The electronics were done various ways. If it was a one time deal or was needed ASAP it was thrown together. If we knew their would be more than a few we would create "better" PCBs.
For example the "First Contact" medical tricorder. I had a short time to design and build the electronics. I really wanted to incorporate blue LEDs into a tricorder. Back then when this was built blue LEDs were costly and not plentiful. SMT LEDs were not an option. I had to machine all the blue's by hand to make them fit! I used some of my stock driver boards to quickly get it up and running. These driver boards are smaller than a postage stamp and they were typically used for cortical stimulators, scanners or anything that needs flashing lights. I hand wired these little boards together to get it out the door.
The Voyager Relativity tricorder (24th century) and the Endgame tricorders were built using these same methods.
The Mark 9 and 10 tricorders had a lot more time to design and build so they had custom etched PCBs.
Brian