minimum space between two PCB s Over each Other

[fences]

Hello,
I have two PCB s with difference part. i want connect those over each other like this :
( because there is limited space )


How could minimum space between two broad be?

Thanks.

 

[FvM]

Not less than sum of component heights. :smile:
Or the stacking height of the used connectors. Or...

 

[fences]

thanks, but is there any standard concepts?

 

[schmitt trigger]

Voltage difference?
Temperature gradients?
Electromagnetic fields?
Noise coupling?