Number of Layers on PCB? - Electronic Circuits Projects Diagrams Free

Brokenspring · 26th May 2004, 11:06 PM

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

Russlk · 27th May 2004, 12:18 AM

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.

Styx · 27th May 2004, 08:04 AM

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

dknguyen · 22nd June 2008, 06:41 AM

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

Mikebits · 22nd June 2008, 07:14 AM

@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.

Ubergeek63 · 22nd June 2008, 01:44 PM

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.

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

RadioRon · 22nd June 2008, 11:18 PM

Quote:

Originally Posted by Ubergeek63

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.

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.

Ubergeek63 · 22nd June 2008, 11:37 PM

Quote:

Originally Posted by RadioRon

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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26th May 2004, 11:06 PM	(permalink)
Brokenspring	Number of Layers on PCB? 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

27th May 2004, 12:18 AM	(permalink)
Russlk	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. __________________ see my website: www.geocities.com/russlk

27th May 2004, 08:04 AM	(permalink)
Styx	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

22nd June 2008, 06:41 AM	(permalink)
dknguyen	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 __________________ NO, that picture isn't me so don't bother asking if we can be friends. Last edited by dknguyen; 22nd June 2008 at 06:52 AM.

22nd June 2008, 07:14 AM	(permalink)
Mikebits	@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. Last edited by Mikebits; 22nd June 2008 at 07:16 AM.

22nd June 2008, 01:44 PM	(permalink)
Ubergeek63	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. That said, if you can maintain the core thickness the impedance is not a problem using microstrips or striplines. Last edited by Ubergeek63; 22nd June 2008 at 01:49 PM.