flexDF2: chip up or down?

I’ll be implanting my flexDF2 between 2 metacarpals in my hand. Unlike the flexM1 it’ll be replacing, the chip is on one side and in the middle.

I’m thinking of implanting it chip down, to leave the flat PCB facing up. My thinking is that the PCB would shield the chip somewhat if I happen to hit the implant, the antenna will be a bit closer to the reader (not by much though), and there won’t be a bump sticking out on my skin.

On the other hand, I’m a bit worried that the chip would chafe on my tendons or on the carpal bone: the antenna side of my flexM1 sits squarely on the carpal bone, while the chip at the other end has sunk in the space between the metacarpals. But the flexDF2 has the chip in the middle, so there a very real possibility that it’ll end up being over the bone, permanently arcing the implant (because the bump of the chip would have nowhere to nestle in) and damaging my tender bits underneath over time.

Advice? Does it even matter?

I would put the chip down for one reason… direct impacts to the exact center of the potted silicone die (the black square) could be diffused a bit better (only a bit) by the pcb + encapsulation vs the encapsulation alone. The chip itself only adds about 0.15mm height vs the surrounding pcb area so I wouldn’t worry about chafing.

Okay groovy. Exactly what I was thinking then.

.15 mm… yes, that ain’t much. Somehow I read .5 mm in the product description and pictured a .5 mm bump in the middle of the implant. But that’s the overall thickness of the implant, polymer packaging and all. Silly me.

Thanks man!

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Amal, is the chip side the silvery side or the black side on the flexNT? Would you recommend implanting that one face down also?

Incidentally, it’s gonna go fully over bone. I changed my mind: I’ll be implanting it in my finger like yours. So maybe there’s a “proper” face to present to the bone, as it’ll comform around the bone. Maybe it’s better that the silvery face gets compressed instead of stretched as it does so.

The flexNT has the chip on the silver side. I guess chip down makes sense but the chip is flip chipped to the PCB with a tiny bit of potting overtop.

Okay, silver side down it is then. Thanks!

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