EMI reduction and PCB stack up
To reduce EMI, we should keep the prepreg height less than 10 mil and clearance between tracks greater than or equal to 10 mil with FR4 material which has Dk of around 4.3. My Question is solder mask has a Dk of around 3.3 which is less than FR4 so will these emitting charges will go through FR4 to GND plane or through solder mask to affect nearby track?
You don't need to worry about the properties of the solder mask with respect to cross-talk. I am quite sure that its contribution to the cross-talk is negligible.
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