EEVblog Electronics Community Forum
EEVblog => News/Suggestions/Help => Topic started by: stevenhoneyman on July 19, 2015, 06:45:46 pm
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There's plenty of people that never have and never will wear an antistatic wrist strap and can truthfully say they've worked with electronics/computers for X years and not broken anything, and I've never heard of a case of someone destroying parts accidently... but it's (obviously?) a real issue. Or maybe it's all just because some guy that worked in a Van de Graaff generator factory once had a component fail!
I think an episode dedicated to destroying a bunch of stuff with/without cheating would be interesting, and useful in demonstrating this. E.g. a quick breadboard test rig, bag of 555 timers/MCUs/whatever is cheap, then zap 'em after running around on carpet etc. With and without the wrist strap. I'm sure there's some more scientific way it could be approached as well, but until I see/experience a component failing due to ESD in an 'everyday' scenario, I'll always have my doubts.
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See here: https://www.eevblog.com/forum/beginners/esd-confirmed-kills/ (https://www.eevblog.com/forum/beginners/esd-confirmed-kills/)
And: <copy... paste... >
ESD is a subject which is very poorly understood, even in the electronics industry where people should know better. Spare me a few minutes and I'll clear up a few misunderstandings that'll hopefully save you an expensive repair bill one day.
First off, a few things you may already know about ESD:
- Your DRAM is designed to work off 2.5V or less. Walking across a carpet can generate voltages in the order of 5,000V or more.
- Rubbing two insulators together (eg. two layers of clothing) causes static electricity to be generated, by transferring electrons from the surface of one to the surface of the other
- Static electricity that's just sitting there on the surface of an insulator isn't doing any harm. What causes damage is when that electricity is suddenly allowed to flow from one place to another via a conductive path. At the moment the conductive path is formed, the instantaneous current can be huge, and if your SSD (Static Sensitive Device - could be a DRAM module, CPU, motherboard - anything with exposed electronic components) is in that path, it can be damaged.
- The discharge current causes a heating effect, just like when you connect the mains to an electric fire. Too much heat in a small device burns it out, it's that simple. The smaller the device - a transistor, for example - the more sensitive it will be to ESD damage.
And a few things you probably DIDN'T know:
- You DO NOT have to actually touch a Static Sensitive Device (SSD) such as a DRAM module in order to damage it. Merely passing your hand near it can be enough.
- An ESD event can be strong enough to cause damage well below the threshold where you'll feel it - so you can destroy a device without even knowing it.
- A device damaged by ESD DOES NOT necessarily stop working straight away, but its performance and lifetime can be drastically reduced. So, just because you put a machine together and it seems to work DOESN'T mean you've got away with it.
- An SSD enclosed within a conductive anti-static bag is NOT completely immune to ESD damage, because although it's protected from electric fields, it's not protected at all from magnetic fields. A spark outside the bag causes a rapidly changing magnetic field, which can induce a current in any conductor inside the bag. (Think: that's how a generator works!)
- the correct way to package an SSD is to put it within a conductive bag, and then to package that bag in a reasonable thickness of 'pink' bubble wrap or other packaging. The bag protects against electric fields, and the pink material provides enough physical space around the SSD that large magnetic fields (from sparks) can't be generated physically close enough to cause damage.
- 'pink' packaging material is coloured that way by the manufacturer to indicate that it's made so that rubbing against it doesn't produce a charge. It is NOT conductive and it does NOT protect equipment from electric or magnetic fields. It is, however, the correct material to use to package SSDs that are already enclosed in conductive bags.
- the pink colour is just an identifier. Retail boxed CPUs, for example, come in clear plastic because it looks nice, but that's OK - Intel & co know what they're doing.
Be aware, though: an awful lot of PC component vendors DO NOT know the correct way to package an SSD. If you order a component, such as a CPU or memory module, and it's not correctly packaged, you'd be within your rights to send it back - IMHO, of course
So, with all that in mind, what can you do to protect your equipment?
In order to damage a component, you need a potential difference between the component itself and the thing you're going to touch it with. No PD = no current = no damage.
So, normal practise in an electronic assembly plant is to ensure that everything is at the same potential all the time, and that means:
- everything is conductive: bench, floor, tools, lab coat, even the waste paper bin. Unnecessary insulating materials (crisp packets, coffee cups etc) are banned from assembly areas.
- everything conductive is grounded - NOT because there's anything 'magic' about ground, but that it ensures everything in the plant is at the SAME potential as everything else.
- conductive materials used still have some resistance - they're not made of good conductors like copper and aluminium, but instead they use carbon loaded rubber or plastics. This ensures that when a potential difference does exist, the current involved is small and safe. Charge leaks away relatively slowly rather than suddenly.
These basic precautions mean that everything the SSD's are likely to touch are at the same potential; no difference in potential = no current = no damage.
So, assuming you don't have all that kit, what can you do to protect your equipment?
- borrow the correct equipment! There really is no substitute for a dissipative bench mat and a wrist strap. Really! If your PC packs up in 6 months' time and you didn't use the proper equipment, you only have yourself to blame.
...but if that's simply not possible...
- on a desktop PC, DO plug it into the mains, but turn off the power at the wall - you only want the earth connection. (Disclaimer: safety, safety, safety!!! If you're not absolutely 100% sure about the implications of this, get someone else to upgrade your PC for you! I am NOT RESPONSIBLE for anything YOU CHOOSE to do with your PC, REGARDLESS of whether YOU CHOOSE to treat my comments as advice or instructions!).
- don't wear nylon or other synthetic fabrics - wear cotton instead. Or do the upgrade naked if that's your thing! But whatever you do, don't pull a sweater off over your head and THEN grab your shiny new DRAM module. All those little clicks you heard when you pulled the sweater off were ESD events - you're now charged up to 10,000 volts and your DRAM is doomed/
- touch the EARTHED bare metal case of your PC.
- touch the silver or black bag that your DRAM comes in to the bare metal case of your PC as well. There's no point in you being earthed if the SSD is charged up to 10,000V when you get it.
- The moment you first touch the SSD after opening the conductive bag is the moment at which you're most likely to damage it, because you don't know what potential it's at. Get this into your head! A proper wrist strap contains a 1MOhm resistor to limit the current that'll inevitably flow through your shiny new DRAM when you first touch it. If you had a proper wrist strap on now, you wouldn't be about to risk blowing it up. Now is the time to decide NOT to open the bag today, and to pick up a wrist strap for a few quid off Ebay.
- Remove the module from its bag and install into your PC. Try to maintain a finger or elbow in contact with the chassis of your PC at all times, it only takes a moment to 'recharge' once you let go!
- Reassemble your PC and test.
