Generating Static

Table 4-1 shows how different activities generate static electricity and 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 trays

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 PCBs

26,000

V

20,000

V

7,000

V

 

 

 

 

 

 

 

 

Packing PCBs in foam-lined box

21,000

V

11,000

V

5,000

V

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NOTE: 700 volts can degrade a product.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Preventing Electrostatic Damage to Equipment

Many electronic components are sensitive to ESD. Circuitry design and structure determine the degree of sensitivity. The following proper packaging and ground precautions are necessary to prevent damage.

■Protect all electrostatic sensitive parts and assemblies with nonconductive or approved containers or packaging.

■Keep electrostatic sensitive parts in their containers until they arrive at static-free stations.

■Place items on a grounded surface before removing them from their container.

■Always be properly grounded when touching a sensitive component or assembly.

■Place reusable electrostatic-sensitive parts from assemblies in protective packaging or nonconductive foam.

Use transporters and conveyers made of antistatic belts and roller bushings. Mechanized equipment used for moving materials must be wired to ground and proper materials selected to avoid static charging. When grounding is not possible, use an ionizer to dissipate electric charges.

4-2Removal and Replacement Preliminaries