0.5mm pitch BGA FPGA without HDI

 0.5 and without HDi? Seems impossible, but sometimes it works, see here:

This is TE0747 from Trenz Electronic, it is 4 layer no HDI, there is 0.5 mm pitch BGA (the FPGA) on top red layer and there is 0.8mm pitch NAND flash device on the opposite bottom blue layer. This board was built and it worked with modified HDL from Google's project vault. There was one user LED and connector for JTAG+4 GPIO. SPI flash and two DCDC converters.

Adam Taylor has gone further and developed an FPGA evaluation board with Spartan Ultrascale+ device in FCVA289 package:

Looking at the package, I'd say that routing out ALL pins without HDI is not possible. But limited pins can be fanout on non-HDi board as well. But interesting to see how Adam solved the escape routing.

I checked my own design and to my suprize I used 0.3/0.1 THT vias. I think Adam uses same vias, then it becomes possible to route out more than 3 rows. Still routing out all I/O would be real challenge.

Info about Adam escape work will be accessible on 17h September webinar need wait!!!

It seems Adam will publish an open-source project where he shows how the escaping is done.

This is how Adams PCB looks like. 0.3mm VIA und via offset placement do the trick.