Hi everyone....

I was wondering at what point in the design cycle for a board layout
is it appropriate to request specifications?

AND:  Should the specification for the Impedance to the Board house
be in stack data, or Impedance value?

To clarify the reason for the question:
A recent layout (done as a favor for a friend) with his firm resulted
in  much rework due to several people making changes as work
progressed.   It was a fixed Price and Should have been renegotiated
based on the changes, I know!       I actually laid out the board
seven times, with an additional five sessions of major rework.

This board had a 14 pin equivalent density of 125 parts on 4 square
inches.  Almost all surface mount, and was impedance controlled.
After much indecision the placement was approved and I did the first
of many layouts.  After the third engineer was assigned to "Shepard
the board / circuit" into production reviewed it, and more major
changes were made, and a faraday shield was added, with much
rearrangement to connect it in place.

I realize now, that my "Friend" was only trying to get off the hook.
But the original questions remains!

Oh yes, I am an Electronic Engineer, with experience in Emissions and
virtually all phases of design and Fabrication and test.  I also lay
out almost all my OWN boards, and occasionally (Rarely) for a
customer.  For myself, I always have ALL requirements called out
BEFORE starting any layout!

Roger Gathright
Sr. Project Engineer
Astromation Company

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