ADLINK PXIS-2700 - Manual (Page 13)

Installation ● 7
2.4 Grounding on the Mounting Holes
There are two kinds of grounding for the mounting holes of the backplane.
The mounting holes labeled as “GND” with “circle soldering mask” are
connected to the logic ground plane of the backplane. The mounting holes
labeled as “FGND” with “square soldering mask” are not connected to the
ground plane therefore it provides the isolation between the logic ground
and the chassis ground.
The backplane is mounted on the PXIS-2700 through all mounting holes
by default, therefore the chassis ground is short to the logic ground. For
applications that require isolation between the logic ground and the
chassis ground, users can remove the screws on the GND mounting
holes.