I am now confused about vias. When I choose Track and Via properties, I have a choice of Through or blind/buried or micro vias. If I choose Through, then I can only connect the start and end layers are locked to top and bottom. If I choose buried/blind, then I can have any start and end layer.
Does this mean that a through via only connects to top and bottom layers?
What do the options for Annular Rings mean? How do I know which option to pick?
No.
Through via is standard via. It connects all layers. At each layer you can have a copper circle (pad) connected to via and you can connect track to it. If at any layer track is not connected to via you can left or delete that circle. I think some PCB clear function deletes unused âvia padsâ (I donât have KiCad here so canât name exact menu selection). Not long ago I supposed that may be some manufacturers need to have that âvia padsâ at each layer (for example to make hole plating) but now I suppose that no one of them needs it.
I have never used other then top and bottom as signal layers so I donât know where it is, but certainly there is a way to specify a routing layer pair you are using at the moment. When routing at one of these layers and pressing V (via) moves you to the second layer of that pair.
I donât remember options for annular ring. If you mean its size than you take it from manufacturer information. They specify minimum annular ring (sometimes different for external layer and internal layers). This comes from drilling inaccuracies. Minimum annular ring is to ensure that even a hole will be little shifted the connection will be good.
Just in case, these option only relate to board with more than 2 layers.
So 4 or 5 layers boards.
They have no meaning on a 2 layer board.
The goal is to âreduceâ the size taken by a via in the inner layer, by removing the annular ring (the round metal part around the via) in the inner layer if the via is not connecting to this layer.
This allow to pack more trace in the inner layer, or to have a âbetterâ plane for EMC.
PCBâs generally only come in an even number of layers. (except for some special cases) If yo order a 5 layer PCB it is most likely made by etching away the complete 6th layer.
âNormalâ vias are always drilled though the whole PCB and you can connect a track on any of your layers. It is custom (but not necessary) to work with layer pairs, and I think I once saw an ability in KiCad to set up these layer pairs, but Iâm not sure about further details.
In KiCad you can right click during routing a PCB track and use the popup menu to switch to any layer you like.
âNormalâ viaâs (though all layers) are standard and included with any PCB manufacturing process (except exotic things like IMS) Other via types (Blind, buried, micro, VIPPO) are not free. Those require exra process steps and therefore always come with extra costs.
I am using KiCad 7 and have a 4 layer board.
What is confusing to me is when I select properties on a via, I get the attached popup.
Note the the via type is Through, and the start/stop layers are locked into top and bottom.
If I select Blind/Buried for the Via type, I get the second image.
Note the Start/End layers can now be changed to any of the 4 layers in my design.
Why are through vias limited to the top and bottom layers, and blind/buried are not?
What is meant by Annular Rings? The options are All Copper layers, Start, End and connected layers, and Connected layers only. Is the annular ring where the connection is made to a layer, so the correct choice is Connected layers? How is that different than Start, end and connected layers?
A through via goes through the whole board, so it must start and end on the outer layers by definition.
In a 4 layer pcb, a blind via can go from top to inner2 or bottom to inner 3. And a buried via from inner 2 to inner 3.
I donât know if a manufacturer can do blind vias from top to inner3 or bottom to inner2.
Yes, because a normal via always goes through the whole PCB. But you can connect to is from any layer.
Because they donât go to the whole PCB. That is harder to manufacture but possible (you have to look up the designs rules and options of your PCB manufacturer).
A blind via either starts at the top or bottom layer and ends at a layer you choose. You can connect to it on this layers and layers in between but not on the other layers.
A buried via starts in a inner layer and ends in a different inner layer.
The copper that is around the via so that a trace is properly connected to it and (on the top and bottom layer) that the via holds in its place.
You should do a image search for âvia typeâ, it may explains it better than words.
Indeed. Information on different via types is easy to find. There are also a bunch of videoâs on youtube about PCB manufacturing, and when you see how they are made you also may understand the differences better.
Itâs obvious but not been blatantly mentioned . . . the clue is in the name.
Through vias meaning through all layers.
Blind or buried vias meaning one or both ends start or stop buried inside the board. (you wouldnât specify a Blind/Buried via that went through all layers as it would potentially needlessly cost you more money)
OK, I think I am beginning to understand. Whereas it is technically possible to have a through via connect to any layer, practically and in KiCad 7, it only connects to the top and bottom layers. I assume it is the cost of manufacturing that drives this restriction because buried/blind vias are much more expensive to make.
I ran a small experiment in KiCad. I drew some traces on a blank 4 layer board and then looked at the 3D projection of the interior.
Note: Via #1 is on the right in the 3D image.
No, that is not the way it works at all.
The âthrough viaâsâ always go though the whole PCB, and you can connect a track on it on any layer where the via has an annular ring (By default all layers) KiCad does have an option to remove the annual rings for unused layers, but that is a user preference.
There is no production problem at all for this. for the PCB manufacturer itâs all just the same, so no extra costs.
I use only normal (through) vias and at 4 layer PCB I didnât noticed problems to connect to them at inner layers.
In KiCad 7 a through via only has the option to connect to the top and bottom layers. See the pictures of the Track and Via options in my earlier post. I cannot change the start and end layers in a through via. I have to specify a blind/buried via to connect to an inner layer, and then I get a via as shown in the 3D picture I posted with vias 3 and 4.
@Piotr I stand corrected. I can attach a track to a through via as shown in the attached pictures. I just cannot start or end on an inner layer.
Just so I understand, does via 2 electrically connect the inner layer 2, top, and bottom layers? It seems to show that in the third image. I see copper rings on the top, bottom, an inner 2 layer.
Yes, that via has a track connected on three different layers. Have another look at the screenshot I posted earlier. It shows the popup menu from the right mouse button that lets you select other layers to branch off from the via.
Let me (us) know what do you understand with âI cannot start or end via on an inner layerâ ?
Chose one of two possibilities:
Specify which one of these meanings you have in mind.
If 1.
You are right. But then what is the whole thread from the beginning about? If via is through the whole PCB then obviously it starts and ends at external layers as going through PCB in this direction these are first and last what you meet flying right through the PCB. This is obvious.
If 2.
You are wrong.
I think, you are misinterpreting the meaning of âstartâ and âstopâ in this context. In the âvia propertiesâ dialog âstart layerâ and âstop layerâ signify the layer where the via itself starts and the layer where it ends on its way through the pcb. It has nothing to do with the layer where a track can be connected to the via. The via starts and stops, rather than a track.
Therefore on a through-via âstart layerâ and âstop layerâ are greyed out because any through-via starts at the uppermost and stops at the lowermost layer. For blind- or buried vias you can chose at which layer the via-hole starts and where it stops.
@bossamba I agree 100%! Giving the wrong meaning to start and stop is a big source of my confusion. Thanks!
@Piotr The whole thread was about my confusion about through vias and buried/inner vias. A part of it was what @bossamba said above. The other part was a conversation with a PCBWay tech about how they make vias and what I can have in my design for a standard board. Basically, the tech said I cannot connect to inner layers with a through via, and a through via only connects to all layers. I have learned since then that is not true. I am not sure if it was a language issues with the PCBWay tech, or he/she was trying to up-sell me to the Advanced board with buried/blind vias. Thank you for your patience with my questions.
This is self-contradictory. It is not possible that via connects to all layers and cannot connect to inner layers. Inner layers belong to set called âall layersâ. I suppose they said something different then you quote here or they made mistake in for example translating.
