I agree with you, as far as trimming leads before soldering. I agree, a solder - cut - solder process should be avoided if possible. But, I can't find any place in the J-STD-001C or IPC-A-610C which bans exposed copper. In fact, I can only find places where it is specifically acceptable, even including nicked leads unless the damage is greater than 10% of the lead diameter or thickness. Unless the damage is the result of careless or repeated bending. Is this a topic worthy of discussion? Have I misinterpreted the standards? > -----Original Message----- > From: TechNet [mailto:[log in to unmask]]On Behalf Of > [log in to unmask] > Sent: Thursday, May 02, 2002 8:05 PM > To: [log in to unmask] > Subject: Re: [TN] Wave solder re-runs/re-work > > > One thing I've learned in my 20+ years in electronics > manufacturing is that > one should pre-trim leads prior to soldering, not trim them afterwards, > especially with the plier type lead cutters. The shock to the solder > joints when the leads part with that snap is very high, and joints, too > numerous to mention, have been damaged in the process. Even > high-speed lead > saws aren't much better, and often tend to smear leads rather than cut > them. I've also known these cut right through a joint and into a > board when > the board is a bit bowed (bowed boards weren't so critical back then with > plated-through-hole components). > > Also, on class 3 boards anyway, exposed copper is banned, so all trimmed > leads had to be put back through the wave solder to cover them up. This is > an additonal and unnecessary thermal excursion that should be > avoided. It's > detrimental to the life of the board and takes extra time and cost for the > additional processes involved. It's better to trim the leads to length > prior to soldering then wave solder only once. Clinch or half-clinch two > opposing leads on each component before trimming if you're worried about > the components rising in the wave, or put a pad over the > components to hold > them in place. > > One holding technique I saw years ago is to vacuum-form thin plastic sheet > over the populated board that can be peeled or lifted off after the > soldering process. We never tried it, and I never saw it used "for real", > so I don't think it caught on. Another technique was to secure a foam pad > over the components (wave resistant, of course) > > Anyway, in your current curcumstances, I would opt for doing a second wave > solder pass, in spite of what I just said, especially if you have a lot of > leads to do on a lot of boards. It will be kinder to the board > that locally > heating lots of areas, though your no-clean residues will build up. Maybe > our TN cleaning experts can help with that one. > > Good luck > > Peter > > > > David White <[log in to unmask]> 02/05/2002 11:14 PM > Sent by: TechNet <[log in to unmask]> > > Please respond to "TechNet E-Mail Forum."; Please respond to David White > > To: [log in to unmask] > cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group) > Subject: [TN] Wave solder re-runs/re-work > > > > > > > > > Advice please. We have had a problem here we have cut in the > solder fillet > while trimming leads (pretty deeply, we have also seen cracked solder > fillets) which is a violation of IPC. There are several hundred of these > asm. I suggested to Re-run them through wave. Has anyone else had to do > this and what have the results been, this sure beats touch-up on every > lead. I am not re-fluxing the asm, we spray no-clean and some > gets on the > top the 1st time around which is acceptable, but 2nd time it is just to > much. Anyone have any comments? Any help would be great. > Dave > > ------------------------------------------------------------------ > --------------- > > 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 > To temporarily halt delivery of Technet send e-mail to [log in to unmask]: > SET Technet NOMAIL > To receive ONE mailing per day of all the posts: send e-mail to > [log in to unmask]: SET Technet Digest > Search the archives of previous posts at: http://listserv.ipc.org/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 > ------------------------------------------------------------------ > --------------- > > > > > > [This e-mail is confidential and may also be privileged. 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Thank you.] > > ------------------------------------------------------------------ > --------------- > 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 > To temporarily halt delivery of Technet send e-mail to > [log in to unmask]: SET Technet NOMAIL > To receive ONE mailing per day of all the posts: send e-mail to > [log in to unmask]: SET Technet Digest > Search the archives of previous posts at: http://listserv.ipc.org/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 To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/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 ---------------------------------------------------------------------------------