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Number of Layers on PCB?

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Brokenspring

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Hello All,
I am fairly new to the PCB world and have my first job in it...:)...I am designing a board for with RF components in the range of 2.4GHz and 900MHz. Can anyone tell me how should I determine the number of layers on the board? How do I make that decision? Pointer to any good books that I could buy would be really appreciated...
Thanks
 
If cost is a factor, the fewer layers, the better. You don't want any long PC runs at those frequencies, so if multi layers will make short runs, it may be worth it. You will want a good ground plane, but that can be on the top or bottom layer.
 
if you are dealing with RF you def need

1) a GND plane
2) 5V plane

Then depending on other conciderations

3) & 4) layers for tracks -depends on how complex teh cct is
5) & 6) if used and needed planes for +/-15V
 
Have you scoped out the price range for PCBs capable of handling 2.4GHz to determine whether this project is feasible or not? An RF PCB should not be your first (and even intermediate) project. From my understanding you need controlled impedance PCBs like microstrip for 2.4GHz, and the prices of those PCBs can easily exceed the budget of an entire project for most people (not to mention they seem to need more layers than normal too because they are so sensitive). Their sensitivity also means the physical layout of the circuit can make or break the board which might mean multiple board revisions before it will work. It also means prior experience helps a lot.

A regular 4-layer board (from a regular service) costs me about ~$500 and 6-layer is ~$800 if I recall properly. Controlled impedance services will cost more (I won't say much more because I can't actually get a quote because it's a specialized service, but I am certainly thinking it loudly).

I just know that I wasn't able to afford a microstrip board when all I needed was one impedance controlled trace to connect the PCB mount antenna to the GPS module.

PCB Stack-Up - Introduction
 
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@2.4G Your layout is critical. Top layer use Microstrip surrounded by GP. Next layer, solid ground plane. Next layer, power. You can have digital signals on top layer, but you must be carefull and have the area seperatd by enough GP. If the digits are running fast then you might want them sandwiched between power and ground. Each layer adds mucho cost. If you are really brave you can do it with bottom ground plane and microstrip + power + ctl signals on top.
I have found that if you use digits on top, then try to RC filter your digits so the edges are not so sharp as the high freq component can seep into your RF, but take care not to violate timing.
 
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It borders on imposable to get anything special. They tend to get hung up on the final dimension instead of listening to what you tell them to put inside.

I asked for very specific minimums on both copper and core that I need for medical isolation in a transformer and I never get it. They seem to understand statements about copper but never listen to core thickness statements.

My next revision I am going to have to specify the isolation ratings. CE requires 9mm between the line and the user and a 5KV hipot rating. I am not certain I am getting that now. :mad:

That said, if you can maintain the core thickness the impedance is not a problem using microstrips or striplines.
 
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It borders on imposable to get anything special. They tend to get hung up on the final dimension instead of listening to what you tell them to put inside.

I asked for very specific minimums on both copper and core that I need for medical isolation in a transformer and I never get it. They seem to understand statements about copper but never listen to core thickness statements.

My next revision I am going to have to specify the isolation ratings. CE requires 9mm between the line and the user and a 5KV hipot rating. I am not certain I am getting that now. :mad:

That said, if you can maintain the core thickness the impedance is not a problem using microstrips or striplines.

Must be the vendor that you are dealing with is incompetent or you are not speaking their language. I've never had a problem specifying and getting precise core thicknesses in my projects. It is almost always necessary to consult with the pcb maker on what core sizes they have in stock and what their tolerances are, but other than that it should be easy.
 
Must be the vendor that you are dealing with is incompetent or you are not speaking their language. I've never had a problem specifying and getting precise core thicknesses in my projects. It is almost always necessary to consult with the pcb maker on what core sizes they have in stock and what their tolerances are, but other than that it should be easy.
language.. Chinese PCB house. We got the 2oz copper, but last I knew 11x0.2mm (total core) was more than 0.1"!

I just hope the isolation is good enough... Of course US houses charge $4-$6 instead of $1.50 for the board.
 
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