Electrostatic Discharge Precautions

Electrostatic Discharge Precautions

This article addresses the following objective in the "Domain 3.0: Preventive Maintenance" section of the A+ Certification exam:

• 3.2: Identify ESD (electrostatic discharge) precautions and procedures, including the use of ESD protection devices.

The first way to avoid electrostatic discharge (ESD) is to be able to identify when and why it occurs.

Identifying and Avoiding Electrostatic Discharge

Static can easily discharge through digital computer equipment. The electronic devices used to construct digital equipment are particularly susceptible to damage from ESD. As a matter of fact, ESD is the most damaging form of electrical interference associated with digital equipment.

The following are the most common causes of ESD:

• Moving people

• Low humidity (hot and dry conditions)

• Improper grounding

• Unshielded cables

• Poor connections

• Moving machines

When people move, the clothes they are wearing rub together and can produce large amounts of electrostatic charge on their bodies. Walking across carpeting can create charges in excess of 1,000 volts. Motors in electrical devices, such as vacuum cleaners and refrigerators, generate high levels of ESD.

ESD is most likely to occur during periods of low humidity. If the relative humidity is below 50%, static charges can accumulate easily. ESD generally does not occur when the humidity is above 50%. Any time the charge reaches around 10,000 volts, it is likely to discharge to grounded metal parts.

Although ESD will not hurt humans, it will destroy certain electronic devices. The high-voltage pulse can burn out the inputs of many integrated circuit (IC) devices. This damage might not appear instantly, but it can build up over time and cause the device to fail. Electronic logic devices, constructed from metal-oxide semiconductor (MOS) materials, are particularly susceptible to ESD. The following section describes special handling techniques to observe when working with equipment containing MOS devices.