Confused by vias, plated, and un-plated holes

Thread Starter

phillipsoasis

Joined Aug 22, 2022
63
I am a total beginner to pcb design. I have a schematic in KiCad 7.0 and I want to make a PCB for it. In one of the KiCad forums, PCBWay was recommended as a low cost PCB fabricator, and the prices looked OK. I created a 2 layer board, but it is too big for my needs, so I started to design a 4 layer board - inner layers are power and ground, and the outer layers are signals. I have a handful of signals left to add, and I need to run some signals on both layers so I can cross tracks - i.e. start on the front, jump to the back, then jump to the front and connect the signal. I was reading about vias and plated/un-plated holes and have managed to confuse myself. The cost of a board with blind/buried vias is 8-10 times the cost of a standard board from PCBWay. Do I need to use a via, or can I achieve what I want with a through board hole?
 

dl324

Joined Mar 30, 2015
16,696
Do I need to use a via, or can I achieve what I want with a through board hole?
To make connections between layers that don't involve a component lead, you have to use vias.

The advantage of blind/buried vias is that they don't consume routing resources on all layers, whereas vias and pads do.
 

Thread Starter

phillipsoasis

Joined Aug 22, 2022
63
To make connections between layers that don't involve a component lead, you have to use vias.

The advantage of blind/buried vias is that they don't consume routing resources on all layers, whereas vias and pads do.
Thanks for your quick reply! PCBWay has two types of boards - standard and advanced. Standard only has through holes (plated or non-plated), advanced has vias. Am I understanding you correctly, that with the standard board, I cannot run a track on the top of the board, then to the bottom of the board and back again unless I use a via (i.e the advanced board)? Is there normally a very large increase in price for using vias?
 

Jon Chandler

Joined Jun 12, 2008
992
Let's try to clarify:

A non-plated hole is just a hole through the board without any electrical connections. These are often used for mounting holes for the board.

A through-hole pad is a plated hole with annular rings of copper on each side of the board, used for mounting through-hole components.

A via is the same as a pad described above, usually with a smaller hole diameter, used to connect different copper layers of the board. This is a standard feature of all types of standard circuit boards – no extra charge for through-hole vias will be made, unless there are an excessive number of them.

Blind vias are a special case. They are used to connect internal layers of a multilayer board without penetrating to the outer layers of the board. These might be used on an extremely crowded board to allow more space for track routing on the outer layers of a circuit board. Blind vias are only applicable where a board has more than 2 layers, and there is and extra charge to use them.
 

BobTPH

Joined Jun 5, 2013
8,665
If you just need to connect the top to the bottom layer, use a via. It is no blind, since it goes all the way through.
 

Thread Starter

phillipsoasis

Joined Aug 22, 2022
63
I looked at their website and they show 3 via options for their standard boards.
View attachment 304652
Don't see why they would cost any more than pads.
OK. Now I need to understand Tenting vias, plugged vias, and vias not covered. When would I specify on over the other? Where my confusion started is in a chat with PCBWay - the PCBWay person said I had to use the Advanced board if I need vias.
 

Thread Starter

phillipsoasis

Joined Aug 22, 2022
63
If you just need to connect the top to the bottom layer, use a via. It is no blind, since it goes all the way through.
Let me see if I understand.
1. to connect top to bottom layer on a 4 layer board, I use a through via, and I can use that on a PCBWay standard board.
2. to connect from the top or bottom to an inner layer, I need a buried/blind via, and that requires a PCBWay advanced board.
Am I getting close?
 

Jon Chandler

Joined Jun 12, 2008
992
A through via will go from one side of the board to the other connecting anything it runs through on the way (if it's the same net list).

A tented via means it's covered by the soldermask. An open via is just like a pad, where the angular ring is exposed.

You might consider starting with a simple 2 layer board and trying different things to see the differences.
 

Thread Starter

phillipsoasis

Joined Aug 22, 2022
63
A through via will go from one side of the board to the other connecting anything it runs through on the way (if it's the same net list).
So I can't use a through via to jump from top to bottom layers because it will also connect electrically to the middle layers?

A tented via means it's covered by the soldermask. An open via is just like a pad, where the angular ring is exposed.
When do I use one over the other?