Finally, be aware that there's some scarily bad misinformation around about ESD. From this very thread:
- "It doesn't matter, I've never had a problem" - see above. You can damage a module without realising it, and the damage may not show up for months. Now you know that this 'latent damage' can occur, you'll be in a better position to put 2+2 together when your PC 'inexplicably' packs up next year.
- "Touch a metal object" - pointless. You need to ensure that you, your PC and the component you're installing are all at the same potential. If it's plugged in then your PC is at earth potential, so if you touch a metal water pipe (something which is connected to earth and, therefore, at the same potential), then that's good. But touching a door handle just makes you look stupid.
- "Latex gloves" / "rubber" - WTF?! You're not trying to protect it from some biological infection - latex is an insulator and can therefore hold a charge. It's probably the worst thing you could possibly do from an ESD point of view. (Sometimes workers in a clean room use them to avoid contamination, but that's not the problem in this case).
- "One hand in the back pocket" - is a good rule for personal safety if you're working on live equipment, because if you touch a live conductor it helps prevent current from passing through your chest. But your PC is switched off at the wall. Right answer to the wrong question. Ditto for insulating boots - workers in ESD protected areas wear conductive heel straps, and NEVER work directly on live equipment.
- "Switch on after removing the battery to discharge the equipment" - wrong again. This has nothing to do with ESD, it's to ensure that the power supply caps in the PC have drained. All you need do is wait 10 seconds after switching off and you'll be fine. This has nothing to do with static.
Hope that helps!!
Andy.
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I use to be an ESD denier, it took an assembler walking across the floor with plastic shoes, wearing pantyhose and handing me a VCO I hand tuned (spent ten hours doing so). The spark from her to me and my grounded chair and cotton cloths put an end to most of that ten hours of work.
A failure report for QA
Authorization to rework
De-Potting the VCO,
Replacing the burned open varicap diode.
Inspection
Retuning the VCO...
An operational test over temperature to make sure the VCO drift, deviation sensitivity and power output were all still in spec....
Inspection
Re-potting the VCO.
Finishing my part of the failure report, send to my QE for final disposition...
One day later I am back to where I was the day before.
The VCO sent back to top assembly to be mated with the remainder of the power train.
Three months later the transmitter line was shut down for ESD refit and education for one day.
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I use to be an ESD denier, it took an assembler walking across the floor with plastic shoes, wearing pantyhose and handing me a VCO I hand tuned (spent ten hours doing so). The spark from her to me and my grounded chair and cotton cloths put an end to most of that ten hours of work.
A failure report for QA
Authorization to rework
De-Potting the VCO,
Replacing the burned open varicap diode.
Inspection
Retuning the VCO...
An operational test over temperature to make sure the VCO drift, deviation sensitivity and power output were all still in spec....
Inspection
Re-potting the VCO.
Finishing my part of the failure report, send to my QE for final disposition...
One day later I am back to where I was the day before.
The VCO sent back to top assembly to be mated with the remainder of the power train.
Three months later the transmitter line was shut down for ESD refit and education for one day.
Result :-+
See here: https://www.eevblog.com/forum/beginners/esd-confirmed-kills/ (https://www.eevblog.com/forum/beginners/esd-confirmed-kills/)
It's an interesting read, although a lot in common with the other info out there (as you'd expect). What it's lacking though, and the reason for my episode suggestion is any repeatable proof. The software guys handed you some broken boards, how can you be sure that ESD was to blame, and not a moisture damaged component or faulty power supply they connected it up to (for example)?That's the type of thing I was thinking could be settled once and for all in an episode!
"Look, flashing LED"
*run around room*
*pick up the 555 timer*
"Look, it died!"
Demonstrating this in an eevblog video should/might end doubts people have.
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I am too mean to buy real ESD earth plugs for the mains, I use a UK plug with the L/N pins removed, solder a 1M resistor to a length of wire and screw it to the fuse connector and the other end of the resistor to the earth pin, fix the lead through the strain strap and let it hang out the plug , either solder a loop on the end to fix a croc clip to for your regular ESD wrist lead or fix a regular cupboard bar handle under the bench and fix all your leads to that. cheap enough.
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I've just found ep 247, might have been done already... I'll go watch it and see.
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No doubt ESD gets the blame for a lot of poorly diagnosed failures, but at what point does failure analysis our weigh its value?
In the example sited above you really don't have the money to do a conclusive failure analysis.
Not the same as manufacturing gear for the aerospace industry where when a failure pattern begins to develop a few killobucks spent on good failure analysis can save tens of millions, and maybe a contract or two.
Repairing a PC that can be replaced for a few hundred dollars, labor is the most costly component. I have worked in aerospace where an S-Band power transistor cost two weeks worth my wages, trust me when you blow two of these hand tuning a 40W S-Band PA (this was a couple of decades ago) they start asking questions with the intent of shutting down a line to get to the bottom of the problem.
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it just like to me that ESD like most time as mafia Protection racket ,listen some ESD specialist and you end up whit ESD safe toilet paper :palm:
it also kind of stuff that ING like to blame to when it no find better answer for a defect :-DD or a bad design...
look carefully all electronic assembler ,you will notice almost never have ESD floor or have whist trap or else ,that plain normal since it handel part in REEL and PCB by it edge
that was the key ,so NOT put your finger on any IC pin ,keep humidity high and monitor ESD on the shop ,and if do rework do it in ESD safe bench and tool
one funny thing is that when PCB was on the Reflow Oven it surrounded by forced circulating hot air so very dry and Very static prone :scared: :popcorn:
some oven have negative ion generator on cooling Zone ,that nice HV arc strait to air under the PCB |O
a good example i have make ESD floor on my facility ,ESD gourou what to sell me ESD tile for 10$ per scare foot !!! and tile have same conductivity that a plain concrete Floor
have end-up whit Epoxie paint made for munition facility and that one was truly conductive not the Disipative stuff that have Giga-ohm resistivity that cost arm and a leg
after have play whit ESD meter for some time have happy to find that most usually stuff was already static safe ,but ESD mafia still ask for buy stuff that ESD logo on it and big price tag ....
as final note 99% of the small computer repair shop have absolutely no idea about ESD or and protection on any kind and manipulate bare hand CPU and DRAM stick
did every home computer handle by that small shop fail mysteriously after after fix ?
most offer warranty on computer in assemble and sold ,did it all back-rout later since ESD damage warranty repair ??
ESD was just like lead-free solder "issue" it greatly over exaggerated ,yes must be carefully but gourou like to create itself full time job based on it fear O0
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- An SSD enclosed within a conductive anti-static bag is NOT completely immune to ESD damage, because although it's protected from electric fields, it's not protected at all from magnetic fields. A spark outside the bag causes a rapidly changing magnetic field, which can induce a current in any conductor inside the bag. (Think: that's how a generator works!)
