I am still recommending .035" pad on .050" centers, though not all our
     customers are able to go that high.  I'm letting our CAD folks go down
     to .030 pads (round) under duress, but NOT as a rule.

     A number of ICT fixture vendors are claiming to be handle much smaller
     test pads and spacings (TTI, ECT to name a few).

     The rule of thumb here is: the smaller you go on spacing and pad size,
     the higher your ICT fixture development and maintanence costs are
     going to be.  I've seen a fixture for a 2"x3" double sided board that
     cost $20,000 because of size of the test targets.  Try and explaing
     THAT fixture cost on a board that costs ~$100 to produce and is only
     going to be made in lots of 100 per year.

     Rob Green


______________________________ Reply Separator _________________________________
Subject: Re: [TN] ICT Test Pin Attributes
Author:  Jeff Seeger <[log in to unmask]> at smtplink-hadco
Date:    10/11/99 5:57 PM


Dave Hoover wrote:
>
> Curious about what designers are using now for
> ICT test pin location access pad size (S/M also)
> along with closest distance between two test points.
> (Of course those flying probe ICT 's can bend
> major rules but I'm thinking standard fixture/high
> volume.)

        Hey Dave!

        Am seeing high resistance to going lower than .035" sq. pads
        on .050" centers.  IOW not fine enough to cope with large
        1 or .8 mm pitch devices, at least when connected together...

        Preferred granularity remains .040" pads on .100" centers,
        and at worst a preference for surface pads only.

        Break out the board stretchers, or "abandon all hope ye who
        require off-chip series termination".

        IMHO we're reaching a point where in-fixture JTAG, with
        multiple JTAG chains, is a must for testing complex product.
        Of course, that's not a very practical solution either.

        Perhaps this is why we see occasional posts from folks in
        search of the non-contact technologies, sure wish they'd
        gotten some answers!

        Hoping you get responses from leading-edge ICT folks w/hints
        on how to cope....
--

      Jeff Seeger                         Applied CAD Knowledge Inc
      Chief Technical Officer                  Tyngsboro, MA  01879
      jseeger "at" appliedcad "dot" com                978 649 9800

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