positive and negative plane ?

[jasmine]

what do you mean by positive and negative plane in powerpcb?.

[phillipr]

Imagine looking at a black and white printout of a plane

Positive image (Split/mixed Plane)
Copper will be Black void white

Negative image (Cam Plane)
Void Will be black Copper will be white

Both Ways have there advantages and disadvantages.
For example It is alot easier for the cad tool to output a couple of circles and lines (Negative) Than it is to Flood Large pieces of copper (Positive)

[royl]

Its not just simpler for the cad tool to output. There are other things too. One has to understand the "draw" Vs. the "flash" in Gerberland. Assuming one does get this, one can see that Fab houses prefer negative planes as the clearances around holes on planes are flashes rather than draws. Flashes are editable, draws are not. (or at least not easily) Since every fab house "tunes" your data to their process its easy to see that if flashes are present on planes they are easily brought in to the fab process because they are editable. If there is a tuning issue with draws (positive planes) the gerbers are not as editable and usually the fabricator has to place a job on hold and contact the designer. This usually ends up with the designer making the adjustment and resending data. Negative planes are more stable in the database, easier to work with at the fab house, and certainly more easy on the eys when printed. Because of the nature of the "draw", positive planes use more memory than negative planes do...therefore the database is a bit less stable, especially on a very large design. The gerber files on negative planes are MUCH smaller too, as they don't have all that "draw info". There's more but I think you get the initial point.

[phillipr]

Jasmine

I agree We royl on all his comments.
But before you make a choice on which method to use you should hear the arguments for using split/mixed planes as the last 2 posts would definetly stear you down the "cam plane" Route.

One onther Cam plane plus is there is less testing time at your fab shop as splitmixed usses losts of lines to fill in the plane.


The main positive Point for using splitmixed planes is its inteligence when checking connections to the plane.

[royl]

Ah yes! The only argument for split planes that exists. Split planes are only checked in PADS when you have a positive "Split/Mixed" plane.This is really how this situation was "forced" on us. PADS has never supported split negative planes. I have been complaining to PADS since the days of PADS-PCB about this one. Every rev...2-3 times per. I'm notorious for "bringing it to their attention" at user group meetings too! You might say I try to champion the cause but so far...I have been unsuccessful. I have CAM 350 which does support negative split plane checking. Therefore the only time I used "Split/Mixed" is when I have a mixed situation.

[PRoehl]

With the speed of computers now, and the speed of the internet, who cares about file size anymore. Being able to verify split/mixed planes within your given tool is priceless. Who cares if the files are larger.

Paul

[phillipr]

Its not the file size thats the problem.
It takes tens of Hours to check our boards at the fab shops
front end.

[royl]

I wonder if this forum can "lean on" Pads to put negative plane split checking. What do you say?

[PRoehl]

U mean lean on Mentor, right???

[royl]

Yes I do....funny how this business plays musical parent companies.

[petehouwen]

There are more critical factors than computer speed as it relates to file size. How about more bytes = more chance for error? How about having to re-flood every time you need to make a change or output CAM files? Or trying to move your split in a split/mixed plane, vs dragging a copper corner around in a CAM plane. Or constantly turning plane display on and off.

You can check CAM splits in most gerber editors. Why can't PowerPCB do that? That would make splitting a plane much less cumbersome.

I've rarely seen anyone who has used negative planes champion split/mixed planes.

[royl]

Amen! How hard is it to see if all hits within the same closed polygon are of the net? and are there any outside? Duh.

[PRoehl]

to each his/her own, you know!

Paul