ESD Safety: Have I just ruined 100 microcontrollers?  - Page 1
Forum section: electronics / general

author: OwenH
author_rank: Contributor
timestamp: January 23, 2021, 01:36:17 pm
content: Hi,I have a potential issue regarding ESD exposure to 100 microcontroller IC's. I am building a small run of boards using PSOC4 chips for a professional camera accessory. The chips come from Mouser in a cardboard ESD box and there were about 100 in it. Somehow I lost my brain and took the box out of the vapor proof ESD bag and opened it to remove about 50 chips without using a grounding strap and not over an ESD mat like I should have. To make it worse I was wearing a knit hat and a light fleece jacket. I did use ESD tweezers to remove the chips form the packaging and never touched them directly. I also cut some other tape and reel packaged IC's off their reels. The flooring is ceramic tile and the humidity was around 50%, so I do have that in my favor, but I'm curious how much risk I just put the chips in? I realize what I did was totally amateur and I can only blame myself, but I still have to make a decision wether to use the chips or not. Can I be reasonably confident that they are still fine?Thanks,Owen

author: Yansi
author_rank: Super Contributor
timestamp: January 23, 2021, 01:43:29 pm
content: Almost zero risk. (but not zero, mind you).

author: Ian.M
author_rank: Super Contributor
timestamp: January 23, 2021, 01:54:52 pm
content: The hat is totally irreverent as its extremely unlikely for it to have come in contact with any parts or for it to have rubbed against anything other than your head, which, if it had, could have charged your body.If you had one hand on the packaging if it was static dissipative, when picking the chips and dropped them into an ESD safe static dissipative container, odds are they are fine. Cutting lengths from the reels is more problematic, if the carrier tape is only anti-static not dissipative, and if you accidentally brushed the strips of tape with your sleeve, or put them down on a non-ESD safe surface you may well have damaged them.If you have damaged them there is a small but significant chance of early mortality even if the assembled products pass a soak test, so it all comes down to the relative costs of replacement parts vs the support costs and possible damage to your reputation even if you offer no questions asked advance replacement for any failed units in that batch.

author: Feynman
author_rank: Regular Contributor
timestamp: January 23, 2021, 02:13:44 pm
content: The point is: You can't tell. Most of the time ESD damaged devices work just fine initially. They might fail in days or months, or in special circumstances, e. g. wondrous resets/freezes with high temperatures.From a professional point of view you should assume that the parts are damaged. What you conclude from this assumption is your business decision.And please be careful with people stating "I do this and that all the time and never had ESD problems". That is most likely a sign of lacking knowledge. Just like I said: You can't tell. You only could tell by cutting open the chips and inspect the semi-conductor structures with a microscope. Most ESD failures occur with time delay. And who associates a mysterious system crash with handling errors months or even years earlier?

author: OwenH
author_rank: Contributor
timestamp: January 23, 2021, 03:59:26 pm
content: With the ICs in the ESD box, I was holding the box down to the table to keep the flaps open with one hand and picking up components with the ESD tweezers with my other hand. Then I placed the components into a second ESD box, still using the ESD tweezers.In regards to the cut tape ICs, my understanding is that it is dissipative in the cavity the IC sits in, with an antistatic cover tape to hold it in place. So I cut a length of ICs off the larger reel but none of them came out of the cavity in the tape, nor was the antistatic cover tape removed.Both chips have an HBM of 2000V and a CBM of 500V.

author: Ian.M
author_rank: Super Contributor
timestamp: January 23, 2021, 04:15:49 pm
content: IMHO you've got away with it and they should be ok.Reasoning: The capacitance of an individual loose chip to ground is negligible, so the charge to equalise potentials is small, and the high resistance of the tweezers, packaging and second box will have limited transient ESD currents to well under what the chips' pins' internal ESD protection can withstand. Similarly, even if you ESD 'zapped' through the tape cover, the carrier will have limited the current, so it should be OK if you weren't working on a highly conductive surface.You probably wouldn't have got away with handling unprotected gate small signal discrete MOSFETs or other extremely ESD sensitive parts the same way.

