Identifying the Chassis, Routine Care, and Disassembly Preparation

5.2Electrostatic Discharge Information

A sudden discharge of static electricity from your finger or other conductor can destroy static-sensitive devices or microcircuitry. Often the spark is neither felt nor heard, but damage occurs. An electronic device exposed to electrostatic discharge (ESD) may not appear to be affected at all and can work perfectly throughout a normal cycle. The device may function normally for a while, but it has been degraded in the internal layers, reducing its life expectancy.

Networks built into many integrated circuits provide some protection, but in many cases, the discharge contains enough power to alter device parameters or melt silicon junctions.

5.2.1 Generating Static

The following table shows that:

■Different activities generate different amounts of static electricity.

■Static electricity increases as humidity decreases.

 

 

Relative Humidity

 

 

 

 

 

 

 

 

Event

55%

 

40%

 

10%

 

 

 

 

 

 

 

 

Walking across carpet

7,500

V

15,000

V

35,000

V

Walking across vinyl floor

3,000

V

5,000

V

12,000

V

Motions of bench worker

400

V

800

V

6,000

V

Removing DIPs* from plastic tube

400

V

700

V

2,000

V

 

 

 

 

 

 

 

Removing DIPs* from vinyl tray

2,000

V

4,000

V

11,500

V

Removing DIPs* from Styrofoam

3,500

V

5,000

V

14,500

V

Removing bubble pack from PCB

7,000

V

20,000

V

26,500

V

Packing PCBs in foam-lined box

5,000

V

11,000

V

21,000

V

*These are then multi-packaged inside plastic tubes, trays, or Styrofoam.

✎700 volts can degrade a product.

5.2.2 Preventing Electrostatic Damage to Equipment

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

■To avoid hand contact, transport products in static-safe containers such as tubes, bags, or boxes.

■Protect all electrostatic parts and assemblies with conductive 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.

■Avoid contact with pins, leads, or circuitry.

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

Service Reference Guide, dc7600

390742-002

5–3