Do you have to make 7 layers PCB in Power PC?

[Vonn]

Working with Power PC

I am designing a project using power PC .. is it must to make the PCB 7 layers even if i don't need it .. i e . if i can merge the 3.3v and 5v in one layer and the routing takes 3 layers and a layer for GND ..
or this is some thing in the precautions ?

 

[Tezkaplipoka]

I have some experiences by MPC860,since it has high frequency bus and signal rise times are important you should pay extra attention to signal integrity when you layout.I think having VCC plains and VCC plain cuts are mandatory for the MPC pll to lock. and its strongly emphesized on it in motorola documents. My board was 8 layer board.

 

[shawndaking]

ppc layout

it depend on PACKAGE DIMENTION - I GUESS YOU ARE USING BGA - SO YOU SHOULD HAVE ANOUT 1 SIGNAL LAYER PER BALL ROW, OR COLUMN !

ALSO YOU MUST HAVE A VCC, GND PLANES AROUND THE PPC !

SO YOU CAN USE SOME OF THE 5V PLANE TO PPC 3.3V ISLAND.

I GUESS YOU WILL NEED MIN. 8 LAYERS

 

[jodokus]

The ususal signal speeds in a powerpc processor based design are such that logic supply planes and ground planes are needed. In case of dual logic supply I would go for a plane for each supply. It is by the way not handy to have 7 layers (or any odd number). The pcb manufacturing process is such that layer numbers are always even. In other words: if you make a 7 layer design you will pay for an 8 layer board anyway.