author: tooki
author_rank: Super Contributor
timestamp: January 23, 2021, 10:05:15 pm
content: Quote from: Feynman on January 23, 2021, 02:13:44 pm^^^This.I absolutely hate when people say "I've been doing electronics for 40 years without taking ESD measures and I've never fried anything", because they almost certainly have, but just don't know it, and are too arrogant to think otherwise.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 23, 2021, 10:50:32 pm
content: Highly unlikely you have damaged anything. ESD is a very small risk for individual components as the capacitances involved are so small that the available energy for discharge is small.Assembled PCBs are a bigger risk as the PCB itself can have enough capacitance to ground to hold a potentially damaging level of charge if discharged to a vulnerable node.

author: james_s
author_rank: Super Contributor
timestamp: January 23, 2021, 11:19:22 pm
content: It's extremely unlikely to be any problems. The risk is never zero, no matter how careful you are there is a non-zero risk of damage but I would be absolutely shocked if there was damage. If this was a part going into a multi-billion dollar satellite in orbit or a critical component in any kind of device where people will die if it fails I would feel differently but for a consumer product? Just put it through its paces and ship it, in the unlikely event that somebody experiences a problem send them a new one.

author: jmelson
author_rank: Super Contributor
timestamp: January 24, 2021, 01:28:26 am
content: I agree that damage is quite unlikely. Now, if you had chips or boards with chips installed, sitting on a table, and walked across the room with some non-static dissipative clothing and touched the chips or boards first, then you could definitely have damage. Getting out of a chair with synthetic fiber seat while wearing clothing with synthetic fiber and then touching something will often draw a spark you can feel.But, sitting at a table, opening a package and transferring chips from one package to another is very unlikely to generate much charge.Your body is the static dissipative object there. The 50% relative humidity will help immensely.Jon

author: Psi
author_rank: Super Contributor
timestamp: January 24, 2021, 01:47:37 am
content: It's really only an issue on a production line where repetitive takes are being done.The repetitive task builds a charge up and up until it arcs to something and then it starts to build up again.If that something is a sensitive PCB the factory might notice a high failure rate.For a hobbies it's very very uncommon to damage a part from ESD.It's a little more common if you're prone to static shocks, but even when you do cause a static arc to an IC most of the time the protection diodes built into the chip handle it just fine.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 24, 2021, 08:09:53 am
content: It's equally unlikely to winning $10 million in lottery three times in a row.This is not saying bypassing ESD procedures isn't risky. But thisparticulardescription is clearly low-risk. It would be different if you had actually touched the chips all over the place, or dropped thechipson regular table. It wouldstillbe a low risk, but something more considerable.ESD safety isn't an on-off thing. Perfection is impossible to achieve in real world. There are very small, small, big and very big mistakes. Your's sounds like being on the very small side.But do mind the Moisture Sensitivity Level rating. If they are out of the bag for a certain time, they may need baking.

author: james_s
author_rank: Super Contributor
timestamp: January 24, 2021, 08:19:16 am
content: I've certainly damaged parts by being careless with ESD, but it has been my experience that most modern stuff is pretty robust. Early CMOS ICs and stuff like small RF mosfets though not so much. Early laser diodes were also extremely delicate but modern ones seem to be able to tolerate quite a lot of abuse. SRAM is about the only "modern" part that I'm pretty sure I zapped from a static discharge but even that was probably late 90s so not exactly state of the art. I've actually been amazed at just how tolerant some stuff is, I've had ICs come all the way from China in an ordinary plastic bag with chunks of white styrofoam in there, practically a recipe for static electricity and still no apparent problems. Was there hidden damage? Who knows, but if it can tolerate that abuse and still work it can probably tolerate a little less than perfect handling. As with anything though, YMMV.

author: Psi
author_rank: Super Contributor
timestamp: January 24, 2021, 11:54:25 am
content: Quote from: james_s on January 24, 2021, 08:19:16 amThat's due to better manufacturing processes that produce higher powered diodes.The modern red diodes sold as 1mW or 5mW are actually more like 50 or 100mW diodes. They can handle massively higher bust current than the early diodes that were being run right on the edge of overload.Modern low power diodes often don't even bother with the feedback photodiode, something that was critical on older diodes to keep them from blowing up.

