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June 2000

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From:
"Stephen R. Gregory" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 8 Jun 2000 16:51:20 EDT
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In a message dated 06/08/2000 11:11:40 AM Central Daylight Time,
[log in to unmask] writes:

<< I also have questions about tinning components with respect to automated
lead forming.  Is tinning usually done before or after lead forming?  We are
working high rel and several of our contracts still spec NHB5300 and MIL2000,
so a blanket "No-tin" directive will not be acceptable to our customers and
quality folks.  I am actually also working on developing a reliable (read
repeatable) method of tinning as our assemblers are doing it by hand
currently.  (suggestions on this are welcome as well).

 Thanks in advance,


 Eric Kalgren
 BFGoodrich Aerospace
 Space Flight Systems
 [log in to unmask]
 (505) 938-5139 >>

Hi Eric!

Everybody has pretty much answered your questions about PTH forming...GPD and
Hepco are pretty much the standard with a lot of people.

As far as SMT tinning, and form and trim, we have a Mannix press with an
adjustable die. There's one job we do here that requires this type of work
and we only build these boards twice a year...maybe 50 or so a pop, so it
doesn't justify the nice automated equipment out there. Winslow Automation
makes automated tinning systems as Graham pointed out, and Robotic Process
Systems makes this stuff too...

We do it by hand here...the 50-mil stuff isn't too bad, but there's this
20-mil pitch, 352-pin, ceramic QFP that we have to do that is a MONSTER!
(Texas Instrument PN# sm320c40hfhm40)

With this guy (and I know some will frown) we pre-tin it first, and then cut
and form. The reason that you should cut and form first, is that you that you
want to keep your cutting die as clean and pristine as possible. If you tin
first and then cut, the plating may start accumulating on the die. Also you
will tin over the exposed copper toe after the cut and form..

The reason that we tin first though, is because there is no way (that we've
found anyway) to tin this beast without bridges unless we do it while it's
still in the carrier ring...we've tried it both ways.


-Steve Gregory-

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