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December 2001

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Subject:
From:
"Stephen R. Gregory" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 18 Dec 2001 00:12:22 EST
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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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