Jim, Ken,

Let me give you my experience and see if it helps. I've seen it done a
number of ways, but two are probalby most common.

1) Both scenarios require a signal probe and a ground probe point at
both ends of the "coupon", for each impedance layer of the board. The
gnd probe points were .1" from the signal probe point

2) Coupon must be a "true" representation of the board. (e.g. it shall be
as the actual layering and line widths of the board, and preferably the
smae conductor spacings)

3) Coupon #1 was built right into the actual board. Impedance traces
were a minimum 6" long. This board ran 300Mhz to 2.4Ghz in range. (the
75 ohm coupon was actually 4.5" long because of board space, but the
50 ohm coupon was 6" min!) The engineer wanted it tested to 200 Mv. I
think the fab house generally tested to 20Mv, so they had to send it out
for testing.

4) Coupon #2 was built on the board too, but was 2" long, same
construction, and apparently was applicable to the engineer. I'm fairly
certain the fab house still put a coupon on the panel for testing (at 6").

There is a "coupon" pattern defined in IPC-D-317A and I beleive there is
one in IPC-D-2141, but I don't have that one handy. They tell you
essentially the same thing. If you really want a "fab" coupon, any of your
fab houses should be able to give you a generic one in whatever format
you might be able to import to your cad system.

Good luck,

Mitch Morey
Sr PCB Designer
ComStream Corp
San Diego, CA

>>> Ken Brown <[log in to unmask]> 04/02/98 03:34pm >>>
greetings:

is there a particular coupon layout for controlled impedance boards that
you would recommend?  a gerber file attachment would be appreciated.
thanks for your input.

jim henderson
colonial circuits, inc.
540-752-5511 x118

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