Dear developers at KiCad,
I would like to work on implementing backdrill support in KiCad. In this
regard, I have thought of 2 possible choices and I need your help in
choosing what works best.
*Option 1:*
1. Update via definition to include another sub-type called 'backdrill'
2. Have an additional field in the via definition to have backdrill
diameter.
3. Use layer information to indicate what remains after backdrilling.
4. In drill generation, emit one PTH (through hole top to bottom), and
either one or two backdrops based on layer information.
A backdrill based via would look like following in the s-expression:
(via
backdrill
[(locked)]
(at X Y)
(size DIAMETER)
(drill DIAMETER)
(backdrill DIAMETER)
(layers LAYER1 LAYER2)
[(remove_unused_layers)]
[(keep_end_layers)]
[(free)]
(net NET_NUMBER)
(tstamp UUID)
)
*Option 2:*
Create a new BOARD_ITEM for backdrill which is free-standing and has no
direct bearing to vias. S-expression in this case would be something like:
(backdrill
[(locked)]
(at X Y)
(drill DIAMETER)
(mustnotcut LAYER)
(from TOP | BOTTOM)
(tstamp UUID)
)
In both cases, a tool can be added which detects backdrill worthy vias and
prompts addition/cleanup of backdrill for different vias.
Any other options?
I look forward to your opinions and suggestions in this regard.
BTW, as a workaround, currently I am using regular via as backdrill with
pad size almost same as the drill size overlaid on the actual via that
needs backdrilling. Of course, the backdrill's drill size is made bigger
than the pad size of the actual via that needs backdrilling. However, this
is not like having native support requires some extra management off hand
to indicate what is not plated.
Regards,
Prasad
--
Prasad H L Bhat
Chairman and CTO,
Astrome Technologies Pvt Ltd (www.astrome.co)
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