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Hardware

How Serious is Static Electricity? 95

Posted by Cliff
from the no-myths-just-the-facts dept.
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?"
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How Serious is Static Electricity?

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  • by tchuladdiass (174342) on Friday August 30, 2002 @02:32PM (#4171743) Homepage
    They started using the shoe straps, and the defect and return rates went down more than enough to make it worth it.


    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.

  • by b_pretender (105284) on Friday August 30, 2002 @02:32PM (#4171745)
    It's easy...

    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.

    • 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

      If *I* was dealing with things that couldn't be damaged, I wouldn't worry at all about ESD, since it sounds like security for something that's just not gonna happen anyway.

      (note: I know what the poster meant, I'm just one of those people who likes to nitpick about the language. If you don't like people to do this, maybe Slashdot isn't the site for you)

    • In order to do a benefit/loss analysis you have to have some quantitative estimate of how likely static electricity damage is.

      I believe that is what the poster was really looking for.
  • Granted, Silicon Valley is a fairly humid area...

    Which Silicon Valley are you talking about? Unless you're incredibly close to the water, you're in the desert.
    • Silicon Valley is a subset of the Bay Area; basically a small strip that surrounds a lot of water (the Bay). Now, we aren't as humid as the east coast (by far), but we still get a lot of moisture in the air (just look at the hills by highway 280; the fog flows over them almost every night during summer). It isn't Mojave, by a long shot.

      • Silicon Valley is a subset of the Bay Area; basically a small strip that surrounds a lot of water (the Bay).

        When I was working in Silicon Valley, I found the working conditions to be very dry indeed, and the lab I worked in needed static control to minimize damage from ESD.

        The air outside may have had a lot of humidity, but the air-conditioned inside air was very, very dry because the place refused to put in humidification equipment to compensate for the dehumidification effect of the A/C. Something about needing to service it too often because of salt buildup, as I recall, and at worst the "problem" caused by airborne particulates. It doesn't have to be the SF Bay area to be true; you can be in Louisiana or Florida and still have ESD problems in your factories and labs and offices.

        It is Mojave when you look at humidity levels. Or worse.

      • Silicon Valley is not humid. Yes, you will see fog up on 280 or over the hill on 17 (once you get up into the Santa Cruz mountains), but those places are not really Silicon Valley. Silicon Valley can basically be bound as Santa Clara County, which only leaves a few areas (as mentioned above) where you get any humidity. However, all the tech companies aren't there. They are in places like San Jose and Santa Clara where it's incredibly dry.
    • Having grown up in San Diego I can attest to the possibility of high humidity and minimal rainfall, which is the definition of desert.

      Less than about 10 inches of rain per year qualifies for desert, which makes most of the San Diego coastline (and more) desert climate. This has nothing to do with the day-to-day humidity, though. Some nights you can barely see the lane markings due to the fog.
  • by macdaddy357 (582412) <macdaddy357@hotmail.com> on Friday August 30, 2002 @02:36PM (#4171792)
    ESD is a very real problem. Don't trust a conveyor belt salesman who says it is not. He will say anything to get the product sold. If that conveyor belt is made of something non-conductive, plastic bins placed on it will generate static. Soles of shoes, if not grounded with a heelstrap geneate static. Once at work, My heelstrap had slipped off. I found this out when I touched my workbench, and got a nasty shock. If I had touched any electronics, they would have been toast! Fortunately, I did not have a system on the bench at that time.
    • by ivan256 (17499)
      If I had touched any electronics, they would have been toast!

      I understand that you are trying to make a point, but you should be honest. If you had touched electronics, they may have been toast.

      I know many people who think that ESD is not a problem, and they think that because "i've shocked equipment before, and it still worked later" or something like that. It is quite possible to shock equipment and do no damage. It's the times that you do cause damage that count.
      • by Anonymous Coward

        But it's unlikely that the shock did absolutely no damage. Shocks don't necessarily destroy electronics completely. But severely reduced lifetime and sporadic malfunctions are not desirable either. On the contrary, these are hard to detect and therefore even more problematic.

        Everybody who thinks "I'm always touching the circuit board of my PCI cards when I install them and I'm never grounded" should think again: The traces on the board are covered by a protective coat. In assembly, raw and unprotected electronic devices are much more at risk of being negatively impacted by electric shock.