author: Kasper
author_rank: Frequent Contributor
timestamp: January 29, 2021, 10:38:20 pm
content: A start-up I worked at ignored my warnings about ESD and seemed to get away with it until we moved to an office with carpet and then 2 boards stopped working. After that, people were more cautious and the problem didn't recur.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 30, 2021, 09:04:44 am
content: Fluffy carpets made of plastic fibers in dry environments can generate massive ESD problems, so bad the risk becomes two-digit percentages and will be realised even in small-scale prototyping.Bare minimum ESD procedure is to remove absolute stupid problem generators such as said carpets, and develop a habit of touching some grounded device case / mains ground connections every now and then while working. This reduces the problems by like 1000x, and practically costs nothing to implement. Then, if you try to manufacture 10000 devices in such conditions, one may fail two years later on the field due to hidden ESD damage.Real ESD controlled furniture and everything then becomes a costly item but is a necessary investment when high yields and high reliability is needed, especially if traceability of right procedures is needed.

author: 48X24X48X
author_rank: Frequent Contributor
timestamp: January 30, 2021, 12:24:07 pm
content: Carpets and door mat are the easiest generator of static charge. Used to work in a carpeted office. Was zapping everything even when holding door knobs and door frame let alone electronics.

author: james_s
author_rank: Super Contributor
timestamp: January 30, 2021, 07:37:47 pm
content: I keep a ESD wrist strap at my bench and wear it religiously during the winter when I'm working on anything expensive.I also attached one of those to the belt sander at my friend's shop. That thing was like a Van de Graff generator, rubber mat on the floor around it and in the winter I would get terrible static zaps, reach for the power switch to shut off the sander and it was not uncommon to be hit in the fingertip with an inch long lightning bolt. The wrist strap took care of that but I still find myself cringing as I reach for the switch.

author: JPortici
author_rank: Super Contributor
timestamp: February 02, 2021, 06:31:10 am
content: Quote from: Psi on January 24, 2021, 01:47:37 amHow sensitive could a LED be?We have one board we hade been producing for 5 something years before we began using another contractor. Starting that moment we had a huge failure rate for the LEDs. They were the bog standard 3mm green leds you buy one million for a penny, low light emission with that green-yellowish tint. It was the only board they manufacturered with such huge failure rate. We demanded to change the LED and problem solved, not a single failure again.

author: Psi
author_rank: Super Contributor
timestamp: February 02, 2021, 08:11:52 am
content: Quote from: JPortici on February 02, 2021, 06:31:10 amAn LED? not much at all, but a laser diode is EXTREMELY sensitive. Especially the first generation low power ones.

author: Miti
author_rank: Super Contributor
timestamp: February 03, 2021, 03:43:29 am
content: The ESD danger is waaay overstated these days. At 50% RH, no chance you accumulate a significant charge, unless you rubbed that hat with one hand, the jacket with the other hand, and you touched the components with... your tongue. Don’t worry, they are good.The ridiculous requirements the ISO standards imposed are mainly for commercial purposes.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 03, 2021, 03:11:14 pm
content: Quote from: Miti on February 03, 2021, 03:43:29 amDepends on who you talk with.Others overestimate the risk and require massive (expensive) mitigation strategies even for small scale prototyping.Others downplay the issues to oblivion.Neither is very good.Large scale production where end result must have guaranteed functionality benefits from quite stringent procedures and the cost of getting it right once is amortized over years to come.Similarly, some specific parts require better-than-average procedures. For example, very small low-capacitance MOSFETs are orders of magnitude more sensitive than power MOSFETs.If you use "typical" general purpose parts like microcontrollers, modern-day logic chips, power conversion ICs, etc., and do prototyping or very small batches, usually the risk becomes completely negligible if you do a basic ESD sanity check removing worst offenders like fluffy carpets, add a bit of humidification if very dry winter air (say RH < 30%) is a problem, and install very simple&low cost ESD mats (a few $ each) on the workbenches - and develop a habit of touching a ground connection before and during handling boards and components. This doesn't cost much money or time.