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Doing mostly micro-controller work, I have never bothered with grounding myself with a wrist-strap or any other implementation.
Should I be worried about this? How serious is ESD when working at my workbench on projects?

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I once saw someone touch the (house)radiator to discharge before working inside a PC. Does that really help? –  Lars Jun 11 '10 at 19:53
    
It helps if the radiator is properly grounded. If it is not, it could act as something to help you charge. –  Kortuk Jun 11 '10 at 20:06
    
Tie it to ground with a wire, through a resistor of 100k or more and you will be fine. –  Kortuk Jun 11 '10 at 20:06
    
If you walk across carpet from the radiator to PC, it does not help at all. If you walk around in clothes that generate static, it does not help. –  Kortuk Jun 11 '10 at 22:14
    

11 Answers 11

I know most people will yell at me for this. And I do honestly take some ESD precautions day to day, but ESD is a vary rare failure mode in modern electronics.

For my background, I take part in teaching the capstone design class at my university, and they have to build many many things, in 4 phases. Many students(almost all) will not listen to us when we warn of ESD precautions.

I have seen at-least 10 projects where they blamed ESD, only one that was probably ESD. In that project a board was working and a student walked up and touched it and you could audibly hear the shock as he discharged static electricity. This failed.

For the other 9, they blamed ESD only to find at a later point that they had a design flaw that was not easy to track down and only reared it's ugly head in very specific conditions.

I have heard many more than 10 projects blame esd and find a problem within hours, but only 10 have sworn they should be allowed to continue to the next phase because it worked but ESD fried it.

On that note, when you are working, you should check datasheets. Most modern devices have ESD protection, rated to some voltage using HBM(Human-body model). If this is below 1kV it is quite susceptible. if it is rated to 2k, it is semi-resilient, for the most part you would have to be dumb to damage it. if it is 4k, it is pretty resilient. if it is 8k you will hear a spark before you hurt it.

Be wary of those that blame ESD, but wear a wrist strap just in case. you can get a mat and strap for almost nothing.

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Side note, if you have tile floors and your building is very humid you have fewer risks as you discharge through the air at a higher rate. –  Kortuk Jun 10 '10 at 21:07
    
Good tip about the ESD ratings. These should guide the decision about the amount of protection needed on a case by case basis. –  jpc Jun 13 '10 at 0:56
    
Yes, We have a device that is <500V rated, which means almost nothing can destroy it, luckily it is soldered down in a professional facility and other devices lend it protection. –  Kortuk Jun 13 '10 at 3:16

Yes you should/must be worried about this. The simple case is where you blow the device completely. This is easy, it just does not work. The problem is where you damage the IO driver circuit - quite common as this is the bit that is exposed by the pin. In this case the driver may appear to work for some of the time. If it has to operate at high speed for part of the time then it may well fail giving intermittent and hard to diagnose faults. (Been there and got several t-shirts!!)

This is becoming more and more necessary as device geometries are shrinking and core voltages are dropping. Microcontroller manufacturing processes have often been slightly behind the bleeding edge but as oxide layer thicknesses are reducing with the device geometry size the required ESD voltage required to damage the device is reduced.

The bottom line is that you can get away with ignoring ESD precautions for a while but for how long? As Clint Eastwood said “You've got to ask yourself one question: 'Do I feel lucky?' Well, do ya punk?”

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most things like microcontrollers sport diodes in the pins that allow ESD to discharge harmlessly. They are called ESD protection diodes normally. –  Kortuk Jun 10 '10 at 15:48
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They are a palliative that provide some protection but are often themselves damaged as they protect the main device. On the second ESD event there is no protection left on the pin. –  Ian Jun 10 '10 at 19:47
    
I had never been told that, nor have i seen common failures were people do not use protection. I would like to know more about it. On that note Ian, do not take me wrong, I am a strong supporter of ESD protection, I just feel being honest with people about what protections already exist is worthwhile. You have said the same thing in your post, so no worries. –  Kortuk Jun 10 '10 at 20:44

The tricky thing with ESD is that even when it doesn't seem to affect anything, every small discharge does cause some damage, whether it's pitting of the silicon, vaporizing a little bit of the bonding wire, removing some of the metalization on one of the semiconductor layers, or some other effect, it will physically alter the product.

