In SX Microcontrollers, SX/B Compiler and SX-Key Tool, SteveW wrote:

Note that the power plane isn't the _cause_ of EMI. Taking great care to keep noise off the power supply (by reducing the current drive required from IO pins, reduce the number of transitions, shorten driven traces, reduce loads, blah), decoupling the power with great care as it enters the chip, and all the other good practice things mean that you gain many dB without spending money per board, just at design time. Extra ground and power layers, while almost always a good thing, do cost money. If you don't have the luxury of re-spinning the board a few times to fix issues, and your customer's not too price sensitive, then 4-layer is the winner every time. 
Many consumer products, with EMC challenges of the same or worse levels than an SX52, are made on 2-layer boards, but are done exceedingly carefully, and are rarely the designer's first attempt :)

Steve

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