kicad-developers team mailing list archive

[Lorenzo Marcantonio <l.marcantonio@xxxxxxxxxxxx>]

On Sat, Apr 27, 2013 at 03:36:17PM +0200, Simon Huwyler wrote:
> - How many impedance controlled lines are there?
> - On how many different layers do I place them?

Stop there. *If* you do impedance controlled lines then you *need*
different constraint for each layer, because: a) not every layer has the
same copper plating (usually there is less inside) and b) you need to
take in account the distance of the reference plane. Differential traces
are even harder to handle. Even more fun when the reference plane is
alternatively a ground plane and a power plane; but these are things to
be taken in account when setting up the rules.

> So, the most flexible way, would indeed be sort of a matrix. Each
> net has a set of constrains for each layer.

Actually each class would have a constraint with each other class and
this for each layer. And I hope you don't want to do cross layer DRC
(I guess IBIS simulators are better for that)

But that's only for a few classes, so it should be handled 'by
exception' (i.e. if not specified in some default) otherwise
a combinatorial explosion would come...

-- 
Lorenzo Marcantonio
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