Help me design a 4-Layer Board with SDR SDRAM

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Hi guys,
I will be doing my first design with an SDR SDRAM. I'll be using the LPC1788 (in BGA), which has an SDRAM controller built-in, case and a 32Bit 3.3V SDRAM. The maximum speed will be 120MHz. My first question is regarding the layer stackup; would this be correct?

- Top Layer (signal)
- GND
- 3.3V power plane
- Bottom layer (signal)

Also, where should I try to route the most of the signals, on the top or on the bottom signal layer? Any advice on signal routing (and termination, if needed) will also be much appreciated.

Thanks and best regards,
George
 

Stackup is correct but i advice you to control impedances.
Try to route most hi-speed traces on top. For correct termination read appnotes for both SDRAM and controller.
 

You may find i a challenge on 4 layers.
Will your power plane be one contigous plane or split into different voltages.
 

if you go with a four layer board you need to space the outside layers close to the planes (less than 0.25mm) and have a large core in the centre (>1mm). It gives you better coupling and reduces crosstalk and EMI. I would go for a six layer board if you cost is not a big factor.
For termination you will need to see how long the traces are to determine if termination is required.
 

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