At 09:03 AM 11/30/01 -0500, Jenkins, Charlie wrote:
>Why would I want to keep extra copper where it's not wanted?  Electrically I
>might want the copper to separate sensitive areas of a board where a gnd net
>was missing.

 From my understanding, this will increase crosstalk by increasing the 
capacitance between the noise source and the sensitive circuit. Floating 
copper does not function as a shield. That, in fact, is the primary reason 
for removing dead copper.

>  For my purposes I like to keep as much copper on board as
>possible. One because it makes my etchant last longer and two because if I
>route the prototype and keep as much copper on the board as I can I get to
>control the clearances with rules and speed up the routers performance when
>it rubs out the bare areas of the board.

Certainly this makes sense. But it would be better, I'd think, to ensure 
that any substantial copper areas were grounded (or tied to something with 
low impedance to ground. The remaining dead copper could be very quickly 

If the design is not noise-sensitive, of course, there should be no problem 
leaving dead copper to speed up your prototype router.

>I use the fill instead of the track because it's easier find and highlight
>under the mess of tracks that get poured when you lay down a polygon. I turn
>on polygon draft and they pop out.

Well, you could use any primitive similarly. Polygon draft would leave a 
free track or arc visible just the same. But a fill will certainly have a 
distinctive appearance, and once it is decided that you must prevent dead 
copper removal, partially, then I agree that a free fill assigned to the 
polygon's net is a good way to do it. To prevent it completely, of course, 
one would simply turn it off in the polygon setup dialog.

>If you haven't guessed I do mostly prototype work for my clients.

Tough business. There is a narrow place for machine-cut PCBs. For reasons 
have been raised in this discussion, boards designed for efficient cutting 
are not necessarily the same as board designed for efficient printed 
circuit fabrication and noise control. Since printed circuit prototypes 
(onesies and twosies) have become quite cheap, the only advantage I see to 
routing them is that the turnaround can be cut by a couple of days.

I've known a couple of companies that had the machines gathering dust....

Abdulrahman Lomax
Easthampton, Massachusetts USA

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