Btw how did you mount the rp2350s? I literally just reflowed the thermal pads on these onto the stud backs with hot air and was surprised how well that worked.
I used a lead from some random through hole component that was still on my desk (I guess a capacitor) and bent it 90 degrees with a little extra hook in the middle. Soldered it to the pads and made sure to have enough solder on the thermal pad to bridge to the side (which adds some weight as well!)
Ah, I wondered. That makes sense. With the BGA ones, I may try and use a clear epoxy, since the solder balls won't provide a lot of hold compared to the thermal pad, and I'm not sure I want a big blob of solder on the backs.
I kinda want to make a set of earrings where the mcu actually isn't just cosmetic. Probably not with the nrf52840, though. It's a bit big and needs too many external parts. I know of an absolutely tiny WCLSP Renesas chip which could be good for it.
I actually used the homebrew blind via trick he did there on a board of mine. Two 4 layer boards back to back with a flex pcb interposer to get an effective 10 layer rigidflex stack-up. My earring chips came off the predecessor to that board.
It's super easy to do. I reflowed the stud base onto the big thermal pad on the bottom of the chip with my hot air station and a bit of extra solder paste. I just used cheap earring parts from amazon, I think I'll get some higher quality parts and redo at a later date.
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Btw how did you mount the rp2350s? I literally just reflowed the thermal pads on these onto the stud backs with hot air and was surprised how well that worked.
https://mitxela.com/projects/ledstud
https://www.aliexpress.com/item/1005005230850978.html