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 V.

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

 

 

 

4–8

Maintenance and Service Guide