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There's some new EU directive in the pipelane which is supposed to be banning lead in solder completely from a certain date. Some suppliers seem to have already stopped stocking it already.

Yup - I think that date is going to be quite soon too - remember something like summer of 2006. Three guys one year ahead of me at school did a project "lead-free soldering of solar modules", and they weren't overly impressed of the new stuff either I think. Though they mostly blamed it on the early stage of development of must of the stuff they had to use.

Yikes! I hadn't realized the deadline was that close, but it seems you're right:

DIRECTIVE 2002/95/EC


There are some exemptions listed in the annex, and a temporary reprieve for lead in solder for certain applications:


Time to start stockpiling as much of the good old 60/40 as possible!

Trouble is, if I'm to believe what I've read in popular electronics mags', that lead free soldered joints subsequently repaired with leaded solder will be weak and unreliable.

Anyone know if that's actually true, or is it just propaganda from the enviromental fanatics ?

Geoff, if I were designing a lead-free solder from scratch, I'd start with the basis of triple, quadruple or higher eutectic alloys of tin, adding perhaps antimony, bismuth, copper, lithium, etc. to get the melting point down. The problems foreseen would be conductivity of the solid solder, corrosive effects short and long term, liquid phases of the alloying metals appearing at the dendritic boundaries on solidification, mechanical strength of joints, ductitity, effective formulations for fluxes, actual melting temperature, clean melt with no pasty-stage as in plumbers solder; the list is almost endless. So if you re-solder a lead-free joint with tinmans' my guess would be it would be a poor joint, if only because the new alloy created would not be a clean melting eutectic but probably a wipeable joint! So, stocks of pb/sn will be ok for new work but for repairs .....

Alan

late ps. A quick shufti at my metallurgy books last night confirms that lead and tin alloy perfectly in all percentages without liquid phases of either metal appearing at the crystal boundaries, and that electrical solder [63/37] sits right on the eutectic- ie. the alloy percentage of lowest possible melting point, with a definite crisp solidification temperature similar to a pure metal. 176C/349F melting point, with good tensile, shear, elongation and creep properties.



[This message has been edited by Alan Belson (edited 01-29-2006).]

I'm more concerned about compatibility the other way, i.e. how would the lead-free solders mix with traditional lead/tin solder on older equipment.

Alan, Many thanks. Your knowledge of metallurgy is way above anything I ever attained, (never mind remember!).
Does your ps indicate that modern lead-free produced gear will, in practice, be OK if repaired with standard old 60/40?
I'm mostly only a hobby electronician these days, and one aspect that concerns me is that we won't actually know what's been used in manufacture. I suspect there may be frequent doubts in the commercial repair world too.

Geoff,
From what I can glean from the Net, most lead-free solders are /will be alloys of silver-tin, copper-silver-tin and possibly bismuth. The melting points are generally going to be ABOVE 217C, quite a big leap from 63/37. None of the many alloys proposed/patented appear to be true eutectics and thus will have melting point ranges of a few degrees, say 217-220C. The fluxes used will also be different formulations. No need for despair, you simply have to clean off as much of the lead-free solder and flux residues as possible from tags, pins etc, [there are little suck-pumps available, and the old wireman's trick of wiping with a sponge] & cut-short and re-tin wires if possible prior to resoldering with 63/37. The new solders, being predominantly tin, won't generate any problems with 'take' or wetting. My earlier comments related to attempting a repair with a large quantity of lead-free left on the joint- in this case a new alloy would be created of unknown properties. At a cleaned surface interface, [with a tag for example], a tin-alloy will still exist, [which may not even melt on resoldering], so it has to be clean [which is normal procedure anyway]. A reasonably cleaned off joint should re-solder very well with 63/37, [as long as you stockpile enough when it isn't sold any more!]

Alan

I've read that some alloy of lead free "repair solder" is coming in. It is as good as the old one, but too expensive to use in mass production. Instead, cheaper solders with a higher melting point and less forgiving properties will be used for this.

We figured we might have chance at getting the industry to start welding instead of soldering. No such luck.