Re: gEDA-user: Composite/negative layers in gerbers

[Karel Kulhavy <clock@xxxxxxxxxxxxx>]

On Tue, May 02, 2006 at 10:49:55PM +0100, Chris Emerson wrote:
> Hi,
> 
> My board house[1] has complained about my gerbers having "negative
> plots" and "composite layers".  I understand that pcb does this in some
> cases.  (I've found

When I wanted to make the first Ronja board, I picked up a board house
that claimed to support Gerber RS274-X. It didn't, because they couldn't
load a file with negative layers. Negative layers are a part of Gerber
RS274-X, so they didn't support RS274-X and were just misleading
customers.

I went to a different manufacturer and he took it without objections.
Since then, all Ronja boards are done at the second manufacturer. The
first manufacturer lost significant amount of job, because the boards
have been made in hundreds or maybe thousands.

> http://www.geda.seul.org/mailinglist/geda-user33/msg00055.html).
> 
> My two questions are:
> 
> 1) (Main question) How can I tell if my gerbers are negative and/or
> composite so I can check?

They contain the command "IPNEG".

> 2) What can I do to affect whether pcb uses negative and/or composite
> outputs?  Is that what the "Invert positive/negative" tick box on the
> printing page does, at least for the negative stuff?

Nothing. PCB always uses them. The IPNEG command is the only way how to
accurately represent the board layout with Gerber. Any other method
(crosshatching polygons with lines) is inherently inaccurate and takes
up unnecessary space in the Gerber file.

I suggest you select only from manufacturers that claim to support
"Gerber RS274-X". If they refuse a negative layer, just go to somewhere
else, it doesn't make sense to work with manufacturers that lie, because
people who lie tend to be pathological troublemakers.

> I have looked through the manual and the archives, but haven't quite
> answered these as much as I'd like.

The problem is not in you, neither in the PCB program. The problem is in
the manufacturer.

> 
> Best regards,
> 
> Chris
> [1] Olimex

Thanks for information. Someone suggested making Ronja boards at Olimex.
It's good to know that this manufacturer should be avoided.

CL<