      • Sometimes the damage doesn't show up right away. ESD damage frequently causes the difficult to diagnose intermittent failures that give repair technicians, and end users fits. If the guy telling you ESD is not a problem is working on commission, and selling something that could cause ESD, Don't believe him.
      • Its possible that you do no damage that has any noticable effects NOW. Its very likely that there is unperceptable damage, this can cause failures in the future. You can damage sensitive components even if you DON'T touch them if the static field comes into contact with them.

        Anti-static precautions are something you should take very seriously.

        Alex
    • Don't trust a conveyor belt salesman who says it is not. He will say anything to get the product sold. If that conveyor belt is made of something non-conductive, plastic bins placed on it will generate static

      Where did you get all this about conveyor belts? An SMT line includes no belts of the kind you're describing. The only thing vaguely like it would be the steel conveyer used inside the oven (it's sort of like chain-link fencing).
  • by Incongruity (70416) on Friday August 30, 2002 @02:37PM (#4171799)
    I've handled tons of electronics over the years and have never been able to attribute a single failure to ESD damage.

    Just a note here... unless you can actually explain, with 100% certainty (or something close to it) the causes of all the other hardware failures, then you can't say for certain that any of the failures that you have observed are due to damage done from ESD. Just because a failing component doesn't sit up and shout "you shocked me with static three months ago and now I'm on my death bed" doesn't mean that a damaging static discharge didn't occur.

    Additionally, note that what might be explained at a higher level as the failing of a certain component doesn't mean that the root cause wasn't a static discharge. Moreover, what if there was a ESD that you didn't notice. Just because you don't see a spark or feel one, it doesn't mean that there wasn't an ESD.

    just some thoughts... -tcp

    • At the place I'm at we're required to wear footstraps. But I've never seen it go wrong directly...

      OTOH about 10 years ago I got through 3 'super IO cards' (ISA IDE+RS232+parallel) in one night while repairing a mates PC, after installing them, they always worked first off then failed. If it wasn't static, I'm a banana.
    • well, not for nothing, but you also can't say that the failure was not due to elves or car key gnomes.
      • well, not for nothing, but you also can't say that the failure was not due to elves or car key gnomes.

        Somebody mod parent up please - this was EXACTLY the point of my post, and this is the only reader to get it. The reason I sent this question to askslashdot was because I figured there must be at least ONE person out there who has some scientific evidence wrt ESD. Notice that every singele +5 in this story contains NO real evidence - just anecdotal reports of lower defect rates and lots of vague warnings about "latent effects". The only papers I could find on Google were written by guys who sell static control products.
  • Are you serious? (Score:4, Insightful)

    by twoflower (24166) on Friday August 30, 2002 @02:38PM (#4171821)
    Are you serious? ESD is an extremely serious threat. You can't possibly think of setting up a commercial assembly line for electronics and not worry about things like anti-static wriststraps. Serious places install expensive conductive flooring just to mitigate the buildup from walking around.

    Why are you asking Slashdot about this? Ask people who know about this.
    • Are you serious? ESD is an extremely serious threat. You can't possibly think of setting up a commercial assembly line for electronics and not worry about things like anti-static wriststraps. Serious places install expensive conductive flooring just to mitigate the buildup from walking around.

      Useful advice.

      Why are you asking Slashdot about this? Ask people who know about this.

      But why did you throw this gratuitous barb in at the end? Of the 11 comments rated 3 or above, more than half give the same advice: ESD is very real and failures won't be immediate.

      So what's your gripe with Slashdot?

  • by BobMcD (601576)
    If you use surge supressors for your modem lines, the you're probably the type to use ESD protection. Electricity is an unpredictable sort of thing, but you can be sure that if you don't use protection you'll eventually get burned (as is true with most of life). Now, what are the odds? And is it worth it? For the record, my DSL modem doesn't have a surge supressor on it, but all of my analogue modems always have - isn't that weird...
    • Surge supressors are usually more useful for the guarantee some of them come with than anything else. Lightning conductors to excellent grounds (e.g. a buried length of copper pipe attached to chunky wire) are the way to go, though even they won't help all that much for phone lines.
    • When I head off to work, and I know there will be a reasonable chance of thunderstorms and lightning, I just unplug all the computer surge suppressor power cords from the wall sockets, and unplug the modem line. I have four machines in one room, running off two surge suppressors. I usually only run two computers at once, sometimes only one. I know they give you an "insurance policy" against damage, but I'd rather not come home to anything like that. If I'm home, working on the computers, or asleep or otherwise indisposed, that's when a lightning strike nearby could affect my setup, so I do need the supressors. As for ESD, I ground my hands on the frame, powersupply, before removing components like cards, memory, HDD's. I appreciate the use of straps, etc. and have read some of the posts about their use in commercial enviroments, and will get one next time I'm in the store ;-)
      Using one can't hurt.
    • Electricity is an unpredictable sort of thing

