Hi Prasad,

We are planning on implementing pad stacks during version 8 development. We currently are not planning back drill support for the initial pad stack implementation but it's certainly something we would like to implement.

That being said, pad stacks will require massive internal changes to the KiCad board code base. I doubt this will be something that a new developer will be able to manage given the complexity of the KiCad code base. Once pad stacks are implemented, adding back drill support to them will be a more manageable task for a new developer. When pad stack support gets implemented is difficult to say so we might have to wait a bit longer to get back drill support into KiCad.

I'm sure there will be an announcement once pad stacks are in KiCad. We can revisit the back drill support that that time. Thank you for your interest in helping the KiCad project.

Cheers,

Wayne

On 1/12/23 10:10 PM, Prasad Bhat wrote:
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 <http://www.astrome.co>)



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