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I am curious now why its not feasible to basically just solder the silicon directly to the PCB, foregoing the package. Obviously the silicon would need a bit of

I am curious now why its not feasible to basically just solder the silicon directly to the PCB, foregoing the package. Obviously the silicon would need a bit of environmental protection, but it seems possible (probable?) to flip the die over so its typically wirebonded pads are against the board, and then same process as we have now with SMT devices, reflow oven, ready to go. I know that some dies are super tiny and this could make it difficult at the pcb bonding level, but surely we can shrink down our usage of plastic and the alloys that go into the IC packages. Theres a lot of unused space inside an IC package, with most of it being empty or pin arms. That would allow for smaller and more dense boards.

Kirby64 3y ago
This is done in many places. The problem is that a lot of silicon dies the die costs much more than the package. There’s a limit to how small you can make pins on a package for manufacturing onto a PCB, so if you need a certain number of pins, you either would need to grow the die (which is expensive) or switch to a packaged part. Mobile phones today largely use chip scale packages that do not use any sort of wire bonding, for instance.