      On the contrary, electricity is a totally predictable sort of thing. The problem comes when we overlook the most basic rule of electronics - it will follow the path of least resistance. Even though those paths may not be obvious at first and you might not notice them, be assured that electricity will.
  • Climate may be key. A co-worker who previously worked in Denver (pretty dry) in aerospace said they (actually he) fried lots of valuable equipment by forgetting some of the more onerous precautions like shoe straps.
  • The tinier the circuitry gets, as a rule, the more dangerous an unexpected jolt of static electricity will be to it. Granted, a lot more consumer hardware has dissipators built in nowadays, but ICs in particular are at risk and we're using a lot more of them.

  • Modern carpet has anti-static material already built in. It is actually difficult to find carpet without anti-static material now, I was told in a survey of carpet sellers. To have static, it is necessary to have something that generates it. Carpet was, in the past, the biggest generator.

    I think it is possible to develop a useful feel for this kind of thing. The issue is this, I think. If you don't have any condition in which you can make sparks jump from your fingers after vigorously trying, you are (probably) okay. To have static electricity, it is necessary that the air be dry. My understanding is that, above 40% humidity, there is no static buildup under normal conditions of generation. In Portland, Oregon, if I can slide across my car seat without generating static electricity, then I don't generate any in buildings with good carpet.

    Semiconductor devices usually have excellent input overload protection (diodes on the inputs and outputs). There is an issue of putting voltage directly into an internal device that might not be protected. However, if you pick up a board by its grounded metal flange, or by an exposed ground trace on the perimeter, there then can be no differential, and thus there can be no spark to internal devices, because the electrons in your body quickly bring the board to the same voltage.
    • Modern carpet has anti-static material already built in.
      Conductive flooring isn't anti-static; it's a method of draining and neutralizing the charge you're already carrying.
      I think it is possible to develop a useful feel for this kind of thing. The issue is this, I think. If you don't have any condition in which you can make sparks jump from your fingers after vigorously trying, you are (probably) okay.
      You think wrong. A discharge of a few dozen volts is enough to damage a modern CPU or memory chip, and you'll never notice that type of discharge with your senses. If you can see or hear a spark when you touch something grounded, you were carrying a charge in the thousands of volts.
      • The guy who wrote the original story is correct. After handling "tons" of electronic gear, he has found no problem.

        People who handle electronics a lot develop the habit of contacting the ground or case first, anyway. The resistance of your skin lowers the current of any low voltage discharge. Considerable energy is needed to damage semiconductors, and it is just not there in mildly humid environments.

        The equipment manufacturer mentioned in the story was not lying.
  • by muonzoo (106581) on Friday August 30, 2002 @02:59PM (#4172030) Homepage
    I worked for many years as a contractor at a large US-based defense company [raytheon.com]. They make lots of neat useful things [raytheonaircraft.com], and some nasty things [raytheon.com].
    One thing was always stressed, in the hardware departments, in the software departments, in the finance departments, wherever. If you go into a lab, you must have ESD training. At least 3 levels of training existed. Level 1 was little more than awareness training. If something had an ESD warning label, stay clear of it. Don't touch. Etc. Why? The training also emphasized the costs associated with ESD damage to components. A great deal of effort was spent making sure that we all understood that ESD damage to components might not be visible or even detectable at test / QA time, HOWEVER, in the field, the defect rate over time was dramatically lower when ESD controls were in place on the assembly and test / QA lines. This was serious stuff, the examples ranged from deployed PCs going inop after years of reliable service up to air-to-air missiles not functioning due to static damage. In the end, a very large sum of money was spent investigating the effects of ESD on the reliability of components in the field and it was determined that the benefits far out paced the costs of training everyone and taking precautions in the labs.

