I once saw a company that solved this problem buy creating a stairstep of
the layers copper along the edge of the panel where each layer had a
specific place it was to be in the step pattern. As a part of their source
inspection they just sanded across the edge and if the stair step was
correct you could tell the layers were in the correct plane. Also if you
have quality conformance test coupons you can put it in the edge of the
coupon.  One caution, don't do this on the actual board itself unless you
can tolerate copper to the edge of your board and also don't connect it
electrically to anything else.

> -----Original Message-----
> From: Genny Gibbard [SMTP:[log in to unmask]]
> Sent: Tuesday, October 16, 2001 10:07 AM
> To:   [log in to unmask]
> Subject:      [TN] PCB layers swapped
>
> Good morning,
> My morning has not been so good.  I have a build of PCB's (over 300
> boards)
> where two inner layers have been swapped.  The board fabricator
> constructed
> the board in the wrong order.  These boards are RF in nature and have
> frequencies approaching 2GHz on them.  In many places we put a signal
> trace
> on the inner layer furthest from the component side and then a wide
> grounded
> trace over it on the closer inner layer as shielding.  So not only is
> there
> no longer shielding over many traces, these signals are also about .03"
> closer to the component circuitry than they used to be.  Can you
> contemplate
> the nightmare of spurious issues that have been created?  We did not
> notice
> the problem until they were fully populated and almost thru our testing
> process and started failing one of the tests miserably.
> Needless to say, we will be revising our inspection techniques to try to
> catch occurrences like this much sooner.
>
> I was wondering if anyone knows of a way that layer order could be
> electrically tested for on a bare board, that we could require our
> fabricator to complete?
>
> Genny Gibbard (mailto:[log in to unmask])
>
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