Gerbers from EDA

[Robert Baer]

Say one lays out a one-sided board with the letter "G" in the lower
left corner.
Then make four gerbers: X asis, Y asis; X mirrored, Y asis; X asis, Y
mirrored; and X mirrored, Y mirrored.
That is to say, you *TELL* the EDA to do those operations, eXplicitly!

Please tell me the following:
1) What does -->your<-- EDA generate - ie: what did it *really* do?
2) What is the *standard* for the fab shops, and exactly why?

 

[martin.shoebridge]

You only need to make one gerber for manufacturing - boardname.gbl- the
bottom layer ( solder side). When you put on the "G" it should be placed
mirrored so that when it is plotted, it reads correctlly

 

[DJ Delorie]

Then make four gerbers:

PCB doesn't mirror gerbers; it plots all gerbers as viewed from the
component side, with the same orientation.

If you ask it to *print* the layers (i.e. for home etching), it has
mirroring options (auto and manual), but the (default) alignment marks
include an "orientation" mark so you know which way the board is. You
only get one mirror option; if you want the image rotated, just pick
up the paper and rotate it ;-)

 

[Peter Bennett]

Say one lays out a one-sided board with the letter "G" in the lower
left corner.
Then make four gerbers: X asis, Y asis; X mirrored, Y asis; X asis, Y
mirrored; and X mirrored, Y mirrored.
That is to say, you *TELL* the EDA to do those operations, eXplicitly!

Please tell me the following:
1) What does -->your<-- EDA generate - ie: what did it *really* do?
2) What is the *standard* for the fab shops, and exactly why?

All Gerbers that I send to a board shop are as viewed from the
component side of the board - even those for the solder side of the
board. Any lettering I put on the board will be readable on the
finished board, so lettering on the solder side is mirrored in the
design program (Protel).

 

[qrk]

Say one lays out a one-sided board with the letter "G" in the lower
left corner.
Then make four gerbers: X asis, Y asis; X mirrored, Y asis; X asis, Y
mirrored; and X mirrored, Y mirrored.
That is to say, you *TELL* the EDA to do those operations, eXplicitly!

Please tell me the following:
1) What does -->your<-- EDA generate - ie: what did it *really* do?
2) What is the *standard* for the fab shops, and exactly why?

I can only do a true mirror (x-axis flip) which is only useful for the
solder-side assembly layer documentation.

When I send stuff to the PCB house, all Gerbers are non-mirrored, i.e.
all layers are viewed as shown on your monitor. Makes it easy for you
to check your Gerber plots on your Gerber viewer. The PCB fabricators
will probably like to see all layers as non-mirrored so they can
generate netlists for their probing fixture and look for errors and
design rule issues. The PCB fabricators will mirror layers as required
by their process. There is no need to second guess what they require.

 

[DJ Delorie]

i.e. all layers are viewed as shown on your monitor.

Doesn't apply to PCB, which can flip the board both horizontally and
vertically on the monitor, plus rotate it 180 degrees.

The gerbers aren't rotated or mirrored, just the monitor.

 

[Robert Baer]

You only need to make one gerber for manufacturing - boardname.gbl- the
bottom layer ( solder side). When you put on the "G" it should be placed
mirrored so that when it is plotted, it reads correctlly

OK; if i understand you correctly, the one side that i look at has
copper and all i see is the "G" and it is called the ?bottom? layer.
And from the instructions,i should tell the EDA to mirror (X mirror
seems to be the presumption) for creating the gerber, and the result is
non-mirrored.

 

[Robert Baer]

PCB doesn't mirror gerbers; it plots all gerbers as viewed from the
component side, with the same orientation.

If you ask it to *print* the layers (i.e. for home etching), it has
mirroring options (auto and manual), but the (default) alignment marks
include an "orientation" mark so you know which way the board is. You
only get one mirror option; if you want the image rotated, just pick
up the paper and rotate it ;-)

So you are implying that PCB creates gerbers that are not mirrored if
you do not tell it to mirror?
If so, then am i correct in assuming that you get a gerber that looks
eXactly what you tell it to do (*all* 4 cases)?

 

[Robert Baer]

All Gerbers that I send to a board shop are as viewed from the
component side of the board - even those for the solder side of the
board. Any lettering I put on the board will be readable on the
finished board, so lettering on the solder side is mirrored in the
design program (Protel).

So Protel "automatically" mirrors the top side when it makes that
gerber, but the actual file is normal reading?

 

[Robert Baer]

I can only do a true mirror (x-axis flip) which is only useful for the
solder-side assembly layer documentation.

When I send stuff to the PCB house, all Gerbers are non-mirrored, i.e.
all layers are viewed as shown on your monitor. Makes it easy for you
to check your Gerber plots on your Gerber viewer. The PCB fabricators
will probably like to see all layers as non-mirrored so they can
generate netlists for their probing fixture and look for errors and
design rule issues. The PCB fabricators will mirror layers as required
by their process. There is no need to second guess what they require.

That sounds ideal, but (in my EDA and it seems some others) if one
does not mirror in creating the top gerber, the resulting file *is*
mirrored.
And don't get fussy when one tries all 4 options i mentioned as no
mirror option works as one would "expect".
I like things to be straight and plain; if i say "G" that is what i
should get, not something that looks like a "9" or other variants that
are obscene (non-creatable and non-viewable).

 

[DJ Delorie]

So you are implying that PCB creates gerbers that are not mirrored
if you do not tell it to mirror?

No, PCB doesn't create mirrored gerbers *ever*, and it doesn't give
you the option to mirror them either. Why would you want to? Fabs
want them all oriented the same way, *they* can mirror them if their
tools want them mirrored, but how can *you* know when they need to be
mirrored?

*Printing* doesn't involve gerbers, it uses Postscript. *That* you
can mirror.

 

[Peter Bennett]

Peter Bennett wrote:

So Protel "automatically" mirrors the top side when it makes that
gerber, but the actual file is normal reading?

No. When working on the board layout in Protel (or most other CAD
programs, I think), you are looking at the component side of the
board. All the Gerber files Protel produces are also oriented as if
you are looking at the component side (with X-ray vision, for the
bottom and inner layers.) No mirroring involved.

When the board shop processes the Gerbers to produce their
manufacturing tooling, they may mirror some layers - (I recall a
requirement to have the film emulsion against the board for best
resolution - don't know if that still applies, or exactly what steps
the board shop uses to get from Gerber file to their tooling)

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
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[Robert Baer]

No. When working on the board layout in Protel (or most other CAD
programs, I think), you are looking at the component side of the
board. All the Gerber files Protel produces are also oriented as if
you are looking at the component side (with X-ray vision, for the
bottom and inner layers.) No mirroring involved.

When the board shop processes the Gerbers to produce their
manufacturing tooling, they may mirror some layers - (I recall a
requirement to have the film emulsion against the board for best
resolution - don't know if that still applies, or exactly what steps
the board shop uses to get from Gerber file to their tooling)

Your answer seems to be the norm.
What has been frustrating, is that i have had to tell my EDA to
X-mirror the top side and that resulted in a normal-reading (!) gerber.
And i finally got very curious and did all 4 variations mentioned,
with the gerbers never matching in any of the mirror requests.
Rather messy..