    I now work somewhere much smaller and have a really hard time getting people to believe that ESD is real. I even had to fight a bit to ESD mats at the workstations where we do assembly.

    There are a lot of myths and misperceptions surrounding ESD incidents, and I think that people would be well served by understanding that damange to electronic devices is not either fatal or non-fatal. A FET device might have it's gate region severely weakened by an ESD incident, but it would appear to function normally for an extended period of time. Perhaps the thermal efficiency has been compromised because the gate has partially broken down. The added thermal stress on the part over time will lead to early failure. The reason, naively, would look like a bum part or a thermal problem. The ESD problems don't always reach out and slap you across the face with a sign that says: "Zapped by poor assembly / handling techniques".
    • I'd like to second this opinion. When I worked as a co-op student at a semiconductor manufacturing facility, I wrote computer-based-training software to educate employees about ESD. I got to work with the engineers who were ESD specialists.

      One of the major points that the training we developed emphasized is latent failures. Sure, sometimes you had a major discharge that fried something on the spot. However, the much more serious problem was that a smaller discharge would damage and weaken a part of a circuit. The chip would pass probe and final test, but fail later in the field. Of course, this cost the company much more than a failure caught before the chip shipped.

      The bottom line is that the cost of employee education, grounded workstations, heel/toe straps, wrist straps and proper handling equipment was much less than replacing failing parts in the field.

  • Some data sheets give information on the static sensitivity of some or all of the contacts on a part. So you can either have an engineer spend days reviewing all of the data sheets for all the parts you use and plan to use in the future, or you can buy a humidifier. The humidifier will cost less.

  • by Kowh (61371) on Friday August 30, 2002 @03:07PM (#4172112) Homepage Journal
    Just because you can't immediately establish a cause and effect with ESD, doesn't mean it's not causing damage. ESD can happen without you even noticing and it's especially hard to detect if it doesn't cause a failure outright. I.e. if a discharge doesn't outright kill a product, it can still do damage that increases the likelyhood of failure further on in the life of the product, or even worse, variability. Far worse than a product that you know doesn't work, is one that appears to work but produces wrong or variable output. Combined with the sheer number of products that have the potential to be damaged, increasing your ESD defence will likely give a decent increase your product's overall reliability.

    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.
  • by WolfWithoutAClause (162946) on Friday August 30, 2002 @03:10PM (#4172134) Homepage
    You have to make sure that all things that touch are at the same potential before they touch.

    This means, in practice, that there must be a conductive, resistive path between them prior to this happening.

    This is easiest to achieve if you just connect everything together, the wrist straps, the conductive shoes, the whole 9 yards.

    For example of what can happen. I have a component in my hand- but that's fine, I have my strap on, and the component is at the same voltage as me. I take off my strap with the component in my hand, and walk across the floor and touch someone on the shoulder with my other hand.

    Zap! That component is now toast! The problem is that myself and the component built up a few thousand volts when I walked across the floor, and the person I touched instantly discharged me, and a large current came out of the component too... 90% of such components work for a while before failing.

    You don't have to have all of these gadgets, but if you don't; you have to move very deliberately, and even then you can screw up sometimes.


    • The problem is that myself and the component built up a few thousand volts when I walked across the floor, and the person I touched instantly discharged me, and a large current came out of the component too...

      It's actually not a large current, just a large voltage. Static electricity discharge currents are on the order of microAmps. That's why it's called "static" electricity, almost no current. The voltages can be in the kiloVolts, though.

      Milalwi
  • Ask Benjamin Franklin, inventor of the static strap.
  • I'm not positive what electrical field strength is required to cause disassociation of silicon dioxide but ESD can result from a discharge of as little as 10 volts. Most people can't even feel a static discharge unless it has about 2500 volts behind it, so IMHO straps, mats, etc. are one of those Really Good Thing(TM)s.

    Just my US$0.02
  • by shaka999 (335100)
    Most people don't see issue when working with electronics because of built in ESD protection. I'm an IO designer and we go to extreme lengths to make add ESD protection to our devices. That said, this isn't that exact of a science.

