Removal and Replacement Preliminaries

Table 4-1 shows how humidity affects the electrostatic voltage levels generated by different activities.

Table 4-1

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

✎A product can be degraded by as little as 700 volts.

Table 4-2 lists the shielding protection provided by antistatic bags and floor mats.

Table 4-2

Static-Shielding Materials

Material

Use

Voltage Protection Level

 

 

 

Antistatic plastic

Bags

1,500 V

 

 

 

Carbon-loaded plastic

Floor mats

7,500 V

 

 

 

Metallized laminate

Floor mats

5,000 V

 

 

 

Maintenance and Service Guide

4–7