Tin whiskers: What happens when they spontaneously erupt? (2018)

https://www.microcontrollertips.com/when-tin-whiskers-spontaneously-erupt-faq/

by forgotthepasswd • 4 years ago

200 126 4 years ago

microcontrollertips.com

mmastrac4• 4 years ago

After seeing the articles on ice spikes, I wonder if this is somehow a related phenomenon.

thanatos519• 4 years ago

Indeed. Maybe they are also related to bone spurs!

jerf• 4 years ago

Remind me more of this, only in slow-mo: https://www.nature.com/articles/nature.2015.16771

dmitrygr2• 4 years ago

Use lead solder, like NASA does: easier to use, and no whisker issues. Just wash your hands afterwards

mmastrac4• 4 years ago

Better to solve these issues long-term. Lead's external costs in full product lifecycles are just too high.

iancmceachern• 4 years ago

Yeah, and we're not allowed to even put it in products anymore by law (RoHs, reach, etc)

dmitrygr2• 4 years ago

As you read in TFA, there is no known solution, nor even a known cause for whiskers

Flozzin• 4 years ago

I wouldn't recommend this. If you do use lead soldering, make sure you don't breathe in any fumes.

the-dude2• 4 years ago

The boiling point of lead is 1749 °C (3180 °F).

semi-extrinsic2• 4 years ago

The vapor pressure of lead at 300 °C is around 10^-6 Pa. In laymans' terms, there is zero evaporation of lead happening during soldering. Ice at -40°C evaporates (sublimates) 10 million times faster.

The fumes from soldering are from the flux or rosin, and that is just as dangerous if you are using lead free solder. Always use adequate ventilation and/or filtration to avoid inhaling fumes.

foldr6• 4 years ago

The trick is not to end up inhaling or eating the solder in its solid state. This is actually quite difficult to avoid, as cleaning the tip of your iron will create lots of tiny solder balls that fly everywhere and can persist in your environment.

Personally I would say that in hobbyist electronics tin whiskers are the least of your concerns when it comes to the reliability of the devices you’re making. I wouldn’t risk using leaded solder even if the risk is low.

myself248• 4 years ago

Or just get your blood lead level measured.

A few months ago, I happened to be at the doctor getting some other stuff checked out, and the week prior to the appointment I had done a ton of soldering, like two 12-hour days bashing out a whole batch of boards, both paste reflow and hand-PTH work, with a fair bit of sucker rework, and of course after that the lab needed a good tidying so I emptied all the suckers and tip cleaners as part of that. All tin-lead solder.

Zero gloves, and I only wore a mask part of the first day (when there were other people around). And actually the several weeks leading up to that also saw a lot of SMT rework and other up-to-by-elbows-in-solder sort of activity.

So I figured, that's kind of a worst-case for my lead exposure, hey Doc, can I get my blood lead level checked? Sure why not, it's one extra vial on top of the bloodwork already being ordered!

And the results came back below the test's detectable level.

So as far as I'm concerned, if that didn't do it, I don't think I have anything to worry about. Now, I'm sort of a germophobe and I never eat with my hands, so this doesn't necessarily generalize, but as far as skin absorption or vapor inhalation, I've gone from "not very worried" to "abjectly unconcerned" after getting that result.

I would encourage everyone to get their level measured and have actual data to make decisions with. Superstition does not become us.

Steltek3• 4 years ago

On the contrary, I am not NASA. I'm not even a consumer electronics company. I'm a hobbyist at home, soldering things at my desk or table. Lead-free is the least of my problems when building something and I don't believe "just wash your hands" is sufficient for cleaning my workspace (or kitchen table?) of possible lead contamination.

JaggedNZ• 4 years ago

Fellow hobbyist here. Actually your biggest health risk is industrial asthma from flux fumes. I know professionals who have spent a good fraction of there lives soldering with no lead poisoning issues. Lead needs to be consumed or inhaled for it to be an issue. The guy I meet who did have lead poisoning, large bore rifle shooting coach, from spending to much time at the “wrong end” of the rifle range. Lots of lead dust there.

alar44• 4 years ago

It definitely is enough. I don't know where the myth that looking at lead kills you started, but unless you are eating it or breathing it in (soldering is not hot enough to vaporize lead) there's nothing to worry about.

adrian_b5• 4 years ago

Besides lead, there is a second element which greatly reduces the risk of tin whiskers, when alloyed to tin: antimony.

