Read an interesting article tonight about the implications of removing lead from solder to keep it out of our landfills. It seems that lead was alloyed with tin in solder in the first place to prevent "whiskering", where small hairlike filaments naturally grow out from the surface of the soldered joint, similar to rust or other corrosion. It's not completely understood why tin and a few other metals used in soldering do this in the first place, but alloying the metals with lead eliminates the problem. When the whiskers grow long enough to come into contact with the nearest neighbor's soldered joint on a circuit board, it results in.. yep.. a dead short. Seems the problem affects most of the alternative alloys proposed or mandated by "green" legislation in various countries (including the United States, most recently). So the price goes up and the MTBF (mean time between failures) drops to half that of things made with lead based solder due to whiskering. Just a heads up- it will be interesting to see in the coming years how this affects the work we do .. commerical lighting control boards come to mind, as well as the myriad types of dimmers, photocells, and various other devices we work with. It will probably take a good year before the existing stock of products made with leaded solder are sold off the shelf and all that is left are products made with the new lead free alternatives. I suppose it will become a script we have to memorize, explaining to customers why their expensive electronic device failed so quickly. Whiskering also begins from the time of manufacture, so maybe we will need freshness dates on the things we buy, similar to milk, cheese or beer.
A link to a NASA article on problems they have had with whiskering
and some good pictures of what it is and what it looks like: http://nepp.nasa.gov/WHISKER/ http://nepp.nasa.gov/WHISKER/reference/tech_papers/2007-brusse-metal-whiskers.pdf
Wikipedia article on whiskering, including what metals/alloys are most
afflicted by it: