Slashdot Mirror
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?"
grow whiskers. That would be a major bummer. But then lead would be pretty heavy.
My cat gets through tins of Whiskas extremely rapidly. Perhaps scientists can interview him.
SnAgCu Rohs solder(with 3% silver and .05% copper) joints don't appear to whisker but they appear dimpled and shitty compared to the smooth, shiny joints of garden-variety tin/lead. At least in the electronics industry, your percenteges and mileage may vary.
One thing to remember is that safety control and monitoring products like fire alarms, but probably also car electronics, are excepted from the RoHS directive until at least 2012, possibly until 2018, but there's really no fixed date set yet. So yes, your DVD player might die, your car probably won't.
c++;
Well, NASA Goddard are worried about the situation and they have done extensive studies on the subject:
http://nepp.nasa.gov/WHISKER/
Ganty
Tin whiskers are, in fact a reality. They are a problem with pure tin specifically. The older tin-lead, and newer tin-vanadium alloys don't have the problem. However, many manufacturers still manufacture parts in a pure tin variety. The reason for all of this pure tin madness is that the EU passed strict anti-lead regulations and so the lead had to be removed from electronics. EU manufacturers immediately started using pure tin parts. In the US, many manufacturers followed suit, partly because pure tin parts were now more available than tin-lead (and at the time there was hardly any tin-vanadium), and partly because they wanted to maintain a good environmental image. Some manufacturers, having been burned by the whisker problem insisted on a better solution hence the tin-vanadium solders now available. The problem is there are a lot of electronics out there with pure tin parts in there. For example, I'm no fan of flying on Airbus aircraft manufactured in the late '90s and early 2000s (pure tin baby). The thing is, the hardware will work perfectly... until it doesn't, then an errant short will cause a malfunction and in the act, the tin whisker will vaporize. The only way you'll find the problem is with electron microscopy.
Look at it from the manufacturer's point of view. There's a chance that any piece of consumer electronics is now going to wear out and die even faster, causing people to buy replacements more frequently. Sounds like a great deal for the manufacturer with no downside. They don't have to pay to dispose of these things properly. And no, chucking your old electronics in the trash is not the proper way of disposing of them, unless you like cadmium, mercury, hexavalent chromium, and brominated flame retardants seeping into your drinking water.
Make manufacturers bear the ENTIRE cost of properly and safely disposing of their products, and overnight we'd have cleaner, greener, more long-lasting and durable products.
You have wasted your time reading this signature I think I wasted my time reading the entire comment...
#DeleteChrome
I used to buy into Wikipedia's stated ethos until I realized that any one person can (and all too frequently do) hijack articles to push and protect their point of view and once that happens you can forget about the "Five Pillars" and objectivity.
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.
Beta sux! Join the Slashcott! http://hardware.slashdot.org/comments.pl?sid=4760465&cid=46173047
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!
-Billco, Fnarg.com
Did he have tin whiskers?
If you are going to troll, at least be on-topic.
Knowledge is how to play a game, intelligence is how to win, wisdom is knowing what game to play.
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.
Knowledge is how to play a game, intelligence is how to win, wisdom is knowing what game to play.
Remember also the phenomenon of melting-point depression: when two substances are combined in an alloy (e.g., lead and tin) the melting point of the alloy can be lower than the melting point of either individually.
The Pb-Sn eutectic temperature is around 183 C. That's what the summary is referring to.
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.
The board was in the field in a T&M application for about 1 year. Root cause pointed to 2 factors. First the board had very poor (actually out of spec) via to pad alignment. The result was significantly increased voltage density between the offending 12V via and the ground plane. The second factor WAS RoHS compliant board prep and solder. Basically drilled and plated via holes are not 100% sealed (rough bits of fiberglass can still protude through the plating). The solder was one of these high Tin (97%) varieties, and we got dendrite growth (not the more common whisker growth) INSIDE the board along the fiberglass fibers between the via hole and the ground plane, creating a short from a ~30A power bus to ground. The board caught fire. Indications are that it creates a crappy short that repeatedly fries open, and regrows causing intermittents, then eventually enough heat for fire if the power supply can handle it. Higher power electronics with dendrite growth or tin whiskers may fail only briefly (or not at all) when a wimpy short occurs. Low power signal lines won't always have enough juice to overcome the short and may fully die on the very first short. Our safety/reliability group said dendrite growth is a known, but poorly talked about issue that is greatly exacerbated by the lack of lead, and greatly increased board densities today. To a previous post about melting points. Yes, Tin/Lead solder melts well below the melting point of either element in the alloy, at about 175-180C depending on the particulars. NASA literature indicates that conformal coating is ineffective against whisker growth. At a previous defense sub-component job we had to resort to getting many parts re-plated with a tin/lead finish over their matte tin finish to comply with contract requirements. Most commercial off the shelf parts (COTS) are no longer available with anything but matte Tin, or other RoHS finishes. Many vendors changed finishes without any notice, creating havoc in our stick room.
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.
Light travels faster than sound. This is why some people appear bright until you hear them speak.........