My suggestion, which personally I rate at the top of my list,
is the following:

Currently, not all layers are created equal. In particular,
the handling of the silk sreen layers and the mechanical
layers in the DRC is different from that of signal layers.
I want to apply DRC rules (where appropriate) between
entities on ANY layer, whether a copper layer or not.

An example: I do a lot of high density layout with 0402
components. When placing 0402s close to each other, I want
to align the silkscreen rectangles so that the right line
of one lies on top of the left line of the next. The current
design rules allow only for a non-zero gap between components,
so I have to turn component clearance checking off. The
definition of a component boundary leaves a lot to be desired,
since the outermost entity (whether pad or silkscreen entity)
is used to determine the component size.

What I'd like is to have a component Outline Definition Layer
that is used for checking that components don't overlap each
other (which the Component Clearance rule would use). This
layer would be independent of the overlay (silkscreen) layer,
save for a back-compatibility rule that would use the current
component size calculation method if there were no primitives
on a component's Outline Definition Layer.

In addition, I want to be able to define a design rule that
enforces a minimum clearance between a primitive on the overlay
layer and either a pad edge or a soldermask opening (so that I
don't need to rely on the fab shop to "pull back" silkscreen
entities that would otherwise overlap a pad or an exposed copper
region such as a ground connect boundary on the PCB.

The combination of real component clearance rules, plus
overlay rules, would allow me to more effectively use the
design rules. The overlay rules, as I mentioned, could be effected
simply by removing the artificial constraints of the design
rule system (where rules are restricted as to which layers they
work on).

At the moment, I have to turn component clearance constraints
off altogether - which is a pain, since I can't check for
either components being too close together or for silkscreen
to copper overlaps.

Just my little rant,

John Haddy

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