I absolutely would not count on a snapped in half MicroSD to protect the data that’s on it from someone determined to find out what it was. You don’t even know if you actually managed to break the memory chips themselves or just the connections between them, which with time and patience and the right equipment could be reconnected, and even if the chips are broken a great deal of the data on them will still remain intact, etched in silicon for eternity and vulnerable not only to current technology but also future technology.

Your goal is turning the data stored on your MicroSD card into a puzzle. A 2 piece puzzle is likely quite solvable even today. To properly vaporize the card and make it actually unreadable you’d likely need to do some experimentation and try things you would potentially have access to in war like fire, gunfire, explosives or corrosive chemicals, some combinations of which may serve to well and truly annihilate any hint of structure. The question is how many tiny pieces can you break that MicroSD card into, if that number is a human-countable or even human-comprehensible number like the number of pieces a document typically gets shredded into, then it’s probably not safe enough to consider it reliably destroyed.

If people can tape back together shredded documents to get the basic idea of what was written on them, someone can likewise theoretically repair your MicroSD to get a large proportion of the stored data from it if they are absolutely intent on doing so. It’s probably a lot of work, and maybe not even a not-worth-it amount of work depending on how important your data might be, and there might be a substantial amount of data unrecoverable and missing, but it can be done. Unless you make it a puzzle with so many pieces that doing so is mathematically implausible and just as likely to be an incorrect reconstruction of data that might say anything the reconstructor imagines it does, without actually giving them any confidence that it is real and correct. The only thing that’s certain is that 2 is probably not a good enough number of pieces to rely on for that to be the case.

As an alternative to the fire/gunfire/explosives/acid style methods, you might also use sandpaper (would take awhile), or better yet a grinder tool of some sort (dremel, angle grinder, bench grinder) to give yourself some confidence that the card has truly been turned to a pile of arbitrary dust. Even then, I’d still concerns as the data density increases, a single speck of MicroSD dust from a 1TB card shredded into millions of pieces might still contain 1 MB of data – that’s an awful lot of text and even potentially some images if it can be decoded. They really prove surprisingly hard to destroy. Electrical attacks, even Microwave ovens, reportedly have mixed results and don’t sound like reliable approaches either.

If you can get it to a molten state, that’s your highest confidence method. Silicon has a melting point of 1,414 °C, good luck.