You might consider starting with a simple 2 layer board and trying different things to see the differences.
I started with a 2 layer board, but it became too large for my project, so I went to a 4 layer board with power and ground on the inner layers and signals on the top and bottom.
 

WBahn

Joined Mar 31, 2012
29,867

WBahn

Joined Mar 31, 2012
29,867
So I can't use a through via to jump from top to bottom layers because it will also connect electrically to the middle layers?
Why not? If you want a via to connect a signal on the top layer to a signal on the bottom layer without connecting to the inner layers, then don't connect it to the inner layers.

1696983293131.png

The left via connects a trace on the top layer to Plane 1.

The right via connects a trace on the top layer to Plane 2 and it also looks like a trace on the bottom layer.

Picture a solid copper layer for each of the layers. When you drill through the board, the edges of the copper are exposed one each layer. You now plate the hole with copper, and it's going to connect to every layer.

But now go in and make holes in the copper on the layers you don't want to connect to and make them larger than the hole that is going to get drilled (larger by some minimum amount). When you drill the hole through the board, the copper on those layers with the large holes won't have any copper at the hole, so when the hole is plated, no connection will be made to those layers.
 

WBahn

Joined Mar 31, 2012
29,867
Thanks for your quick reply! PCBWay has two types of boards - standard and advanced. Standard only has through holes (plated or non-plated), advanced has vias. Am I understanding you correctly, that with the standard board, I cannot run a track on the top of the board, then to the bottom of the board and back again unless I use a via (i.e the advanced board)? Is there normally a very large increase in price for using vias?
No, Advanced has BLIND and BURIED VIAS. Those are special types of vias. Anything other than a one-layer board would be pretty useless if it didn't support vias.
 

BobTPH

Joined Jun 5, 2013
8,665
But now go in and make holes in the copper on the layers you don't want to connect to and make them larger than the hole that is going to get drilled (larger by some minimum amount)
Even my homegrown PCB CAD program allows you to connect or not connect a via to each layer. I don’t have to go and make separate holes on layers not connected.
 

WBahn

Joined Mar 31, 2012
29,867
Even my homegrown PCB CAD program allows you to connect or not connect a via to each layer. I don’t have to go and make separate holes on layers not connected.
And if you look at the artwork that is generated, layers that you don't want to connect to are going to have a hole on them that is sufficiently larger than the drill size for the via so that when the hole is drilled and plated no connection is going to result to those layers.
 

Thread Starter

phillipsoasis

Joined Aug 22, 2022
63
Why not? If you want a via to connect a signal on the top layer to a signal on the bottom layer without connecting to the inner layers, then don't connect it to the inner layers.

View attachment 304661

The left via connects a trace on the top layer to Plane 1.

The right via connects a trace on the top layer to Plane 2 and it also looks like a trace on the bottom layer.

Picture a solid copper layer for each of the layers. When you drill through the board, the edges of the copper are exposed one each layer. You now plate the hole with copper, and it's going to connect to every layer.

But now go in and make holes in the copper on the layers you don't want to connect to and make them larger than the hole that is going to get drilled (larger by some minimum amount). When you drill the hole through the board, the copper on those layers with the large holes won't have any copper at the hole, so when the hole is plated, no connection will be made to those layers.
Thanks for the picture, it helps a lot. It looks like in theory I can jump from the top layer to a middle layer, then to the bottom layer using a through hole. It is interesting that KiCad does not allow that. Through holes can only connect top and bottom layers. One has to select a buried/blind via to connect to an inner layer. I guess I can only jump from top to bottom with the Standard board, and I would need the Advanced board to connect to an inner layer.
 

Thread Starter

phillipsoasis

Joined Aug 22, 2022
63
Thanks for the picture, it helps a lot. It looks like in theory I can jump from the top layer to a middle layer, then to the bottom layer using a through hole. It is interesting that KiCad does not allow that. Through holes can only connect top and bottom layers. One has to select a buried/blind via to connect to an inner layer. I guess I can only jump from top to bottom with the Standard board, and I would need the Advanced board to connect to an inner layer. The chat agent at PCBWay really confused me.
 
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