>> Solarwind, It is necessary to reverse the pattern on many parts.
> Could you please provide an example? I don't understand why
> you would need to reverse the design if all you are making is
> a single sided PCB with only through-hole components on one
> side (the FR4 side, not the copper side.

Engineer-brains tend to work in images of components as seen from above.
You don't have to do it that way, but it's convention and it makes sense in
almost all cases.
Through hole ICs have pin1 at the left end of one side and the pins number
anti clockwise therefrom.
Other devices which are polarity sensitive and with 3 or more pins also look
different from above than below.
SO PCB layout is "always" done from a looking down from above the 'top" or
component side.

When looking at copper on the "bottom" non component side of a a single
sided through hole PCB the pattern will be the mirror image of what you saw
from the above layout view.

If a photographic mask is made it can notionally be reversed BUT when actual
film is used for this the emulsion side is placed against the PCB to avoid
parallax due to the distance the light shadow can be offset when the image
is on the outer side of the film (who would have thought ! :-) ).

Worse, or better, a top side copper image has the emulsion "down" and the
bottom side has it "up" , so you get right-reading and wrong reading films
and ... .

Some of this translates into fully electronic systms and some doesn't.

Some translates into iron on toner transfer and some doesn't. The toner must
ALWAYS be against the copper, right ? ;-). So the top toner sheet would be
printed in mirror view and the bottom in normal view compared to what you
see during layout.

What do you think of it so far ? ;-).

Then we have drill masks and paste masks and component overlays, top and
bottom, with their various rules.
So it can be easy enough to get a layer "upside down".

I have seen a commercial h all the through hole ICs with the legs bent up
"above their heads" and soldered in 'upside down' because somebody made too
many boards mirror image. Makes it hard to read the component IDs ;-).



   Russell McMahon
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