The Electrostatic Theory of Metal Whiskers

wiskersThanks to that wonderful ROHS stuff the EU passed more than a decade ago, we should be seeing a few high-profile failures of electronic components due to tin whiskers. These tiny hair-like extrusions of metal found most commonly in lead-free solder have destroyed billion dollar satellites and shut down nuclear reactors, despite no one knowing exactly how these whiskers form. Now there’s a new theory of metal whisker formation (abstract, unless you have access to APS) that actually has predictive power. Here’s the free version of the paper

[V. G. Karpov] from the University of Toledo suggest these whiskers are formed by differences in charge induced by metallurgical anomalies – contamination, differences in the grain of the solder, and oxides. Because of the difference in charge, the whiskers are extruded, for lack of a better word, out from the surface of the solder.

The theory of whisker growth is generally consistent with observed rates of whisker growth and other properties. With this theory, it should even be possible to grow tin whiskers. Why anyone would want to do that other than, ‘because it’s cool’ is anyone’s guess, but there you go.

Comments

  1. lja says:

    Even when soldering with lead based solder vs tin based solder you can tell the lead solder is far better

    • Garbz says:

      The difference can be accounted for in the amount of flux used and the realisation that lead based and ROHS solder have different melting points. Actually there are several different soldering alloys which are lead free and have special purposes depending on what you’re trying to do.

      If you’re having trouble:
      1. Don’t forget to crank up your iron. +30 to +50degC over your leaded solder.
      2. Switch brands for one with a different flux core composition.
      3. Switch alloys to one with Silver or Bismuth in it.

      It doesn’t solve the tin whisker problem but you shouldn’t find it any difficult to actually use lead free solder.

  2. Gerrit Jan says:

    “These tiny hair-like extrusions of metal found most commonly in lead-free solder have destroyed billion dollar satellites and shut down nuclear reactors”
    The RoHS is non applicable for aerospace, automotive, nuclear and a lot of other fields. Using RoHS IC’s in applications that should be extreme reliable is kind of stupid.

    • Cliff says:

      Nice theory, but those markets are too small to justify production of most non-RoHS devices.

      • Gravis says:

        umm… have you seen the cost of aerospace grade parts? they will make anything you want if you pay them enough money.

        • Cliff says:

          Yes I have. They are expensive generally due to is low demand. But there is an opportunity cost and a small thing called a budget. Many industries do not want custom parts. In fact there has been a push in .mil to use COTS parts. Out of the ~$200 billion semi market, .mil is at best a single digit percentage. There are also obsolescence issues as well. This is where companies like Rochester Electronics thrive.

    • Sven says:

      Automotive was only given a grace period, it is true though that most critical fields (medical, military, powerplants and anything that flies) are exempt.

      It is however also true that some satellites were killed by some malfunction that was probably tin whiskers, but that was long ago and not related to RoHS.

    • Isotope says:

      I worked in a nuclear power plant that tripped because of tin whiskers. I saw the board that caused it. It was at least 30 years old. Maybe it will be more common now, but tin whiskers was a problem long before lead-free solder.

  3. Florisvdk says:

    The seccond link does not work.

  4. There’s also a non-paywalled version on arXiv if people want to read the paper. Looks pretty interesting! http://arxiv.org/abs/1401.7689

    • LOL says:

      Thanks for posting a scamwall free version :)

      Galvanic corrosion and https://en.wikipedia.org/wiki/Tin_pest are old problems.

      Some popular Japanese RoHS solder pastes do not form whiskers as the impurities inhibit seed crystal formation.

      However, many chip manufacturers still dip their pins in a cheap tin coating. Most agree lead solder also flows at a lower temperature, less likely to damage newer chips, and reflows most of the coating into the alloy.

  5. Anthony says:
  6. solotrek says:

    New nano tech tin whisker batteries anyone?.. Any mention of preventing tin whiskers?

  7. Paul says:

    Engineer, some years ago:
    With all this new RoHS stuff we’ll probably see that whisker problem returning again.
    Marketing:
    What’s whiskers?
    Engineer:
    Well… (bla bla bla , you know the story).
    Marketing:
    How long does it take for these things to grow?
    Engineer:
    Might take a few years.
    Marketing:
    So it’s not a problem then. Case closed.

  8. It appears to be available on arxiv:

    http://arxiv.org/pdf/1401.7689v1.pdf

  9. So what is the alternative if you wanna go lead free and tin free?

    • pelrun says:

      Schedule a change in career one year before the first failures happen?