    If your setting up a production line that will move a lot of material it only makes sense to take precautions.
  • It *is* a problem. (Score:2, Informative)

    by Atzanteol (99067)
    I once had a pair of wool slippers (great for cold winters). I walked accross my rug, and went to touch my mouse. I got a shock that went *through* the plastic and killed the serial port (mouse was fine).

    I've taken static electricity *very* seriously since...
  • by cybermace5 (446439) <g.ryan@macetech.com> on Friday August 30, 2002 @04:03PM (#4172579) Homepage Journal
    I recently toured at a major manufacturer of airbag controls...definitely a very critical and defect sensitive operation. Approximately 3 million parts are placed every day at this facility.

    The floors have conductive particles embedded in them, all employees are required to wear either two ESD sole straps or take advantage of the conductive-sole shoe discount program. In addition, all employees venturing onto the production floor are required to wear an ESD smock. All handling equipment is grounded, conductive rubber used for conveyors, and many transport mechanisms are wire brush rollers. The environment is rigidly temperature and humidity controlled.

    It's easy to develop huge static potentials when you have equipment running for a long time. Look at devices intended to generate high voltage static electricity: Wimshurst generators, Van de Graaf generators, etc work with simple components such as a rubber belt or rotating disk. Even dropping components can generate electricity; one high voltage generator works by dripping water from two tin cans.

    Since the effects of static electricity may not show up until later, when the operating limits of a gate or two are much lower than necessary, it makes no sense to manufacture any electronic devices without rudimentary ESD protection.
    • Can you give reading or examples/urls of that generator that uses dripping water? I would like to play with that.
    • I used to work for Toshiba America Medical Systems, which makes things like MRIs, CT scanners, PET scanners, and other such fun and highly-sensitive stuff that cost anywhere from a couple hundred thousand dollars to over a million. Though I was a simple desktop support monkey at the time, I occasionally had to step into the QA department to fix their computers. Before doing so, we had to ground ourselves and put on an ESD smock. Mind you, I never went closer than maybe five or six meters to any non-desktop-computer equipment, but the simple fear that I could transfer something was enough reason to enforce the rules rigidly. Of course, *I* thought it was cool, though my older colleagues thought otherwise.

      Possible failures here carry an extra problem, similar to the problems mentioned by another poster and his references to Raytheon's Missile Systems division. In my case, if something in the scanner didn't work quite right, it could potentially cause a misdiagnosis, and in the Raytheon case, if that's the last missile the pilot has in a dogfight and it doesn't explode when it's supposed to, he could be toast.

      ESD failures for most people are a nuisance. For others, they can be downright deadly.
  • Static protection is too cheap to not take seriously. Wrist straps are dirt cheap. Humidifiers are cheap, (and you need some other enviormental controls anyway) so are smocks, shoes, and the other protections.

    Sure it all costs money, but compare protection with the cost of repairs. As a good engineer it won't take more than a few hours to find and repair something. Oh, at $75/hour (remember benifits), and you are taking those hours away from time I could be working on something new to make money. Sure tech can be trained, but only after engineers know the common problems to look for. Better to have so few problems that you never

    Don't forget that customers remember products that fail before they are obsolete. For just a little protection you can make sure that poor quality doesn't drive them away.

    Last, I have personally destroied electrions with static. I was known (when it happened) as one of the more careful persons in the office, yet I still managed to destroy things with static. It only takes one moment of in a hurry to cost a lot of money.

  • Some devices (microwave RF transistors) tend to be more sensitive than others. (Atmel AVR microcontrollers, generally regarded as nearly invincible.)

    It's probably not critical for a small-scale development lab.

    As soon as you're manufacturing, that's a different story. Note the one guy that worked for VisionTek and said their return rates plummeted after they implemented strict ESD procedures.

    In addition, if you're a large supplier to another company, they may audit your quality control processes. (There are a number of ISO quality control certifications that are pretty much required to be on the supplier's list for many companies.) If you don't have ESD control in your manufacturing facility, you're NOT going to pass the audit.
  • Not that serious, if you buy it a beer and take a little time to see the world from its perspective. It'll lighten up considerably.

  • Silicon Valley is a fairly humid area so that may be a contributing factor.

    Is this a joke? I just moved here from the NYC area. This place is dry as a bone. You obviously don't know real humidity.

    Secondly, I just had a floppy drive die from ESD the other night. I guess thats what I get for not having it (or I) properly grounded. Oh well. It was old.

