At 10:31 PM 2/26/2002 -1100, Douglas McDonald wrote:
>Doesn't any unpaired layer (mechanical or otherwise) preclude the 
>implementation of a true flip board function in the future?

Let's back up and go for the ultimate functions which are presently lacking 
except through workarounds:

(1) The ability to produce bottom-view assembly drawings.

(2) The ability to truly flip a design or design section for re-use in a 
new design which might predominantly be oriented bottom-up from the point 
of view of the first design.

(3) The ability to associate mech layers (or even copper layers) with top 
and bottom, in pairs, such that when a component is flipped, layers 
interchange as do, presently, top and bottom. This allows library parts to 
contain specific mech layer information such as an assembly drawing outline 
of the part, or height information.

(2) and (3) are closely related.

One feature that would serve the bottom-view assembly problem, which is 
*common*, would be display-linking of one layer with others. Someone 
described something as being part of PCAD that I thought sounded like this. 
So an assembly drawing, a mech layer, might have a section which was the 
PCB, bottom-view, offset, with layers enabled differently (i.e., in the 
normal view top overlay and top padmaster might be enabled, in the reverse 
view, bottom overlay and bottom padmaster.) We'd like to be able to have 
separate top and bottom assembly drawings *or* common drawings, a single 
drawing showing both sides of the board. I do this now with re-imported 
photoplots, the down side being that it all must be done again when the 
board is edited.

The others are less common as needs, but note that all three problems are 
solved or made easier to solve by extended layer pairing with top-bottom. A 
few hard-wired pairs would be nice, but I'd also like to be able to pair 
mid layers, this might be essential for design re-use where 
impedance-controlled structures existed on the copper layers immediately 
under the parts.

It might be considered that *all* layers could be paired, with an option 
for each layer to turn it off. If the pairing were turned off, flipping 
parts or board sections containing primitives on a pairing-disabled layer 
would not change that layer. Perhaps a new dialog box which controlled 
layer pairing would accomplish this. An advantage of having controlled 
pairing would be that libraries could then contain standard information.

Yes, we should have dedicated assembly layers. This should have been done 
long ago....

Abdulrahman Lomax
Easthampton, Massachusetts USA

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