Defining microvia from bottom layer

I don’t know if I am a dumb dummy or something, but I am having an issue with microvias.

For my design I have a four layer board, where I have microvias starting from the top copper layer (layer 1) and ending in the second copper layer (layer 2). I also want to have microvias starting from the bottom copper layer (layer 4) and connecting to the third layer (layer 3).

For microvias from layer 1 to layer 2, there is no problem, I can define them just fine. However I can’t define a microvias starting from layer 4 going to layer 3.


In the picture the microvia start and end layer is from layer 3 to layer 4. If I try to change it from layer 4 to layer 3, it changes itself back. 3D viewer also does not show the via starting on layer 4.

I guess electrically, it don’t think it really matters. Am I misunderstanding something though, about microvias or kicad functionality?
Thanks all.

I don’t understand you (I have never designed 4 layer PCB, so also never used microvias).
You want microvia from layer 3 to layer 4.
You have microvia from layer 3 to layer 4.
You are trying to change something. Why, when you have what you want?

Below is a picture of a microvia I found online. I wanted to laser drill from the bottom outer layer inwards, rather than from a inner layer outwards.

Or like in this picture:

Currently the orientation of the bottom via is in the opposite direction of that in the picture, that is the orientation I want to flip.

EDIT: In 3d viewer you can see the vias on the top layer but not the bottom.

Top layer:

Bottom layer:


This might just be a rendering issue as Kicad might not consider the orientation of the uVia

I didn’t know that via (or may be only micro-via) has an orientation. Really?
I would expect that one manufacturer has one way of doing it. But as I said I have never designed even 4 layer PCB.

3D viewer lies sometimes. When I do the bridge between 2 PCBs where Edge.Cuts goes through holes (made to easier break PCBs) 3D viewer shows the tiny wall where really there is nothing.

Well microvia’s sort of do as they produce a cone when their a “drilled” but this is a fabrication concern and something only visible by a microscope. The designers job is to indicate which via’s are microvias and between which layers

Hmm ok, I guess I’ll see if I can specify with the fabricator. It manifests itself in the drill files too when I view it online (PCBWay online viewer) which is why I was mainly concerned.

The drill files are mostly just a documentation on “there need to be a hole of some diameter located at this place”.
Exactly which process the fabricator uses to do it, or from what orientation, the drill file does not say. Just as how there is no file saying what color are the vias tented in.

I think that’s the only way they can drill something like this. But I had not really dug into the process of 4 layer boards.

The 3D viewer is not very accurate. Sometimes it draws fake surface pads when in reality nothing is there (not even on the back side)

Microvias are between two adjacent layers and are made before the pcb stack up is assembled. Which direction they are formed is dependant on the manufacturers process.
A useful video on multilayer stack up assembly.


Thanks for the link. It was very informative.

I’ve only designed 2 layer PCB’s, so I can’t add much here.

I do rember a setting for layer pairs. It’s: Pcbnew / Tools / Set Layer Pair …. This may influence the way your micro via’s behave.

Just changing the layer of a micro via after it’s created is likely to cause a DRC violation, and it’s possible KiCad therefore refuses to change the layers of your micro via. So at least check that those other layers are empty on that location.

Or, probably better: Just draw a new track on the right layer pair, and then let the interactive router remove the old track with micro via’s.

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