EMC / PCB Design rule of thumb

[hamdi.tn]

Hi everyone 
So i have a large design that involve high voltage generation among other stuff ( a lot of analogue measurement, micro current measurement, stepper motor control and AC motor command via triac or relay ) and it's sensitive application that need some security.

What am worried about is EM, for years i have read AN that talk about EM and how to immune the board from it. Still a bit a mystery for me though. So any rule of thumb when designing a board, am totally aware that it's almost every time case depending. That include ground plan, track clearance, impedance , paralleled track ... but am not sure how each parametre influence for better immunity or worst. 

The second thing is the micro current measurement, i saw a board that do the same and the designer separate this particular circuitry from the ground plane and put it in a separate ground plane with large clearance between both, it still the same ground cause they are connected with a single track. Does this help in anyway giving a cleaner ground reference. Does it help to put a inductor to connect both ground.

Thanks 

[KJDS]

In an ideal world, you'd put the microcurrent measurement in a separate screened box from everything else. If you can't do that then you'd put it in a separate screened section on the same board with no connections apart from screened leads to provide the power and signals. If you common all the grounds at one point then you'll prevent switching spikes on the ground going through your sensitive circuitry, providing you chose the correct point. Depending on the spec you require, you may not need a screened can over the sensitive circuitry, however if you lay the board out so it's possible to put in something like a Perancea enclosure on the board then it's easy not to fit it.

[hamdi.tn]

Thanks for your answer  i already kept some space around the uC measurement and clear of all signal except those needed for the this part of the board obviously. Putting a can over it is not releasable but common ground in one point sure is.