I can't believe that's plausible. Inverse square law for starters, combined with tiny loop area inside any device to pick up sufficient energy to cause damage.
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If you live in a very humid place ESD precautions might be a waste of time for you. If the humidity is moderate to low, and you don't take reasonable case about static on a production line, failure rates at the product test stage can be horrendous.
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ESD is real, of course... we can measure it, we can test for it, we can reproduce the results.
But I think it is massively over-inflated beyond it's real dangers. I have never used an ESD strap, and in 15+ years of working in electronics and in all my life, I've never ever damaged something from ESD to my knowledge.
I've also not had any unexplained failures that could be chalked up to ESD. I think ESD damage is probably like turning your engine off when you refuel. Yeah, it makes sense... and yeah, some serious accidents have occurred from ignoring the advice, but the chances of anything going wrong are statistically miniscule.
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- Your DRAM is designed to work off 2.5V or less. Walking across a carpet can generate voltages in the order of 5,000V or more.
The voltage not the issue, it's about potential discharge current. The 5kv figure is meaningless without reference to the capacitance it's stored on.
It's all about the D, not the ES
It basically boils down to risk vs. consequences. In a lab/development environment, it's usually not a huge issue, as anyone working with semiconductors will understand the risks and know not to do stupid things like wear synthetic clothes. The cost consequences of ESD damage are also relatively low at this stage
However in a production environment, many of the staff handling devices and boards will not have sufficient technical knowledge(and may care less).
The potential costs of damage that doesn't surface til a product is much further down the production line, or even in the field are orders of magnitude higher, and difficult to trace back to a root cause.
Therefore imposing some rules that have a high probability of avoiding risks is a very pragmatic way to reduce risks. It may be the case that some precautions are redundant, but the risks of getting it wrong will often outweigh any cost savings.
The only ESD precautions I've ever taken are to install anti-static carpet in the workshop, and touch earth before putting an expensive CPU in a motherboard. I've blown stuff up in many interesting and dramatic ways but ESD hasn't been one of them.
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I believe damaging ESD events curve goes down as far the product is from the manufacturing stage. For a finished board with proper design it would be really strange to systematically fail due ESD.
Alexander.
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one of common guilty that blamed to be ESD in manufacturing was popcorning
customer order part for it project made 2-3 prototype for test it then later start the production ,then find production board fail when prototype worked and blame ESD in assembly shop
what happen in reality was during delay from prototype to production humidity migrate into IC epoxy body ,then on reflow that humidity simply "explode" like pop-corn
that generate all king of trouble from plain DEAD IC to intermittent issue ,so very similar to ESD damage
simple cure was store part before assembly for 24H in sealed container filled whit desiccant Bag ,that bag may reuse to infinity by "reflow' it
and not forgot that in assembly shop no one actually toutch part ,that come in reel that ESD if need the pick place handel it no human , one pick place finish no one tout the part or trace
board was handel by it edge 9 Before V-score border was remove) ,same for reflow and wash ,only time a part may touch it during TEST or rework ,so very unlikely that damage occur at that stage
most of time ESD was check as last option ,even if some Gourou point it first and miss the point ...
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Some time ago, one of the products I had worked on started to get a lot of warranty returns - all for the same fault. We spent ages trying to find the issue - they all worked when they left the factory but failed within about 6 months.
We ended going the the chip suppliers, who did all sorts of tests on the failed chip (including X-Rays) and concluded that there was some ESD damage. After a lot of investigation, it turned out that our supplier had re-reeled the devices and the glue they had used to hold the tape on the carrier caused a huge potential when removed. This built up and eventually discharged damaging the chip.
Ironically, during the time taken to do these investigations the problem seemed to go away - we believed that as we had started using more of the chips we bought larger quantities and the supplier stopped re-reeling.
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I would have been in that supplier's face so fast :box: ; >:(
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If I am doing some work at a place that dictates the use of varying degrees of ESD protection, I will universally abide by the local instruction, irrespective of whether I think it's poppycock or not.
In my situation if I have to dress up it is typically in a clean room and the stuff I'm working is on stuff that will be going into the vacuum of space. Strapping up, one way or another, is the norm.
Although my own experiences suggest that ESD itself is overplayed, this is as much to do with the psychology of taking care as much as anything else. Once you've donned your special shoe covers, hair nets, nitrile gloves and lab coats (or whatever is dictated in the given environment, ask three different clean room managers you'll get three different answers), you feel a bit special, you take extra care. A bit like going out for a special occasion, you dress up, and behave appropriately, well most of the time anyway.
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Worked in aerospace where we spent the money to find out what caused failures. De-lidded components, did photomicrographs, stripped metallization and so on. Often found that there was a little crater in the chip. So "something" caused a localized rapid heating event. Most events with supply voltages supply heat slowly enough that when a crater is generated it is large. So the something was a short high power event. ESD can never be proved in a case like this, but it is the most likely and one of the few possible causes.
More interesting were the times when craters or burns in the metallization were found that did not prevent function of the part. The most common case was in the wiring for or the actual ESD protection diodes themselves. So the ESD protection diodes had done the job, and since they are not directly involved in circuit operation everything still functioned. But the protection was now gone, so the next event would get something else. Other cases included metallizations that still had a conductive path, but were significantly narrowed. Not good for the life of the component, but maybe OK, and would fall in the "I've never had an ESD failure bucket. In other cases a device or subcircuit had been destroyed, but that function either wasn't used, or wasn't obviously necessary for circuit function. The circuit might have more bias current, or higher crossover distortion or some other factor which wouldn't be noticed unless your circuit depended on that element of the part performance AND you tested the resulting performance. These cases would also go in the "I've never had an ESD failure bucket".
The bottom line. If you care whether your device works next week or next year, and if your environment does not naturally prevent ESD then take ESD precautions. If you never get zapped as you slide out of your car or touch a doorknob you may not need to do anything special.
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For me it has been location, location, location. I have always worked in places where we take the issue quite seriously and except for one instance it was never a problem. At a previous job where the combination of rolling lab chairs and vinyl floor tiles made it a very real problem. The mistake here was that the tiles were standard warehouse style tiles with no concern for anti-static. You could sit at a bench, roll back one foot and then roll back to the bench and draw a spark pretty easily. That building had undergone many reconfigurations through the years so using the incorrect tiles was just a leftover from when that particular area was used for something else but since it was a test lab and not a production area they left it that way and we just had to be extra careful.
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... it turned out that our supplier had re-reeled the devices and the glue they had used to hold the tape on the carrier caused a huge potential when removed. This built up and eventually discharged damaging the chip.
An amusing thing to do when it's dark and you're bored.
Get a reel of sellotape. Go into a dark room - proper pitch black. Give your eyes five minutes to adjust to the dark. While watching, pull six inches of tape off the reel at a normal speed. Watch the miniature lightning as the tape pulls off the reel.