    • AKA the A says:

      Gallium based alloys? ($$$)

      • Leithoa says:

        I can’t speak to the solder capabilities of gallium, but this would be a bad idea. Gallium attacks aluminum, completely compromising its structural integrity. This would destroy any heat sinks as well as ban it from use in aerospace, and most transportation industry.

    • Me says:

      Your best bet is just to use lead. Keep it out of your mouth, wash your hands and you will be fine. The alternatives (once you consider the rosins they use) are more toxic anyway!

      • Pat says:

        Lead free solder isn’t to protect *you*. It’s to prevent lead from leaching out in landfills after obsolete electronics gets thrown out.

        • r4k says:

          And it is very debatable whether this is really an issue. Elemental lead is not nearly as dangerous as many people believe. It is the lead salts and organic lead compounds that you really need to worry about.

          • Leithoa says:

            Lead oxidizes rapidly into lead(II) which isn’t too soluble(0.05-0.1 g/L) but this is still above the EU, US and China’s water quality standard of 0.0001 g/L.
            You’re half right about lead toxicity. To adult humans lead isn’t too terrible. Only 1% of lead ingested gets integrated into our bodies but with children it’s 32%. It is also a known cause for delayed or poor mental development.

            Given the construction techniques in most modern land fills contamination from garbage is less of a factor than the recycling cottage industry in most developing countries. Few if any safety precautions are taken for the people let alone the environment. The regions where this is the main source of income are veritable toxic waste dumps.

          • Pat says:

            Lead solder in plumbing results in lead in your blood. There are plenty of documented cases of children getting lead poisoning whose only exposure to lead was lead solder-joined copper pipes. Lead solder was banned in plumbing in the 80s because it absolutely does bad things to kids.

            If you want to say it’s debatable that lead from lead solder in electronics could get into a water supply via a landfill, OK, that’s fine. But lead solder getting to your water supply is very bad.

  10. Jehu says:

    There could be plenty of uses for Tin Whiskers. If they are of the right size and an easy method of mass production, there might be some practical use for them in the field of nanotech. We are still trying to grow carbon nano tubes and wires so why wouldn’t you want to grow tin whiskers? Apart from a few hipsters that might think it’s cool/not cool to have a tin beard. That might make you think twice.

    • medix says:

      I’m wondering if this process could be applied to CNT growth – not necessarily as a method to grow them, but more to see if electrostatics will influence the growth and make it more controllable. Time for a literature search!

      • Leithoa says:

        Vapor deposition of gold or carbon is a common practice in electron microscopy and was all but required a few years ago. This same technique to plate the whiskers could greatly enhance surface area of conductors.

        • medix says:

          I use sputter coating of gold for SEM samples about once / week. ;)

          I’m not talking so much about vapor deposition – I’d be interested to see if an electrostatic field can influence the structure directly during growth using traditional methods. For instance, can the growth direction be influenced? (yes, I’ve seen papers using electrostatics as a form of self-assembly) How about the structure (i.e. single or multi-walled?)

          In fact, we’ve got a setup for growing CNTs that uses a laser to heat the catalyst to initiate growth. I’ll bet the chamber could be modified with an ITO coating on the window for the upper electrode.

    • Z00111111 says:

      Plus if you can grow them reliably, you can work to reliably stop them growing.
      You need to make sure something will happen before you can prove that you stopped it happening.

  11. salec says:

    Perhaps growing metal whiskers in controlled manner could get us cheap atomic force microscope probes and maybe even massive parallel (multi atomic force probes bed-of-nails) nano-assembly machines, something like 3D printing on the single atoms scale … simultaneously on a matrix of nano “building sites”. And all that even on one’s desktop.

    But there is more: If you have electrostatic theory of forming whiskers, you have electrostatic theory of moving metal atoms around as you wish. You can use it to make something different, like a small Eiffel Tower made of tiny metal threads. You can use it to make ultra small wavelength high gain resonant or aperiodic radio (light?) antenna. Maybe you could use it to make metamaterials that could cloak objects from visible light. You could use it to make tiny little metallic snowflakes. You could use it to make “slabs” of metal which are fractals – mostly empty in volume, strong and very light, potentially storing hydrogen atoms in its voids. You could use it to make things I could never imagine!

    lunatic babbling mode off

  12. Nathan says:

    There is a little known exception in the RoHS directive which says that so long as it’s a safety application it is still possible to use Lead solder industrially. I would be very surprised if they didn’t still use it in electronics manufacturing for nuclear power plants and satellites.

    • pcf11 says:

      Aerospace, and the military are completely exempt from having to use lead free solder too. I am not sure how widely known that is. But what is good enough for everyone else is not good enough for them. Lead free solder really isn’t good enough for me either. I’ve a fair amount of lead solder spools still here that I use.

