I have never heard of doing this. Interesting . . . Why would a tin copper
alloy sink in a pot of molten tin/lead? I thought tin/copper had a higher
melting point than tin/lead. Sounds like you've done this before. Do you
have to add tin then?
Guy Ramsey
American Competitiveness Institute
Senior Lab Technician / Instructor
610 362-1200 ext 107
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Ryan Grant
Sent: Friday, December 08, 2000 10:01 AM
To: [log in to unmask]
Subject: Re: [TN] Copper contamination is wave solder
Lou,
You don't have to dump the pot. The copper is soluble in solder
because it combines with tin to make a couple of forms of intermetallics
having a melting point lower than your solder pot temperature. However,
that "alloy" is not liquidus at 183 degrees Celsius. That means, if you
lower your solder pot temperature to just above the melting point of
eutectic tin lead solder, all copper tin intermetallics will precipitate or
solidify and fall to the bottom of the pot as a sludge. You can scoop that
sludge out to reduce the copper content, as well as other metals that don't
belong.
I'm sure there are many other Technetters using this method.
Ryan Grant
Advanced Technology Engineer
MCMS
(208) 898-1145
[log in to unmask]
> -----Original Message-----
> From: Lou Hart [SMTP:[log in to unmask]]
> Sent: Thursday, December 07, 2000 3:50 PM
> To: Ryan Grant
> Subject: FW: [TN] Copper contamination is wave solder
>
> Ryan, thanks for your comment. I just talked with a solder expert from
> Com-Kyl, and yesterday called Kester. I thought we were skimming copper
> when we cleaned the dross every day. They tell me that the copper is
> soluble in solder, so continues to build up, except for a little of the
> oxide that can be removed. It comes from exposed ends of leads that are
> trimmed, it seems. We have started running more trimmed leads (3 shifts
> vs no more than 1.5 shifts), so copper may jump up. So maybe I need a
> regression SPC chart, with a sloping center line. We only sample once per
> month, so data are not plentiful. I have a year's worth - 12 points. I
> don't want to dump the solder sooner than needed. The thing I learned
> that's most valuable about SPC is that it tells you to leave things alone,
> don't waste time and money trying to fix things that are in control. Stay
> tuned. Lou
>
> ----------
> From: Ryan Grant[SMTP:[log in to unmask]]
> Sent: Thursday, December 07, 2000 4:04 PM
> To: [log in to unmask]
> Subject: Re: [TN] Copper contamination is wave solder
>
> Lou,
> While not addressing your original question, why don't you just
> skim
> the copper out? Your SPC chart will let you know when to do this.
>
> Ryan Grant
> Advanced Technology Engineer
> MCMS
> (208) 898-1145
> [log in to unmask]
>
>
> > -----Original Message-----
> > From: Lou Hart [SMTP:[log in to unmask]]
> > Sent: Wednesday, December 06, 2000 1:03 PM
> > To: [log in to unmask]
> > Subject: [TN] Copper contamination is wave solder
> >
> > TechNetters,
> >
> > I've made SPC charts to track tin, copper, gold, and antimony in our
> wave
> > solder machine. The operator skims dross from the solder pot every
> > morning. We send a solder sample the first of each month to Kester for
> > analysis. Over the past 7 months, there has been a monotonic increase
> in
> > copper concentration and the past two months have been above the upper
> > control limit. The copper concentration is still well within spec
> (0.3%,
> > if I am correct, according to the relevant IPC standard) at 0.14%, but I
> > want to make sure we know what is happening.
> >
> > Any comments on these observations? Some years back I had charts for a
> > HASL machine and over perhaps 12 months the semimonthly copper
> > concentration wandered between 0.21 and 0.24 %.
> >
> > Lou Hart
> >
> >
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