iMX8M Nano -- What are these holes in the PCB for?

[jaredwheeler]

In the EVK SoM board for the 8M nano, the processor is surrounded by 6 unplated holes drilled thru the PCB.  I've attached a screen grab of these holes in a PCB layout.

Can anyone shed some light on the purpose of these holes?  Are they for EMC? Are they used during manufacture?  What parameters govern their effectiveness? 

Any help with vocabulary or pointers to documentation about these would be helpful!

Thanks!

[jaredwheeler · Accepted solution]

Thanks for the replies, folks.  I’ve found the purpose for these.  They aren’t holes at all, I was just mis-reading the PCB layout files.  

They’re local component PCB fiducials.  Used by the vision system on the PCB assembly pick and place machine to accurately position the 0.5 mm BGA pitch 8M processor.

The size and layout requirements are defined by the vision system in use at the PCB fab.  So when designing your own PCB layout, you have to contact the assembly engineering staff at your PCB fab to get the specifics.

[carotte]

Thats wrong.

They are holes indeed...

[jaredwheeler]

Yeah, you’re clearly right about that.  Not able to unmark my incorrect fiducial solution post.

[carotte]

My guess is, that the four big ones were intended for mounting a heatsink. 

Definitively not for EMC.

[Rita_Wang]

Are you using NXP reference board? Or the third company design board?