I am interested to know and I am not sure I understand but why do PCB manufacturers seem to offer only 1,2,4,6,8......Etc. layers (only 1 and even number of layers)
Why do they not offer 1,2,3,4,5,6....Etc. layers?
Surely if you wanted a 3 layer PCB you could have:

Copper top layer
Substrate/Core
Copper middle layer
Substrate/Core
Copper bottom layer

Is this not possible, or am I not understanding something?

 

My usual suppliers don't offer a "1-layer" board. You get a 1-layer board by specifying nothing (no traces or copper pour) on the second layer. The only time I did that, I got solder resist on the bottom, which was OK. I suspect you could also order without solder resist too.

Thus, the options are 2,4,6... layers.

As for reason, I suspect the boards are panelized and the standard PCB layer is plated on both sides. Just as for the 1-layer board, your middle layer probably does not need to have copper on both sides. I have never checked whether that is possible. Of course, I you are ordering several full panels, your choices may be more.

 

You can have a three layer PCB, but it will cost you the same as a 4-layer (because it will be made as a 4-layer, with one of the core layers blank). It is just like a single layer PCB - one layer is blank.

Here's how a typical 4-layer PCB board is stacked-up:

1) Top layer is usually a COPPER SHEET (no insulative layer at all).
2) The next layer is a copper free PRE-PREG layer (just an insulative layer not fully cured).
3) Layers 2 and 3 are usually a double sided CORE.
4) The next layer is another copper free PRE-PREG layer (just like #2 above).
5) The bottom layer is another COPPER SHEET (just like the top layer).

The above stack-up is then put in a press which cured the pre-preg layers and gives the final thickness that you require.


I'm curious, tho, as to why you would want a 3-layer board?

 

A friend just made a 3-layer remote control board. His issue was corrosion in a salt water atmosphere.

 

My usual suppliers don't offer a "1-layer" board. You get a 1-layer board by specifying nothing (no traces or copper pour) on the second layer.
Thus, the options are 2,4,6... layers.

Normally, PCB manufacturers do offer 1 layer boards. These are normally made with the copper trace on the bottom so that the components are placed on the top and soldered on the bottom - (I am not talking about SMD components but I suppose you could have a 1 layer board with SMD components).
Have a look at this Chinese PCB manufacturer - https://www.allpcb.com/
They offer 1,2,4,6,8,10,12,14 layers.

You can have a three layer PCB, but it will cost you the same as a 4-layer (because it will be made as a 4-layer, with one of the core layers blank). It is just like a single layer PCB - one layer is blank.
I'm curious, tho, as to why you would want a 3-layer board?

Why would I not want a 3 layer board? Some people may have a simple circuit but not need 4 or more layers.

 

I think the main reason is that the board nees to be symmetrical - in case of the three layer board the two substrates would have to have the same thickness, and that could be a problem to stack up. If the layers and thicknesses are not symmetrical, the board will warp after it is released from the laminating press.

 

Normally, PCB manufacturers do offer 1 layer boards. These are normally made with the copper trace on the bottom so that the components are placed on the top and soldered on the bottom - (I am not talking about SMD components but I suppose you could have a 1 layer board with SMD components).
Have a look at this Chinese PCB manufacturer - https://www.allpcb.com/
They offer 1,2,4,6,8,10,12,14 layers.
Why would I not want a 3 layer board? Some people may have a simple circuit but not need 4 or more layers.

Are you sure 1-sided boards start with panels that are only plated on one side to begin with and are not simply 2-sided panels that have been etched to make "1-layer boards" for the few boards on a whole panel that want only 1-layer? (The same holds true for additive or subtractive processes. In the additive process the routine is to plate both sides. Those parts that are 1-sided are masked to as not to be plated. See: http://www.madehow.com/Volume-2/Printed-Circuit-Board.html). I am referring to current practices, not what may have been done many years ago before the big board houses in China providing low-cost boards were in business. If you want an odd number of layers, just specify in your files those areas that need to be copper free.

Can you tell us why it matters to you whether the panel from which your boards are made starts as 2-sided or 1-sided, or in an additive process, are only plated one side instead of 2-sides?

 

Can you tell us why it matters to you whether the panel from which your boards are made starts as 2-sided or 1-sided, or in an additive process, are only plated one side instead of 2-sides?

I may only want a very simple circuit that only requires 1 layer as below.



....but may want several hundred/thousand. The overall cost would/should be cheaper than 2 layer board
But my question was...why are 3 layer boards are not normally produced but only 1,2,4...etc.

 

I may only want a very simple circuit that only requires 1 layer as below.

....but may want several hundred/thousand. The overall cost would/should be cheaper than 2 layer board
But my question was...why are 3 layer boards are not normally produced but only 1,2,4...etc.

Underlined is a faulty assumption. It is far cheaper to produce as they do routinely rather then a one-off like you want. Most important, the design you seem to want can be made (see next paragraph). Have you considered making your own so you have full control of the process?

Your second question has been answered already by several people here. Why keep asking it? You can get any number of copper layers you want. All you have to do is submit a coherent design. If you do not know how to do that, gave a specific example and others here can help.

 

Underlined is a faulty assumption. It is far cheaper to produce as they do routinely rather then a one-off like you want.

I did not know 2 layer boards are cheaper than 1 layer boards. I assumed that because of the extra layer of copper on a 2 layer board (as opposed to a 1 layer board), it would be more expensive.