However the proposals of replacing the tin-lead alloys withe tin-antimony alloys have been rejected due to the fear that antimony is also toxic.

While antimony in high doses is indeed quite toxic, it is less dangerous as a pollutant than lead, because it does not have the same tendency for very long time accumulation in animal bodies and such a strong effect on the nervous system.

RicoElectrico• 4 years ago

No one has been able to eliminate whiskering, as the phenomenon is not yet fully understood.

It's the kind of stuff we should be embarrassed not to understand. I get that understanding living things can be tricky due to complexity and issues with controlling conditions, but a lump of metal? Whatever we find out will at least save us money in damaged devices, and hopefully drive some progress in metallurgy as well.

We had an era in semiconductor manufacturing when despite the relative simplicity the process was not understood/controlled fully, which took the toll on yield. E.g. CMOS was super fussy due to difficulties in creating gate oxide - impurities in air like halogens made the yield seasonal [1]. But now I assume that if any problems arise, they're due to bona-fide complexity.

[1] https://news.ycombinator.com/item?id=28178612

semi-extrinsic2• 4 years ago

A lot of the challenge here AFAIK is that the process needs to be understood at the molecular level, where we measure time in picoseconds (10^-12), while this process takes something like 10^6 seconds. The disparity is an absolutely astronomical factor of 10^18.

robomartin7• 4 years ago

It's the kind of stuff we should be embarrassed not to understand.

We understand it. Onset is stochastic. Mitigation is impossible given current regulations in consumer-land. Read my longer comment for further details.

EDIT: What I mean by "we understand it" is that we know that lead-free solder chemistry leads to tin whisker growth. When I was taking a deep dive into this many years back, the researchers I was working with at NASA told me "Growth onset can be 0 days to 3 years after manufacturing. Your guess is as good as mine.". And, BTW, you can have growth start in a few days in one corner of the PCB and a few months later elsewhere. It's a complex relationship of materials properties.

We know that tin whisker growth in lead-free solder is as much of a reality as gravity is between two celestial bodies. In other words, it will happen. We simply have no way to predict when or how quickly they will grow. It might just be too complex to compute/predict given the variables involved.

gowld• 4 years ago

That sounds like not understanding it.

prutschman• 4 years ago

Could potting prevent this, or can the whiskers "push through" epoxy?

dr_orpheus• 4 years ago

Yes? In my experience (some spacecraft electronics stuff) this is also on the list of things where we think conformal coating/potting helps prevent tin whiskers. But there are still instances where Tin whiskers have grown and pushed through conformal coating on a PCB.

Edit: Go look at the more detailed response from robomartin

robomartin7• 4 years ago

No. Can't prevent it. Yes, they can push through epoxy or buckle under it (which isn't a solution). Read my longer answer for details. These things are a nightmare.

jccooper• 4 years ago

Yes; satellite boards tend to have conformal coatings, it helps but it's not a complete solution. (The coatings also help avoid shorts from junk floating around, and launch vibration.) Because of the inherent unreliability and difficulty in replacement, they also try really hard to avoid lead-free solder requirements.

robomartin7• 4 years ago

I have dealt with the tin whisker problem in the context of aerospace applications (both space-borne and terrestrial flight), including extensive consulting with subject matter experts from NASA.

The bottom line is quite simple:

Tin whisker growth onset is a stochastic process. We cannot predict when it will start and we cannot prevent it.

Once they start growing it is almost impossible to contain them. They will poke through conformal coatings such as parylene and arathane. If they don't, they will buckle (coil-up) under the coating.

While buckling sounds like a desirable outcome, this could lead to shorting of adjacent contacts in todays fine pitch integrated circuits and components.

Growth rate can be in the order of 10 mm per year. This means that adjacent leads of something as mundane as a SOIC-16 package can be shorted by a tin whisker in 28 days or less.

The take away is: There's nothing we can do about tin whiskers that is 100% guaranteed to prevent growth or slow it down by a non-trivial amount. The only path that prevents their growth is to use lead-based solder. This is why, as an example, we would do such things as send out BGA's with RoHS compliant solder balls to be re-balled with leaded solder.

