Carry PCB across carpet and get ESD damage? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: October 26, 2022, 09:24:55 pm
content: Hi,At work recently, i could hear them talking about a board with ADC and DAC chips on it, etc etc, and micro's. (0.5mm pitch and 0.65mm pitch)..it had previosuly worked, but now was malfunctioning...a strange delay of some 15 seconds was holding up a signal.I had seen them carrying this board bear handed, whilst walking across the office carpet...several times.I mentioned that ESD could be the problem but they poo-poo'd the idea strongly.Have you any good videos , or proof, that such PCBs should not be carried bear handed across office carpets?People say its OK to do it in eg UK , as the climate is humid and ESD charges dont build up, even if walking across an office carpet.

author: TimFox
author_rank: Super Contributor
timestamp: October 26, 2022, 10:05:36 pm
content: Lots of stuff on the web, such ashttps://www.industrial-electronics.com/proeeap_6.htmlWith your UK spelling, you seem to believe in the right to arm bears...Back in college, the corridors in my dormitory were carpeted. During Minnesota winters, with almost no indoor humidity, I needed to walk down the hall with a 10 k resistor borrowed from the physics lab, touching metal door frames as I passed. Otherwise, the electrostatic discharge was actually painful.

author: edpalmer42
author_rank: Super Contributor
timestamp: October 26, 2022, 10:35:28 pm
content: Carrying the board is okay. The problem comes when you set it down.Back in the 1980s, HP published a document on this question. It's still extremely relevent. But note that today, I think there are more synthetic materials in our clothing and carpeting than there were back in the 1980s. Synthetics typically build up more static charge than natural materials.http://hparchive.com/Bench_Briefs/HP-Bench-Briefs-1983-03-05.pdf.It's very hard to set up a demonstration of this problem unless you want to test 100 cards and see how many fail. There are just too many variables.I've heard of companies where failure to follow antistatic procedures after you've been trained on them will get you fired. That's not a policy that a company would put in place on a whim.Ed

author: tomgat
author_rank: Regular Contributor
timestamp: October 27, 2022, 12:18:07 am
content: Quote from: Faringdon on October 26, 2022, 09:24:55 pmI cant speak for all chips, but allot of my designs use 24-bit delta sigma ADCs, and once the chips are mounted on a board I dont think I have ever had any issues with static damage whatsoever. By themselves they can get static damage, however. Im not saying its not possible, though. Just not very likely. Obviously I dont know what your design is, but if this issue happened immediately after reflowing, well then you probably know the drill to fix it. If it happened over time, then I would suggest looking for a cold solder joint (assuming your running SAC) before thinking of static damage taking out the ADC. If it was me, (I'm lazy) I probably would just dip the board in liquid flux and reflow it again. Sure it looks ugly when it comes out, but will look brand new again once it comes out of the isopropyl bath.

author: twospoons
author_rank: Frequent Contributor
timestamp: October 27, 2022, 12:23:30 am
content: ESD is a very real possibility. Worst is the damage can be subtle instead of catastrophic - instead of instant silicon death you can have parts slowly degrade in normal use after an ESD hit.Why take a chance? Just use anti-static bags to carry boards about, and have an ESD mat on every desk. Its dead simple, and a good habit to get into.One office I was in I would get zapped just getting off my chair.

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: October 27, 2022, 12:41:50 am
content: Once components are soldered into a pcb they are safer.However, if some pins are straight to an edge connector then damage could still be done.

author: TimFox
author_rank: Super Contributor
timestamp: October 27, 2022, 02:45:57 am
content: The source I cited above has useful suggestions for rendering an assembled PCB safe against ESD.The main thing to avoid is having a "naked" connection from the edge of a board to a susceptible device (without series resistance or shunt protection).

author: Faringdon
author_rank: Super Contributor
timestamp: October 27, 2022, 11:07:50 am
content: QuoteThanks, this says it all to me.....unless you can be sure you can set it down on an ESD mat, then the board can be considered very possibly ESD damaged.

author: twospoons
author_rank: Frequent Contributor
timestamp: October 28, 2022, 02:10:42 am
content: Assume ESD can hit anywhere, not just the edge. Also expect voltages in excess of 20kV, which will go wherever they damn well please.As for built boards being safer, it true they aresaferbut they are by no meanssafe. I have seen built boards, in a box, fail ESD testing.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 28, 2022, 02:39:38 am
content: In my work they would rip your insides out if they spotted you carrying a board bare-handed, although we had to use anti-static heel straps, so it was absolutely impossible to get charged.Accordingly to the managers, doing so was extremely dangerous for the board, except, you know, if they were the ones doing it, then it was fine because they "knew how to handle ESD", probably they had the same superpowers as Magneto from X-Men, thus being able to control magnetic and electric fields.But yeah, ESD can damage lots of stuff, ESD-protected devices are never 100% proof.Recently I killed a friend's router while doing a RAM upgrade because the ground became disconnected at the wall socket.Switching PSUs usually have ~100pF caps to earth at the primary side, so my computer was slightly energizing it, normally ok but now was floating!I noticed a slight electric tickling in my fingers when soldering, couldn't be more than a few microamps or I would have had a serious shock.Then a CPU pin was no longer working, it measured open circuit, like if the internals had completely blown up.And I hadn't touched the CPU by any means!Never happened to me before, but that was it!,Luckly new cpu from AliExpress did the job for little money.Interestingly, the DRAM, traditionally very sensitive devices, was ok.Of course, instantly fixed the earthing.

