www.pbs.org/cringely/pulpit/2008/pulpit_20080221_004346.html
com The Pulpit Poll Will lead-free solder really create serious reliability problems for electronic equipment? Yes: Brittle connections, tin whiskers -- how can these not create problems? Any problems that arise will be swiftly solved or companies won't remain in business.
see results The Pulpit Poll Will lead-free solder really create serious reliability problems for electronic equipment? Yes: Brittle connections, tin whiskers -- how can these not create problems? Any problems that arise will be swiftly solved or companies won't remain in business.
Pulpit Poll Opinion Cloud If you have ever seen my show Triumph of the Nerds well then you've also seen my car, a 1966 Ford Thunderbird convertible very similar to the car used in the movie Thelma & Louise (I play the role of Thelma). It is heavier than anything else on the road, so in a collision with anything less than a dump truck I win. And thanks to analog technology that handily predates the Clean Air Act, it somehow manages to do all this while getting 22 miles per gallon on the highway, 16 in town. Everything is good about my T-Bird, in fact, except for its wires. And shortly YOUR car will have bad wires, too, as will everything else you own that has soldered electrical connections. My T-Bird was built at the absolute apex of 20th century electromechanical automotive technology. A convertible, it has a fully automatic electric top that relies on eight electrical relays firing in sequence to put the top up or down. Quickly I run to the car, start it, and hit the button to raise the top. First the suicide trunk lid opens until it is fully vertical. Next the electric tonneau cover opens until it is vertical, too. Then the canvas top begins to retract, raising until it, too, is vertical, at which point everything grinds to a halt and I drive my car home in the pouring rain at five miles per hour, traffic honking behind me, and all three broken parts sticking eight feet into the sky. Victim to a succession of good and bad mechanics, some well-intentioned but all in it for the money, I have spent thousands of dollars over the years replacing electrical parts -- window motors, switches, relays for both the top and the sequential tail lights -- all to little avail. Eventually I abandoned all hope of viewing my car as a restoration and replaced the relays with brilliant little computers from British Columbia. Now the hydraulics worked beautifully but all it really meant was that the top no longer failed in mid-sequence: it would either work fine or not at all. When you've replaced everything else the problem has to be with what's left, which in the case of my car was the wires, themselves. Over the years the wires had somehow corroded inside their insulation and the terminals had lost their mojo. I had been replacing perfectly good switches and motors (and knowledgeable folks had been selling me switches and motors) that would have been helped more by simply replacing the terminals or, better still, the wires. Some experts think Ford just got a bad batch of wire back in 1966 -- that this problem is isolated -- but I don't care. All her parts seem to be working just fine, why shouldn't my T-Bird? Which brings me to you, or rather to all of your soldered devices that are two years old or less. Most of these are now assembled using solder joints that have no lead in an effort to save our groundwater and our health. The fact that the lead has been generally replaced with silver or bismuth, both of which are actually greater health risks than lead, well we'll leave that one for Ralph Nader if he decides not to run for President. The longer-term trend is toward all-tin connections, anyway, but they don't work very well, either. I wrote a column about this back in 2004 (it's in this week's links) that was heavy on information and therefore low on readership. Costs have gone up, mean time between failures (MTBF) has gone down (accelerated MTBF tests, which are the only MTBF tests we do anymore, don't reliably pick this up, by the way), and reliability has suffered. Since we don't fix things anymore, it's hard to say whether your gizmo failed because of bad solder or not, but the problem is becoming worse as a greater percentage of total circuits in use have lead-free solder. The military was especially concerned, even before the whisker crisis. We're talking about tin whiskers, single crystals that mysteriously grow from pure tin joints but not generally from tin-lead solder joints. Nobody knows how or why these whiskers grow and nobody knows how to stop them, except through the use of lead solder. Whiskers can start growing in a decade or a year or a day after manufacture. And when they get long enough they either touch another joint, shorting out one or more connections, or they vaporize in a flash, creating a little plasma cloud that can carry for an instant hundreds of amps and literally blow your device to pieces. Since 2006 we have been exclusively manufacturing soldered connections thousands of times more likely to create tin whiskers than previous generation joints made with tin-lead solder. Because of the universal phase-in of the new solder technology and the fact that the solder technologies can't reliably be mixed (old solders mess with new solder joints in the same device through simple outgassing) this means that it is practically impossible to use older, more reliable technology just for mission-critical (even life-critical) connections. Some experts confidently say that the disparity of joint reliability we are seeing today will go away and that the new joints will become as reliable or even more reliable than the old tin-lead joints as we gain experience with the new processes. What's disturbing, though, is that these experts don't actually know how this increased reliability is likely to be achieved. Just like extrapolating a Moore's Law curve to figure out how fast or how cheap technology is likely to be a decade from now, they have no idea how these gains will be made, just confidence that they will be. They are much more common than most people -- even most experts -- think. The reason for this is that most tin whiskers can't even be seen. "Maybe it is worth adding," said one expert who prefers to remain anonymous, "that whisker diameters range from 01 um to 10 um, while the diameter of a human hair is 70 um to 100 um --- so the largest whisker is only some 15 percent of the diameter of a thin hair, and most are less than 5 percent. A good fraction (of these are) so thin that light waves just pass them by, scattering a bit but not reflecting. So the optical microscope images that (typically used to illustrate whiskers) show only a small fraction of what is really there. Scanning electron microscope (SEM) images are a bit better, but only show a small zone of the sample; also, not many folks are able to acquire SEM images of their equipment. So all too many folks have the idea that whiskers are something that happens to someone else, but never to them. What I wonder is whether a cost-benefit analysis of this solder technology changeover was ever done? And if you think this problem is minor, I have been told that just the cost of changing to lead-free solder stands right now at $280 BILLION and climbing. Maybe dumping lead solder was absolutely the right thing to do. The truth is we haven't the slightest idea the answer to that question and anyone who claims to know is wrong. We didn't know what would happen when we started this and we don't know what we'll get out of it, either, or whether it will be worth the cost. Fortunately I have new shock absorbers (and a new wiring harness) on my T-Bird.
add a comment The problem fits well with the culture of "Planned Obsolescence" Also like my uncle has pointed out to me on numerous occasions, "We put a man on the moon with wire wrap".
org/wiki/Apollo_Guidance_Computer Doran | Feb 22, 2008 | 5:04PM It is not an environmental problem - it is a problem in the heads of people who do not understand the chemistry of lead in solder. com) states: It is widely accepted in the engineering community that the recent ban of lead in solders for use ...
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