PCB design is becoming more and more difficult as the development of portable products in the direction of miniaturization and high density,and higher requirements are put forward to the production process of PCB. In most of the portable products, the 0.65mm spacing below BGA package need use blind& buried hole design process, then what is blind buried hole?

Blind vias: blind vias connects the inner layer and outer layer of PCB , the via does not penetrate the entire board.

Buried vias: the buried vias only connect between inner layer and inner layer, so it is not visible from the PCB surface.

How to set up the blind&buried vias in allegro?

Blind&buried drill set up

Blind&buried drill can be edited from existing through hole,blind&buried hole related layers.

E.g. a 8layers PCB, you can design blind via from L1-L4 and L5-L8 or L1-L3 and L4-L8. If blind vias from L1-L4 , you need remove all regular pads, thermal pads, anti pads of the L5-L8 layer, , and then save it,that is the blind hole from L1-L4 layer.

Set up padstack

Set up through layer of BB via, the layers don’t need through set to Null of regular pad,thermal relief,anti pad,then you can see BB hole L1-L2 in XSection.

The difference of Normal via and BB via:

Update padstack to design

BB drill gerber out

create drill schedule&drill gerber

Follow the common method to create drill schedule，The via of closed layer will don’t create drill symbol,one by one create drill schedule of other layers,then can put out gerbers or create detail to put out gerber files.

Create drill table

Follow common way to create drill table when gerber out, allegro recognize drill automatically.