It rather depends on which ICT machine you are using. We are going to use
an HP machine whose preferred pad size is 0.050" with 0.075" spacing and a
clearance area around that for access by the test probes. We argued the pad
size down to 0.035" to maximise board real estate, but the  main danger of
going any lower than that size is false error readings.

If the pads are too small or too close together, or both, there is a risk
of the probes not contacting properly and returning open or even short
circuit failures where none actually exist. Check with your ICT test
machine manufacturer and/or your test jig vendor and make sure from them
that you understand why the smaller pad sizes could be a problem and what
it would mean to you in terms of false readings.

It may be that you can go to smaller pads, but the downside could be
greatly increased jig costs owing to the greater precision required of the
jig and of the probes. You will also find that tight tolerence probes have
to be replaced more often as they can tolerate less wear before replacement
than a less stringent requirement.

Hope this helps.

Pete Duncan




                    Michael Forrester
                    <michael.forrester@L        To:     [log in to unmask]
                    ECROY.COM>                  cc:     (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
                    Sent by: TechNet            Subject:     [TN] ICT Test Points
                    <[log in to unmask]>


                    07/16/01 09:14 PM
                    Please respond to
                    "TechNet E-Mail
                    Forum."; Please
                    respond to Michael
                    Forrester






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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