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August 2001

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Subject:
From:
Mike Fenner <[log in to unmask]>
Reply To:
Date:
Wed, 15 Aug 2001 15:58:46 +0100
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This explanation for the concentration of copper and reducing it by cooling
and skinning is effective but could also explain why the analysis is so
high. Taking the sample from this region would give a high number. If you
are not already doing so try taking your sample by collecting material in
your ladle from the wave itself after pot has been on and up to temperature
for a few hours. This will ensure the pot is evenly mixed and sample is
representative of what is going onto boards. Also best practise dictates
that the sample is then chill cast for all the same reasons.

Mike Fenner
Indium Corporation of Europe
T: + 44 1908 580 400
F: + 44 1908 580 411
M: + 44 7810 526 317
W: www.indium.com


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Furrow, Robert Gordon
(Bob)
Sent: Wednesday, August 15, 2001 3:08 PM
To: [log in to unmask]
Subject: Re: [TN] Solder analysis results


I am not sure that it is stratification so much as different solubility
levels at different temperatures. The copper in a solder bath does not stay
as elemental copper, but rather forms a tin/copper compound. The solubility
of the tin/copper compound in tin/lead decreases with temperature. As you
lower the pot temperature the tin/copper will come out of solution and since
it less dense than the bulk tin/lead will accumulate on the top of the pot
along with dross. The tin/copper rich compound looks like tiny
needles/slivers in the dross. By skimming this out of the pot you remove
much more copper (and also tin) than you do lead and thereby drop the copper
concentration. To get the copper to stay in solution up to a concentration
of 1.7%, it seems to me the solder pot temperature must have been elevated,
because in my experience, even at normal operating temperatures and daily
dross skimming, the copper level is hard to get above 0.5%.

Thanks,
Robert Furrow
Printed Wiring Board Engineer
Strategic Supply Global Account Manager
Supply Chain Networks
Lucent Technologies
978-960-3224    [log in to unmask]


-----Original Message-----
From: Lou Hart [mailto:[log in to unmask]]
Sent: Wednesday, August 15, 2001 9:21 AM
To: [log in to unmask]
Subject: Re: [TN] Solder analysis results


Any comment on Steve's stratification theory?  A few years back I had SPC
charts at a HASL pot at a PC fab, with analysis every two weeks.  Cu
content stayed 0.21% to 0.24% over a period of 1+ years, even though all we
were doing was skimming stuff off the top.  Lou Hart

-----Original Message-----
From:   Stephen R. Gregory [SMTP:[log in to unmask]]
Sent:   Tuesday, August 14, 2001 10:04 PM
To:     [log in to unmask]
Subject:        Re: [TN] Solder analysis results

Dave,

Surely, not ALL 1700-lbs.? Wooo-doggies! I can only imagine what a task
that
would be!!! I've read some stuff that if you keep the pot static, and keep
it
at a stable temperature for a period (what this really is, I don't
know...there's varying opinions), the metals will seek their own level
(according to the different opinions, the copper will be towards the top),
then you scoop out out the top layer, and replenish what you've removed
with
fresh bars.

The question that I have though, how did the pot get so out of balance with
copper? I've never had a problem with copper content, even when waving OSP
boards...tin levels dropping, yes. But not excessive copper...somebody
throw
some pennies in the pot?

-Steve Gregory-


> RJ Klien Wassink suggests [bible p 169] pouring contaminated solder at
about
> 190?C through a 20 mesh stainless steel stariner to reduce copper content
to
> 0.25%.
>
> Dave Fish
>


 << File: ATT00002.htm >>

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