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. The fact that they connect without vias doesn't mean to me they are the same physical layer. 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. ;^)
Rick
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