Time for a bit of a rant: All my work in this area led me to look at the RoHS initiative as yet another example of something that, while well intentioned, it will likely have precisely the opposite effect from what was intended.

The fact that lead-free solder is susceptible to tin whisker growth means that 100% of all consumer electronic products are ticking time bombs when it comes to failures. This means that all kinds of consumer, commercial and industrial electronic products will fail over time in ways we might not be able to explain. The reason for this is that nobody does deep forensics when products fail. There is no reporting from the likes of Apple, Samsung, LG, Visio, Sony and myriad other manufacturers on failure rates and causes. In fact, they might not even have this data as consumer, commercial and industrial users simply replace the devices as they fail and move on.

In other words, it is likely RoHS has caused --or will cause-- massively more garbage in landfills. As a simple data point, my 40 year old HP-41 calculator still works perfectly fine. It is impossible to imagine a RoHS-compliant calculator not ending up in a landfill way earlier than 40 years.

There was a bit of a movement to roll back RoHS around the time it was being enacted. Going up against many nations and politicians using "save the planet" to get elected proved impossible for those who rightly brought-up that the transition to lead-free solder required far more research before we fully understood the potential consequences.

It wasn't about not wanting to go lead-free, it was about making the move when the science and math indicated that it would not create the massive problem we now likely have on our hands. The data on electronics waste due to tin whiskers is probably impossible to find. It might not even exist. Which is a tragedy.

If you want to learn more about this, here are a couple of good links:

https://nepp.nasa.gov/whisker./background/index.htm

https://nepp.nasa.gov/whisker/reference/tech_papers/kadesch2...

https://www.google.com/search?q=tin+whisker&hl=en&tbm=isch

https://web.calce.umd.edu/tin-whiskers/

twofornone• 4 years ago

Are there any easy ways to clean up a PCB that's developed whiskers? And once a whisker erupts on a given PCB, does that generally indicate that others are likely to form on that board in short order?

robomartin7• 4 years ago

All else being equal, once growth starts it is likely to start everywhere on that board. This is a probabilistic assumption based on the likelihood of all of the solder on that board being from the same batch and having been applied with the same process parameters. The same cannot be said of the device leads, where each manufacturer and batch could very well be different.

It's quite a nightmare, particularly when you are trying to figure out if this stuff can kill people you want to send into space. The only real mitigation is lead-based solder and coatings on components.

Cleaning? That can be both dangerous and highly ineffective. The whiskers are very strong due to their molecular scale. Mechanical brushing might fracture longer whiskers. Then you have the problem of ensuring that they don't go under devices or in-between contacts. The process would likely have to be repeated many times and include both manual and automated optical inspection as well as x-ray imaging (which might not be able to detect fine whiskers). And then there's the reality that you probably don't want to inhale these things at all.

So, off to the landfill we go. It is likely better to build a new board than to try to clean one. I can't even begin to compute the delta in carbon footprint between making a board with lead-based solder that will last decades and the "clean/green" RoHS board that is sure to end-up in a landfill (cleaning/fixing it is bound to have a massively larger carbon footprint that making a new board).

oceanplexian2• 4 years ago

Well actually, there is a way, but you might kill said PCB.

Heat everything up in an oven, the solder will reflow, and you might temporarily fix the board. It’s a similar idea to the Towel/Xbox 360 fix. I can attest to having successfully saved lots of random electronics this way.

All of this started with the eco-friendly alternatives to lead solder, I have a lot of old computer hardware and motherboards, and the hardware from the early 2000s is the least reliable, whereas most game consoles, motherboards, etc. from the 80s and 90s works flawlessly. To this day I swear by the leaded stuff for personal use, it flows better, doesn’t crack, and is superior in every way.

stefan_2• 4 years ago

The Restriction of Hazardous Substances Directive (RoHS) is not about preventing garbage in landfills, and frankly it's been 18 years and the sky is not falling.

MisterTea• 4 years ago

Yes but the parent is not stating that. They are stating that a "save the environment" effort is not very environmentally friendly if it makes more waste.

adrian_b5• 4 years ago

The sky is not falling in large part because the transition to lead-free solder was simultaneous with the transition to electronic devices that are not repaired and which frequently have a lifetime not much longer than their warranty time.

