or other conductor can destroy static-sensitive devices or microcircuitry. Even if the spark is neither felt nor heard, damage might have occurred.

An electronic device exposed to ESD might not be affected at all and can work perfectly throughout a normal cycle. Or the device might function normally for a while, then degrade in the internal layers, reducing its life expectancy.

CAUTION: To prevent damage to the computer when removing or installing internal components, observe these precautions:

Keep components in their electrostatic-safe containers until you are ready to install them.

Use nonmagnetic tools.

Before touching an electronic component, discharge static electricity by using the guidelines described in this section.

Avoid touching pins, leads, and circuitry. Handle electronic components as little as possible.

If you remove a component, place it in an electrostatic-safe container.

The following table shows how humidity affects the electrostatic voltage levels generated by different activities.

CAUTION: A product can be degraded by as little as 700 V.

Typical electrostatic voltage levels

 

 

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

 

 

 

 

38 Chapter 4 Removal and replacement procedures