Mitch -

   The techniques you are describing are sometimes used in the output path
of high frequency RF designs.  These designs are generally developed by guys
with wands and pointy caps, so they make little or no sense to us mere
mortals:<D.

The engineer will need to tell you more than the basic path for the
components and traces but also trace width, acceptable signal delay, and
trace impedance/capacitance/inductance.

This type of tuning arrangement may require some thieving like pads placed
near the end of the run for post assembly fine tuning adjustments. While
backseat CAD drivers are not really appreciated, this is one time you're
going to want the engineer sitting there as you work.

As to tricking the cad system your guess is as good as mine.  I had settled
on just making a note of the errors the system would return because of the
design and moved on.

Best of luck,

Jeffrey McGlaughlin
Designer
Battelle
Columbus, Ohio


        -----Original Message-----
        From:   Mitch Morey [SMTP:[log in to unmask]]
        Sent:   Friday, March 13, 1998 1:18 PM
        To:     [log in to unmask]
        Subject:        [DC] DES:"tuning" etch pattern

        This question came up recently, and I'm unfamiliar with the
practice.

        A circuit was described to me that has a "few" traces going between
        components, and then they go off the last (first?) component a
"certain"
        distance then tie to ground. Sound familiar? This "certain" distance
is to
        be determined during routing, and then the three or four (or more)
traces
        will be "adjusted" accordingly to satisfy the circuits function.

        First off, this makes no sense to me.

        Secondly, is there a preferred way to tie these traces to ground,
and
        what methods have been used to "trick" the software package you're
        using into doing this (other than showing them as ground signals)?

        Any help is appreciated.

        Mitch Morey
        Sr PCB Designer


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