Re: gEDA-user: next PCB release - 1.99za vs 4.0

[John Doty <jpd@xxxxxxxxx>]

On Sep 12, 2010, at 1:49 PM, Rick Collins wrote:

> At 03:42 PM 9/10/2010, you wrote:
> 
>> On Sep 10, 2010, at 1:01 PM, DJ Delorie wrote:
>> 
>> > I figure we need each layer to specify:
>> >
>> > * type (copper, silk, mask, anti-copper, keepout, etc)
>> 
>> There are no types, there are only properties.
>> 
>> The conductors may not be copper. I've even worked with a board that had two different conductive materials on the same physical layer.
> 
> Wouldn't that by definition then be two different physical layers, just like the solder mask and silk screen are two physical layers.

Perhaps.

>  The fact that they connect without vias doesn't mean to me they are the same physical layer.

Well, in this case they didn't "connect without vias". The low current traces used a metal with low thermal conductivity, while the high current traces were copper.

>  I've worked with boards that had buried resistors.  The resistors were a layer of conductive material that had a controlled resistivity in contact with a copper layer.  The resistors were considered a separate layer.
> 
> 
>> The support layers are also not always FR4. The board I noted above had different numbers of layers in different places, and the support layers weren't all the same material and thickness.
> 
> Sounds suspicious.  Are you sure you aren't talking about an assembly with boards and a case?  Bolts aren't normally considered vias.  ;^)

No, I'm talking about a narrow board with two rigid parts at the ends and a flexible part in the middle. The rigid parts had more layers: that's how they got to be rigid.

It lived inside a cryostat, with circuitry that ran cold at one end, and circuitry that ran warm at the other.

The point here is that the insulating planes are layers also: they need representation in the board description. They have their own shapes and material properties. And I think the only way to do blind/buried vias, buried components, and odd boards like this in a non-kludgy way is to treat the insulating planes as layers, each with its own geometry.

> 
> Rick 
> 
> 
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John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd@xxxxxxxxx




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