Maplin, CMOS & static - Page 1
Forum section: electronics / general

author: grumpydoc
author_rank: Super Contributor
timestamp: October 26, 2012, 07:36:46 am
content: I'm not generally a big fan of Maplin - it's overpriced especially for components, frequently short on quality and has a very restricted choice of stock as well so it's quite rare for them to carry the item I want.But....the local shop is less than 10 minutes drive away so it does sometimes get used for one offs when I can't wait until the Farnell list is long enough to place an order.So, last night I wanted a couple of CMOS chips - a 4021 and a 4094 - and they happened to a) have them in stock and b) at not too bad a price so I went over.So the guy picked the two chips out of a plastic tray and popped them into a plastic zip-lock bag. No anti-static precautions or protection.I said "no thanks"Did I overreact?

author: Rerouter
author_rank: Super Contributor
timestamp: October 26, 2012, 07:42:14 am
content: possibly, i myself have never fried a 4000 series chip with esd, and my parts bin is an prime example of how little i worry about them,but equally if i know something is critical, i have a little circuit to test the truth tables of the various chips, and would probably throw them in it before i stuck them in my circuit,

author: AndyC_772
author_rank: Super Contributor
timestamp: October 26, 2012, 07:42:43 am
content: Depends what you wanted them for. If you're throwing together a prototype that will only ever be used in a lab environment and doesn't need to last all that long, then they're probably fine. If you need a product to last, then you're quite right to reject any parts that haven't been handled correctly.

author: grumpydoc
author_rank: Super Contributor
timestamp: October 26, 2012, 08:55:22 am
content: QuoteI think I did once but it was more than 20 years ago when a) the shop I worked in really didn't take any precautions and b) possibly chips weren't as well protected.QuoteMy understanding has always been that while static can cause complete failure at the time it can also be the cause of premature failure down the line so proving that they work now might not be enough for future reliability.QuoteRepair of a 2022 signal generator so I would like them to last more than 20 minutes, especially as the digital side feeds into the various DACs that control the unit.

author: Fraser
author_rank: Super Contributor
timestamp: October 26, 2012, 01:42:34 pm
content: No you did not over react.I used to work in an electronics shop when I was a student in the 1980's. I would have been in serious trouble if I had handled CMOS in the manner you describe. All our chips were in ESD protective foam, ESD protective holders or wrapped in tin foil.I have often heard the comment that static damage is a myth and the quote "I have never damaged one" from fellow techies BUT have those people attended a Hewlett Packard ESD safety training course ? Having done so I can advise that many chips continue to function normally after an ESD event has hit them, but they are very likely to fall over at a later date or behave erratically due to the damage that has occurred. Many CMOS chips contain diode protection to help against ESD but don't rely upon it.I have seen microscope pictures of common CMOS and LSI wafers that have received an ESD hit from simple human static discharge....the wafer looks like the surface of the Moon at the point of contact ! Not pretty and definitely not good for the chips health.I would never claim to have followed all ESD protection measures at all times but I do not handle static sensitive chips or PCB's by the pins or connections. I use an ESD safety wrist strap whenever possible and ensure that I am grounded through its 1MR resistor. On expensive or important kit, why take the risk ?Take a look at the attached pictures or Google "ESD damage" to see some impressive damage !Also take a look here:http://electrostatics.net/library/articles/ESD_damage.htmMaplin's has become a mere shadow of its former self....I would not place any faith in its employees either. Its not right to generalise but all of the Maplin assistants that I have met were, quite frankly, unqualified to give advice on electronics. Now DISCO equipment or kids Toys they may know about.... but that is of no interest to me.Fraser

author: Zero999
author_rank: Super Contributor
timestamp: October 26, 2012, 03:31:09 pm
content: Wow Maplin really have gone downhill. I used to go there often and all the semiconductors were kept in anti-static packages so the shop worker didn't need to follow any ESD precautions.

