Best way to do blind/buried RF vias?

If you are using 17.2 then you can define the BBVia directly in padstack editor, add the layers you need and you can add keepout openings above and below.

When I try to set Keep Outs on adjacent layers it appears to work, but it doesn't 'stick'.  The image below shows me setting those, but then when I save and reload the pad the Keep Out field gets reset to None.  I've tried both just setting it for the BEGIN LAYER and setting for both TOP (which is the name of L1 in my design) and BEGIN.

Thanks.  That works.  But then the Pad shows up in PCB Editor as going from 1:4 and when I generate the drill files it puts that hole in the 1-4 file even though there is no regular pad on L1 or L4.

This is really a bug... PCB Editor should be checking if there is a REGULAR pad on each layer for the purpose of determining which drill pair a pad belongs to.  But it's making this determination if there is ANY pad on a layer.  At very least there should be an option to specify how the drill-file generation handles this.

Going back to my original post, I wonder how people handle this when they have large number of RF b/b vias that need to have anti-pads on adjacent layers.  I can define a Keepout for the ADJACENT LAYER on the pad, but that doesn't seem to do anything (at least, it doesn't put a void in my planes above/below the via and it doesn't prevent me from routing over the via on adjacent planes).

Hi,

Using the ADJACENT_LAYER Pad geometry is the way to go. 

It is a two step process

1. Add the ADJACENT_LAYER Pad geometry to the padstack
2. In the design, add the property ADJACENT_LAYER_KEEPOUT_ABOVE and ADJACENT_LAYER_KEEPOUT_BELOW

The property can be added directly to a Pin/Via in the design with a value representing how many layer to add adjacent layer keepouts after the last pad layer.

I good application of this is to add the property to an SMD Pin that requires voiding on the adjacent layer, entering a value of 1 would generate the keepout on the first adjacent layer.

Hope this helps,

Mike Catrambone

Mike,

Thanks so much.  I just got the same advice from Ron at EMA.  This is exactly what I needed. 

Jay

So if my 16.x customers that need this would upgrade to 17.x we could save a lot of time!  Most are still reluctant to move up to 17 since it lacks a backwards compatibility which is a huge issue in most companies.

For RF designs we will typically also add a Backdrill and the necessary Backdrill information. This is pretty easily accomplished in Allegro v17.2.

Setting up Backdrills is under Manufacture..NC...Backdrill Setup.

Setting up the padstack correctly is the real 'art' to getting this to work properly and leverages off of the anti-pad discussion above.

Here is one example of a 12 layer stackup with a 1-6 pad and a 7-12 backdrill.

You will end up with a unique drill file for each backdrill.

For RF designs we will typically also add a Backdrill and the necessary Backdrill information. This is pretty easily accomplished in Allegro v17.2.

Setting up Backdrills is under Manufacture..NC...Backdrill Setup.

Setting up the padstack correctly is the real 'art' to getting this to work properly and leverages off of the anti-pad discussion above.

Here is one example of a 12 layer stackup with a 1-6 pad and a 7-12 backdrill.

You will end up with a unique drill file for each backdrill.