Simple questions about Planes and internal Layers

[qasmi]

Hello all,

I have some questions regarding Layer and Planes, I hope you will patient to read them and then answer them with patience.


1. I have designed a digital board with 6 internal layers and 2 power planes. I've further splited the Power Plane into 5 Power supplies. and the ground plane into Analog and Digital. The highest frequence of my board is till 20 MhZ. My question is, My Layer Stack is

TOP-signal--signal--signal-VCCPLANE--GROUNDPLANE--signal-signal-signal-bottom

Is the above Layer Stack recommended or any suggestions.

2. Now I'm designing the Power Module which will go into the above mentioned Digital Board. This Module will supply 3 seperate voltage supplies for FPGA, a VCC3.3V and VCC1.8 volts for the overall system. AS I have mentioned above that I've splitted the POWER PLANE of the Digital board for these voltages to go into it. My question is, IS it recommended that I insert a PLANE for each of the Power Supply in my POWER module Board.


Thank you, and take care


Best Regards

 

[v_kumar]

You have to plane the layer for routing the crictal signal and the non critical signals, CLK etc...

1) I think that the arragement must be something like this
TOP --> PLACEMENT & FANOUT
SIGNAL --> NON CRICTICAL SIGNALS (Since no referance plane)
SIGNAL --> CRICTICAL SIGNALS
PLANE
SIGNAL --> CRICTICAL SIGNALS
SIGNAL --> CRICTICAL SIGNALS
PLANE
SIGNAL --> CRICTICAL SIGNALS
SIGNAL --> NON CRICTICAL SIGNALS (Since no referance plane)
BOT --> PLACEMENT & FANOUT

In the above if you want to have impedence matched traces on the layer adjecent to the TOP & BOT than you must add referance plane on TOP & BOT.

2) If you are splitting the plane for multiple POWER and GND than take care that you route the respected signals on the same reference plane. For critical signals do not cross the planes and route.
Analog section signals must be routed in the same area where it has analog reference planes.
Do not route Digital signals on analog plance else it will induce noise in analog section.
If power distribution is not possible than you need to add more planes depends on the Density of the board etc...