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Copper thickness in inner layers

Bermell , 07-18-2022, 03:53 AM

Could you give me any recommendation about the copper thickness in inner layers? I mean, is there any criteria for choosing 1oz (34um) or 0.5oz (18um) with high speed design ?

Thanks a lot in advance

qdrives , 07-18-2022, 04:05 PM
I am not of high speed, but would say that thin copper is more for high density as the traces can also be narrower.
robertferanec , 07-22-2022, 08:48 AM
I would recommend you to talk to your PCB manufacturer. They don't like to use thick copper layers inside of PCB - so double check with them. I can't remember why, but I think there are some reasons for it (e.g. maybe when prepreg melts, more may flow between the tracks and then it is harder to control thickness of layers and things related to it e.g. impedance?? I don't remember I am just guessing).
qdrives , 07-22-2022, 03:35 PM
@robertferanec I know that there are some limitation in prepreg thickness with regards to copper thickness, but I think here is more a question on thin copper.
binayak , 07-27-2022, 11:41 PM
For inner signal layers, half ounce copper is more than sufficient; you won't need thick copper.
You may need to have 1 oz. copper for power layers depending upon current requirements.
suleymancskn , 08-08-2022, 06:25 AM
Hello everyone, I have a memory related to this topic.
@robertferanec Could this be what you can't remember?

The reason why 18um copper is used in the interlayers is that the "Copper Deposition" process is shorter than 35um, that is, 1oz copper.
I got such a response from a manufacturer I talked to.
qdrives , 08-08-2022, 01:58 PM
@suleymancskn Copper deposition is only used to plate the inside of vias. As a side effect, the outer layer copper is also thicker. Do note that outer here means the outer layers when plating the vias. If you have burried vias, then those layers will also gain thickness.

To describe the process that @robertferanec mentioned - it that the resin has to fill the gaps between the tracks. Thicker tracks is more loss of thickness between copper. This can be calculated.
Thicker copper means thicker boards. Thicker copper means wider tracks are needed (width to height ratio) and also the spacing between the track needs to increase.
suleymancskn , 08-09-2022, 06:55 AM
@qdrives I agree with the designer's point of view.

But manufacturer change etc. stackup suggestions come up. And every time something has to change. Since one of them is 1/2 oz copper, I looked at the event from the manufacturer's side.
I got an answer close to what I said in my question. And they said it increased the production time. While unwanted areas from copper are removed by chemical means, 1 oz of copper is removed in a longer time. You know that copper needs to be removed from unwanted points.
qdrives , 08-09-2022, 02:07 PM
Ah yes, production time in removing copper, but you mention "deposition".
I am sometimes called "word perfect".
If you are producing > 10k products a year, than the shorter production time may start to be topic.
However, during my time at various companies, I never heard them talking about thinner copper to save production time.
Company A produced products > 100k /year, B > 20k/year.
suleymancskn , 08-10-2022, 12:34 AM
Sorry @qdrives , the word "deposition" was wrong.

qdrives, 08-10-2022, 03:19 PM
No problem
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