author: Faringdon
author_rank: Super Contributor
timestamp: October 28, 2022, 02:45:30 pm
content: Thanks, i must admit, i reckon if you work at a place that carries PCBs with <= 0.65mm chips on it..........ie, carries them bare handed when walking across a office carpet.....then that company is asking for problems, and i would go so far as to say that if after giving advice, they still continue to do this....then the best thing you can do is just leave that company.So i am a little surprised at the general kind of layed back consideration of this issue?Specially when its so easy to carry the board on say a big EMC bag, and then put a wrist strap on when handling the board with hands.

author: jmelson
author_rank: Super Contributor
timestamp: October 28, 2022, 04:48:46 pm
content: Quote from: Faringdon on October 27, 2022, 11:07:50 amThe trick is to touch "ground" with the OTHER hand than the one holding the board. Whatever you are going to place the board on, touch that first to discharge any charge on your body, then place the boad on it. If you hand the board to someone, touch their hand first, THEN hand the board over to them.This way, it is almost impossible to have a discharge through the board.Jon

author: tomgat
author_rank: Regular Contributor
timestamp: October 29, 2022, 01:32:27 pm
content: Quote from: Faringdon on October 28, 2022, 02:45:30 pmOn the wrist strap... From a practical manufacturing perspective, it has been my general experience they are for the most part worthless objects. No one wants to wear them, and on the rare occasion you force people wear them (only while your looking btw), they pretty much always wear them too loose to be of real value other than tethering them to their physical workstation. In short, if your seeing static discharges in rework or lab areas, then you more than likely should invest in a big humidifier for that room to monitor/control its humidity levels because it is way too low.Also, once again just my 2 cents.. But from a EE designer perspective... If an assembled board is so easily static damaged that you can put it in your hand and damage it by walking across a carpeted room, then this should be considered a massive design fault. Edge card designs are unavoidable, but if the board is designed well, this really should not matter. Meaning, from a practical real world perspective, if a board is so susceptible to static damage, then you can just assume your going to get back 100% from customers because even though you might gingerly handle them in manufacturing insuring their always in perfect anti-static bags, and have techs which always wearing wrist straps (which simply wont happen), most end customers have no idea what that little bag is for and will immediately throw it away. They will then proceed to 100% of the time tell you that the board never worked after drop kicking it across their 0% humidity carpeted floor sparking like a christmas tree.In short, ESD recommendations arent there because electrical components are so susceptible to static damage because in general virtually none are. If they were, we couldn't manufacture them reliably and would swap components. Its literature is there because the manufacture wanted to add a little more CYA to their product documentation to fill up their page.

author: wraper
author_rank: Unknown
timestamp: October 29, 2022, 01:57:20 pm
content: Quote from: tomgat on October 29, 2022, 01:32:27 pmNobody says device will necessarily fail because of ESD. It's about failure rates. There is a 100 times difference between 5% and 0.05% failure rate. And most of those failures are not immediate, or result in total non-functionality of the component. It may be degraded performance or delayed total failure. Modern components usually have built in protection so you don't see huge failure rates but some are still very susceptible, like 2N7000.

author: tomgat
author_rank: Regular Contributor
timestamp: October 29, 2022, 02:59:46 pm
content: Quote from: wraper on October 29, 2022, 01:57:20 pmJust my opinion, but this gets to a larger discussion, which is overall intended lifecycle of a device. In todays ROHS(ie no lead) world, I think it is safe to say that the by far #1 lifecycle failure is solder joint faults, and not ESD degradation. I could be wrong, however, but I can count on 1 hand the number of suspected static failed components I have seen come back from customers.

author: TimFox
author_rank: Super Contributor
timestamp: October 29, 2022, 03:37:12 pm
content: In back of this discussion, it should be noted that ESD can cause subtle damage to semiconductors, short of total failure, that can impact performance.