author: Neilm
author_rank: Super Contributor
timestamp: October 26, 2012, 03:42:09 pm
content: Not the first time unfortunately. I watched an employee getting a PC motherboard out of the cabinet that they show them in. I guess that someone had placed an order for that part and it was the only one they had in stock. He just walked over to the cabinet, opened it grabbed the motherboard without even trying to just hold it by the edge then put it into the box.Neil

author: free_electron
author_rank: Super Contributor
timestamp: October 26, 2012, 04:28:20 pm
content: Quote from: Aurora on October 26, 2012, 01:42:34 pmwhich is a surefireway to really fry them ....first of all : it's not tin foil but aluminum foil... aluminium that oxidizes like the pest and becomes nonconductive.second : it is NOT the static voltage that damages chips. it is the CURRENT induced in a system by giving that voltage a chance to equalize...So , a hard 'short' conducts a way larger current than the foam which is in the 10 to 100 kiloohm per square range .it is perfectly safe to 'zap' a device across a foam bridge. it is NOt safe to disharge through metal. the peak current will fry the structure.hence : wrapping devices in aluminum foil gets them fried easier. wh : you hold device in your hand and are charged. as you approach the aluminum foil an equalisation current flows in to the low-ohms foil... poof goes the juntion. do the same approaching the foam. and no harm done as the foam is 100 kiloohm.... even with a 10 kilovolt charge on your body the balancing current is 100mA. no problemo.it get wors : people take styrofoam (isomo) wrap alumium foil aroud it and poke the chips in there...then move them around. the surface fo the hole oked by the pin oxidizes and loses contact with the pin. the pin rubs against the styorfoam which happily lets go of electrons en-masse.styrofoam is a very happy electron donor and produces static charges like the pest ... poof goes the junction...it's ESD foam and antistatic bags ( and even there yo need to know what to use and when to use.... )

author: ejeffrey
author_rank: Super Contributor
timestamp: October 26, 2012, 05:01:59 pm
content: Quote from: Neilm on October 26, 2012, 03:42:09 pmAssembled circuit boards are *much* less ESD sensitive than bare components. The bypass caps and the input protection diodes can really work effectively in that case. It is definitely desirable to handle them carefully, but it isn't in the same class as throwing 4000 series CMOS devices in a ziplock bag.

author: SeanB
author_rank: Super Contributor
timestamp: October 26, 2012, 05:56:25 pm
content: Biggest anti static bags I use are 1m by 1.2m, that are used to supply empty capsules in. Not used for the antistatic properties but for the metallised mylar layer used for environmental protection. I reuse them as a camping blanket, slip inside with a blanket on top inside a tent and you are not going to notice the cold.

author: Dago
author_rank: Frequent Contributor
timestamp: October 26, 2012, 06:50:25 pm
content: I personally think people are waaaayyyy too much paranoid about ESD. I've personally never worn an ESD strap or any other ESD protective equipment and never killed a single chip. Even my soldering iron is not grounded. I've personally never heard of anyone even killing anything FOR SURE due to ESD.I'm not saying ESD does not exist or is not a real threat but unless you live in a really dry environment and handle really sensitive stuff like microwave HEMTs I doubt you'll have a problem.

author: grumpydoc
author_rank: Super Contributor
timestamp: October 26, 2012, 06:52:10 pm
content: QuoteOh dearI must admit a lot of my old stock is like that.In my defence I put it there over 30 years ago in my teens and didn't know any better! I bought conductive foam to move them to, but haven't got around to it yet. It will be doubly interesting to see if any of it works.It's worrying that I can combine "over 30 years ago" and "in my teens" like that thoughQuoteThat's one of the things that struck me as odd. The guy that served me did say that they hadn't been given instructions that they needed special handling but if they'd simply been delivered to the store in conductive foam then as long as the staff didn't actuallyremovethem it would have been OK. So it seems to be a central failing. Previously things I've bought have been in foam, as I'd expect.QuoteThere was a definite point where they seemed to massively expand the number of stores and start stocking more cheap gadgets and toys which I think corresponded with the decline.

