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. If you are not the
intended recipient, please delete it and notify us immediately; you should
not copy or use it for any purpose, nor disclose its contents to any other
person. 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
---------------------------------------------------------------------------------
|