  13. phlt says:

    Lead free technology is sure problem now, but on the other hand lead pollution is generally a problem (So it is kind of wonderful, without being sarcastic). Also maybe in few years we will have really good and working conductive glues? (Or something other) Which would not be beneficial if cheap lead tech was still available.

    • Me says:

      Are glues really going to be more environmentally friendly than lead solder? What compounds are released into the environment as part of their production? What kind of VOCs will they off-gass as they dry? What chemicals from the glues disolve in landfill leachate?

      Don’t get me wrong, I don’t think conductive glues are a bad thing. They might make some really good stuff possible. I just think the threat of leaded solder is HIGHLY over-rated and that alternatives get a free assumption of being better even though they may not be.

      • phlt says:

        As many other things, but I like the idea. I would prefer if in that manner would be more movement. If we segregated all the stuff there would be probably no need for landfills, I’m a daydreamer here though :P I won’t write more as it’s not on topic any more :)

      • Leithoa says:

        I would think VOC’s a much shorter lived than heavy metal contamination in most cases. Though I don’t know how much that will help if both are beyond the usefulness in terms of human lifetimes.

  14. Kaijuu says:

    RoHS: Restriction of Helpful Substances.
    Already lost a great deal of equipment due to tin whiskers. When I explain the problem to a non-tech, the best you get is a blank stare and some disbelief as a bonus.

    • cantido says:

      Helpful and highly toxic. As someone above mentioned it is still allowed to use lead where it would be very dangerous to do otherwise. For all the bitching and moaning you see about lead free solder on sites like this I doubt many of said bitchy moaners has actually had much of an issue with lead free aside from adjusting how they solder slightly. Yes, lead free solder can develop tin whiskers but I doubt many people properly clean all of their boards to remove flux residues that could become conductive over time.
      This is like people moaning about the latest parts not coming out in dip versions.. The boat has sailed, get the hell over it already.

  15. Dan B says:

    First thing I do when one of my guitar amps needs service (if it was made post RoHS) is have it resoldered with lead. My tech don’t give a damn about RoHS.

    • Greenaum says:

      You can still buy and use lead solder. It’s just companies, or businesses of some description or other, that can’t. Individuals still can. In the UK anyway and we’re still thankfully part of the EU. I know cos I bought some yesterday to replace the stupid lead-free stuff Maplin stock.

  16. Telimektar says:

    This is really problem. Its better to use lead-free because its presumed to be more ecological, But how much ECO is this way with plenty malfunction devices layed around all world?

    • JadedHobo says:

      Mobile phones don get dumped because they’re malfunctioning but because they’re not in-style anymore! And of course they don’t get dumped in /our/ backyard either. But just remember that innercity violence dropped sharply when lead was banned from gasoline.

    • Zoidberg says:

      The main problem with lead, according to some, is actually the mass abandonment of CRT technology in recent years. CRT displays can contain far more lead than most other electronics, in some cases pounds of the stuff. Sure, we’re supposed to recycle them, but there are still a lot of lazy bastards (like my old boss) that just bury them in the dumpster.

  17. ejonesss says:

    maybe we should go back to leaded solder and just use fume extractors when soldering and bring in hazmat when disposing of stuff.

  18. qwerty says:

    I keep wondering how many fatal airbag accidental deployments may have caused by tin whiskers that were attributed to driver error.

    • Salokcin says:

      I’m not sure I understand. Do “accidental deployments” (deployments without a collision?) ever get blamed on driver error?

      • qwerty says:

        If the airbag deploys accidentally it may actually become the cause of a collision rather than the effect, and in case of fatal accident nobody will blame a faulty airbag (read: the multi zillion $ car company behind it) rather than the driver.

  19. DracoBengali86 says:

    Maybe it’s just my pessimism, but I don’t envision the military searching for non-RoHS components (unless that’s the only thing presented to them). I believe more something like “oh, here’s the 555 they need 10K of. Order it” not bothering to notice RoHS or not. Someone please tell me I’m wrong.

  20. Torque says:

    “Thanks to that wonderful ROHS stuff the EU passed more than a decade ago, we should be seeing a few high-profile failures of electronic components due to tin whiskers.”

    It’s that or continuing with the mindless lead pollution with commercial products.
    And if I’m not mistaken, devices that ARE 100% mission critical (basically anything used in medical or military sector) can apply for an exemption.