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An amusing thing to do when it's dark and you're bored.
Get a reel of sellotape. Go into a dark room - proper pitch black. Give your eyes five minutes to adjust to the dark. While watching, pull six inches of tape off the reel at a normal speed. Watch the miniature lightning as the tape pulls off the reel.
Wait for collegue to suddenly open door and find you with a piece of tape, ready to attack. Explain to boss.
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A long rime ago I had an argument with my fellow worker when I worked in mobile phone repair shop. We made some rearrangements at work and I put ESD mats on my new workplace and correctly wired them, while most of another desks had ESD mats but were not wired. He said why I would bother, nobody ever seen failure due to ESD anyway. I then asked him: "how many times you disassembled some phone and it died after that?" He then shut up. I don't think there were that many cases I can certainly say I killed something with ESD, but there were a few that I'm pretty sure about and I've seen an actual spark a few times which resulted in dead component. Once I moved expensive 2 years old Intel CPU from one motherboard to another, and it died next day. I cannot think anything other than ESD damage, as replacement CPU worked 2 years since then on the same motherboard.
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Sainsmart sent me two 3.2 inch TFT displays with the pins stuck in white foam, packed in clear ziploc bags. Both were damaged, the displays had lines and would not work correctly. They also shipped four 2.4GHz transceivers with the pins stuck in white packing peanuts, held on with plain clear packing tape and stuck in clear ziploc bags.
None of them worked properly. An email conversation with someone at Sainsmart revealed that their shipping department seems to be entirely ignorant of ESD and protection against ESD.
I've had a variety of sellers on Amazon ship with no ESD protection, or just in pink bags as if that provided protection. I got tired of testing and finding damage, now I just immediately file a return if they aren't in silvery gray or black ESD shielding bags.
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I built and repaired computers growing up (now 40) in the UK and not once did I wear anything to strop me zapping the bios, memory etc.. My home was fully carpeted in the SE of England.
Moved to mid/north sweden 7 years ago. My fantastic Sony Vaio laptop, I zapped 3 motherboards in 2 years :-( Since then, never work without one either PCs/laptops or electronics. My drier here in Umeå, colder. Not really sure what is worse / better.
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I built and repaired computers growing up (now 40) in the UK and not once did I wear anything to strop me zapping the bios, memory etc.. My home was fully carpeted in the SE of England.
Moved to mid/north sweden 7 years ago. My fantastic Sony Vaio laptop, I zapped 3 motherboards in 2 years :-( Since then, never work without one either PCs/laptops or electronics. My drier here in Umeå, colder. Not really sure what is worse / better.
In the 70s and 80s there were still lots of electronics production lines in SE England, and they had lots of issues with static damage in the summer, until they started to effectively control it. The winter is damp enough that the aren't so many natural problems there. However, its easy to create problems with inappropriate heating systems, that make the humidity plummet.
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I built and repaired computers growing up (now 40) in the UK and not once did I wear anything to strop me zapping the bios, memory etc.. My home was fully carpeted in the SE of England.
Moved to mid/north sweden 7 years ago. My fantastic Sony Vaio laptop, I zapped 3 motherboards in 2 years :-( Since then, never work without one either PCs/laptops or electronics. My drier here in Umeå, colder. Not really sure what is worse / better.
In the 70s and 80s there were still lots of electronics production lines in SE England, and they had lots of issues with static damage in the summer, until they started to effectively control it. The winter is damp enough that the aren't so many natural problems there. However, its easy to create problems with inappropriate heating systems, that make the humidity plummet.
I think you got it exactly opposite. When air is cold, it can hold much less water. When air from outside is heated up in the building, relative humidity becomes much lower, even though amount of water in air remains the same.
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I think you got it exactly opposite. When air is cold, it can hold much less water. When air from outside is heated up in the building, relative humidity becomes much lower, even though amount of water in air remains the same.
Ah, you'd think so wouldn't you. You make the mistake of assuming that a British boss would do something so effete as to, in winter, warm the area his staff were working in. :)
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I built and repaired computers growing up (now 40) in the UK and not once did I wear anything to strop me zapping the bios, memory etc.. My home was fully carpeted in the SE of England.
Moved to mid/north sweden 7 years ago. My fantastic Sony Vaio laptop, I zapped 3 motherboards in 2 years :-( Since then, never work without one either PCs/laptops or electronics. My drier here in Umeå, colder. Not really sure what is worse / better.
In the 70s and 80s there were still lots of electronics production lines in SE England, and they had lots of issues with static damage in the summer, until they started to effectively control it. The winter is damp enough that the aren't so many natural problems there. However, its easy to create problems with inappropriate heating systems, that make the humidity plummet.
I think you got it exactly opposite. When air is cold, it can hold much less water. When air from outside is heated up in the building, relative humidity becomes much lower, even though amount of water in air remains the same.
If you look at curves for static potential generation or static discharge rate vs atmospheric moisture level they are expressed in terms of the relative humidity. For much of the UK winter the outside relative humidity is near 100%, and dew or frost forms most nights as the temperature falls, and relative humidity goes above 100%. Trying to generate a static buildup in those conditions in very hard. Go into a heated building, with no dehumidification system. The amount of water in the air is the same as outside, but the relative humidity is much lower. Its very easy to build up considerable static charges in that environment.
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For much of the UK winter the outside relative humidity is near 100%, ...
That's a bit high. Here's the averages for January, generally the coldest month:
(https://www.metoffice.gov.uk/pub/data/weather/uk/climate/averages/maps/uk/8110_1km/RelativeHumidity_Average_1981-2010_1.gif)
In recent years I'd say 70% RH, based on my own outdoor readings, was a more typical figure for my little corner of the world (urban East London).
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For much of the UK winter the outside relative humidity is near 100%, ...
That's a bit high. Here's the averages for January, generally the coldest month:
(https://www.metoffice.gov.uk/pub/data/weather/uk/climate/averages/maps/uk/8110_1km/RelativeHumidity_Average_1981-2010_1.gif)
In recent years I'd say 70% RH, based on my own outdoor readings, was a more typical figure for my little corner of the world (urban East London).
The chart says much of the UK is in the 86-88% range. Over large areas the RH certainly exceeds 100% night after night for much of the winter, because there is frost or dew on the ground each morning. If its that high at night and 86% on average, that suggests a typical midday figure might only be 70% or so. That seems lower than measurements I made in North London/South Hertfordshire in the 80s. Typically, 40-70% RH is considered the comfortable range.
Winter is certainly characterised by a pretty high exterior RH over much of the country, but heated buildings can drop that figure so much that people complain of the dryness, and wooden furniture often warps.
