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Tin Whiskers — Fact Or Fiction?
bLanark writes "Some time ago, most electronics were soldered with old-fashioned lead solder, which has been tried and tested for decades. In 2006, the EU banned lead in solder, and so most manufacturers switched to a lead-free solder. Most made the switch in advance, I guess due to shelf-life of products and ironing out problems working with the new material. Lead is added to solder as it melts at low temperature, but also, it prevents the solder from growing 'whiskers' — crystalline limbs of metal. The effect of whiskers on soldered equipment would include random short-circuits and strange RF-effects. Whiskers can grow fairly quickly and become quite long. Robert Cringley wrote this up this some time ago, but it seems that the world has not been taking notice. I guess cars (probably around 30 processors in a modern car) and almost every appliance would be liable to fail sooner than expected due to tin whiskers. Note that accelerated life-expectancy tests can't simulate the passing of time for whiskers to grow. I've googled, and there is plenty of research into the effects of tin whiskers. I should point out that the Wikipedia page linked to above states that tin whisker problems 'are negligible in modern alloys,' but can we trust Wikipedia? So: was the tin whisker problem overhyped, was it an initial problem that has been solved in the few years since lead-free solder came into use, or is it affecting anyone already?"
Years ago I used to work on GE radio equipment. GE radios (Master II series) had tin-plated resonant cavities in their receivers. Tin whiskers were seldom a problem in the mobile radios as vehicle vibration tended to keep the whiskers knocked off. But in base stations the whiskers would grow along the lines of current until they shorted out the coils within the cavities.
The symptoms were always the same. The radio would be working fine one minute and be stone-deaf the next. Sometimes just opening the cabinet door would be enough to dislodge the whiskers and remove the short. But it always returned a few days or weeks later. We got to the point where whenever we were sent out to fix a deaf base, our first repair technique was to take a large screwdriver and rap the cavities with the handle a couple of times, hard. We got some funny looks from the customers but they were happy to be back on the air.
GE finally admitted that the plating was the problem and shipped us a bunch of cavities with a different alloy to use as replacements. They never would tell us what the difference was. Curious, we disassembled some of the old cavities and shook out tiny metal slivers that were finer than a human hair. Some were up to a centimeter in length.
All of the radios we had problems with were less than five years old at the time.
On a somewhat unrelated note, a friend of mine works for a company building avionics. They're still using Lead/Tin/Silver solder for US military contracts. He thinks they know something the rest of us don't.
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This, of course, is not always what happens. The whiskers, being very fine, don't have much current carrying capacity so they are quite likely to just vaporize. Nevertheless, there is risk.
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I understand the rationale for getting rid of lead in various products due to its toxicity, but is the amount of lead in solder really dangerous ? It seems like it would be such a small quantity, and perhaps more importantly it's sealed away in some plastic or steel enclosure... it's not like I go around licking motherboards all day long, and quite frankly if your kid wants to lick lead solder and you let him, brain damage might be an improvement!
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Several times editors on both sides of an issue have been banned for edit-warring and aggressively reverting changes they don't agree with. Usually this happens over controversial political and religious articles. This process usually takes months and is preceded by other means, including attempts to resolve the dispute peaceably, administratively-protecting the article, and other mean.
Also, when a philosophical-minority or fringe group tries to take over a highly-watched article, administrators eventually silence them if they insist on using unreliable sources or not keeping the article in "proper balance," where "proper balance" reflects the real-world opinions on the subject. Pseudoscience, alternative-history, and similar-subject proponents tend to get banned if they aren't careful.
Low-traffic articles nobody cares about are very vulnerable to this kind of abuse though.
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The problem of tin whiskers is real but the consequences ascribed to them by Cringley are not. A printed circuit board like the one in your computer or TV is made of fiberglass and copper layered in a sandwich. In the early days of electronics the copper was plated with tin to prevent corrosion, but scientists discovered that pure tin tends to form hairlike growths, causing the circuits to fail. Adding lead to the tin prevented the growths, and had other desirable properties, so the tin/lead alloy became a universal standard.
