Biggest circuit board I ever saw was roughly 500mm x 800mm, hot swappable "printed wire board", that is, it was a basic double sided FR4 type board (power and ground), then each side had an 'epoxy' type layer covering it, with two layers of thin enameled wire embedded into the 'epoxy'(or whatever the compound was). This was back before micros came into general use, so all TTL, over 400 chips per board. The developers spent untold $millions designing these boards and building test and debugging logic into them so that faults could be diagnosed to chip level and several guys from oz were sent overseas and trained to repair them.
What eventually happened was that someone back in the US "repaired a card" so badly that it had to be scrapped. After that ALL cards had to be swapped out and faulty ones returned to the factory, that was the start of us becoming card jockeys.