    • Is this a joke? I just moved here from the NYC area. This place is dry as a bone. You obviously don't know real humidity.

      NYC is dry as a bone compared to New Orleans, so what's your point? Drive down to Phoenix if you want to see a dry place. Silicon Valley is "fairly humid" - it's all relative.
  • A great place for info is at the ESD Association's website. More specifically, there page about ESD
    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.
  • by Ashurbanipal (578639) on Friday August 30, 2002 @05:30PM (#4173246)
    I fried a dozen uVAX 3100e motherboards (back when they were cutting edge and majorly expensive) with static electricity. We had a maintenance contract with DEC, and they kept coming out to replace 'em.

    We tried conductive floor materials, jumpering all the machines in the room together, stringing tinsel across all the paper trays, etc. etc. etc. ad nauseum but we kept frying motherboards every time a jumper wire slipped off or a floor mat got insulated by shoe crud.

    Eventually I put a bunch of spider plants in the room and watered them every day. Humidity in the room went up to a reasonable level immediately from aspiration of water through the plant leaves.

    Never burnt a single board after that. The plants were still on the job five years later when I visited the site again.

  • Everybody is pretty much right around here if it's a manufacturing line you should do it because it costs almost nothing and the payoff can be significant. But if you're just making research components in small batches that will be used for 10 days and disgarded then go with the tech's idea of ESD. If she thinks she's more productive without the wrist strap she'll buy a couple extra components and hopefully save you multiples of that in her labor costs.

    But I bet if she's working with CMOS chips or anything without well protected IO pins she'll probably want all the static protection she can get. If she's making passive filters with surface mount components, why bother? (resistors, caps & inductors aren't likely to be damaged.)
  • by austad (22163)
    I've handled tons of computer parts without taking static precautions, and nothing has ever been damaged by it. However, if you're really worried, putting a little Downy and some water in a spray bottle and spraying down the floor and work area will make the area meet some ISO standard (forget which one). I read an article on it awhile back, however I can't seem to find it now.
    • No, you only THINK nothing has ever been damaged by it. Over 95% of all ESD damage results in either latent failure or reduced performance (can't handle high clock rates, can't handle heat, can't handle RFI.) NOT total failure.

      You've damaged plenty, and so has almost everyone else who thinks that way. You just thought that hard drive or Mobo that died after a couple years wore out, when the real problem was you shortened it's life.
  • Static electricity is perhaps the most jovial and funloving of all forms of electromagnetic energy.

    For instance, lightning tends to be very pissy, like it woke up on the wrong side of the bed. And it's like this all the time, I think it needs medication.

    And AC house current is always in a hurry, rushing this way and that, up to 60 times a second, a real workaholic.

    But static electricity, you can always count on too liven things up, without going all apeshit. You'll be trying to scratch your ass, or touch your girlfriend's tit, and all the sudden it jumps out... and it always gets a "Eeep!" out of you or her. I wish I had half the sense of humor and comedic timing that it has...
  • by Sxooter (29722)
    I used to do ESD training in the USAF a long time ago, and here are some examples I remember:

    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

    - - - - - - - -

    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.
  • I thought I'd chime in on this since I used to do technical work for a company specializing in ESD control equipment. I worked some time on the production line doing actual assembly of products and the rest of my time was spent either troubleshooting returned equipment or helping to design new stuff. It was a fairly small company so most people did double duty this way.

    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.

  • If you want to grow and deal with the big boys, use ESD protection. If the Cisco's and Lucent's come down and see you don't have any, it's unlikely they'll want to do business with you.

    The reason is simple, ESD damage is REAL. The effects often manifest themselves in subtle ways in which damage is not totally obvious.

    For example, one potential problem is a shift in the Vt threshold values of the transistors on the I/O pads of CMOS logic devices. It may still work, but perhaps slower or out of spec. And sometimes the conditions get worse in the field, so that even if it works now, it may not work in 1 year time.

    Lastly, YOU may not generate much ESD, but you hire some guy, he wears different shoes, has sweaty or dry feet or whatever, and he zaps a lot of chips.
    (Don't laugh, this has happened to us. One guy, we don't know why, kept zapping chips. I suggested he change shoes, and the problem went away. But you need to avoid the problem in the first place with proper ESD protection).

