Peter,
Well said!!
David A. Douthit
Manager
LoCan LLC
[log in to unmask] wrote:
> 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
> ---------------------------------------------------------------------------------
---------------------------------------------------------------------------------
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
---------------------------------------------------------------------------------
|
