kicad-developers team mailing list archive

[Dick Hollenbeck <dick@...>]

The last board I did had all the components on the back, and the ground 
plane on the front. It was a daughter board card and the front of the 
board is sometimes exposed in the end product to the user.

Imagine how awkward the PCBNEW layer stack up terminology was which 
wanted to call the back of the board the copper layer, and the front of 
the board the component layer. My components were on the back and my 
copper was on the front, making the PCBNEW layer naming terminology 
quite unhelpful.

A second justification for a change is this:

The Specctra DSN format specifies a layer stack up description which 
starts at the front of the board and works its way down to the back of 
the board. See <layer_descriptor> on page 51. Also, components are 
specified according to which side they are to reside on, and Specctra 
uses the terms 'front' and 'back' to specify these sides. See <side> on 
page 119. This specification is known to most all EDA software 
companies and to many PCB designers within the industry, so the chosen 
terminology is no way obscure or odd ball.


These were the justifications for the changes I made recently in the 
terminology of layers within PCBNEW.

The new layer setup dialog window shows an implied layer stackup 
sequence. Speaking for a moment only about the copper layers, the new 
UI presentation shows the copper layer stackup in the same order as what 
a user familiar with the specctra <layer_descriptor> would expect. 
First comes Front layer, then first interior layer nearest the front of 
the board, then 2nd down interior layer, .... until the back of the 
board which is last.

I like this UI, and think that moving forward all UI presentations 
should remain consistent with this board model. It is intuitive and 
superior to the combobox which you see at the top of PCBNEW.


OK, having said that, now to the little man behind the curtain:


(But remember the UI is golden in my view, and should not be compromised 
to satisfy an implementation difficulty.)


The difficulty I have on the table at the moment is backwards 
compatibility with existing boards. In an ideal scenario I would like 
to swap the layer mask for BACK with FRONT. This would be easiest, but 
it breaks old boards. 

In the layer setup dialog, I have shown a layer stack up which is not 
true. And need to work out how I can make it true without breaking 
existing boards.

Jean-Pierre let me know your thoughts on this. After this dialog is 
fully implemented I will then move on to a layer selection/visibility 
control which will replace the color setup dialog which I expect we can 
remove.

One idea to put on the table is an actual layer stack up sequence, which 
would be a modifiable data structure which defines the order of layers 
within a board. The current notion of layer mask would stay, it's just 
that a person could not assume that a layer with a mask of (1<<0) is 
next to a layer with a mask of (1<<1) unless the layer stackup sequence 
says it is.


Dick