More recently we got something called "the restriction of the use of certain hazardous substances in electrical and electronic equipment" or RoHS. RoHS prohibits the sale of materials containing more than 1% lead in the EU. (Old-style electronic assemblies use 37% lead solder.) RoHS came into force in 2006 but research into lead-free electronics began decades ago. Initially researchers tried pure tin plating, which lead to tin whiskers. Some products marketed in the late 90's even failed from this problem. But researchers did not throw up their hands in despair. RoHS has led to innovations in metallurgy to the extent that a circuit board designer can now choose from half a dozen different alloys. Today only 2% of printed circuit boards use tin plating.
Some of these new alloys use gold or silver finishes over copper. These are completely immune to tin whiskers. The most popular new system eliminated the plating step, attaching components directly to the bare copper using chemicals called Organic Solderability Preservatives. OSP leads to stronger and more durable assemblies than even the old tin/lead process.
The whining we see today on the subject of RoHS mirrors almost perfectly the doomsaying seen when California began regulating automobile emissions. There was at that time a tremendous amount of yelling about how the catalytic converter spelled the end of civilization as we know it, and only a moron would take the lead out of gasoline. But soon afterwards we saw the introduction of clean, efficient, powerful cars by Honda. Honda was even able to meet California emissions standards without using catalytic converters or even fuel injection. Their brand of engineering eventually trickled down to even the most benighted American car maker, and California emissions standards are now in force in every industrialized nation.
I would expect to see the same thing with RoHS. We have only just entered the initial stage of complaining. The tin/lead dinosaurs with backwards-looking engineering departments face an existential crisis. In other design houses the challenge of lead-free assembly is being embraced as a competitive advantage. Those who can adapt to RoHS will thrive and those who cannot will clearly suffer.
Cringley brags about a 1966 Thunderbird with a 428 cu. in. motor, a car so heavy, so polluting, and so slow by modern standards that it would be impounded by CARB and laughed off a drag strip by a base model minivan. As time goes on I think Cringley's views on the metallurgy of printed circuit boards will seem as antique at that T-Bird.
Many vintage amps from the 1950's just need a few capacitors replaced, and they will work perfectly, 50-year old vacuum tubes and all.
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Yes, "newer alloys" are better. Tin whiskers can appear before your eyes. I've recently seen a whisker grow between two tin plated component leads while I watched (under a high power microscope). While I use new CuAgSn solders, many of the "RoHsS complant" parts I buy use pure tin finishes on the leads and there are no other finishes available yet. Classic Tin/Lead solders producted joints that were easy to visually inspect - the shape and surface texture of a good joint were fairly unique. Modern non-leaded solders produce a variety of lumpy grey results even when carefully applied. Aiding an abetting the RoHS issues are the use of fluxes that are easily cleaned without CFCs. Old school rosin based fluxes worked well and left beautiful joints - but were nearly impossible to clearn off without CFC based solvents.
Yup...back to a day when people AND companies took pride in their engineering and craftsmanship.
I know now why some of those old McIntosh tube amps from the 60's still sell for $1200 and up. Things built back then were built like tanks.....and meant to last.
Sad you no longer see that in today's disposable society. Strange that in this day or people trying so hard to be "green", that these same people don't demand that companies built products with such quality that they will last and not have to be replaced every other year.
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It all about upbringing. My niece is an ME/AE Junior and is appalled at the soldiering abilities, and general electronic ineptitude, of her classmates, including EEs. She wonders what these kids were doing in high school when she was building amplifiers. Of course, her dad used to make her solder with a torch half the time. One time a neighbor knocked on the door to say, "Do you know your daughter is in the driveway taking a torch to a disassembled car door?" her dad was like, "Yeah, she got new speakers, what's your point?" That girl was brought up right. :-)
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While poor process may explain some of it, I know that American automotive companies are a major force in the microcontroller world, and probably the only reason leaded parts are still made in quantity for many chips. Turns out lead free boards are more vulnerable to vibration, so until the lead free stuff is more durable it is unlikely that cars will use the RoHS compliant parts.