My 2 cents worth, since we do this regularily.

        The edge plating will make a significant difference in board
emmisions with GHz frequency signals depending on the board material used.
It gets worse the higher your frequencies go. The problem is that the board
material is a dielectric and thus will conduct high freq. signals between
the copper of the other outer layers. It is essentially a waveguide. The
vias will block some of the signal but the higher the frequency the closer
you have to space the vias until you are almost hole to hole and your board
has no structural strength along the line of vias.
        The additional cost for the edge plating should be minimal. The only
operation or labor is to route the board edges before doing the intitial
electoless plating, instead of doing it after the board is processed. There
is no additional work or effort unless there is also still unplated routing
to do after the board is processed.

Sincerely,
Brad Velander.

Lead PCB Designer
Norsat International Inc.
#300 - 4401 Still Creek Drive,
Burnaby, B.C., Canada, V5C 6G9.
Tel   (604) 292-9089 (direct line)
Fax  (604) 292-9010
Website: www.norsat.com


-----Original Message-----
From: Abd ul-Rahman Lomax [mailto:[EMAIL PROTECTED]]
Sent: Friday, November 09, 2001 12:22 PM
To: Protel EDA Forum
Subject: Re: [PEDA] keepoutlayer and planes ??


At 09:44 AM 11/9/01 -0700, Bob Fearon wrote:
>Abdul-Rahman
>     Yes I have seen an inner plane layer come all the way out to an edge.
>     The design was supposed to be "better for RF", but made no difference
>     in board performance. The two outside layers were plated aound the
edge
>     and shorted ( on purpose ) to the inner layer. This was a nightmare to
>     build and cost "extra".
>     The same performance was achieved by placing a row of vias 100 mils
>     from the edge on a "regular" board, at a much lower cost.

This is not an example of what I asked for. Instead, this was a board 
deliberately fabricated without edge clearance. Yes, it was not a great 
idea from the start, as anyone who knows HF design would have anticipated, 
unless -- maybe -- one was trying to squeeze the last percent out of noise 
emissions *and* board space was very limited. I could see doing this with 
very small PCBs, where the via ring would take up an appreciable percentage 
of the board space.

It should not have been much more expensive. In fact, as I recall, 
depending on the process, panel edges plate if you don't do something to 
prevent it!  (The same electroless copper used to plate the inside of holes 
also plates the panel edge, I'd think, I don't remember actually seeing 
this; however, that edge is normally routed away when all the processing is 
done, leaving the unplated edges that we normally see. So to accomplish 
this relatively inexpensively, one would route the boards as one routes a 
breakaway board *before* going to the electroless copper; this would leave 
some unplated tabs but one might hide the unplated tabs behind mounting 
holes....)

Edge effect with regard to radiated noise is a controversial subject, but 
actually plating the board edge I have never before seen suggested.
[EMAIL PROTECTED]
Abdulrahman Lomax
Easthampton, Massachusetts USA

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