[sdiy] DIY PCBs -Lead-free solder

[KHeck73 at aol.com]

In a message dated 7/25/2001 9:32:07 PM Eastern Daylight Time, 
patchell at silcom.com writes:



> 
>     You can get "no lead" solders now.  Seems like somebody I talked to said
> they don't  wet quite as well.
> 
>     I would like to know what alloy they are using.  Most of the metals that
> have low melting point, well heck, most metals, are poisonous.  Getting rid 
> of
> lead right now seems to be only politically correct.  Will the metal that is
> substituted be any better?
> 


I haven't used lead-free solder, but most I've read about for electronic use 
are tin-base with a few percent silver. Some also contain a percent or two of 
copper, and some a little bismuth or antimony. When you mix some metals 
together the mixture melts at a lower temperature than either element 
separately (if they form a eutectic). 

Claims are that they make good sound joints, but the main problem is that 
they still melt 30-50C higher than the typical lead-tin. Most electronic 
components, PCBs, and assembly equipment are designed to handle the lower 
soldering temperatures. Components have to be manufactured to higher 
temperature specs for assembly if the lead-free solder is to be used in mass 
production. 

I think the drive towards the use of lead-free solder is due more to disposal 
concerns than worry about the actual handling of the lead. Lots of electronic 
gear ends up in landfills (horrors!). There is also concern that the lead 
will build up in the scrap steel supplies as more cars with lots of 
electronic gadgets are recycled. Lead can be a bad actor in some alloy 
steels, and most manufacturers rely on quality scrap metal to keep costs 
down. There's also concern about solder used to plumb water lines, but that's 
a slightly different issue. I think the EC is planning to ban lead in solder 
by the year 2007 (?). I'm not sure about the US, but I think we're all one 
world order now, or something like that.

-Karl.
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