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

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

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

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

 

 

 

 

Packaging and transporting guidelines

Follow these grounding guidelines when packaging and transporting equipment:

●To avoid hand contact, transport products in static-safe tubes, bags, or boxes.

●Protect ESD-sensitive parts and assemblies with conductive or approved containers or packaging.

●Keep ESD-sensitive parts in their containers until the parts arrive at static-free workstations.

●Place items on a grounded surface before removing items from their containers.

●Always be properly grounded when touching a component or assembly.

●Store reusable ESD-sensitive parts from assemblies in protective packaging or non-conductive foam.

●Use transporters and conveyors made of antistatic belts and roller bushings. Be sure that mechanized equipment used for moving materials is wired to ground and that proper materials are selected to avoid static charging. When grounding is not possible, use an ionizer to dissipate electric charges.

20 Chapter 4 Removal and replacement preliminary requirements