Types of lead-free solder

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Still no industry standard?  Which alloy do you like for repair of new
boards?


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Re: Types of lead-free solder
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If you mean wire solder, we use pure tin. If you mean paste, it is SAC?
and I don't recall the number.

Paul

Re: Types of lead-free solder

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Wire.  But pure tin, not even 0.3% copper?  I thought that was only for wire
bonds or something.


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Re: Types of lead-free solder
On Sun, 27 Nov 2011 19:20:15 -0500, "Tom Del Rosso"

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Pick a solder formulation:
<http://en.wikipedia.org/wiki/Solder#Solder_alloys
<http://www.farnell.com/datasheets/315929.pdf
For general repair, when I must use RoHS solder, I have several rolls
of 0.031" 96.5% tin, 3.0% silver and 0.5% copper alloy with no clean
flux:
<http://www.mcmelectronics.com/product/TENMA-21-1042-/21-1042
<http://www.all-spec.com/products/KWLF27565.html
I have no clue if this solder is better or worse than any other type.
I bought a case fairly cheap, and plan to use it until it runs out.
There are cheaper formulations without the silver which might be
useful.

I also use 63% tin, 37% lead solder for older devices.  It works MUCH
better than the RoHS stuff.  I'll sometimes use it on boards that use
RoHS solder, but only if I suck off the RoHS solder first.  Mixing the
two solder types results in a dull dross-like mixture.

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Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Types of lead-free solder
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I've wondered about this too. Are you saying that every time I do a
component level repair on a board that was built according to RoHS
specs I need to remove all the RoHS solder associated with that/those
components first? That would just about involve everything new that
comes from Europe or Asia wouldn't it? Lenny

Re: Types of lead-free solder


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When the directive first came in, I did a lot of research on this for a
couple of trade magazine articles that I wrote. I had some very detailed
discussions with a very highly qualified metallurgist (PhD level) who was
part of a government-sponsored agency to advise industry on the implications
of the legislation. He was quite adamant that leaded and lead-free solder
should not be mixed in the same joint, as this would lead to the joint
integrity being compromised. As he was far more 'expert' at this than I was,
I took it to be the case, and have always advised anyone who has asked me,
that mixing was a bad idea. I certainly don't do it myself, but it is
actually quite rare to find non-RoHS equipment that was constructed using
lead-free, ahead of the requirement in June 2006. Sony was one such company.
However, in variance with what my metallurgist doctor said, Sony insisted
that all of their service agents changed over to using lead-free solder for
repair of  *all* of their products, irrespective of the solder type that
they had originally been constructed with. Rather than being a reasoned
response to the impending legislation, I believe that it actually came about
as a mis-understanding of what was required. It was amazing how many
companies and individuals within the industry, mistakenly believed that the
use of lead-free solder had been either totally banned ahead of the
legislation date, or was going to be immediately after. One of the major
soldering equipment manufacturers - I think it was Cooper (Weller) but might
have been Pace - even published their own document, incorrectly advising of
this total ban that never was. Again, I think it was an honest wrong
interpretation as a result of a knee-jerk reaction to the legislation, but
since most people believed that they were going to have to buy all new
soldering equipment to cope with the higher temperatures that lead-free
required, the more cynical amongst us, might believe that it was a
deliberate ploy to increase sales of replacement stations ...

 I continued to advise against using lead-free to carry out repairs on items
originally constructed with leaded solder. As the regulations stand, there
is no requirement to use lead-free to repair any item 'brought to market'
prior to June 2006, irrespective of whether or not it was constructed using
lead-free. After that date, all items brought to market have to be RoHS
compliant, and it is a legal requirement that the compliance is not
compromised in any way by the process of repair, which means that as service
engineers, we are legally obliged to use lead-free solder, and RoHS
certified components to carry out any repair on such equipment. Of course, I
don't think that there is any such requirement to maintain the original
certification on your side of the pond. So I would say, go right ahead, and
use 'proper' solder to carry out your repairs, but suck or wick as much of
the lead-free solder off the joint as you can, before remaking the joint.

Arfa


Re: Types of lead-free solder

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Will there not always be a residual film of the original solder, and would
that not cause a crack along the entire interface?


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Re: Types of lead-free solder
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It is the absence of lead rather than presence of tin that is causing the
problems, you have tin in both leaded and lead-free solder. It is the lead
that gives the forgiveness, perhaps someone knows the technical rather than
folksy term for this



Re: Types of lead-free solder

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Sorry, I misread your previous post.  I was thinking of the opposite.  If
the joint used SnPb originally you would never be able to remove all the
lead, so could you use Pb-free after cleaning?


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Re: Types of lead-free solder
On Sun, 4 Dec 2011 14:54:07 -0800 (PST), klem kedidelhopper

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Yep.  That's about it.  If you want to use tin-lead solder, you have
clean off the tin-silver-copper RoHS solder first.  Try mixing the
solder for yourself.  The resultant dross-like joint should be
obvious.

After some experimentation, I've found that it's not really necessary
to totally remove the RoHS solder.  Just clean it up to the point
where it looks like solder plating on the pads.

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# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
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Re: Types of lead-free solder


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Yes, agreed

Arfa


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