Factors to consider are the number of test points required by this design,
size of the card, probe types, etc.
We had a design with close to 2000 test points on a 9"X11" card. Our
standard test point is 40 mils; for this product test signed-up for 30 mil
pads due to "lack of space". We had significant contact-related problems;
i.e., probe not hitting the pad, on virtually every ICT cycle. The fixture
was reworked to ensure tooling pin accuracy, in addition, a "funnel plate"
was added for increased probe precision. While much improved,
contact-related false failures were still evident. Our resident statistics
expert calculated that, with 2000 30 mil test points, the probability for a
false contact failure was one out of two ICT cycles, taking into
consideration tolerances on board fab, ICT fixture, etc. With 40 mil pads,
the probability for success is virtually 100% (in this particular case).
New designs since use 40 mil pads; JTAG is used on dense boards to eliminate
test points.
I'm not a test engineer, but learned alot about ICT probing dynamics from
this episode. Your board size, style and quantity of test points will
significantly influence success with 25 mil pads. A small board with few
25 mil test points is likely to succeed when coupled with a quality ICT
fixture.
I like to see the TE's shooting at the biggest target, it keeps the first
pass yields high!
Ellsworth D. Berkowitz, P.E.
NPI/Production Engineering
Paradyne Networks Inc.
"The opinions expressed above are solely those of the writer and do not
necessarily reflect the views of Paradyne Networks Inc."
On Mon, 16 Jul 2001 09:14:27 -0400, Michael Forrester
<[log in to unmask]> wrote:
>Does anyone have any statistics on ICT reliability based on test point
size?
>What I am looking for
>is information on what am I giving up, other than cost, by going from a
.035
>test pad to a .025 test pad.
>Is there a reliability curve based on test point size? Any help would be
>appreciated. Thank you.
>
>Best Regards,
>
>Michael Forrester
>LeCroy Corp.
>
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