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I built and repaired computers growing up (now 40) in the UK and not once did I wear anything to strop me zapping the bios, memory etc.. My home was fully carpeted in the SE of England.
Moved to mid/north sweden 7 years ago. My fantastic Sony Vaio laptop, I zapped 3 motherboards in 2 years :-( Since then, never work without one either PCs/laptops or electronics. My drier here in Umeå, colder. Not really sure what is worse / better.
In the 70s and 80s there were still lots of electronics production lines in SE England, and they had lots of issues with static damage in the summer, until they started to effectively control it. The winter is damp enough that the aren't so many natural problems there. However, its easy to create problems with inappropriate heating systems, that make the humidity plummet.
I think you got it exactly opposite. When air is cold, it can hold much less water. When air from outside is heated up in the building, relative humidity becomes much lower, even though amount of water in air remains the same.
If you look at curves for static potential generation or static discharge rate vs atmospheric moisture level they are expressed in terms of the relative humidity. For much of the UK winter the outside relative humidity is near 100%, and dew or frost forms most nights as the temperature falls, and relative humidity goes above 100%. Trying to generate a static buildup in those conditions in very hard. Go into a heated building, with no dehumidification system. The amount of water in the air is the same as outside, but the relative humidity is much lower. Its very easy to build up considerable static charges in that environment.
:-// You just basically confirmed what I wrote, and contradicted your post I quoted. If you have 100% relative humidity at 0oC, it becomes 25% if heated to 25oC. So regardless of how damp it is outside, you need air humidification system to keep acceptable humidity level at winter. On the other hand, UK is so damp so there should be no low humidity issues at summer.
(https://www.ctgclean.com/sites/www.ctgclean.com/files/wp-content/uploads/Relative-Humidity-Graph-e1367505504127.jpg)
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You just basically confirmed what I wrote, and contradicted your post I quoted. If you have 100% relative humidity at 0oC, it becomes 25% if heated to 25oC. So regardless of how dump it is outside, you need air humidification system to keep acceptable humidity level at winter. On the other hand, UK is so damp so there should be no low humidity issues at summer.
What makes you think a UK summer is damp? For most of a UK summer the RH is quite low, and static shocks are common. The RH surges on rainy days, but drops back quickly to a low percentage.
A warm UK building, summer or winter, will have a fairly low RH across most of the UK. You might want to humidify the air for comfort. For electronics assembly work the use of things like static dissipative materials and benchtop ioners is generally a more effective solution to static issues. A lot of electronics assembly actually occurs in places with minimal heating, so the RH might be a lot higher than you expect in the winter.
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There's plenty of people that never have and never will wear an antistatic wrist strap and can truthfully say they've worked with electronics/computers for X years and not broken anything
Those people most likely do not wear hard hat in construction site, don't use seat belt, data backups or insurance :) Youtube episode most likely will not change their mind. Some even believe that earth is flat BTW.
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What makes you think a UK summer is damp? For most of a UK summer the RH is quite low, and static shocks are common. The RH surges on rainy days, but drops back quickly to a low percentage.
(https://www.eevblog.com/forum/suggestions/episode-suggestion-esd-is-a-myth/?action=dlattach;attach=374698;image)
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A lot of electronics assembly actually occurs in places with minimal heating, so the RH might be a lot higher than you expect in the winter.
Unless you work at 10oC, you will have low humidity problem.
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What makes you think a UK summer is damp? For most of a UK summer the RH is quite low, and static shocks are common. The RH surges on rainy days, but drops back quickly to a low percentage.
(https://www.eevblog.com/forum/suggestions/episode-suggestion-esd-is-a-myth/?action=dlattach;attach=374698;image)
I just found where your table comes from. Those are daily averages. So a rainy July day in London averages 93%. A dry day averages 60%, but the big temperature drop at night means the working day is a lot lower than 60%. That's reasonably dry by static buildup standards.
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What makes you think a UK summer is damp? For most of a UK summer the RH is quite low, and static shocks are common. The RH surges on rainy days, but drops back quickly to a low percentage.
Right. Especially in case when your office/factory is air conditioned but w/o humidity control (as usual), then zapping due to dry air will happen not only winter but summer as well.
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A lot of electronics assembly actually occurs in places with minimal heating, so the RH might be a lot higher than you expect in the winter.
Unless you work at 10oC, you will have low humidity problem.
What makes you think that most assembly shops keep everything heated to even 10 degrees in the winter? Obviously its much hotter than that in parts where soldering and other heat treatments occurs, but it can be damned cold in large parts of a factory.
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A lot of electronics assembly actually occurs in places with minimal heating
This is BS unless you talk about assembly in Joe's garage.
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It affects us all in different ways. It can be location and therefore humidity, floor coverings (synthetics) or personally as we are not all built the same so some individuals can be more prone to ESD buildup than others.
A mate, a Dr. of EE lecturer tested all students in his class groups and some were advised that a path of handling ESD sensitive components may be not their wisest career path.
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A lot of electronics assembly actually occurs in places with minimal heating
This is BS unless you talk about assembly in Joe's garage.
I would think that a small operation is much more likely to be well heated throughout, as all operations are probably going to be in one room. A large factory is much more diverse.
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I would think that a small operation is much more likely to be well heated throughout, as all operations are probably going to be in one room. A large factory is much more diverse.
Now you think? Recently you were sure that "A lot of electronics assembly actually occurs in places with minimal heating".
So now please tell which large electronics SMD assembly factory(factories) does not follow 20-25oC and 40-65% humidity industry standards. Many would like to know.
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I just found where your table comes from. Those are daily averages. So a rainy July day in London averages 93%. A dry day averages 60%, but the big temperature drop at night means the working day is a lot lower than 60%. That's reasonably dry by static buildup standards.
Even if what you say about RH variation during the day is true (I didn't check that), do you assemble PCBs outside outside or with windows fully open? Or do you see more or less average RH within the building? Also there should be less than around 45% RH to call that a problem.
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I just found where your table comes from. Those are daily averages. So a rainy July day in London averages 93%. A dry day averages 60%, but the big temperature drop at night means the working day is a lot lower than 60%. That's reasonably dry by static buildup standards.
Even if what you say about RH variation during the day is true (I didn't check that), do you assemble PCBs outside outside or with windows fully open? Or do you see more or less average RH within the building? Also there should be less than around 45% RH to call that a problem.
Most buildings in the UK are not air conditioned. On a warm summer's day enough windows are open that they should keep the internal and external humidities fairly similar. At night the closed windows probably create a substantial difference.
Static discharges on a summer's day in the south of England can be quite a PITA for many people.
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What makes you think a UK summer is damp? For most of a UK summer the RH is quite low, and static shocks are common. The RH surges on rainy days, but drops back quickly to a low percentage.
