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annular ring.

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alphadog

Banned
Hey fellows.

Through my study of Orcad and Layout, i ran into the term annular ring.
I've watched some pictures of it and wanted to ask a question regarding that issue.

Is the annular ring for conducting current better from one layer to another?
Meaning, more current that goes through the through hole components will require a wider annular ring?

Thanks.
 

Willbe

New Member
Is the annular ring for conducting current better from one layer to another?
Meaning, more current that goes through the through hole components will require a wider annular ring?
I'd think the through-hole part of the ring needs a thicker wall thickness for more current. It's like a very short tubular conductor.
 

Roff

Well-Known Member
The annular ring is not the barrel of the via. It's the copper surrounding the hole after it's been drilled out. It is needed for proper hole plating to occur, and for solder to adhere to in the case of through-hole components. Boards with small annular rings are generally more expensive to produce, due to the more precise alignment required between layers.
 
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alphadog

Banned
But annular ring is like a cylinder that is hollow inside but has a thickness outside.
(meaning a cylinder with radiuses 0<r1<r2).
Isnt it?

Because if it it, then why do you need it to be a cylinder, and not just two rings in top and bottom if its for solder to sit well?
 

JBrock

Member
Construction of a Via

Mister A-Dog, you need to look up a diagram and think about how a via is constructed, and what it's true shape is. The annular ring is a circular pad on one layer of a PCB. It becomes a ring when a drill hole is made through the center. You need a ring on top and bottom layers, and any other layers where a trace connects to the via. After these rings in the padstack have been drilled, they are connected by a copper plating process that forms a conductive tube on the inner wall of the drill hole. Hence Willbe's comment on wall thickness being the current limiting feature. Wall thickness around 1 mil is pretty standard. The size of the ring is limited mainly by how accurately the drill can be placed in the center of the pad. The ring will typically be at least 5 mils wide without getting into premium fabrication methods. To some extent the ring should be wider for larger vias.
So, in general, it is the size of the plated hole that determines how much current can be carried. Too much current will heat the via. A safe rule of thumb for a rough estimate is 1 amp of current per 10 mils diameter of via. Beyond two or three amps, use multiple vias.
Hope this answers your question!
-Brock
 

Roff

Well-Known Member
But annular ring is like a cylinder that is hollow inside but has a thickness outside.
(meaning a cylinder with radiuses 0<r1<r2).
Isnt it?

Because if it it, then why do you need it to be a cylinder, and not just two rings in top and bottom if its for solder to sit well?
Did you Google "annular ring"?
Not all holes will have component leads in them. In fact, many boards have only surface mount components. Vias are still needed to get signals and power routed from one layer to another.
 
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alphadog

Banned
I dont get it.

I understood my mistake that i though that annular ring is a cylinder.


How can the ring help conducting current then, if it only sits on the top and bottom layer?
And why should it be placed also in every layer when traces connected to the hole, as Mr. Brock has said?
 

alphadog

Banned
You need a ring on top and bottom layers, and any other layers where a trace connects to the via.
I understood everything you said but this.
What is the ring for?
Why do need need it if not just for the solder to sit well on the PCB when through-hole components are used?

Thank you very much for the detailed answer.
 
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Roff

Well-Known Member
I understood everything you said but this.
What is the ring for?
Why do need need it if not just for the solder to sit well on the PCB when through-hole components are used?

Thank you very much for the detailed answer.
I said in a previous post:
It is needed for proper hole plating to occur...
 

Roff

Well-Known Member
Yes, i read it i just dont understand what is proper hole plating?
What is it used for?

Thank you very much.
I also said in a previous post:
Not all holes will have component leads in them. In fact, many boards have only surface mount components. Vias are still needed to get signals and power routed from one layer to another.
A via makes connections between layers. A via is made by plating the inside of a hole, making connection between two annular rings. The annular ring is needed so that the copper can make a complete "barrel" in the hole, assuring a good connection.
 

alphadog

Banned
Oh, so the annular rings are placed only in the layers which have traces that connect to the vias, to have a good connection between the traces and the via?
 

Sceadwian

Banned
I think it has to do with the way the plating is applied to the boards alphadog. The bigger rings allow the plateing to build up in the holes better? I'm not sure what plating methods are used for multilayer PCB's in general but the hole sizes of vias are extremely tiny and present trouble to plating.
 

colin mac

New Member
The PCB manufacturers specify a min. annular ring and drill the holes a certain size bigger so that they end up the correct size after it's plated through.
If your annular ring is too small the hole won't plate, and the bigger it is the more copper that will surround the hole.
 
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JBrock

Member
Plating Process

α-Dog, good job on locating the diagram.

What no one has mentioned, to answer your question, is that the plating process is performed by a chemical reaction called electrolysis, whereby copper ions in a chemical solution are deposited onto existing copper. This is the reason you need a pad on the top and bottom layers. Otherwise the via will not form all the way through the board.

Your quest for these details is a good thing! :p
 
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