    But, as someone pointed out, if you're making $10 disposable devices, then who cares...
  • Consider the following solutions when you want to find out if static discharge is a concern:

    1) Install plush polyester carpeting. Instruct employees to wear wool socks (no shoes). Your employees will appreciate this on those long, cold winter nights.

    2) Make sure all screwdrivers are magnetized. This makes assembly SO much easier.

    3) Remove all ground wires/straps/conductors. You don't want zaps coming in the back way!

    4) Install dehumidifiers to reduce condensation and corrosion on sensitive parts.

    5) Wrist straps just get in the way and disgruntle your employees.

    6) Pack electronics in styrofoam peanuts (make sure the peanuts are BLOWN thru a plastic hose into the box). Save the planet by not using anti-static bags. (er, um, styrofoam doesn't harm the planet, that's right)

    I recall when we first got wall-to-wall carpet in our house, we'd wear wool socks and scuffle along then go and touch something grounded, just to see how big an arc we could get. I think maybe 1/4 inch (1/2cm) was the best we got.
  • The SMT equipment vendor says that it's unnecessary, and I would tend to agree.

    Do you really expect the vendor to tell you to do something that will reduce the amount of product that you purchase?

    That's like a lightbulb manufacturer including a pamphlet within each box of lightbulbs explaining that you can make incandescent lightbulbs last a lot longer if you slowly dim them on and off rather than flipping the switch to instant full voltage.
  • In my experience, static shock accounts for a large portion of buggy parts and buggy computers. The real danger with ESD and electronic components is that the damage can take a long time to escalate to a noticeable level. Even though the computer runs fine for the 24/48 hour burn-in, the customer finds it begins behaving extremely erratically a few months later. ESD damage is probably on par with defective part percentages if not greater. Let's face it folks, nanometer scale parts are going to be sensitive no matter how good the manufacturing technique is.

  • Not working on a commercial production line, the only time I need to worry about ESD is when I'm fiddling with my (or my family's) PC. Or occasionally my PC at work.

    So, just make sure you leave the PC plugged in but switched off at the socket, leaving it earthed, and touch the bare metal of the inside frame before messing with any of the cards. (That includes the cards you're about to get out of their protective bags, as well as the ones already in the PC). Be sure to touch the frame regularly while working, just in case of ES build up, and you should be fine.

    K.
  • try to find anyone. ESD may mean death there. i know for at least one example at the local fireworks factory ...
  • If you don't know the answer to the question you're asking, you shouldn't be setting up an SMD assembly line. Clearly, you don't have somebody who's really familar with SMD board manufacturing, which is a reasonably complex process.

    It's also one you can easily outsource in Silicon Valley. Things are slow right now, and there's lots of capacity. Call up somebody like Solectron or Flextronics and find out what they'd charge you to do the job. If your job is too small for them, they'll probably recommend a small shop.

    As for static issues, you can get simple instruments that detect static charges in your work environment, and beep at you. I had one on my bench when I was building prototype boards. Even components that have protection circuitry are vulnerable until mounted to something with a ground.

    Biggest single item: maintain humidity between 40% and 60% at all times.

    • If you don't know the answer to the question you're asking, you shouldn't be setting up an SMD assembly line. Clearly, you don't have somebody who's really familar with SMD board manufacturing, which is a reasonably complex process.

      I'm not afraid to learn. I suppose you only ask questions to which you already know the answer?

      It's also one you can easily outsource in Silicon Valley. Things are slow right now, and there's lots of capacity. Call up somebody like Solectron or Flextronics and find out what they'd charge you to do the job. If your job is too small for them, they'll probably recommend a small shop.

      We're already using a contract manufacturer, but we're looking to shorten lead times and reduce production cost and invetory float. Managing a relationship with any kind of manufacturer is not a trivial task - when your cost of goods is substantial and you need to grow, long production lead times are a big problem.

      Anyway, thanks for the advice on equipment, but you really haven't shed any new light on the question I was asking.
  • I workd for a companyy in hte UK which, you may have gathered, is pretty humid. We have anti-static wriststraps etc., but they get pretty well ignored, and we don't lose much kit to inexplicable (i.e. might be ESD) failures. But sometimes we take kit to exhibitions in Las Vegas which, as you might also have gathered, is pretty non-humid. And if we don't do it just right there, equipment dies by the rackful (particulalry before they close the big doors and turn on the aircon). And for one product I worked on, one customer in Phoenix, AZ, has almost as many failures as the whole of the rest of the world untils somebody clicked and installed the full gamut of ESD precautions.

