I’ve been reading of 0.3 mm pitch BGAs, but those aren’t totally new. I’m not sure if we’ve done any 0.3 mm pitch before, but we’ve been doing 0.5 mm for years and have done plenty of 0.4 mm pitch as well, even in package-on-package (POP) forms.
Speaking of really fine-pitch BGAs and CSP type things, one topic I found interesting has to do with pitch switching adapters. It’s basically a small PCB platform that has an underside footprint of a 1mm or 1.27 mm pitch BGA and a land pattern on top for a fine pitch BGA. It has solder balls on the bottom, so once sandwiched together, it’s treated just like a big BGA for assembly purposes. [Credit where credit is due: The image below came from the Aries Electric website.]
Such a part can negate the need to re-spin the PCB if your big part is updated and replaced in a new fine-pitch form factor. (Although, personally, I can only imagine that if the chip is rev’ed, there will be some other change that has to be made to go along with it.) The theory is, if you’ve got a really expensive design, this might be a viable option, allowing you to upgrade without a relayout.
Certainly though, at the very least, this could allow you use some newer fancy chips without having to resort to filled microvias and tiny trace and space advanced (expensive) PCBs. Could be quite handy and same some money.