Xiao nrf52840 Surface mount

R_M · March 10, 2025, 4:02pm

Hello,

I’m wondering if anyone has any experience with surface mounting the XIAO nrf52840 to a PCB. I’m trying to use it for a wearable and so avoiding the thickness/height of headers would be good.

I’d also like to use the VBATT pads on the underside connected to the battery which will be VDD. Doing it this way because the NRF52840 can’t output enough current for what I have on the rest of the PCB so I was going to use the battery as Vdd and Gnd and connect these to the Vbatt pins so I can deliver appreciable current (~0.5A) from the battery but still make use of the charging circuitry of the XIAO nrf52840.

I’ve seen there’s a surface mount footprint for the board on the getting started page, I just haven’t seen anyone use it as surface mount so was wondering why.

Any info/ideas would be appreciated!

gmrck · March 10, 2025, 7:48pm

Check this out for some ideas:

https://fabacademy.org/2024/labs/charlotte/students/richard-shan/lessons/week4/rp2040/

PJ_Glasso · March 11, 2025, 12:45am

Hi there,

Oh’ you haven’t lived until you SMD solder the Xiao…
Totally fine, Keep READING buddy

here is some fresh ones, those are some older Pics.
and don’t do like the first one, from a user on here, was using a potato to solder.

The 3 channel EMG board it the grove EMG Board x3 (i squeezed it on there 45mm roundy round, the concept for adding the xiao directly on SMD pin Header receptacles.

The Evolution is to OVAL the Battery Pad Through holes and plated through also. a little bigger is better but not Wider the the Xiao’s PAD
AMA

HTH
GL PJ

Solder “Paste” is your friend.

R_M · March 17, 2025, 10:03am

Hi,

That’s massively helpful thank you

So it is possible. You say “The Evolution is to OVAL the Battery Pad Through holes and plated through also. a little bigger is better but not Wider the the Xiao’s PAD” but I’m not too sure what is meant. Is OVAL a technical term or oval as in an ellipse? Also not sure about the “battery pad through holes” they are just pads no? Are you suggesting via in pad for them and if so can I not just route them on the same layer?

I was also wondering if there are any requirements for below the antenna. Should I have this as a “keep out” on the below board?

Thanks again!

PJ_Glasso · March 17, 2025, 2:43pm

Hi there,

So , Don’t overthink it. Oval or “Elongated” then would probably define better. Just be sure you go heavier on the Plated through parts.
NO, NO,NO… keep out of that Zone or you won’t get any distance that’s the important part to have good BLE transmission.

Look at this;

the C3 cap in the pic is the closest you’ll want to go.
This 2nd one had a display and when the display cable was connected the BLE was less distance.

HTH
GL PJ

PJ_Glasso · March 18, 2025, 11:29pm

So I found these later pics of the Current tech delivering 100% success

Paste the edges of the ovals on the top side, Paste the the PADS on the bottom of the Xiao. Clamp lightly…, flip it over and solder the bottom. after the paste melts feed the solder roll into the holes (slowly, fill it.)

You can solder only the pins you plan to use or solder them all.
YMMV , and consult your specific technical reference guides.

HTH
GL PJ

R_M · March 21, 2025, 4:14pm

Thanks again! Is that necessary if you have a hotplate or oven to solder it with, or is this just for trying to do it by hand?

PJ_Glasso · March 21, 2025, 11:49pm

Hi there,

So mostly for by hand, but you’ll need to apply paste to both the stencil for the board and on the Xiao’s Batt Pads Only… YMMV but I get percent success when applying this tech.

HTH
GL PJ