[SI-LIST] Re: Help...
- From: MikonCons@xxxxxxx
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 11 Feb 2003 15:08:45 EST
In a message dated 2/10/03 8:11:10 AM Pacific Standard Time,
James_R_Jones@xxxxxxxx writes:
> The current is confined
> to one skin depth time .7 mils thick of trace.... a much smaller
> cross-section, hence lossier.
>
Partially right! However, unless your traces are VERY close together in
space, the coupling (as in current PCB stripline or microstrip construction)
is considered very high if you obtain 15% coupling. Therefore, the bulk of
the energy is still propagated in the dielectric between the traces and their
closest image plane. Practical etching limits on the obtainable trace
separation between pairs is currently in the >2 mils area (for PCBs). The use
of 1/4-ounce copper or thinner can marginally lower this spacing.
Specialized deposition techniques might be available if you HAD to reduce the
separation.
As usual, the best design judgements will be obtained through using a field
solver and assessing whether the losses are acceptable or not for your
particular design at your operating frequency and rise/fall times. You must
also remember to include fab house etching enhancements and meet their DFM
requirements for a successful design.
Mike
Michael L. Conn
Owner/Principal Consultant
Mikon Consulting
Cell: (408)821-9843
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