Electrostatic Discharge (ESD), Killer of IC Circuits

[dailey]

I would like to remind people when handling circuit boards, IC chips or any static sensitive component, that you should always wear a grounded wrist strap. They’re not expensive and can prevent destructive damage to integrated circuits. Also important is packaging material. Always package using antistatic materials such as pink or metalized antistatic bags (Pink is the color code for antistatic).

A few facts:
•   As little as 25 static volts can damage an integrated circuit.
•   Human perception is 4,000 static volts and beyond. You could easily zap a component below this threshold causing irreparable damage and never feel it.
•   The human body is capable of storing a charge as high as 25,000 V.
•   ESD damage to an IC circuit may not be readily apparent but could cause latent failure.

[rokgpsman]

Over the years I've been to several 3M, Motorola and other industry ESD training sessions, ESD damage is real. A big problem is that often the ic is damaged but not killed immediately. So it fails some time after the person zapped it and they don't see that their improper handling was what caused the failure. So they keep doing the same bad handling practices. They showed us several photos taken with microscopes, you could see the craters and half-blown away traces inside the ic caused by static electricity. Everyone knows that static shock you sometimes get when you grab a doorknob, imagine that energy force hitting a small pn junction or tiny wire/circuit path inside an ic.

In the winter time when humidity levels are lower the ESD problem is worse. Heating systems in buildings and homes dry out the air, lowering its humidity. Dry air allows static voltages to increase a lot, into the thousands of volts on your body just by doing ordinary things like walking on carpet or your clothing made of synthetic material rubbing against your skin. That's why you should never use air from an air compressor to blow out & clean electronic equipment. The rapidly moving air contains high static voltages due to its friction moving across the rubber hose. Electronic repair shops I'm familiar with at Rockwell have air pressure hoses for cleaning, but they have a special nozzle with a 3,000-5,000 volt nozzle tip to neutralize the static voltage as the air moves by it.

Heat and ESD damage cause a lot of unexplained failures in electronics.

[qbert]

And remember while you are wearing that ground strap make sure you put your finger in a live light socket so you will be sure your grounded properly and all of that current gets through you.

[rokgpsman]

Haha!    our work stations had the wrist straps with cords that plugged into a monitoring system box on the edge of the work station. If you didn't have the strap making good contact with your bare skin, or if the cable was broken or some other problem then the darn thing beeped loudly. It monitored the grounding system from you to the work station and the level of static voltage present on your body. Anyone caught working without wearing the ESS gear was reprimanded. This went for the stockroom people that pulled the parts from the storage bins.

They used to say "Safety glasses are for your safety - the ESS protections are for the equipment you are working on".

[qbert]

Sorry I couldn't resist. Seriously many of us are working on the machines while they are live (plugged in). Not so sure I want to be grounded. On a repair bench definitely.  Also I live in humid FL so static is rarely an issue for me. I have more problems from the sweat dripping off my nose onto the circuit cards.

[rokgpsman]

I do the same thing on my stuff away from work, a lot of times don't use a grounding strap. I still touch bare metal on the machine when I first get into it, chassis ground is always connected to power earth ground on anything approved by UL. This removes any static voltage on me (if machine's power cord is connected to wall outlet) or at least puts me at the same voltage potential as the machine and makes for little chance of me zapping something. High humidity definitely reduces the chance of static voltage damage.

We had female techs that were always having problem with high static voltage on their body and failing audits. Engineering determined it was all the synthetic clothing they were wearing next to their bare skin (pantyhose, panties, chemise, etc). They had many more square inches of skin contacting synthetic material tightly than a male tech did.

One of the 3M AntiStatic instructors used to tell us "if you are alive & moving you are making static electricity, whether you're in the kitchen making pancakes or in the bedroom making whoopee".

[Badbaud]

My shop rule is if someone hands a PC board to some one else they must touch the bare skin of that person before accepting the board.Another gripe is people who send me boards wrapped in clear bubble wrap or immersed in white peanuts, both generate static.The boards are always sent back wrapped in anti-static bubble wrap. The peanuts are tossed.

[rokgpsman]

Any and all precautions you can take reduce the chances of causing a problem. Many modern ic's have static protection built into them, they have little MOV-like circuits connected to the input and output legs of the ic. But the older stuff from 1980's and 1990's not so much.

Just holding the circuit board by the edges and not let your hands touch the ic legs or other bare metal component leads on it can help a lot.

 

[jay]

Electronics work on smoke.
When the smoke comes out the electronics stop working.