https://devzone.nordicsemi.com/f/nordic-q-a/116748/nrf52840-aqfn73-vias-to-bottom-layerHi We use the nRF52840 (aQFN73) with a 4-layer 1.6 mm PCB for our current project. The top and bottom layers are for signals, the two internal layers are ground and power planes. The reference design connects inner signals to the midlayer with a blinden-USTelligent Community 13Thu, 28 Nov 2024 09:51:21 GMThttps://devzone.nordicsemi.com/thread/512542?ContentTypeID=1Thu, 28 Nov 2024 09:51:21 GMT137ad170-7792-4731-bb38-c0d22fbe4515:ccd3fabe-65b9-4a0a-9647-f93e929fd701Asbj&#248;rn<div style="border:0;color:rgba(0, 0, 0, 1);font-size:11pt;font-style:normal;font-weight:400;letter-spacing:normal;line-height:inherit;margin:0;padding:0;text-indent:0;text-transform:none;vertical-align:baseline;white-space:normal;">Hello Michael,</div> <div style="border:0;color:rgba(0, 0, 0, 1);font-size:11pt;font-style:normal;font-weight:400;letter-spacing:normal;line-height:inherit;margin:0;padding:0;text-indent:0;text-transform:none;vertical-align:baseline;white-space:normal;"></div> <div style="border:0;color:rgba(0, 0, 0, 1);font-size:11pt;font-style:normal;font-weight:400;letter-spacing:normal;line-height:inherit;margin:0;padding:0;text-indent:0;text-transform:none;vertical-align:baseline;white-space:normal;">The 0.2mm drill holes will probably be ok, just be careful with the solder mask and check with the manufacturing place that they are ok with solder mask that supports this. We would recommend using 0.1mm drill holes though.</div> <div style="border:0;color:rgba(0, 0, 0, 1);font-size:11pt;font-style:normal;font-weight:400;letter-spacing:normal;line-height:inherit;margin:0;padding:0;text-indent:0;text-transform:none;vertical-align:baseline;white-space:normal;"></div> <div style="border:0;color:rgba(0, 0, 0, 1);font-size:11pt;font-style:normal;font-weight:400;letter-spacing:normal;line-height:inherit;margin:0;padding:0;text-indent:0;text-transform:none;vertical-align:baseline;white-space:normal;"></div> <div style="border:0;color:rgba(0, 0, 0, 1);font-size:11pt;font-style:normal;font-weight:400;letter-spacing:normal;line-height:inherit;margin:0;padding:0;text-indent:0;text-transform:none;vertical-align:baseline;white-space:normal;">Best regards</div> <div style="border:0;color:rgba(0, 0, 0, 1);font-size:11pt;font-style:normal;font-weight:400;letter-spacing:normal;line-height:inherit;margin:0;padding:0;text-indent:0;text-transform:none;vertical-align:baseline;white-space:normal;">Asbjørn</div><div style="clear:both;"></div>