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.
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.
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.
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...
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.
Like some kind of natural electronics prank.
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
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...
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.
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.
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.
And thermal cycling definitely accelerates whisker formation.
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).
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.
Edit: Go look at the more detailed response from robomartin
I ordered on ebay, sold by a vendor from another EU country that cares less about the regulations.
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.
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.
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.
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.
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.
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.
That doesn't sound right. 15 nm/s is ~47 cm/year.
