Electrostatic 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) might not appear to be affected at all and can work perfectly throughout a normal cycle. The device can 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.

Generating Static

The following table shows that:

•Different activities generate different amounts of static electricity.

•Static electricity increases as humidity decreases.

Table 4-16Static Electricity

 

Relative Humidity

 

 

 

 

 

 

 

Event

55%

40%

10%

 

 

 

 

 

 

Walking across carpet

7,500V

15,000V

35,000V

Walking across vinyl floor

3,000V

5,000V

12,000V

400V

800V

6,000V

Motions of bench worker

 

 

 

 

 

 

 

 

 

Removing bubble pack from PCB

7,000V

20,000V

26,500V

Packing PCBs in foam-lined box

5,000V

11,000V

21,000V

 

 

 

 

 

 

 

 

 

 

NOTE: 700V 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 packaging and grounding precautions are necessary to prevent damage to electric components and accessories.

•Transport products in static-safe containers, such as tubes, bags, or boxes to avoid hand contact.

•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.

•When handling or touching a sensitive component or assembly, ground yourself by touching the chassis.

•Avoid contact with pins, leads, or circuitry.

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

Removal and Replacement Procedures

Service Considerations

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