How to decide the no. of layers of a board

[pal114525]

Hi,

I've a schematic drawn in DipTrace. It is an analog schematic. The schematic consists of 75 components.
I would like do the Layout work with manual placement and manual routing.
How can I decide whether it would be a single layer board or a double layer board?

Thanks & Regards.

 

[shaiko]

single layer board or a double layer board

4 layers is the absolute minimum if you want to adhere to the "thumb rules" of good electrical design.

Other then that, adding layers is a compromise between:

1. Cost.
2. Quantity of signals.
3. Quantity of power nets.
4. Quantity of components.
5. Quantity of high density BGA pins.
6. Power integrity.
7. Signal integrity.
8. EMI/RFI reduction.
9. Maximum allowable board thickness (if such exists).

 

[hobbyckts]

As you are saying it is analog schematic. Definetly there will be more than two power nets and the signals need to be routed properly due to the critical components presents in analog circuit. So atleast go with 4 layer. By dividing the top and bottom layers for signals and middle two layers for power and ground planes.

Tell us what is the size of the board which you are going to use?

 

[pal114525]

As you are saying it is analog schematic. Definetly there will be more than two power nets and the signals need to be routed properly due to the critical components presents in analog circuit. So atleast go with 4 layer. By dividing the top and bottom layers for signals and middle two layers for power and ground planes.

Tell us what is the size of the board which you are going to use?

Hi,

Thanks for your valuable feedback.
The size of the board is 7 inch x 4 inch.

Thanks & Regards.

 

[FlapJack]

Double sided boards are by far the most common PCB. The only reason you would use more layers is if you did not have enough room to run all of the wires or because of high frequency's and you needed a ground plane.

Let us know how fast your signals are. The only rule of thumb i have is 100khz is not considered very fast and you can get away with no ground plane.

 

[pal114525]

Double sided boards are by far the most common PCB. The only reason you would use more layers is if you did not have enough room to run all of the wires or because of high frequency's and you needed a ground plane.

Let us know how fast your signals are. The only rule of thumb i have is 100khz is not considered very fast and you can get away with no ground plane.

Hi,

Thanks for your valuable feedback.
I've 30KHz signal and 12v power supply in the design.

In this scenario, how many no. of layer would be the optimum?
Is ground plane required in this scenario?

Thanks & Regards.

 

[hobbyckts]

Hi,

The size of the board is 7 inch x 4 inch.

The number of components which you mentioned already is almost easy to place in this board size. So it will be so much conjusted and will be easy for routing I guess. So, then you can go for 2 layers.

 

[marce]

Whether to use more layers for analogue has nothing to do with signal speed and everything to do with signal integrity.
These days multi layers are more common.

- - - Updated - - -

Depends on how well you want the board to work... If you go with 2 layers then try and get all the signals on the top layer and keep the bottom layer as clean as possible for a contiguous ground plane.
How big are the components i.e. what area do they cover because you do not want to spread them out, this will create larger signal loop areas making the design more susceptible to noise pick up cross talk etc., especially with no ground plane. One of the main advantages of a ground plane is it minimises the signals loop area.

 

[pal114525]

Whether to use more layers for analogue has nothing to do with signal speed and everything to do with signal integrity.
These days multi layers are more common.

- - - Updated - - -

Depends on how well you want the board to work... If you go with 2 layers then try and get all the signals on the top layer and keep the bottom layer as clean as possible for a contiguous ground plane.
How big are the components i.e. what area do they cover because you do not want to spread them out, this will create larger signal loop areas making the design more susceptible to noise pick up cross talk etc., especially with no ground plane. One of the main advantages of a ground plane is it minimises the signals loop area.

Hi,

I'm designing 4 layers (TOP, GND, PWR & BOTTOM) analogue PCB. I have done auto routing using DipTrace. After the auto routing is done, I've found that few nets
need to be connected manually. It is very difficult to route them manually on the TOP and BOTTOM layer as the rest of the signals are already routed on these layers
during auto routing.

Can I route them (which are not routed during auto routing process) manually on the PWR or GND plane?

Thanks & Regards.

 

[Kick]

Re: Designing 4 Layers PCB

It is possible to route on PWR and GND plane (2 or 3 signals).

But my advice is rip-up all the routing and do it manually, it will give you a very good layout better than auto routing.

 

[hobbyckts]

Worst case you can route that but need to make sure that there is no power plane or ground plane is crossing are running very close to it.

 

[pal114525]

make sure that there is no power plane or ground plane is crossing are running very close to it.

Hi,

Thanks for your valuable feedback.
How can you make sure that?

Thanks & Regards

 

[hobbyckts]

Simple!! While applying the copper pouring for ground plane and power plane don't cover the tracks which are signal lines and these lines should be routed at nominal distance from the copper planes.

 

[marce]

Ditch the autorouting, never very good.
Check your placement, this is critical with analogue to get the best routing pattern.
Do not route on the Ground plane, power planes yes, but never on the ground plane.
How fast is the analogue...

 

[pal114525]

How fast is the analogue...

Hi,

It is around 33KHz signal.

Thanks & Regards.

- - - Updated - - -

Do not route on the Ground plane, power planes yes, but never on the ground plane.

Hi,

Thanks for your valuable feedback.
Why is that?

Thanks & Regards.

 

[marce]

Because the ground plane is king of the board...
That's the short answer I will post a list of stuff later regarding this, but using the above as a search will get plenty of info....