>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 ---------------------------------------------------------------------------------