I have a Beckhoff EL2008 8-channel digital output terminal that I took apart because I'm using an ASIC that is inside the module, Beckhoff's ET1200.
There is essentially a ring of ground pads,some with vias, surrounding the ET1200 inside the module (they all beeped out to the ET1200's ground pins).
I can understand if they're just there for bonding the ground planes, but why expose them?
Through past experience, the ET1200 is a tremendously sensitive device, and this leads me to think that they're exposed for ESD protection, increasing the likelihood that they would conduct the discharge instead of the ET1200.
Can anyone conclusively describe their purpose?
Thanks for looking.
It's likely these exterior (gold bare metal ) pads are to bond the layers together to form a nice faraday cage in situ (as mentioned in OP). Since there are some high speed signals your probes will require adequate grounding during test so they are left open for the probe card to be able to get a clean ground reference. Some have vias in them because they bond through, some don't have vias because the ground is needed close to the pads that are being tested but there are traces underneath. Particularly on the LHS.