This is the first of a three part series of posts that discusses electronic components and static electricity courtesy of Rice Lake’s Jim Daggon, senior product manager, and Chuck Crowley, senior technical support, who use static control wrist straps and use a dissipative work surface to protect sensitive components and circuits from ESD and once you read these three articles, you will probably be interested in doing the same.
Zap! Unseen, unfelt and unheard, electrostatic discharge (ESD), commonly known as static electricity, is damaging millions of dollars’ worth of electronic components every year. Electrostatic discharge is an electrical charge transferred between bodies at different electrostatic potential. “Static” electricity is the buildup of a charge on one object without a circuit for the current to flow through. When the charge builds up to the point where the voltage can “jump” the distance to a lesser charged object, it discharges with a spark. Once that spark occurs, the circuit is completed and current flows along the path of the spark. Lightning is the largest static electricity charge most of us will ever see. But we’ll discuss lightning more later.
That ZAP! you get when you shuffle across the rug in the winter and touch the TV can be annoying, but the voltages that build up can be deadly to today’s electronics. Quite often that damage is unseen. A zapped electronic device may work when it leaves your hands, but more than likely, its length of service has been reduced significantly. You cannot feel ESD below 3,000 volts, hear it below 5,000 volts, or see the spark below 10,000 volts. Many electronic devices can be damaged by ESD of well under 1,000 volts—EPROMs can be damaged by only 100 volts!
If this sounds hard to believe, look at the following stats:
• In low humidity, walking with rubber-soled shoes across a vinyl floor can build up 12,000 volts.
• Pulling tape off a dispenser just 6 inches can build up 4,000 volts.
• Walking across carpet can build up 35,000 volts.
Without a ground path to dissipate the charge, nonconductors like papers, plastics, foam coffee cups, clothing, and people can carry thousands of volts.
While moist air allows charged bodies to slowly drain off an excess charge to ground, dry air inhibits that charge dissipation. Simply adding moisture to indoor air may stop painful charges arcing to your fingertips from light switches in carpeted rooms, but it is not sufficient protection for sensitive electronic components. For this protection, a total system that prevents all damage by static must be in place.
Electronic Equipment Damage—Power Related
Today’s electronic equipment relies heavily on the power supplied to it to maintain its reliability, yet sometimes the power itself causes its downfall. Power for today’s high speed, fast-computing, and full-featured designs are very susceptible to power anomalies that, less than a decade ago, would have been insignificant. In the reel-to-reel tape recorder days gone by, the higher tape speeds were used for higher fidelity, since any noise was then spread over a wider section of tape. This higher speed works against us in today’s microprocessor clock speeds. A single extraneous pulse lasting a mere millionth of a second can disrupt 1,000 clock pulses in a 1 Ghz microprocessor.
Power anomalies come in a variety of types. Four of the more common ones are surges, sags, transients, and faulty wiring. Click here to read the rest of the part one article.