ADLINK PXIS-2630 Series - 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”
connected to the logic ground plane of the backplane. The mounting holes
labeled as “FGND” with “square soldering mask” not connected to the
ground plane therefore providing isolation between the logic ground and
the chassis ground.
The backplane is mounted on the PXIS-2630 series through all mounting
holes by default, therefore the chassis ground is shorted 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.