In a message dated 9/21/99 8:09:44 AM Central Daylight Time,
[log in to unmask] writes:

> Steve,
>
>  As a user of GIL, I have seen suppliers have the same trouble with
drilling
> this
>  material.  It is often a problem of unfamiliarity with the material.  As
> previously
>  mentioned, if you start to "punch" thru GIL with your drill bit, it will
> shatter the
>  GIL material.  You are probably on the right track here as to HOW the
defect
> was
>  created.  Let's ask why the PWB supplier let the board out of his shop.
The
> Fab shop
>  should be able to catch such errors.
>
>  So, lets swim a bit further up stream here.  I was wondering if the hole
is
> a mounting
>  hole that is plated thru and connected to the ground.  I try to discourage
> the practice
>  of plating mounting holes.  If it is a mounting hole, who torqued the
bolts,
> Magilla
>  Gorilla? Torquing down a hole can increase your GIL cracking/crazing
> problems,
>  providing a reason the latent short occurred after assembly, and not at
the
> board shop.
>
>  Lets talk electrical testing now.  What isolation resistance threshold was
> used at
>  electrical test?  100 Megs is the norm.  Now the next question.  Was the
> board tested
>  with a flying probe machine?  Many of these machines will only test
adjacent
> nets for
>  isolation.  This software driven algorithm greatly reduces test time, by
not
> testing
>  nets that are on opposite corners of the board from each other.  The
problem
> with this
>  algorithm is that most of them do not recognize and test nets that pass
near
> planes in
>  the vertical axis.  For example, a trace that comes close to a ground via,
> may not get
>  tested for isolation to ground.  It is quite possible, if your short is
from
> a net to a
>  plane, that the resistance isolation between these were never tested.
>
>  Also, are you happy with the clearance area allowed by the design around
the
> holes?
>
>  Finally Steve, who once graced the golden state, did California Dreaming
> come before or
>  after Monday, Monday?
>
>
>  George Franck
>  "My opinions are just that"

Hi George!

Hmmmm, the last question first; I think it was "California Dreaming"...

Anyway, to your other questions:

1. That's the $64,000 question...I don't know...

2. It wasn't a mounting hole, it was for a 6-leaded power terminal block. The
kind that has screws at each terminal where you put a wire and lug
into...they see about 150 volts DC when fully powered-up.

3. I don't know the requirements of the bare board test. We did a test here
after assembly and the boards passed. The boards powered-up intially at our
customer, and after about 1-3 hours of 150-volts DC is when the short occured.

-Steve Gregory-

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