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Blind and Buried Via

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  • Blind and Buried Via

    Hi Robert,

    Couple of questions regarding week 2 of Advanced layout course:
    1) For the Blind via , what is the track width you are choosing ?
    2) Is there any specific aspect ratio rule for buried vias? In the lecture , we use L1-L2 and then L2-L3 but for fan out of the control signals , we used via from L3-L10 directly.


  • #2
    1) By default I use 0.1mm. It is adjusted by the end of design, when impedance track parameters are applied (so, usually it is something between 0.075mm and 0.1mm). On the L2 I normally use 0.1mm. If you like, you can always double check our designs e.g. you can download the iMX6 Rex projects from here:

    2) Buried VIA is basically manufactured same way as through hole VIA. So normally we use standard 1:12 or 1:10 ratio, but you may want to double check it with your PCB manufacturer.

    Hope this helps


    • #3
      Designing PCB with blind and buried vias is as easy as with regular vias. When adding blind and buried vias into the layout, a designer should make sure that the diameter of via is as small as possible as this creates more routing space and less the parasitic capacitance will be. Firstly drill needs to be done in one or between multiple copper cores of PCB. For this, drill size and aspect ratio is necessary to determine for the hole for blind and buried vias. An aspect ratio is the ratio of thickness needed for the printed circuit board and via pad’s diameter. A blind via pad’s diameter should be no greater than 450 μm containing a range of via diameter between 0.4 mm to 150 μm and an annular ring of 127 μm. And a buried via pad’s diameter should be no greater than 300 μm containing a range of via diameter between 0.4 mm to 100 μm and an annular ring of 150 μm. These ranges may vary according to project’s demand. It is also favorable for a designer to build vias according to PCB manufacturing specifications. Therefore consult your PCB vendor in the early designing stage for the spacing and PCB layer sequence. This significantly reduces the cost of manufacturing PCB with buried and blind vias.