author: Fraser
author_rank: Super Contributor
timestamp: October 26, 2012, 07:19:41 pm
content: Well I have learnt somethong today from this thread (apart from the British term 'Tin Foil' is wrong as it is, of course, aluminium !).I had never before heard that the use of aluminium foil was poor ESD practice. The shop I worked in actually received much of its stock either wrapped in foil or, as you state, pressed into foil covered polystyreneThat was the early to mid 1980's though, so maybe correct handling in the retail market was not common then ? I always use the correct conductive foam these days.As a side note......the very early FET transistors that I have seen and used in older equipment could be destroyed by the slightest ESD event and would even be destroyed by soldering iron tip leakage (much like 'Hot' pHEMTS that I use in microwave converters). I know...I killed a few in my time ! They were so fragile that the manufacturer placed a spring wire around the three legs of the transistor with a loop at one end for removal. Once installed in the PCB the tech had to remember to pull the wire band off of the transistor... failure to do so could result in 'issues'Thanks for adding to my ESD knowledge.Fraser

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: October 27, 2012, 05:02:45 am
content: To the original poster GrumpyDoc - I see you are in Blighty, I guess Maplins gave it away. I also know you have had a rainy summer, with olympics and all that rot, plus we are in October which should be as wet as it is here (Vancouver Island). I moved from the Canadian prairies where winter indoor RH would be down around 15 to 17 % in january - feb. the result of extreme cold air outside (which can hold almost no water) being heated. I no longer get static shocks or nose bleeds for that matter, ambient RH really makes a difference.So I am trying to say maybe you did overreact. I still use a grounded anti-static mat and wrist strap (with bleed resisters) here on the wet coast but I am even less strict than I was when it was dry - which was not very strict. I have never lost anything to static.

author: grumpydoc
author_rank: Super Contributor
timestamp: October 27, 2012, 08:12:04 am
content: Having read Aurora's and f_e's posts I don't think I did overreact. I was very polite anyway and the guy behind the counter didn't try to convince me otherwise, just apologised for the fact that they hadn't been told to handle them specially, it was all very amicable.Damp weather or not the floor is carpeted in standard nylon carpet tiles and it's easy enough to work up enough potential to get a painful shock when touching something which is earthed. I've done it more than once in that branch.

author: free_electron
author_rank: Super Contributor
timestamp: October 27, 2012, 10:30:37 am
content: Its all a matter of knowing what you do. I needed two 2864 eeproms yesterday and not a bit of foam in sight. Si i took the antistatic tube they sit in (dil package) , pulled out the stopper , put the end of the tube in the palm of my hand making sure to touch the black area of the tube. And simply let two of them slide in my hand. I made sure all pins touched my hand .In short i equalized potential between me and the high impedant tube first. And then made sure all pins kept a bleed path via the surface humidity of my hand. No chance for buld up of charge.I walked over to where the device was needed. Touched the heatsink on the 7805 powering the logic board ( not just the heatsink as that may br isolated. I touched the metal tab of the 7805's body. To balance myself with the system. Then put the two chips in.I am confident no harm was done and no charge ever had chance to do any damage as i equalized it prior to making metallic contact.