Right. Especially in case when your office/factory is air conditioned but w/o humidity control (as usual), then zapping due to dry air will happen not only winter but summer as well.
To screw up humidity in summer you need some effort to do that (using air conditioner). Low humidity in winter comes naturally because of temperature difference inside and outside of the building.
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I just found where your table comes from. Those are daily averages. So a rainy July day in London averages 93%. A dry day averages 60%, but the big temperature drop at night means the working day is a lot lower than 60%. That's reasonably dry by static buildup standards.
Even if what you say about RH variation during the day is true (I didn't check that), do you assemble PCBs outside outside or with windows fully open? Or do you see more or less average RH within the building? Also there should be less than around 45% RH to call that a problem.
Most buildings in the UK are not air conditioned. On a warm summer's day enough windows are open that they should keep the internal and external humidities fairly similar. At night the closed windows probably create a substantial difference.
Static discharges on a summer's day in the south of England can be quite a PITA for many people.
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I just found where your table comes from. Those are daily averages. So a rainy July day in London averages 93%. A dry day averages 60%, but the big temperature drop at night means the working day is a lot lower than 60%. That's reasonably dry by static buildup standards.
Even if what you say about RH variation during the day is true (I didn't check that), do you assemble PCBs outside outside or with windows fully open? Or do you see more or less average RH within the building? Also there should be less than around 45% RH to call that a problem.
Most buildings in the UK are not air conditioned. On a warm summer's day enough windows are open that they should keep the internal and external humidities fairly similar. At night the closed windows probably create a substantial difference.
Static discharges on a summer's day in the south of England can be quite a PITA for many people.
If you have a factory with open windows, you're an idiot. As minimum, you'll get a lot of dust inside.
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If you have a factory with open windows, you're an idiot. As minimum, you'll get a lot of dust inside.
What kind of horrible environments do you have your factories in? Unless there is a specific adjacent dust generator, like a farm, or some awfully messy factory, electronics factories are normally fine with the windows open. Its not like general electronics assembly occurs in a clean room. Obviously some processes need their own special conditions, but not the general factory areas.
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Most buildings in the UK are not air conditioned. On a warm summer's day enough windows are open that they should keep the internal and external humidities fairly similar.
Not conditioned :blah: and open windows :blah:
:palm:
Before you spread your stupid uneducated opinion about electronics printed board assembly factories, at least do some research first - about what it takes to properly manufacture modern electronics.
Watch this episode for starters:
https://www.youtube.com/watch?v=bTij7Juj5qE (https://www.youtube.com/watch?v=bTij7Juj5qE)
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Most buildings in the UK are not air conditioned. On a warm summer's day enough windows are open that they should keep the internal and external humidities fairly similar.
Not conditioned :blah: and open windows :blah:
:palm:
Before you spread your stupid uneducated opinion about electronics printed board assembly factories, at least do some research first - about what it takes to properly manufacture modern electronics.
If you have broad experience of electronics assembly around the world, in different climates, it would most interesting to hear your experiences of what those environments are like.
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If you have broad experience of electronics assembly around the world, in different climates, it would most interesting to hear your experiences of what those environments are like.
Many years I used to work for a company that have own fully equipped SMT assembly floor +/- same size as in EEVblog video and briefly visited another, much bigger one. From environmental control point of view they are all the same: controlled temperature 24/7 all round the year both in assembly and components storage places. No freaking open windows for god's sake. Big factory even have controlled humidity so it does not float around when rain comes.
To put it in Laymans Terms: when your pick&place machine alone costs 10x more than ventilation/condition system for whole factory floor then it is insane stupidity to invest in manufacturing equipment but save on climate control.
In case you wonder why it is so important to have control over temperature & humidity in electronics manufacturing (SMT assembly) floor - it's very important ;) If failure rate of boards that comes out of SMT assembly suddenly becomes high, then QA experts of customer will visit factory. If they do not see that factory follows environmental or ESD safety standards (yes, factory *must* have temp&humidity monitors/loggers all over the place), then lawyers of customer will tear it apart.
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If you have broad experience of electronics assembly around the world, in different climates, it would most interesting to hear your experiences of what those environments are like.
Many years I used to work for a company that have own fully equipped SMT assembly floor +/- same size as in EEVblog video and briefly visited another, much bigger one. From environmental control point of view they are all the same: controlled temperature 24/7 all round the year both in assembly and components storage places. No freaking open windows for god's sake. Big factory even have controlled humidity so it does not float around when rain comes.
To put it in Laymans Terms: when your pick&place machine alone costs 10x more than ventilation/condition system for whole factory floor then it is insane stupidity to invest in manufacturing equipment but save on climate control.
In case you wonder why it is so important to have control over temperature & humidity in electronics manufacturing (SMT assembly) floor - it's very important ;) If failure rate of boards that comes out of SMT assembly suddenly becomes high, then QA experts of customer will visit factory. If they do not see that factory follows environmental or ESD safety standards (yes, factory *must* have temp&humidity monitors/loggers all over the place), then lawyers of customer will tear it apart.
You have narrowed "electronics assembly" to a single topic - stuffing PCBs. This is a small part of the overall assembly space in an integrated assembly plant, and these days it is often subcontracted, so it doesn't occupy the final assembly plant at all. What about all the other assembly work? Putting displays, multiple PCBs, connectors and other modules into a final product takes lots of space, and tightly controlling the atmosphere would be a waste of time for most of it, unless the local climate is quite troublesome.
In the assembly plants I have been in, in the UK and Asia, PCB stuffing takes a much smaller space than, say, the final burn in area. Everything beyond goods inward, and up to the case being screwed/glued/welded shut requires a proper static control regime. Burn in is typically something like 48 hours running, followed by probing to ensure everything is functioning to spec. That means burn in happens before the case is closed, to facilitate the post soak probing. You need to manage static all the way through. If you make 10k or 20k TVs a day, that takes a lot of space. The only environmental control worth bothering about during soak testing, for most products, is to avoid a condensing atmosphere and excessive dust buildup.
Environmental control is seldom an all or nothing issue. Most factories control specific areas in specific ways. For example, if there is any paint spraying, that requires a moderate quality clean room to avoid particulates spoiling the finish; it requires efficient capture of waste paint; and if there is the risk of a condensing atmosphere it probably requires humidity control. You don't apply that kind of practice to the whole plant, though. By only applying it in specific areas, the energy costs are kept under control.
