At 04:22 PM 27/02/02 -0500, you wrote:

> > Because it can eliminate having to manually transpose dimensions
> > and therefore, a source of error.
>
>Let keep it in perspective:  PCB design is governed by IPC ,

Not necessarily - for years I have not been "governed" by IPC mainly 
because their footprints have not been appropriate.  Anyone that uses the 
same footprint for wave and reflow is sub-optimal in both attachment and 
density.  In some of our designs density of miniature devices is paramount 
- no IPC footprints here. One example of why I am not "governed" by IPC.

><..snip..>
>Yes  IPC T50 defines the primary side as the side with the most components
>sec 22.184

Primary side is the side I happen to be designing from.  I can cope with 
flipping layers, if a mech engineer is happier viewing one way or tother I 
am quite at ease with flipping to allow this - it all comes down to where 
the least amount of care is going to be taken.  I know that I take a lot of 
care (well, do you admit being careless) but I am not so sure about 
everyone else.  So for us it has been better to let others do as they wish 
and we do what ever dance is required to make it work. A.L. has given some 
real reasons why correct inversion would be useful, another would be to 
facilitate panelisation where alternate rows of boards are flipped - to 
minimise machine setup.  Leaving this to a PCB maker can be a source of 
error.  Doing it in Camtastic is my preferred option but some companies I 
work for like to have the panel in Protel for whatever reason.

<..snip..>

>You can flip x or y now  and it flips correctly

There are problems with doing X and Y flips - they don't swap layers and 
they leave components in upside-down. The L-Flip (layer flip) with 
selections is also fraught.

Ian Wilson


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