Re: gEDA-user: single-sided boards

[Stuart Brorson <sdb@xxxxxxxxxx>]

Hi --

> How often does the need for single-sided boards arise?

The question about single-sided boards is interesting, but the
answer depends upon how you intend to fabricate your boards.

If you're sending the boards to a PCB manufacturer, then the raw
material they use is fiberglass clad with copper on both sides.  In
this case, it's senseless to ask for a single-sided board to save
costs -- they start with a double-sided board in any case.

If you're making the PCBs at home, starting with single-sided
fiberglass from e.g. Radio Shack, then it's totally sensible to make 
single sided boards.  In this case, just throw away the back side
Gerber file.

> this kind of
> cosmetics with gerber files is an additional error-prone manual step.
> Has it been considered to make this an option that is supported by pcb?

I agree that it tends to trip up newbies.  However, there's one Gerber
file per (metal) layer, so you can always discard the back side file
without any problems.

More to the point:  the Gerber, and the related drill file
formats are pretty stupid.  They don't carry any top-level
information about your design.  A particular Gerber file knows only
about its own layer, and knows nothing about any other layer.  The
Gerber files have no concept of "stack-up" (i.e. what order the layers
are supposed to be stacked in).  The drill file only contains
information about what drill diameters to use, and where to put the
holes.  The remaining information, like stack-up, plated
vs. non-plated holes, how thick your copper layer should be, how thick
your FR-4 should be, desired manufacturing tolerances, etc., are all
told to your PCB manufacturer using "fab  notes" (i.e. a
human-readable text file) and a "fab drawing" (a drawing of the board,
stack-up, and other graphical info).

Finally, one of the projects slated for work under the Linux Fund's
PCB project is to update PCB's handling of layers.  Things like the
ability to easily deal with single sided boards from inside of PCB
are part of the work to be funded by the Linux Fund. I'll just remind
everybody that they can make this work happen sooner by making a
donation!

http://www.linuxfund.org/projects/pcb/

HTH,

Stuart


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