Taken from the A+ Certification book by Michael Meyers.

Typical Electrostatic Voltages-

Humans can accumulate electrical potentials well over 25,000 volts. Although we might experience a shock or other sensation when the charge dissipates, it is a very quick, low-current flow that is not harmful. But as little as 30 volts can destroy some of today's more sophisticated integrated chips, so daily activities can generate static charges on your body that are potentially harmful to sensitive electronic components.

Consider the following:

Walking across carpet: 1,500 to 25,000 volts
Walking over an untreated vinyl floor: 250 to 12,000 volts
Picking up a common plastic bag: 1,200 to 20,000 volts
Working at a bench: 700 to 6,000 volts
Handling a vinyl envelope: 600 to 7,000 volts.

Costly Effects of ESD

An ESD must reach a minimum of 3,000 volts of electricity before most people notice the shock. Although most of us feel an ESD of 3,000 volts, we fail to feel smaller charges, and yet these charges still damage semiconductor devices. Many of the CMOS technology components can be destroyed by less than 1,000 volts.

Technology continues to advance, making smaller, more closely packed components. The microscopic spacing of insulators and circuits within chips is increasing the sensitivity to ESD. Proper ESD protection is a must!

Types of ESD Damage

The damage caused by ESD takes on three forms: upset failures, latent catastrophic failures, and direct catastrophic failures.

Upset failures occur when a small ESD causes minor gate leakage. Upset failures are intermittent in nature. This type of damage might not be detected by quality control or end-user test programs, but it shows up as an unexplained loss of data. These ESD cause the most embarrassment to technicians because mishandling parts tends to create this type of error. The embarrassment manifests itself as repeated calls, or worst yet, installing a device such as extra RAM. The RAM takes an upset failure and displays random-memory errors during POST. Who was the last person to touch the system? You! "Everything was fine until you touched it!" Sound familiar?

Latent catastrophic failures occur when the ESD damage causes the transistor junction to weaken; we like to call these zings. This transistor might pass all tests, but over time will react with poorer system performance and eventual system lockups. Because latent failures show up well after installation, the cause of these lockups seems "unknown," and the cost to troubleshoot and repair usually makes system replacement worthwhile.

Direct catastrophic failures, known as zaps, usually occur with ESD shocks of more than 3,000 volts. The device that takes the shock fails completely, and you must replace the part. The obvious failure makes zaps the easiest to find, as diagnosis tends to point quickly to the failed device.

Pages 366-368 in the 2001 revision
As posted by YIN

JTMO- Wrist straps are only a few dollars at the local electronics store. Use them and save yourself some grief later on.

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by Jtmo edited by dbmaven
last modified: 2003-09-05 11:10:30