I am working on some extremely small designs where the entire board is less than 15mm2. There are a surprising amount of very small ICs but I’ve found it’s really tricky to actually do a thorough part search for tiny (sub 2mm x 2mm) parts.
Some vendors have CSP packages that are relatively huge while having other package types like X2SON which are actually smaller. What was called ‘tiny’ and ‘smallest’ a few years ago is actually pretty large by today’s parts.
Any tips on how to find parts?
Honestly, in that scenario, I usually just select all the footprints I don’t recognize in the part selector on Digikey and browse through the images. There’s usually only a few pages to go through if you’ve specified everything else well enough.
Also, if you have the means, I remember seeing a demo from TI(?) where they could bond raw silicon in an inner layer of a PCB. So like, buck converter or whatever inside the board and passives immediately above/below it.
Oh, and on that note, I think they sell some BGA parts that are basically just that. Here’s an example: https://www.ti.com/product/TPS826716 The controller is inside the little PCB with the passives sitting on top.