Have you considered making your own so you have full control of the process?

No, I do not have the experience or equipment to do this, I am purely a hobbyist.

Your second question has been answered already by several people here. Why keep asking it? You can get any number of copper layers you want.

Sorry if I keep asking the question...it was purely a query I had which I wanted the answer.
But thank you all for answering.

 

A 1-layer and 2-layer boards will under most normal manufacturing processes cost the same. Maybe for high volume the manufacturer will order special single-side plated cores which could lower the cost of single sided a little, and also he could skip the plating of holes. But all in all this is not a normal run off the mill process and they will not bother with it unless the volume you need to manufacture requires it.

Also remember, that most manufacturers panel many designs together, so for you it is cheaper to go with the standard stackup and rules, than to make your own special stackup.

 

Single sided boards are still used but the vast majority of them are in high-volume consumer equipment and the process used to make them is quite different (e.g. the holes are punched instead of drilled). I would still expect single sided boards to be slightly less expensive than double sided because the non-recurring costs (photo tools) are lower and the process can be fully subtractive. Non-recurring costs can be several hundred dollars. You simply won't know unless you contact a board house or a broker. Brokers take their cut, but it can put a buffer between you and a board house with very limited ability to communicate in English. A broker typically also has multiple houses they work with, so can help you find the one best suited for your needs. Some board manufacturers will send you away unless you want thousands of boards.

Image at #8
It is hard to evaluate the image due to the poor resolution, but at first glance it is not good. The annulus on some of the holes appears to be very small. If it actually is, this places high demands on the alignment in board fab (usually not a big deal with modern process), but it also means there is next to nothing to hold the foil to the board, making it very likely that the foil will lift if there is ever a need to do a repair.

===
A large board house will not panelize your boards with other jobs. That is something done only by the the small volume fast-turn houses. My absolute last consideration in designing or ordering production boards is any notion of compatibility with what others might want, only manufacturability. I don't do any of it anymore, but the quick-turn prototype board houses I dealt with uniformly produced what would charitably be called mediocre, vaguely tolerable work. If I needed good boards, the jobs went to real board houses and if a small run cost a thousand dollars, well, so be it.

 

I did not know 2 layer boards are cheaper than 1 layer boards. I assumed that because of the extra layer of copper on a 2 layer board (as opposed to a 1 layer board), it would be more expensive.

Actually, in the additive process (see above, which is common), the addition of an unused second layer adds nothing. You have to think in terms of whole panels of which your board is a small part. Even in the etching process, I suspect the removed copper (e.g., Cu(II)Cl2) is recovered and converted rather easily to new plating solution or used to replenish the etching solution (see Cu(II)Cl2 etching).

No, I do not have the experience or equipment to do this, I am purely a hobbyist.
Sorry if I keep asking the question...it was purely a query I had which I wanted the answer.

You have gotten your answer several times. Why keep asking the same question?

Wishing you good luck and a very good buy on your PCB's.

 

Single sided boards ARE cheaper than a two sided board. For a SS board, the process is expose, etch, drill, rout. For a DS board, the process is drill, plate holes, expose top, expose bottom, etch, rout. Your venders MAY be charging the same, but the SS flow is much simpler - even the blank is cheaper than a DS. They probably charge the same because they want to discourage SS boards.

 

Single sided boards ARE cheaper than a two sided board. For a SS board, the process is expose, etch, drill, rout. For a DS board, the process is drill, plate holes, expose top, expose bottom, etch, rout. Your venders MAY be charging the same, but the SS flow is much simpler - even the blank is cheaper than a DS. They probably charge the same because they want to discourage SS boards.

Not all boards are etched! And drilling often comes before etching or plating. You seem to be thinking of DIY boards using pre-plated substrate..

 

Not all boards are etched!

All of my PCBs have been etched. There are machines that can ROUT the circuitry pattern, but that really is etching also, albeit mechanical etching.

And drilling often comes before etching or plating

This is true for a DS board (as I stated, drill, plate, expose both sided, etch...). For a SS board, to minimize underetching (since there is no second layer that is also protected from etch), holes are drilled AFTER etching.

You seem to be thinking of DIY boards using pre-plated substrate..

I don't do PCBs at home (too much bother for too little gain - especially when I can get them professionally done for about the same cost as a DIY version). I am at a loss as to what you mean by using pre-plated substrates. All the substrates I have EVER used were NEVER pre-plated (what sense does that make?). Most substrates start with a 1 oz or 2 oz (or even other thicknesses) copper sheets bonded to both sides of a substrate (assume a DS board). If you want 2 oz copper on your final board, it is PLATED UP from a 1 oz substrated during the hole plating operation to 2 oz.

A lot of what I say is just from my experience with the PCB process, which I preferred to avoid, if possible (I design, you construct). I am NOT an expert, but I am also not a novice. The process that one house follows may be completely different from the process of another and they both are equally valid.

 

All of my PCBs have been etched. There are machines that can ROUT the circuitry pattern, but that really is etching also, albeit mechanical etching.

Are you sure, absolutely sure? How did you determine that?
Read the link in t post #7. In fact, there are several videos that show the additive process (i.e., plating the traces).

 

A fascinating video:
Inside a Huge PCB Factory - in China

PCB Manufacturing company:
https://jlcpcb.com/e