In most cases, most uses of a given part won't be measurably altered by the change. Most people overengineer their designs so they aren't using them anywhere near their limit, so there's a huge margin where a pitted part will work just fine for more uses.

Over time repeated discharges will change the part enough that it will behave slightly out of spec - but perhaps not enough to notice without thorough testing. This is really the worst case scenario - since it works most of the time, then it's really difficult to find out why it's not working when it fails. It's far better for a part to fail completely so it's easy to track down.

Alternately, the one small discharge that happened once damages it enough that when you do use it to full capacity, it then fails. The happens, of course, once you've deployed it in the field and it's a pain to get it back and troubleshoot it.

This kind of damage cannot be detected without removing the silicon from the package and inspecting it, or, in cases where the damage is hidden inbetween layers, by slicing the silicon into very thin sheets where the damage is likely to occur.

So yes, everyone here is right when they say, "I rarely follow ESD precautions and I have never seen an issue." They will never see it, and when it does fail there will be no reason to believe it was ESD related because there was no recent ESD event.

But that doesn't mean I'm going to trust the products that come from their bench, either.

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If you go for the intractable then beware that silicon vendor ratings are most commonly statistical so you still get 1 part out of 1000 that is more than 3 sigma from the mean. It may ruin your design or it may not. :) –  jpc Jun 13 '10 at 0:43

If you don't take ESD precautions, you risk damaging things. The probability of damaging something varies all over the place (temperature, humidity and floor surface being important factors), and it's entirely possible that you'll never damage anything (or at least not such that you'd notice).

I HAVE damaged devices before with ESD. Heck, I once killed a serial port (something that's PROTECTED against ESD because the pins are hanging out there) by shocking to the pins.

Now, that's not to say that you have to have the be-all and end-all of ESD protection. Even if you don't go for the full array with ionizers and wrist straps and conductive tile flooring, try to get an grounded mat for your bench, and try to touch them mat when you sit down. You'll tend to brush the mat with your hands as you are working, and this will keep you mostly at the same potential as the parts on the mat and keep the possibility of problems to a minimum.

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Seconded. The mat on the bench will do wonders. –  Kortuk Jun 11 '10 at 13:54
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Sorry, i meant to ask earlier, how the hell did you total an RS232 port? –  Kortuk Jun 11 '10 at 15:06
    
Grabbed a cable connected to the port and somehow managed to shock to the rcv line instead of the shell. Shouldn't have killed it even so, but apparently I can build up one heck of a charge some days. –  Michael Kohne Jun 18 '10 at 17:59

You should only skip ESD measures if you can bear the pain ($$) of replacing whatever it is. If you do go un-grounded, though, be aware that device failure is not all-or-nothing. Complete catastrophic failure is probably the best failure mode, because you won't waste as much time trying to figure out what went wrong. Personally, I won't handle anything bigger than 7400 series stuff without a grounding wrist strap.

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Yes, you definitely should be worried about it, especially if you're working with CMOS (which is about every digital IC nowadays).

Static electricity can easily build up to several kV on a dry winter day, walking with your leather sole shoes over a synthetic fiber carpet. Just reaching for the door handle may draw a spark from your fingertips and give you an unpleasant shock.

What's the risk with CMOS? CMOS inputs in digital ICs like microcontrollers have a very high impedance; if you apply a voltage it has nowhere to go. And a MOSFET's gate is isolated by only an extremely thin insulation layer from the FET's channel. So if you're charged to say 4000V and you touch the microcontrollers input pin the charge will find the easiest way out, and that may be the gate's insulation layer. If you're lucky the charge doesn't damage the insulation layer passing through it. But it's also possible that it gets damaged, destroying the MOSFET, possibly rendering your device useless.

This may happen when handling a part lying on your desk, but it's also possible in finished products. Buttons are meant to be touched and often leave an air gap through which a discharge can reach a PCB. You can apply mechanical measures like lengthening the path by making it a labyrinth. And you can protect susceptible traces with fast ESD protection devices like transient suppression diodes or varistors.