Most current electronic devices are dumped much earlier than when they would fail due to the tin whiskers.

Many consumer electronic devices made 50 years ago are still usable without any problems caused by the aging of the soldering or of the semiconductor devices (but old electrolytic capacitors may have to be replaced). The electronic devices that are made now do not have any chances of such a long lifetime, with the exception of a few devices made for special requirements, e.g. military/aerospace.

xmodem2• 4 years ago

Do you happen to know if tin whiskers have anything to do with passing current? (in other words, will a device that's in constant use develop them faster than a physically identical device that's switched off and in storage)

londons_explore• 4 years ago

Passing current means thermal cycling...

And thermal cycling definitely accelerates whisker formation.

hulitu10• 4 years ago

Yes. Voltage has a big effect on whiskers.

robomartin7• 4 years ago

will a device that's in constant use develop them faster than a physically identical device that's switched off and in storage

Storage was one of the areas I researched extensively. It was like that scene in the movie "Clear and Present Danger" [0] in that the answer was always the same frustrating one regardless of conditions:

Stochastic growth onset; 0 to 3 years; can't predict growth start or rate; can't stop them; they will penetrate almost anything practical you can put on a board.

[0] https://www.youtube.com/watch?v=PqtjbWJPIgQ

Steltek3• 4 years ago

In other words, it is likely RoHS has caused --or will cause-- massively more garbage in landfills. As a simple data point, my 40 year old HP-41 calculator still works perfectly fine. It is impossible to imagine a RoHS-compliant calculator not ending up in a landfill way earlier than 40 years.

Environmentalists can only wish that people were disposing of their electronics because of tin whiskers. Long lived consumer electronics needs a cultural overhaul more than it needs leaded solder.

ghostly_s• 4 years ago

I did not know these whiskers had been implicated in the Toyota unintended acceleration scandal: https://nepp.nasa.gov/whisker/reference/tech_papers/2011-NAS...

Ottolay• 4 years ago

RoHS does not just restrict lead. It also restricts use of mercury, cadmium, and several toxic compounds.

dilyevsky• 4 years ago

Miniaturization trend definitely doesn’t help here either…

alfor• 4 years ago

Does wisker form inside semiconductor also or do they use metals immune to that?

hulitu10• 4 years ago

Yes they do but slower. In the past gold was used for wires from terminal to pads. Gold as far as i know is not so subceptible to form whiskers. But gold is expensive and now they use copper instead of gold.

FpUser• 4 years ago

Accepting RoHS was in my opinion one of the most idiotic environmental initiatives that was rammed through without much thinking about long term cost / benefit analysis.

hulitu10• 4 years ago

A repaired device is one less device sold new. At the end what matters is money.

Damogran6• 4 years ago

State of Colorado Datacenters got them. The response to them were weird...if any machine were in any of the affected areas, they were persona non grata...they could never leave those datacenters as functional server.

It DID lever some money for an awesome off-site backup datacenter...which was eventually our only datacenter for 'reasons'.

In our case, I think one of the datacenter's raised floors got carpeted (don't judge, it predated me, I was equally baffled) and a grounding issue caused a voltage drift causing the tin to migrate...

walrus01• 4 years ago

raised floors in general are a nightmare for grounding/bonding/differences in potential between racks, the steel floor structure, the building, and electrical conduits.

there's a reason why almost nobody builds them new from a clean-sheet-of-paper design anymore for serious datacenter applications or ISP/telecom purposes, which are racks/cabinet on concrete slab and everything overhead now.

it's much easier to ground/bond everything together using some very fat copper cables run along ladder rack overhead, and bond all the racks to that.

pomian• 4 years ago

Raised floors where a great way to create laminar flow for clean rooms. I suspect that as with manufacturing, the "clean" space is inside the computers now.

tejohnso• 4 years ago

This is very surprising to me. I had no idea that certain conductors had some kind of (stochastic, according to robomartin) built-in time delayed short circuit mechanism that will, without question, manifest itself given enough time.

