FPC is used in billions of devices-- that are professionally assembled, usually assembled only once, well-enclosed, and careful attention has been given to strain relief. It's cheap and compact and allows very small assemblies.
It's not so hobbyist/tinkerer friendly, where you're likely to put a lot of cycles on the connector, bend things back and forth, and end up with an enclosure that does not protect everything as well as one would like. Indeed, you have a sibling comment talking about breaking lots of FPC going to cameras.
Mechanical/connector failure is a small but noticeable share of the SD robustness problems on SBCs. I would expect FPC to be worse.
Again, this sounds overblown. Obviously the cables are somewhat fragile and you can't just be a brute with them... but the alternative is making a PCB that is much larger to accept a M.2 slot. It just isn't possible in the current footprint from what I can tell.
Also, other connectors for this type have surprisingly low durability. Most M.2 slots are rated for extremely low mating cycles. Amphenonol, who I would considered to be an high quality manufacturer, rates their M.2 slots for '25-60' mating cycles total. Less than 100. Most manufacturers do not even specify the number of mating cycles.
> but the alternative is making a PCB that is much larger to accept a M.2 slot. It just isn't possible in the current footprint from what I can tell.
I'm not saying they made a bad choice; they're facing a lot of constraints and have a lot of IO to get out while staying hobbyist friendly.
> Also, other connectors for this type have surprisingly low durability. Most M.2 slots are rated for extremely low mating cycles.
Sure, but I don't -need- as many mating cycles for M.2, as it'd be screwed to the board and done. Whereas if I'm dealing with a Pi stackup and coming in and out of the case, I'm likely to get through the couple dozen cycles I'm allowed with FPC. And if I'm putting it on a vibration-intensive environment like a quadcopter, I need to be pretty dang careful with mechanicals.
> Again, this sounds overblown.
Everything's a tradeoff. Flex is cheap and small and offers versatility. It's also delicate and annoying.
It's not so hobbyist/tinkerer friendly, where you're likely to put a lot of cycles on the connector, bend things back and forth, and end up with an enclosure that does not protect everything as well as one would like. Indeed, you have a sibling comment talking about breaking lots of FPC going to cameras.
Mechanical/connector failure is a small but noticeable share of the SD robustness problems on SBCs. I would expect FPC to be worse.