    Please stop with the mindless and biased editorial posts, I thought HaD were better than this…

  21. Megol says:

    http://blogs.indium.com/blog/an-interview-with-the-professor/tin-whiskers-found-in-nasa-study-of-toyota-unintended-acceleration-issue

    Here is an expert in the area wondering “who knows of any verified tin whisker fails when tin whisker mitigation techniques where used?”.
    And I wonder: how many RoHS electronics devices have failed due to tin whiskers? It’s known they can grow at a high rate so there should be a lot of extra hardware failures if that is a significant failure mode. It should be statistically visible even if the overall whisker growth rate is low enough that most failures will come in some years.
    But there aren’t any numbers supporting that AFAIK (and I have looked) but a lot of people making noise. Or rather FUD.

    And there are so much FUD and little fact when it comes to lead free solder. That these poorly supported myths are propagated on this forum is a bit sad. And I’ll maintain that these are myths until someone can prove this is a real and significant problem.

    BTW I’m from time to time hacking my own solder for different purposes, is anybody else here doing that? Testing tin+zinc/aluminium at the moment and will test tin, indium, zinc, aluminium next attempting to improve ductility and wetting of copper.

  22. Scott says:

    Defense and Aerospace industries may get a free pass on using non-RoHS parts, but that doesn’t matter, because so many parts are only available in RoHS-compliant packages. I work for a defense contractor, and many of the programs I work on are using RoHS parts that have been solder-dipped to help meet our needs. It’s annoying and expensive, and if we’re not *very* careful, RoHS parts can slip through anyway. Maybe if we were still in the Cold War era, we could push manufacturers to still offer non-RoHS packages, but the defense industry just doesn’t have that kind of power anymore.

    Anyway, here’s hoping this new model will yield better ways of managing the tin whisker problem, and perhaps help manufacturers mitigate it while still being RoHS compliant.

  23. Squirrel says:

    How much lead is in the average leaded PCB?

    How much lead is in the average lead-acid car battery?

    • carbohydrates says:

      What percent of PCBs are recycled vs. thrown away each year? (not even close to half)

      What percent of lead-acid car batteries are recycled vs. thrown away each year? (in the US, at least, the answer is “almost all of them”)

  24. Tom says:

    @Squirrel: Lead from a lead-acid-battery is not intermixed with other metals. It can and it is collected and recycled 100% in almost all cases.

    Lead from lead-free solder is not pure and usually not recycled. That is a difference.

    Also, there seems to be a myth about the number of tin-whisker related failures. Mitigation techniques like copper doting of the solder alloy are in place.

    What is more a concern, IMO, is the real benefit of lead-free solder in terms of reduction of environmental contamination. Where tin is mined, lead is a common co-product which may now not be used any more, but simply disposed of in form of mine spoils, or rubble.

    I know not enough about the real severity of lead contamination, but on the other hand, I know that tin-whiskers is not as big of a problem as many say. Lead-free soldering is established for many years now.

  25. tachyon1 says:

    ROHS was green ignorance and bureaucratic stupidity.
    It’s not like people are/were eating electronics. The proper solution would have been to address the problem at disposal time, not manufacturing time. Now we all have to suffer with inferior solder and now this problem.

    • cantido says:

      >address the problem at disposal time,

      How do you stop kids in from getting exposed to stuff when they are extracting materials from e-waste other than stopping the stuff from getting into the products in the first place? Of course RoHS etc go further than just what can go into solder. For example how stuff should actually be disposed of so it doesn’t end up getting heated up over fires by the poorer peoples of the world.. but oh noes lead free solder!

      >Now we all have to suffer with inferior solder and now this problem.

      I’ve only been using lead and halogen free solder for ages and I’ve had no issues with it.

      • tachyon1 says:

        So you chose to completely ignore the actual content of my comment so you could hear yourself talk about the poor lead licking kids of the world and then decided to follow up with some anecdotal evidence about how awesome lead free solder is.
        Great, how about my horoscope next.

        • cantido says:

          >So you chose to completely ignore the actual content of my comment
          While quoting the content of your comment…

          >poor lead licking kids
          It’s not about them licking it moron. It’s about it getting into the water, soil etc when the people of the third world are crudely recycling stuff.

          • tachyon1 says:

            Speaking of morons, thank you for showing us what a moron is.

            You went ahead and quoted from my comment
            >address the problem at disposal time,
            and then just like I said in my second comment, COMPLETELY ignored even the words of the small part you quoted, never mind the rest of the comment.

            IF the problem was addressed by basically anyone even slightly less moronic than yourself, these lead containing products would never be in the hands of third world kids in the first damn place you idiot. They would have been properly handled “AT DISPOSAL TIME”.

            I take it you’ve heard of recycling? It’s what those of us that walk upright do with certain types of waste. In fact here in my country, electronics _must_ be disposed of at a recycling facility where they are processed properly. This is the correct way to handle the issue instead of stupidly replacing the solder in everything and then letting it end up in a slum in India anyway.