ESD threats you hear about are real. When working with ESD-sensitive devices at least use an antistatic mat and an antistatic wrist strap.

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My experience seems to be that you'd probably be ok for months or years (depending on the exact components and how much static charge you build up in your environment) but it's not just a theoretical problem and one day it will bite you. Probably at the most inconvenient time and the most expensive way to fix.

And it's not very difficult to protect against it so just get into the habit of doing it. I've not taken my own advice there, but I really should and do intend to!

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this is the case for most people. I still have never had a problem at work, and we are on carpet. –  Kortuk Jun 10 '10 at 16:11

It interesting how people say something to the effect of "I don't follow ESD precautions, but you should" It's OK ... we never live up to our own ideals. I think your question is like "should I get seven to eight hours of sleep every night?" The answer is "yes, getting enough sleep is important ... but sometimes it doesn't happen"

ESD precautions are particularly important in manufacturing settings where you are making a product and you don't want to deal with field repairs. Typically damage from ESD will not be immediately apparent, but might cause a product to fail after months or years of use.

It's a good thing to be in the habit of using basic ESD precautions. That being said, I wouldn't be terribly stringent with yourself about it for most basic work. If you occasionally pick up a chip without a wrist strap on, don't feel like you've committed a sin.

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I actually intentionally work on a bench that has conductive paint. It is tied to ground properly and I always keep my forearms or elbows touching it as I work. –  Kortuk Jun 11 '10 at 16:28
    
It is not that I think I will fry anything. It is that bugs take weeks to find already, if I spend weeks and it ends up something gets ESD'ed I may think it was a bug and lose a real one. Or actually waste weeks on ESD. –  Kortuk Jun 11 '10 at 21:42

If you're a hobbyist, then you don't really need to care about ESD protection.

If you're building prototypes for an actual project, then you should be concerned about ESD protection...but in reality you probably won't bother too much, aside from periodically touching the nearest convenient grounded piece of metal.

If you're building production equipment that will be sold to paying customers, then you must be concerned with ESD protection. That means a strap and a mat at all times in an area with no carpet.

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We never had any problems with ESD neither in prototyping nor in production and we don't use any wrist-wraps or other stuff. OTOH we don't have any carpets and do not wear wool or synthetic clothing. Because of this we never had a static discharge from you bodies at work.

I would suggest fighting with static build-up at the source if possible (check you clothes, furniture and humidity) and after you've done this, you may buy some human grounding equipment for double protection.

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Most devices are damaged at a level of static discharge far below what you can feel. On that note, I turned on an LED with static once and it still works. –  Kortuk Jun 11 '10 at 16:29
    
The board still works I should say, it was one part. –  Kortuk Jun 11 '10 at 20:06
    
To damage anything "normal" you must cause quite a current. To do this to modern, protected chips through standard human body resistance you need quite a voltage so I still think that if there are no sparks then you should be safe. In production we sometimes get returns from our customers but never any of this could be tracked down to a possible ESD issue. For an example of an issue you should worry about (albeit this one did not pass our Q&A): we once had some eerie problems with one NAND gate which was left with floating inputs. It worked with a chip from one vendor and failed with another. –  jpc Jun 13 '10 at 0:49
    
SUMMARY: In prototyping, unless you got full-custom ASICs or a chip worth more than $50 (translate to you own currency and financial threshold), you should not worry about ESD too much. We find normal precautions, without straps, sufficient. There are multitudes of other very cool failure options you should fear! (like mistaking Vcc & GND ;-) –  jpc Jun 13 '10 at 0:53

My answer is pretty straight forward. I learnt my lesson the hard way.

Just use ESD protection.

Wrist straps are annoying, yes. At the very least, go and get a big and good quality ESD mat and put it on your desk. It makes it much more unlikely that you will touch anything before putting your hands on the table. I tend to rest my arms on the table when working anyway.

My story is that I thought everything was fine, until I got a particularly cold winter and wore the wrong sweater just one day. I messed up all my AVR programmers and dozens of my own boards so that they now work "sometimes". this was actually because my ESD mat was bad quality. This cost me weeks. Its just not worth it.

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