>I thought tin/copper had a higher
melting point than tin/lead.
you're right. So if the temperature of the solder pot is set below the
melting point of tin/copper, the tin/copper will solidify.
We do this about once a year on a particular wave that sees a lot of OSP
boards. We do add tin, but not because of the tin/copper skimming, rather,
because the tin is tied up with the copper regardless of performing the
copper skimming or not.
Ryan Grant
Advanced Technology Engineer
MCMS
(208) 898-1145
[log in to unmask]
> -----Original Message-----
> From: Guy Ramsey [SMTP:[log in to unmask]]
> Sent: Friday, December 08, 2000 8:52 AM
> To: TechNet E-Mail Forum.; Ryan Grant
> Subject: RE: [TN] Copper contamination is wave solder
>
> 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
> > >
> > >
> >
> --------------------------------------------------------------------------
> > > -------
> > > Technet Mail List provided as a free service by IPC using LISTSERV
> 1.8d
> > > To unsubscribe, send a message to [log in to unmask] with following text
> > in
> > > the BODY (NOT the subject field): SIGNOFF Technet
> > > Search previous postings at: www.ipc.org > On-Line Resources &
> Databases
> > >
> > > E-mail Archives
> > > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
> > > additional
> > > information, or contact Keach Sasamori at [log in to unmask] or
> 847-509-9700
> > > ext.5315
> > >
> >
> --------------------------------------------------------------------------
> > > -------
> >
> >
> --------------------------------------------------------------------------
> > -------
> > Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
> > To unsubscribe, send a message to [log in to unmask] with following text
> in
> > the BODY (NOT the subject field): SIGNOFF Technet
> > Search previous postings at: www.ipc.org > On-Line Resources & Databases
> >
> > E-mail Archives
> > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
> > additional
> > information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
> > ext.5315
> >
> --------------------------------------------------------------------------
> > -------
> >
>
> --------------------------------------------------------------------------
> --
> -----
> Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> Search previous postings at: www.ipc.org > On-Line Resources & Databases >
> E-mail Archives
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
> additional
> information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
> ext.5315
> --------------------------------------------------------------------------
> --
> -----
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
|