    So, it depends where you are.

    But, as been sais, ESD precaustionsa re cheap, and kit is expensive. And, I have beeen told by our in-house ESD/RFI expert, a lot of ESD failures don't show up in instant faulures but in shortened lives - so a board will die after six months rather than five years. Doesn't sound to me like a good risk to take.
  • At my old high school, ESD prevention practices for PCs didn't even exist - the tech generally didn't even bother with a wriststrap. For what it's worth, the hardware failure rate at that school was horrible - a lot of teachers would begin complaining of system instability within months of getting a comp. Don't know if this is entirely to do with ESD, though - most of these systems were donations, and the teachers would install all kinds of junk on them.

    One example I've seen firsthand of ESD - my dad was poking around the inside of the family PC because he wanted to see what it looked like, and he didn't bother with a wriststrap. He touched the video card, and it immediately ceased to function. When he turned the computer back on, we got the "bad video card" beep code. Of course, this was a Virge chipset card, but that can't explain away an immediate failure like that.
  • Saying "I've handled thousands of (whatevers) and never noticed any damage" is not a very good use of anecdotal evidence because, as many people have pointed out, sometimes you can cause latent damage.

    I personally have a lot of anecdotal evidence FOR immediate damage, which leads me to be quite concerned with ESD whenever I open something up, and even when I don't (as I'll explain).

    I learned ESD precautions when going through basic training to be a certified level 1 Apple repair tech, many years ago. They had a cute little video.

    Since then, I've frequently NOT used precautions, and damaged a lot of devices, many times with immediate results: video cards, which suddenly have bad pixels... ROM chips, which suddenly won't boot the device... memory chips... ADB ports... etc.

    In Ohio/Michigan it is very, very dry indoors (and out) during certain winter months. The humidity makes an ENORMOUS difference in the chances that you will fry a device. It gets so dry you can get a painful shock just touching your PowerBook.

    A lot of Palm devices have found out the hard way that when their Palm device is connected to their PC, for desktop synchronization, and they are all charged up, and touch the Palm device first... blam. That serial port does not necessarily make a very good safe path for ESD. I've blown out some serial ports and Palm devices that way. The Newton is also susceptible.

    In short, if it is not uncomfortably humid where you are, it's dry enough to want to take ESD precautions. Use that wrist strap, or at the very least, make sure you take a moment to touch a properly grounded object frequently as you work. Be especially careful if you walk away from a disassembled machine and then come BACK. Don't touch anything else until you've made certain you are properly discharged.

    Paul R. Potts
  • If ESD wasn't a critical issue with CMOS devices, the US DOD wouldn't insist so strongly on the use of ESD protection. In working on projects for the space program (International Space Station emergency lighting systems and ethernet hubs/gateways), I found that if the DCMA (Defense Contracts Management Agency) found that a unit had been handled at all without proper controls, they would refuse to purchase it. You can eat 3 million bucks if you're complacent about ESD with the US Federal Government. I recommend you take it seriously because it's cheap to implement, and adds a bit more reliability to your products. Most times you don't see an immediate failure, but even low voltage surface mount capacitors can get thin spots in the dielectric if you zap them. Transistors in ICs or discretes can get dimples in the gate oxides. This will change the interelectrode capacitance, and lead to premature failure or degredation of high-speed performance.
  • In my EECE courses, the intro in fact EECE 241, spent a great deal of time talking about this very thing. IIRC, they told us that all it takes to damages eletronics is +5v, well below what we can actually feel. They showed a video that demonstrated this. A guy wearing a simple blue color button down and tie stood in place. His static electricity was measured. His tie was then raised to his shoulder and dropped against his shirt, sliding down to the middle again. This tiny bit of movement created a large amount of static electricity, more than enough to damage parts. ESD damage can't always be seen right away. In fact only the most servere cases cause instant death to electronics. The damage is usually very slight. It's why RAM sometimes dies after 4-5 years or that nic that has been moved from machine to machine over and over again just died. Take ESP seriously. Good luck

    PS, taking the Intro to Computer Engineering course at you local Unv might prove useful.

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