>extra time and effort to cleanup a two layer board for 12bit a/d.

Properlay laid out, you should be OK on two layers.

>board seemed astronomical. It was $5 per board 2 layer (1000 qty) and $10 for

$5 is high for 2 layers, unless you are getting them screened on both sides.

>3 or 4 layer same qty.

$10 is cheap for 4 layers.

Whenever possible, go with minimalist approach.  1 layer is cheapest (try
using 1 layer for the ADC area with GND plane under it).  Don't worry about
solder mask unless you have to.  Never put down a screen except for
large-run protos that you expect to screw up.

Andy

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     \    |   |    /          Andy Kunz
      \   /---\   /           Montana Design
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