Hi Steve
We are thinking alike. The mass trimmers don't appeal to me, but there is one in another "sister" facility. The process for that one is to trim leads, and then run the boards back through wave. I don't like it because of the maintenance issues you mention, plus in this process the board sees another thermal excursion - and I'd prefer to avoid that. The 10x inspection for fractured joints is amusing - if you have a couple of thousand leads sticking out of an old technology board, inspecting them all for fractured joints is the proverbial search for the needle in the haystack.
Our process:
DIPs are all trimmed to finished length. Axials and radials are put in using a Contact cut/clinch machine, set up to meet our lead length requirements. The only problem parts are connectors, on thin boards we have been known to trim the leads by hand.
Have a happy holiday!
regards
Graham Collins
Process Engineer,
Northrop Grumman
Atlantic Facility of Litton Systems Canada
(902) 873-2000 ext 6215
>>> [log in to unmask] 12/18/01 01:12AM >>>
Hi All!
The subject has come up here about mass lead trimming systems. From what I've
learned, they have their place. But in our situation, I have the opinion that
they aren't warranted here. We do a lot of class-3 electronics, have hardware
(screws and whatnot from connectors) that hang below the lead length
requirements.
Many of the requirements on the asssembly drawings of products we build,
still call out MIL standards, even though they are obsolete, we are still
obligated to build to these standards...those that build product according to
these standards, and have tried to deviate, or change, from what is
documented on these standards know what a task that is...it isn't going to
change.
So, in my opinion, mass lead trimming systems have no place here. There are
too many things that call out extra work that will need to be done because of
these systems.
The J-STD's call out that if lead trimming is performed after wave solder,
then the joints should be either re-reflowed, or inspected under 10X to
ensure that there has been no fractures...
I've also heard that these systems need METICULOUS maintenance. If they
aren't maintained perfectly, they will cause major problems.
Just want to hear from any of you that have direct experience with these
systems..
My position is that you either prep PTH components so that lead length
requirements are met after soldering, and/or you make the adjustments that
are available on your auto-insertion machines so that you meet lead length
requirements...if you have to trim after wave solder, then either you haven't
specified the proper component prep, or you need to adjust the cut and clinch
on your auto-insertion equipment...I come the school that you can do things
before wave solder that keeps lead length requirements within specifications,
and not require mass lead trimming afterwards.
So with that being said, what opinions are out there about mass lead trimming
systems?
As always, all ya'll are the best...
-Steve Gregory-
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