Unintended Consequences

The change to lead free solder makes electronics less reliable. [Link]

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. Everything in that column has come to pass and more. Where's my Pulitzer Prize?

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. They can grow at up to nine millimeters per year. They grow in any atmosphere including a pure vacuum. They grow in any humidity condition. They just grow. 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. So we're all in this tin boat together.