author: wraper
author_rank: Unknown
timestamp: October 29, 2022, 03:42:12 pm
content: Quote from: tomgat on October 29, 2022, 02:59:46 pmYes you are wrong. Soldering failures are not that common. Most of those reflow GPU repair claims blaming lead-free soldering have nothing to do with soldering. Usually it was faulty BGA chip temporarily revived by heating, failure being in bumps between GPU or other die and substrate. It's not really a lead-free issue as such but different thermal expansion of materials and broken design. Solder joint failures on single layer PCBs (=with no hole metallization) are way more common regardless of solder type. I would even say there are way less soldering related issues in modern electronics compared to old single layer stuff where seeing broken solder joints was very common. Currently such issues are common only on cheap single layer PSU boards.

author: jonpaul
author_rank: Super Contributor
timestamp: October 29, 2022, 03:43:01 pm
content: ESD precautions are more and more important as the CPU/GPU geometry shrinks, 14u>10u>7u 4uMost chips have some internal catch diode/substrate inherent diode protection.ESD testing, protection, tools and clothes are a HUGE industry.We used a conductive rubber mat on the benches, with 1 M res to Elath, and ESD safe soldering irons.It is most problematic on cold dry days, or in AC labs, with certain types of carpet fibers like nylon or acrylic.This is why ALL semiconductors and chips are packaged in ESD safe plastic trays or bags.Damages can be hidden or after repeated incidents.Jon

author: Faringdon
author_rank: Super Contributor
timestamp: October 29, 2022, 10:42:29 pm
content: QuoteThanks, yes, but thats probably because the production facility that makes the products has the full suite of ESD protection features going on.QuoteThanks, this is interesting because i recently had a thread on EEVBLOG where i postulated that 0.65mm pitch ICs were more static sensitive than say 1.27mm pitch IC's, but the concensus was against me.

author: wraper
author_rank: Unknown
timestamp: October 30, 2022, 09:30:06 am
content: Quote from: Faringdon on October 29, 2022, 10:42:29 pmPin pitch and die geometry have nothing to do with each other. Not to say a lot of ICs come in both types of packages, and IC with those small dies geometries are not used in such packages anyway, unless you compare BGA with SOIC.

author: Faringdon
author_rank: Super Contributor
timestamp: October 30, 2022, 10:47:32 am
content: QuoteThanks, i am trying to find my post on here where i had fets arrive in a clear plastic tube, and not the usual pink tinted EMC tube.....and i wondered how i could tell if it was "ESD safe plastic"?

author: tomgat
author_rank: Regular Contributor
timestamp: October 31, 2022, 01:37:24 pm
content: Quote from: wraper on October 29, 2022, 03:42:12 pmCan you maybe expand on this a little more? On customer returned boards, I see allot of solder joint fractures around the 4 to 5 year mark. They seem to be the worst on through hole connectors causing intermittent signaling issues, but I also see it on a range of chips in the higher vibration environments. I rarely see this issue on the 63/37 leaded solder, however. The low temp Sn42/Bi57.6/Ag0.4 paste that I have used on prototype boards takes the cake, however. It lasted about 1 month in high vibration production environments on average before having fracturing issues. The BGAs are definitely susceptible to issues as well, but I dont have an 3D X-ray to actually fully diagnose what their issue is. I have had mixed reviews, however, from people who do have them on their usefulness.

author: wraper
author_rank: Unknown
timestamp: October 31, 2022, 02:23:07 pm
content: I was talking about consumer electronics general. If you want to read about BGA failure, google "nvidia bumpgate". In high vibration environment there are different considerations how to build the device properly, not an expert in that. But solder joints should not be used as structural elements for sure. And you may want some particular type lead-free solder. They are far from equal. If connector leads were gold plated, it may be a main source of the issue as it may cause solder embrittlement.

author: aduinstat
author_rank: Contributor
timestamp: December 04, 2022, 03:32:54 am
content: Quote from: Faringdon on October 30, 2022, 10:47:32 amIf you want to be sure, then measure the material with a megohmmeter. The pink color is a dye, and the dissipative properties come from a colorless additive. I would not be concerned if your parts came from a reputable distributor.

author: Feynman
author_rank: Regular Contributor
timestamp: December 04, 2022, 08:24:58 am
content: Of course, ESD could be the problem.It's just stupid to carry around ESD sensitive PCBs carelessly. They should just put them in a shielding bag, whenever feasible.They can take the chances, if they choose to. But "poo-pooing" ESD in a totally uncontrolled area just shows ignorance about basic concepts.Since walking over a carpet can easily build up charges that you can feel discharging when touching a metallic structure (door knobs are common), we are speaking of thousands of volts. Sudden discharge events of thousands of volts can easily damage most semiconductors. To put this in perspective: ESD protected areas according to DIN EN 61340-5-1 attempt to keep potential differences below 100V.It's hard to tell in your case, if ESD was the problem, of course. To proof this you would need to cut open your chips and look for breakdowns in the semiconductor structures. A lab specialized on semiconductor damage analysis may easily charge 1.000 €/$ for that.