The requirements for PCB assembly depend a lot on the climate. In a place like Singapore, where the humidity hovers around condensing for much of the year, humidity control is important throughout an electronics assembly plant. The places where really tight environmental control is needed during PCB assembly, it is ensured by the equipment itself. Most SMD reflow and vapour phase soldering systems are completely enclosed, with a well controlled atmosphere inside. Old through hole wave soldering lines were far less controlled. The use of a dry nitrogen atmosphere within an SMD soldering system is pretty common practice now. Its not expensive to continuously separate nitrogen from the air these days, as long as your requirement is not for perfect purity. That dry inert atmosphere, combined with preheating, helps dry out the components before they reach the high heat of the soldering process. Eliminating most of the oxygen eases the demands on the flux, and results in a less tarnished final product.
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You have narrowed "electronics assembly" to a single topic - stuffing PCBs.
Moreover, the topic of ESD control seems to have been narrowed to assembly. There's also service, repair, calibration and site service to consider. Those four happen in all sorts of environments, from immaculate cal labs to dirty/hot/cold/wet/dry factory floors.
Even managed operating environments have ESD concerns - I used to have to manage rack upon rack of computers, network equipment and telephone switches in an environment where connections were being made and broken on a daily basis, boards swapped, whole chassis swapped. Plenty of room there for ESD incidents. I never had any confirmed ESD kills, but did have quite a few suspicious deaths.
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You have narrowed "electronics assembly" to a single topic - stuffing PCBs.
Moreover, the topic of ESD control seems to have been narrowed to assembly. There's also service, repair, calibration and site service to consider. Those four happen in all sorts of environments, from immaculate cal labs to dirty/hot/cold/wet/dry factory floors.
Even managed operating environments have ESD concerns - I used to have to manage rack upon rack of computers, network equipment and telephone switches in an environment where connections were being made and broken on a daily basis, boards swapped, whole chassis swapped. Plenty of room there for ESD incidents. I never had any confirmed ESD kills, but did have quite a few suspicious deaths.
ESD susceptibility varies widely with assembly level. In a single component there is very little capacitance to absorb any ESD, and often only a single trace and/or component in the ground path.
At the circuit card level there is far more capacitance, and often multiple paths to ground, series resistance and other mitigating factors. Often these features are deliberately designed in to make the boards more robust.
These factors continue at each level of assembly up to the finished and delivered product. Any manufacturer who has a warranty or reliability requirements has done the work to make sure that normal ESD pulses applied to normally accessible parts of the equipment are non damaging.
How much problem you have personally had with ESD will vary with your environment and with the type of work you do. Board swapping entails relatively low risk because it is hard to touch most boards to remove them without touching a grounding element of the chassis, and because the boards inherently are less susceptible to damage. A new board being pulled from packaging has more risk of being exposed than one being pulled from a chassis, but still benefits from the generally lower susceptibility of board level products.
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I have GaN LED's in series with my workbench ESD mat ground, and it tells me everything, they light up with any ESD or AC hum. Great for your workbench, I've caught bad grounds on wiring and equipment with the LED's.
Humidity gets very low during Canadian winter and ESD is pretty harsh. I can make 30kV getting up from my office chair, and that will kill a semi.
For many years, ESD was scoffed at in the service and repair industry. I knew to "touch ground" and discharge static before swapping a board on a computer, as nobody would spend money on wrist straps and bags. Other techs had ESD-related callbacks and problems, the VN10K is the most sensitive-to-static component ever made. They die about a week or two after being subjected to ESD.
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I have GaN LED's in series with my workbench ESD mat ground, and it tells me everything, they light up with any ESD or AC hum. Great for your workbench, I've caught bad grounds on wiring and equipment with the LED's.
Humidity gets very low during Canadian winter and ESD is pretty harsh. I can make 30kV getting up from my office chair, and that will kill a semi.
For many years, ESD was scoffed at in the service and repair industry. I knew to "touch ground" and discharge static before swapping a board on a computer, as nobody would spend money on wrist straps and bags. Other techs had ESD-related callbacks and problems, the VN10K is the most sensitive-to-static component ever made. They die about a week or two after being subjected to ESD.
Can you tell more about those LEDs and how they work?
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You have narrowed "electronics assembly" to a single topic - stuffing PCBs.
Indeed. This is part where temperature and humidity shall be controlled. I indicated that I talk about SMT assembly and you were ok with that. Suddenly you are not? :)
What about all the other assembly work?
When components are on the PCB, then temperature & humidity is not an issue anymore indeed. Workers need comfortable temperatures instead :)
The only environmental control worth bothering about during soak testing, for most products, is to avoid a condensing atmosphere and excessive dust buildup.
Burn in is not assembly, so it does not count here in this context anyway.
Most SMD reflow and vapour phase soldering systems are completely enclosed, with a well controlled atmosphere inside.
:palm: Nitrogen in the oven just reduces oxidation. It's not humidity control.
Avoidance of popcorn effect is why you need humidity control in the component storage and basically in whole SMT assembly floor: https://en.wikipedia.org/wiki/Moisture_sensitivity_level (https://en.wikipedia.org/wiki/Moisture_sensitivity_level)
When temperature outside oven changes by more than 5 degrees oC - you must change temperature profile (preheat) of the oven. Viscosity of solder paste also changes due to temperature. Better just read some specs of solder paste and component temperature profiles to see that it is indeed insane stupidity to not control temperature around board assembly :)
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You have narrowed "electronics assembly" to a single topic - stuffing PCBs.
Indeed. This is part where temperature and humidity shall be controlled. I indicated that I talk about SMT assembly and you were ok with that. Suddenly you are not? :)
What about all the other assembly work?
When components are on the PCB, then temperature & humidity is not an issue anymore indeed. Workers need comfortable temperatures instead :)
When the components are on the PCB the environmental requirements are little different than any other point in assembly, apart from the inside of the reflow or vapour phase system. You need to control humidity, if condensation is a potential issue for you, and you need to control static.
The only environmental control worth bothering about during soak testing, for most products, is to avoid a condensing atmosphere and excessive dust buildup.
Burn in is not assembly, so it does not count here in this context anyway.
How is burn in not relevant, when it requires the same environmental conditions as the rest of assembly - a non condensing atmosphere and good static control? Do you exclude test and other key functions of the typical assembly shop from your thinking? If so, why?
Most SMD reflow and vapour phase soldering systems are completely enclosed, with a well controlled atmosphere inside.
:palm: Nitrogen in the oven just reduces oxidation. It's not humidity control.
Now you are just being a jackass. I said DRY nitrogen is used. Did you miss the word DRY on purpose?
Avoidance of popcorn effect is why you need humidity control in the component storage and basically in whole SMT assembly floor: https://en.wikipedia.org/wiki/Moisture_sensitivity_level (https://en.wikipedia.org/wiki/Moisture_sensitivity_level)
It would be a very poorly run line which keeps components outside their well controlled long term storage conditions (sealed packaging, or low humidity storage area) for long periods, where they could absorb enough moisture deep into their surfaces to be a problem. Popcorning is largely a problem of poor long term storage, and avoiding it doesn't require a tightly controlled atmosphere. It just requires a rather dry one. The key thing in the assembly line is to ensure a non-condensing atmosphere at all points, with no downward temperature shocks leading to sudden condensing.
