nRF5340 aQFN94 PCB trace routing for inner pads (via-in-pad)?

Question

Hi all, 
 
 I'm developing a custom board based on the nRF5340 chip and I'm having trouble routing the traces for the inner SMD pads in the QFN package. I believe that the reference layout uses via-in-pad for the inner pads to avoid the issue of top layer traces conflicting with the outer pads. However, after talking to a lot of circuit board manufacturers, a via-in-pad design will be extremely difficult to manufacture due to how small the nRF5340 QFN pads really are. 
 The pad size is around .2mm, meaning the via pad will need to be no larger than .2mm (~7 mil). This leaves either: 
 a) Extremely small via drill size (under 4 mil) or 
 b) Extremely small via annular ring 
 
 Either way, there were doubts that my design would be manufacturable. Does anyone have advice for routing traces using very small vias-in-pads or another creative method? I'm open to all options for routing traces to the inner pads! 
 
 (Using Ultiboard if that matters) 
 
 Thank you, 
 
 Nick B

ketiljo · Accepted Answer

For via in pads like here, laser drilled micro vias are used. These can only go between the outer layer and next inner layer, blind vias. 
 Many manufacturers should be able to do a PCB with micro vias. If you can't do that, you have to use conventional vias but that will severely restrict access to the inner ring of pads as there's no way to access those.

nRF5340 aQFN94 PCB trace routing for inner pads (via-in-pad)?

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