author: Fraser
author_rank: Super Contributor
timestamp: October 27, 2012, 10:44:59 am
content: I own a weird bit of kit that I picked up on ebay many years ago....its a meter that gives an indication of charge on a surface at a pre-set distance.I never cease to be amazed at how charged some surfaces become in normal daily use. Polythene is a total nightmare material for building up its own high charge relative to anything touching it. A good test is to rub it on clothing a little and then put the back of your hand near to it...the hair's on your hand will likely reach out for the bag ! Its a bit like the old balloon trick where you rub the balloon on your jumper and it sticks there through static attraction.Here is a link to my Static charge indicator:http://www.technotrend.co.uk/pages/as_prod/evm10.htmNot wanting to get too anal about ESD but is this not the EEV forum where industry best practice should be viewed as the correct path to take and short cuts discussed but not without the readers full understanding of the risk they are taking with any alternative methods. I have not worked in a fab facility, but I have walked around a few and I can assure all readers that ESD is taken extremely seriously. As an example...as you walked in the door you stood on a mat and connected your wrist strap to a ESD strap tester....the unit measured your impedance between the strap, your other hand and the floor on which you stood. you could not enter the facility unless you passed the test. All work areas were fully ESD countermeasure equipped with conductive mat's and all tools ESD safe. Conductive sole shoes were worn and all areas that required ESD countermeasures were clearly marked with coloured lines on the floor. If you were found in one of those area without your strap connected you were subject to disciplinary proceedings which could lead to dismissal if you received too many warnings. I think you can safely say that in industry ESD is a serious business...they certainly spend a lot of money trying to prevent ESD damage to their products. The facility I visit is in the UK but overseas facilities may not be as strict ?Fraser

author: free_electron
author_rank: Super Contributor
timestamp: October 27, 2012, 04:53:10 pm
content: yep .esd is taken serious in the business. we once ruined a weeks worth of parts coming out of the automated tester. the ground strap between the ester and the handler was incorrectly installed. so the chip gets teste , passes and then slides , pins up , into the tube held by the handler. problem is the tube sits at a different potential than the tester ... we had to re-test all parts ... about 1% had some form of damage, notable as paramter drift, to them. after a day tesing we scrapped the entire batch since there was no knowing what the early failure rate was going to be in the field.now we have continuity checks on the machines. they send a 4 mA current trhough the connection straps with a 0.1 volt threshold (open) if the current stops tere is a continuity error and the tester stops ejecting parts.since you got a tester : here is an interesting experiment. take a roll of 3m clear tape ( scotch magic tape , the one that disappears of you stick it on paper.. put the roll on a plastic . hold pen and rip off 3 feet of tape in one swift fast movement. do not let it come in contact with anythingthe reason for the pen is so that your body does not equalise between both sides ( roll and the end you are pulling away from the roll )have a second person now measure the field ( you need to keep holding the tape end or it will curl back upon itself ).don't be shocked (pun intended) if that meter goes off scale... i've seen well over 30 kilovolt from such tape.this is how adhesives works : they snare electrons from the surface thay contact with. that tape is plasma treated on one side so the adhesive will stick there harder than on the other side ( or you would not be able to unroll the tape. adhesive would stick on boith sides. ) by useing a fast motion you are ripping away electrons from one side of the plastic tape and trapping them in the adhesive. so the adhesive free side of the tape is void of electrons. the adhesive side has plenty. do this on a long strip and fast and you get tremendous charge differentials. the more since that scotch tape is a happy donor of electrons ( some materials are easier donors than others )

author: SeanB
author_rank: Super Contributor
timestamp: October 27, 2012, 08:23:12 pm
content: And if the air is dry enough you can get Xrays from the charge separation, if you unwind fast enough to build up a massive charge.

author: Zero999
author_rank: Super Contributor
timestamp: October 28, 2012, 05:56:06 pm
content: Quote from: SeanB on October 27, 2012, 08:23:12 pmOnly if it's done in a vacuum.

author: david77
author_rank: Frequent Contributor
timestamp: October 28, 2012, 06:54:11 pm
content: The ignorance regarding ESD practices in retail environments is something that worries me, too. I now work for Germanys biggest electronics retailer and have to say ESD is completely ignored. ESD sensitive parts arrive in big plastic crates only protected by the tubes they come in, no ESD foil in sight anywhere. They are then dumped into small plastic containers in huge drawers.The people selling and handling them pick them out with bare hands and also without ESD protection, nobody's ever even heard of ESD there.I was a bit shocked by so much ignorance, where I worked before the stuff came properly packaged and was handled on ESD safe workstations where individual parts were put into foam for resale.Personally I wouldn't dream of buying anything remotely static sensitive from my employer, it's an absolute joke.