When temperature outside oven changes by more than 5 degrees oC - you must change temperature profile (preheat) of the oven. Viscosity of solder paste also changes due to temperature. Better just read some specs of solder paste and component temperature profiles to see that it is indeed insane stupidity to not control temperature around board assembly :)
What kind of horrible reflow systems have you used? They can't cope with a stream of boards intermixed at different incoming temperatures, but they cope with a slowly changing incoming temperature just fine. Part of their specifications is te incoming temperature range they can adapt to, and how quickly it can change. Their thermostatic control ensures the temperature of the boards are stabilised, and the dry atmosphere ensures a rapid dispersion of any residual moisture.
The solder paste viscosity is usually only critical during the actual reflow, where the reflow machine tightly controls the temperature, and therefore the viscosity. I have never seen it affect the PnP systems. Low viscosity between the PnP and reflow machines used to often be a cause of small parts being shaken out of place. That lead to a huge rise in the use of glue spotting. People tend to just manage their lines better these days, and reduce shaking.
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I have visited this thread from time to time and I find myself wondering when the shape of the Earth will become a topic of debate..........
Oh wait;
Th3ere is already a thread on that.
:palm: :palm:
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I have GaN LED's in series with my workbench ESD mat ground, and it tells me everything, they light up with any ESD or AC hum. Great for your workbench, I've caught bad grounds on wiring and equipment with the LED's.
Humidity gets very low during Canadian winter and ESD is pretty harsh. I can make 30kV getting up from my office chair, and that will kill a semi.
For many years, ESD was scoffed at in the service and repair industry. I knew to "touch ground" and discharge static before swapping a board on a computer, as nobody would spend money on wrist straps and bags. Other techs had ESD-related callbacks and problems, the VN10K is the most sensitive-to-static component ever made. They die about a week or two after being subjected to ESD.
Can you tell more about those LEDs and how they work?
My silly LED's light up with even a few pF stray (mat) capacitance from AC hum, and showed me two bad ESD grounds on my bench. GaN green LEDS are super sensitive, even 1uA you can see.
I had a worn out duplex receptacle that made no connection to GND pin, and an open-circuit snap-clip on the ESD mat.
I tried adding a protective diode-clamp across the LED's but leakage just made them not work.
Try build it. Totally worth it to "see" ESD.
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I tried adding a protective diode-clamp across the LED's but leakage just made them not work.
Try using just the base-collector junctions of small signal BJTs as diodes, or a couple of diode wired low leakage JFETs such as 2N4117s.
You did stack the diodes so that the Vf added up to more than the Vf of your LEDs? Obvious I know, but we've all missed something stupid like that at some point.
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This is what I tried. It clamped hard about 4.3V leaving maybe 40mA for the LED's.
The problem is the clamp starts conducting enough to hog LED current, well below the actual clamping point.
So at 2.5V, it was like 120uA.
The diodes are a poor choice, but I wanted something strong enough to take a high current hit.
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I've just tried a quick simulation with 5 stacked 2N4117 JFETs, diode wired, and they only hog about 3uA at 2.5V BUT they are only rated for a forward gate current of 50mA so just plain aren't up to the job. I don't think you'll find a PN junction with the right combination of characteristics for this job. If you can find a gas discharge tube with a low enough voltage rating you might be onto a winner with that.
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I think a neon lamp or GDT may work as a clamp for the LED's. The ESD pulse rise-time is so fast.
Littelfuse CG75 (http://www.littelfuse.com/~/media/electronics/datasheets/gas_discharge_tubes/littelfuse_gdt_cg_cg2_datasheet.pdf.pdf) gas discharge tubes rated ~75VDC ramp impulse 100V/sec. but rated 400-650V surge impulse breakdown, which is high.
The LED's could take the impulse, say 100mA with a series resistor, or another resistor to limit the whole ESD discharge current?
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IMO if there is already 1 meg resistor in series, you could try connecting small cap in parallel which will smooth the pulse. And likely there is no ESD protection needed with 1 meg resistor at all. If there is say 50kV discharge, current will be limited to 50mA (unless there is flashover in resistor).
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IMO if there is already 1 meg resistor in series, you could try connecting small cap in parallel which will smooth the pulse. And likely there is no ESD protection needed with 1 meg resistor at all. If there is say 50kV discharge, current will be limited to 50mA (unless there is flashover in resistor).
Dielectric breakdown in dry air is ~3MV/m so the distance for a flashover at 50kV would be about 17mm.
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This is really a way to "see" ESD and I need it to be reliable. I can't tell you how many companies I've seen with old trashed bench wiring and nothing grounded properly, or non-ESD floor wax, or worn out wrist straps, yet they are working with delicate electronics. They think ESD prevention is a nuisance, something very informal.
One company had repeated product MOSFET failures about 2-4 weeks after PCB stuffing. The MOSFET controlled a gas-solenoid and shorted, leaving fuel on. Of course explosions resulted :palm: The MOSFET circuit was reviewed, the failed MOSFETS sent back to the semi manufacturer for electron microscopy, and all failures were said due to ESD damage of the gate junction. The company's manufacturing plant had loosey goosey ESD policies, pretty much nothing. It was a debacle. ESD is not a myth, it's just invisible.
These ESD mat/wrist-strap resistors are vanilla 1/4W through-hole parts, so many kV just jumps across them. They are to protect against mains electrocution.
Without the 1MEG resistor, I'm going to try some high level ESD hits and see how it does. Something that can take beyond 61000 Level 4 machine hits
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This is really a way to "see" ESD and I need it to be reliable.
Well you could just buy some of the little alarm boxes made for this job. I've never bought them myself, so I don't know their price, but they aren't very complex. They are used in most labs, so I assume the production volume is high enough for the price to be low.
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These ESD mat/wrist-strap resistors are vanilla 1/4W through-hole parts, so many kV just jumps across them.
Just for the benefit of those not in the know:
The construction of most standard small metal or carbon film resistors involves a spiral groove cut into the film. This means that the breakdown voltage of these parts is mostly dictated by the size of the gap in these spirals, not the overall size of the part. That's why when dealing with high voltages old fashioned carbon composite are frequently specified as in those the element that would have to undergo breakdown is near to the full length of the part. The maximum withstand voltage on a typical 1/4 carbon film resistor is 500V, the withstand voltage on a 1/4W carbon composite resistor is 6kV.
If you want the very best isolation in the face of high voltages use resistors with specified withstand voltages and use them in strings constructed so that they are never individually subjected to voltages above their rated withstand voltages (e.g. 3 x 333k in series in place of 1M, and so on).