Like some kind of natural electronics prank.

voakbasda• 4 years ago

If you were feeling particularly cynical, you might wonder whether this phenomenon has been incorporated into shipping products, such manufacturers would be assured that their goods would fail shortly after the warranty expired.

robomartin7• 4 years ago

assured that their goods would fail shortly after the warranty expired

I have seen a number of similar comments on this thread. Manufacturers were dragged kicking and screaming --they were forced, through legislation-- to switch to lead-free solder. Nobody --nobody-- in manufacturing wanted this. This idea that going lead-free was a conspiracy by manufacturers to have their products fail more often is completely false.

One of the most well-known episodes of mass failures due to tin whiskers happened when the Swatch Group (watch manufacturer) converted to lead-free solder. They had so many failures that they ended-up requesting an exception from RoHS [0].

As I said in another comment. The problem with RoHS as it pertains to tin whisker failures is that we will likely never know what percentage of failing consumer, commercial and industrial products end-up in the landfill because of the forced and premature transition to this lead-free solder. If one studies that history of the transition it is easy to see it includes many companies clamoring for years of additional studies before making the change. We went into it by force in 2006 without having had full data on potential issues.

At the time I was manufacturing expensive FPGA-based real time image processing boards. I made the decision to stop shipping product to Europe.

My decision was based on a very simple reality: I still had to honor a years-long warranty in Europe and could not include any clause stating that we could not be responsible for a government-mandated technology known to have serious problems that could lead to failures at any time, even very early on. Companies were forced through mandate and given absolutely no immunity from the very real tin whisker problem. I did not ship a product into Europe for two or three years. We were busy enough everywhere else, so I did not care one bit. We actually had European customers who needed the hardware buy through a US-based path and then hand carry into the EU through whatever means. Not my problem.

[0] https://hlinstruments.com/RoHS_articles/A-1018_Swatch.pdf

1970-01-01• 4 years ago

Much more info here:

https://nepp.nasa.gov/whisker/

ChuckMcM• 4 years ago

It really is an amazing phenomena. Effectively atoms of tin are moving from the tin out to the end of the whisker. We spent a week talking about whiskering(sp?) in my materials science class at USC because it was such a big deal in the EE world.

Prior to that class my world view was that only electrons could travel through metal, only to find that metal can travel through metal too!

Locally at NASA Ames they had an experiment where they had a bunch of different assemblies being exposed to various conditions (high electric fields, non-ionizing radiation, etc) and one of the things they were measuring was the production of whiskers and other changes in material properties (strength, toughness, Etc.). Always amazing what we know and what we don't know about what we know.

zdragnar• 4 years ago

that metal can travel through metal too!

I recommend watching clips of mercury amalgamations forming (nile red has some great videos on youtube).

There is something about it that is both disturbing and beautiful to me.

cjameskeller• 4 years ago

That was a welcome rabbit hole. Thank you!

pontifier• 4 years ago

My current theory of whisker formation is single atom mercury impurities causing local mobility at the base of a whisker.

rootusrootus• 4 years ago

Effectively atoms of tin are moving from the tin out to the end of the whisker.

Don't tin whiskers get built from the base up, though? So the tip was the first thing built, and just gets pushed farther away.

jwilk• 4 years ago

as fast as 15 nanometer per second to 1 mm per year

That doesn't sound right. 15 nm/s is ~47 cm/year.

greggsy• 4 years ago

I don’t think it’s a steady growth rate.

coryrc2• 4 years ago

They break off if they get too long and will run out of material at some point.

atesti• 4 years ago

Does anybody from Germany know where I can still buy leaded solder? Unfortunately I forgot to order a lifetime supply while it was still available

tinco• 4 years ago

When did that happen? I bought a spool just over a year ago and the sales person didn't bat an eye. This was in The Netherlands, if we don't have the same law then maybe there's your answer?

askvictor2• 4 years ago

Is every package coming into Germany screened for Lead? Could you not just order some from another country?

q-big• 4 years ago

Does anybody from Germany know where I can still buy leaded solder?

I ordered on ebay, sold by a vendor from another EU country that cares less about the regulations.

detaro• 4 years ago

It's trivial to find online shops selling it, even if the large hobby-electronics suppliers have generally stopped stocking it. RS, TME, eleshop, ... all have it.

Tin whiskers: What happens when they spontaneously erupt? (2018)

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