  26. Re. electrostatics, how about growing the whiskers and then somehow depositing nanocarbon on these?
    Would be a cheap way to make cm length CNTs and simply use an acid to dissolve the tin afterwards.

  27. Vic says:

    Ah: The elusive tin whisker rears its ugly head once again. The story never changes. Megol is correct, it is a long term problem if at all. Keep your stuff clean and if its going to be a long term use board conformal coat it. Conductive epoxies used to mount components will fail in less than a year even if boards are retained in an oxygen free atmosphere. Good old tin lead solder is the only answer (for now).

    • medix says:

      ‘Long term’ in what sense?

      No one has made any mention of the voltages typically involved here..

      The paper states that an electrostatic field is usually the driving force behind the growth, which would suggest that growth would likely be more rapid under higher field strengths (i.e. components with higher voltages, etc.. ). I’d be interested to see failure rates versus voltages involved to show a more direct correlation.

      I’ll have to read the paper again too.. ;)

  28. Tom says:

    @medix:
    > No one has made any mention of the voltages typically involved here [...]

    Look at equation no. 7 in the paper.

    This states a typical electric field strength of more than approximately one megavolt per centimeter.

    This would mean, for typical minimum structural dimensions of printed circuit boards of 0.2 millimeters (high-density boards are more likely half than this, but 200µ is a typical value for run-of-the-mill electronics), this corresponds to an external electric voltage difference of 20 kV.

    Because this is not only not typical on high-density PCBs, but also two orders of magnitude above the dielectric breakdown field strength of air, this would suggest to me that any voltages present in a manufactured PCB do not play any role in the formation of tin whisker growth.

    Does anyone agree?

    • Tom says:

      As an addition, the above scenario seems to be relevant in the early stages of whisker growth. When the metallic whiskers reach a certain minimum length, the influence of externally applied electric fields may again be of concern. Charge concentration at the pinnacle of the whiskers may raise the external field strength enough. As I read it in section VIII of the paper (what is and is not understood), this 3D field distribution influences are not understood yet.

    • ukr says:

      The concept of dielectric breakdown requires that the field extends through the distances exceeding the mean free path of ions in the air; the latter are greater than tens of microns. The field strengths suggested in the paper are limited to submicron regions above the surface; hence, no contradiction here: very strong electric field in local regions are possible.

  29. Bubba Gump says:

    Bubba Gump here from the Bubba Gump electronics company. Back in the day, 27 years ago when I was still practicing running when my friends told me RUN FORREST RUN, we wave soldered through hole double sided circuit boards using lead solder after they were sprayed with rosin core flux. Then right after the wave solder they went into a Detrex machine, where they were bathed in a lovely trichlorotriflouroethane (think dry cleaning solution). They came out all nice and shiny, no growth problems whatsoever. Now fast forward all these years. Not one of the ladies that sat at the end of that line handling the circuit boards, not one, but all 8 died of brain tumors from the exact same way.

    Irony? No…sorry. Not possible. Out of 400 people in that plant, 25 died from brain tumors but hey, the company is no longer around…

    As pad geometries shrink the voltage potential has to shrink as well or else you will get tin whiskers. Its not just satellites. It runs the full gamut from satellites to your Xbone One. We know what causes it and you have to dictate everything.

    There are 34 different FR-4 laminates alone. We went so far as to dictate weave pattern, and overall board cleanliness, going to a clean room for our whole SMT line. Nobody in nobody out, look through the windows for your factory tour. Baking boards, components, and so many other things.

    You can use gold infused epoxy and go completely away from solder. Want to pay 6 grand for a TV?

    People throw batteries and CFL’s into the trash…in the USA. China is 100 times worse but people don’t look long term. Long term, we will evolve to drinking mercury and eating lead.

  30. ERROR_user_unknown says:

    The first thing that comes to my mind is Conway’s Game of Life those like like some kind of flyer to me. and maybe pulsing electricity acts as timer ticks

  31. Governor says:

    Ha ha ha…
    RoHS was not introduced with environmental concerns in mind. That is an explanation for the uneducated sheep going along with the crowd, while perfectly blending into the consumer society. Just take a look at e.g. automotive car, traction or gel batteries, how much porous lead is in them and where do they end up.

    Aside from the whiskers forming with time, which is true, lead free solder has far inferior physical durability and so causes cold joints easily. It’s not about one’s style of soldering at all. The soldered bond just breaks over time, so consumer products can break and it’s cheaper to buy a new product than to repair it, thus keeping the business rolling.

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