For some time I’ve considered building my own processor from just gates. A week ago I had some time to waste so I messed around with the idea again. Last w/e I put it on a pcb design. The result is a 4”x6” pcb with 676 gates in a 26x26 matrix.
I used the 74LVC1G58 in the 6pin SOT363 footprint which is ~2x2@.65mm. This is a configurable gate as a 2 input NAND/OR/XOR/INVERT or an AND/NOR with one input inverted. Of course, the footprint also permits the use of 74LVC1G98 (NAND/NOR/2:1 MUX/INVERT or NAND/NOR/AND/OR with one input inverted), or 74LVC1G11 (3 input AND) or any SOT363/SC70 with centre power pins.
At 3V3 operation the gate delay is 6.3ns max.
Wiring is done using kynar wire. Each gate input has a pad with 0.7mm hole and the gate output pad has a 0.5mm?? hole.
These boards could be stacked. I’m thinking a Z80 would probably need some 10 boards stacked, plus a special board for the registers made with 74LVC646 which would probably have a 128KB SRAM too, and maybe some I/O.