PCB-Stack Design Papers

PCB Stack-Up -- Part 3 - Six-Layer Boards
[pic]
PCB Stack-Up
Part 3. Six-Layer Boards
Most six-layer boards consist of four signal routing layers and two
planes.  From an EMC perspective a six-layer board is usually preferred
over a four-layer board.
One stack-up NOT to use on a six-layer board is the one shown in Figure 5. 
The planes provide no shielding for the signal layers, and two of the
signal layers (1 and 6) are not adjacent to a plane.  The only time this
arrangement works even moderately well is if all the high frequency signals
are routed on layers 2 and 5 and only very low frequency signals, or better
yet no signals at all (just mounting pads), are routed on layers 1 and 6. 
If used, any unused area on layers 1 and 6 should be provided with "ground
fill" and tied into the primary groun