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I'm designing a PCB that uses an XMOS XCORE microcontroller (XU316-1024-QF60B-C24) and the only GND connection it presents is the middle ground pad. I couldn't find any example of how this is supposed to be connected, but I'm assuming a via to the ground plane under the chip will be enough.

However, the smallest via I'm allowed to use through my PCB manufacturer is a 0.25mm drill, so the design seems very close to the pads around. Could anyone confirm this is the best approach? And should I add more vias around the pad? Another option, I imagine, could be having a via inside the square. Please see the image below.

Xmos Footprint

XU316-1024-QF60B-C24 datasheet: https://www.xmos.com/download/XU316-1024-QF60B-xcore.ai-Datasheet(3).pdf

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  • \$\begingroup\$ Grounding the whole MCU through a single trace that goes through a via and far away to somewhere does not sound like a great way to ground it. What do MCU design guides say about this? Why can't you use the bottom side as a ground plane? Or should the MCU design require a 4-layer board? \$\endgroup\$
    – Justme
    Commented Feb 20 at 21:06
  • \$\begingroup\$ the layout does not show the ground plane, that trace's path is irrelevant. \$\endgroup\$
    – Emerson
    Commented Feb 20 at 21:08

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After revisiting the datasheet a few more times I realised there is an answer to this on 13.4:

XU316-1024-QF60B-C24 13.4

XU316-1024-QF60B-C24 datasheet: https://www.xmos.com/download/XU316-1024-QF60B-xcore.ai-Datasheet(3).pdf

I will therefore add 16 vias over the ground paddle (if they all fit, otherwise as much as it's possible), according to the datasheet. I also missed the VDD paddles as they will also connect with vias underneath.

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