How Serious is Static Electricity? 95
seanadams.com asks: "My company is considering the purchase of a small surface-mount assembly line so we can do our manufacturing in-house, and the issue of static control has come up. We've all been told to take ESD precautions when handling electronics, but how much precaution is enough? Obviously we plan to do the easy stuff like making sure that equipment and work surfaces are properly grounded. However, many shops go even further - conductive shoe straps, wrist staps, special flooring, humidity control, etc. The SMT equipment vendor says that it's unnecessary, and I would tend to agree. I've handled tons of electronics over the years and have never been able to attribute a single failure to ESD damage. Granted, Silicon Valley is a fairly humid area so that may be a contributing factor. Has the ESD threat been blown way of proportion by the guys who sell those little grey bags?"
When I used to work at Visiontek (Score:4, Informative)
Basically, you don't have problems with static when your only dealing with a small sample, but increase the sample size, you are increasing your chances of causing damages to something within that sample. So, for a manufacturing operation, I'd say it is worth it.
classic benefits/loss analysis (Score:3, Informative)
Perform a benefits/loss analysis. If you handle extremely expensive equipment that can't be damaged, then maybe it would be wise to invest a little more into ESD protection. On the otherhand, if you're manufacturing small boards with little value, then don't invest in ESD protection. You said it yourself, that you have NO cases of ESD damaging electronics as long as you've been there. If one part per million gets damaged and it doesn't cost much to replace, then forget about ESD protection.
ESD damage is not always immediately apparent. (Score:3, Informative)
If your product is so cheap that you don't care about failure and just want to produce as many of them as cheaply as possible, then go ahead and skimp on ESD. Just make sure you have a good system to deal with the failing products that will cost you less than the increased ESD defence.
It *is* a problem. (Score:2, Informative)
I've taken static electricity *very* seriously since...
Static Electricity information and control (Score:2, Informative)
http://www.esda.org/aboutesd.html [esda.org]
This page has information on what causes ESD, ESD testing, and how to control esd in places like your work.
If the machine is automated, I wouldn't think it would be a problem, as long as those pesky charged humans don't touch anything.
If the machine is automated, they most likely have ESD precautions built in, such as discharging any belts that move components, etc...
The real questin you have to ask is if it is worth it. If you have a circuit that you made for $10, and it get's inspected by a human...how do you know that in the process of being inspected the person didn't kill it... not only will the customer not be happy about recieving a dead product, which will hurt you buisness, but that's $10 dollars down the drain... So it has a lot to do with product reliability and cost saving.
I personally don't think that you need all of the things you mentioned...
If your sitting at a little solder station or where many components are going through your hands, then I would deffenitely wear a wrist strap...it will pay for itself even after one kill (assuming about $10)...
As for the flooring, in order for that to work, you would need conductive shoes, so they go hand in hand...but I think that's overdoing it by quite a bit. As for the humidity, if your in a place that has very very low humidity, then you would need some kind of control because you, and many things around you, will accumulate a charge very quickly...and, I would assume that it would be a lot cheaper than buying all the flooring and shoes, because, in your situation, you wouldn't need both.
Re:Real-world ESD precautions (Score:3, Informative)
Some examples I remember (Score:2, Informative)
Static Voltages:
Spark big enough to just be seen with the lights out: 1000V
Spark big enough to be seen, heard, but not felt: 2000V
Spark big enough to be felt as well as seen and heard: 3000V+
Average static charge generated by simply losing contact with ground, standing still, not moving etc... ~500V
Average static charge created when you move only 2 to 3 feet after losing contact with ground: ~1000V
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In the 1960s when solid state devices were first taking off, and ESD became a serious issue, many companies that made chips started doing post-mortems on blown chips to see what went wrong. The failures of more than 90% of all the chips that they got back were due to ESD, even though most were not immediate catastrophic failures, but shortened life problems. The pictures we had in the AF that we had gotten from contractors were simply amazing. The looked like aireal (sp?) photos of WWII bombing runs on bridges and such. Huge craters that had blown out 95% or so of a run, and the last bit of the run inside the chip finally died from heat.
The secret to ESD protection is the EXACT SAME ONE as the one for making a secure computer. The Process and the training in that process. Nothing else will work.
From a Former ESD Product Engineer (Score:2, Informative)
Static electricity is odd in the fact that it isn't generated like "normal" electricity. Typically, at least one insulator, or something with a very high (100 Megaohm or more) resistance, is required to generate a static charge. A person walking across the room can, in moderately dry climates, raise the body's electrostatic potential to several tens of thousands of volts very easily; in Arizona I've charged myself up to 90,000 or so volts walking across the carpet to change CD playing in my stereo. Charges like these are the types that typically kill a device.
By far, the worst type of damage is the "walking wounded" scenario. Walking around on a tile or concrete floor with cotton cotton pants can raise the static voltage 30 to 100 volts, depending on humidity and the conductivity of the floor; concrete conducts much better than most tiles because of the water content. When you think about the super-small dimensions of a typical transistor gate in electonic devices, it's not hard to picture the damage done. In 1992, we were seeing damage caused by 20 or so volts of static. It takes something like 1800 volts to bridge an air gap of an inch. The damage caused to semiconductors occurs at much smaller potentials.
Static electricity kills devices by actually blowing portions of the semiconductor away when an arc occurs. I can see some kind of protection circuit on a piece of silicon working once, but how long does it take to totally destroy the device? The most effective way to protect from static is by grounding the device and dissipating static charge from handling via a resistive coupling to the earth to prevent the fatal arcs.
I don't think you're going to see huge increases in yields from static dissipation devices, but if you keep one or two customers because a wrist-strap or mat prevented the degradation of a chip, it sounds like a win to me.