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Gobi , 03-25-2026, 07:19 AM

Hi Team,

I am designing an 8 layer PCB and planning to use the blind via stackup.

I need to connect the top layer to the Layer 6 using blind via the drill size of 10/20 mils.

All 8 layers - 2oZ copper
1.6mm pcb thickness

Is the blind via drilling is possible for my requirement. Have you came across this scenario?

Thanks

Robert Feranec , 03-25-2026, 07:34 AM

I would highly recommend to watch my videos how PCB is manufactured. Its important to understand the process - instead of answering your question directly, I have a question: What do you think, how the holes in the stackup on the picture would be made? I mean - if you would be manufacturing this PCB, how would you drill the holes?

Robert Feranec , 03-25-2026, 07:35 AM

https://youtu.be/jTBOSob5MLg

Robert Feranec , 03-25-2026, 07:35 AM

https://youtu.be/lVyxlw3rixI

Robert Feranec , 03-25-2026, 07:38 AM

In PCB manufacturing there are two basic typs of drilling - mechanical and laser. Basic mechanical drilling always goes through all the layers, laser drilling can go into specific depth but there are limitations. What exits is also back drilling - this can drill into a specific depth but that is too special.

Robert Feranec , 03-25-2026, 07:39 AM

Drilling through the whole PCB is cheapest ... anything else is adding more and more price

Robert Feranec , 03-25-2026, 07:42 AM

And dont forget plating - the process of putting copper inside of the vias - that also limits what can be done with vias - like how the copper would go 6 layers inside of the hole ... That is why I recomend to watch PCB manufacturing process to understand better how it is done, that will help you tu understand the limitations

Robert Feranec , 03-25-2026, 07:50 AM

to give a clue how this could be maybe done is using buried vias in combination with uVIas ... but it may be unnecessary expensive - depends on your project

Gobi , 03-25-2026, 12:02 PM

Hi Robert. It helped me to understand some basics. But still I need to work on what is mean pressing cycle and how it is related to via stackup design. I will explore. Thank you Robert for your response

QDrives , 03-25-2026, 12:56 PM

In part via production is very simple.
1) You have a rigid board and drill **through**
2) Laser drill micro via
3) Plate the vias and PTH
4) You etch outer layers.
5) You add prepreg, copper foil and other boards - stacking them.
6) Press together
7) Repeat to step 1 if needed
8) Drill non plated holes
All steps are optional.

Laser drilling is limited to about the outer layer to the next inner layer. There are also 'skip vias' that go from L1 to L3.
Laser drilling is limited in diameter and ratio (about 1:1) and therefor also in depth (< 0.2mm).
Most fabricators I spoke to do not do laser drilling 2oz copper.

In short, no your stackuo is not possible.

Gobi , 03-25-2026, 03:04 PM

Hi qdrives thanks for the response. My one more question is, how many layers blind vias can support. It is also like microvia? Top to immediate next layer?

QDrives , 03-25-2026, 03:11 PM

No, blind vias can be multiple layers. Even L1 to L6.

But you are stacking layers.
So you can take core for L2+L3 (B1), L4+L5 (B2) and L7+L8 (B3). Etched all but L8.
Then: copper + prepreg + B1 + prepreg + B2 + prepreg + copper
Press, drill and plate.
Etch L6, but not L1
Take the board L1-L6 + prepreg + B3
Press, drill and plate
Etch L1 and L8.
A "reverse build-up".

Gobi , 03-25-2026, 05:43 PM

Thank you so much

Gobi , 03-25-2026, 05:43 PM

I got some clarity

Gobi , 03-25-2026, 05:44 PM

Thank you @Robert Feranec for your wonderful video references

Gobi , 03-26-2026, 02:29 PM

Hi @QDrives, one more follow up. I had spoken with manufacturer and modified the via stackup. But still they are not convinced. Because having blind vias from layer 1-6 and from layer 6-8, mechanical drill is not possible. This is the feedback I received. But sometimes we can't do pcb without this right?

Robert Feranec , 03-27-2026, 11:05 AM

What I meant by my previous post: you can use uVIAs to go to L1 to L2 and L2 to L3 and then you can use buried via from L3 to L6 and then again uVIAs from L6 to L7 and L7 to L8. This way, they will manufacture L3 to L6 - drill it - then they add L2 and L7 - drill uVIAs - add L1 and L8 - drill uVIAs. The stackup what you are suggesting is not the way how they manufacture it.

Robert Feranec , 03-27-2026, 11:05 AM

Watch this: https://www.youtube.com/watch?v=6aX9lA3W00A

Robert Feranec , 03-27-2026, 11:06 AM

Tip 061 Do Not Forget About Via Aspect Ratio

Robert Feranec , 03-27-2026, 11:06 AM

https://www.youtube.com/watch?v=OGQcXg8Rf8U

Robert Feranec , 03-27-2026, 11:07 AM

Watch these two videos, it will help you

QDrives , 03-27-2026, 10:28 PM

What you show cannot be done.
It does not follow "stacking" as you have 2 blind vias going to the same internal layer.

Check HDI boards and something like a 2+bN+2 8layer board:
https://resources.altium.com/p/introduction-to-high-density-interconnects