Electrostatic Discharge

Electrostatic Discharge

Or how to upset a sibling in one easy lesson

By Mike Dziurgalski

Working in England for the U.S. Air Force was mostly under a line maintenance situation. I had not opened an electronic component for years, much less try to troubleshoot and repair at the card level. Needless to say, I was a little rusty when arriving at Altus Air force Base in Oklahoma to work heavies again. After settling down from an overseas move, it was time to relearn the C-5 avionics systems I left so many years ago.

During training, one of the acronyms that kept popping up was ESD. Now acronyms and I usually get along like an ice cream cone at a blowtorch convention, but I was sure I knew this one. I thought it was something to do with the pulse of energy that emanates from an atomic blast wreaking havoc on computers, communications equipment, and various electronic components. So, when someone offered ESD as an explanation for the untimely demise of an oscillating and smoking computer, I was, needless to say, concerned. Of course, I was wrong in my assessment of a holocaust, and after a time of working with this unseen monster, I started to actually understand it a bit more.

ESD is short for electrostatic discharge - just plain ol' static electricity.

To explain let me take you on a trip back in time to your younger days. For some of you it will be a much shorter journey than mine (and I truly hate you for that) but I digress. Remember when you were a kid? A large portion of your day was likely devoted to making your sister's or brother's very existence a living purgatory. You dreamed of becoming more than you were. You wanted to be a Superhero, a savior of the world, but, alas, this was not to be. Then one day, while shuffling along on the carpeted floor, you reached for the doorknob and instantly . . . you were Electroman. With your U.S. Army wool blanket cape, nylon socks, and cotton Scooby Doo PJs you were set to save the world from evil. You drag your feet, feeling the power build to a crescendo while searching for that most vile super villain of all time, in my case . . . the Big Sister. Slowly you approach her sleeping body. You choose your target wisely, for you have only one shot. The bright blue bolt of hellfire, just before her blood-curdling scream was, in fact, an ESD. Now, let's look at how this natural phenomenon occurs.

The American Heritage Dictionary describes static electricity as, "an accumulation of electric charge on an insulated body or an electric discharge resulting from the self-same charge" (Whew). In layman's terms, when you shuffled your feet on the carpet, you built up a charge of electricity on your body. Now your sister or brother lounging on the couch has less of a charge than you do. When your charged finger came close to their uncharged teeth . . . ZAP . . . instant gratification. Now, apply the same energy to an electrostatic sensitive component and you have a destroyed or severely weakened device. Now don't expect a lightning bolt and a miniature mushroom cloud where your computer used to be. In most cases you won't even feel the harbinger of doom you have unleashed. Moreover you probably will not even feel the discharge. These components are so sensitive they can be dispatched to computer heaven with only a few hundred volts. You can't see or feel anything below around 4,000 volts of static electricity so you will be blissfully ignorant of the damage wrought.

Would you believe just walking on carpet could produce 35,000 teeth jarring volts? "There's no carpet in my shop," you say. How about walking on a vinyl floor? Give that technician 12,000 volts. Even picking up a plastic bag can produce 20,000 volts. And one of the biggest culprits of static production is surprisingly, a common cellophane tape dispenser.

Producing static electricity is inevitable. Destroying electronic components is not. The best way to ensure your components are safe from ESD is to follow the manufacturer's technical data. I'm not going to recite tech data at this time. Most of it wouldn't make it to the best seller's list, if you know what I mean. What I will do is give you some good tips to keep your systems safe. You can read the data sometime with a large supply of coffee and No-Doz.

Tip one: Be sure any time an ESD sensitive item is handled outside its protective packing it is in a protected area. A protected area would consist of a grounded workbench and static mat with an ESD wrist strap grounded to the same point as the bench or mat. Don't worry about grounding yourself around power, the ESD wrist strap has a 5-milliamp current limiting resister built in, so in case you let your fingers do the walking through something nasty, (high current voltage) you don't look like something that belongs in a Colonel Sander's bucket. Ensuring any test equipment you are using is grounded is a good idea also.

Tip two: Keep your area clean of static producing materials. Plastic bags, Styrofoam coffee cups, candy wrappers, bathtub duckies, etc. have no place on an ESD bench.

Tip three: Keep protective caps on connectors of line replaceable units with ESD sensitive components in them. This keeps them safe from someone touching the pins. These connectors are windows to the component heart. One touch could transform an $80,000 computer into a paperweight in record time.

Here is another tasty bit of info for you to mull over. Not only can you destroy an ESD sensitive unit; you can weaken it to the point of failure at a later time. It can pass every bench check thrown at it but still be a loaded gun. This doesn't take a Ph.D. to understand the dangers this could cause. Imagine you are on an adverse weather landing, visibility at minimums, and a planeload of passengers. (We are talking a pucker factor of around 6.5.) Suddenly your screen blanks or you get an un-commanded flight control input, and in one fell swoop, the fun meter is pegged.

Before I go I would like to make one final point, this time on the subject of economics. Many of you are now working on newer aircraft with ESD sensitive components installed. A large amount of them will be under warranty. With technology getting better each day, ESD related damage is becoming easier to detect by the major avionics manufacturers. As in the case of any mishandling of any components, not following manufacturer's ESD procedures could be grounds for revoking the warranty of that new $100,000 unit. Can you or your company afford that?

I hope this information has been useful. With a few simple precautions and very little outlay of resources, the payoff will be higher reliability, less downtime, and of course a kinder gentler purchasing department. When you add it up it equals a safer and more profitable endeavor. ------ Safe Flying. AMT

Mike Dziurgalski is an avionics inspector from the Cincinnati FAA FSDO.

Static Electricity Training
Summit Training Source offers a CD-ROM training program to provide workers with an awareness of the hazards of static electricity.

Static electricity causes millions of dollars each year in product damage. It is also a leading contributor to worker falls, burns, and other injuries.

The training program shows specific methods to eliminate or control static electricity hazards through work practices and engineering controls. For more information or to order visit www.safetyontheweb.com or call (800) 842-0466.