Dunno how the boards are made, but that’s called SLT - Solid Logic Technology.

I think the idea behind the boards was traces are vertical in one direction, and horizontal on the flip side.  You can still get protoboards to do this.  As Stefan says it was an early attempt to automate everything (especially production) I think the board were designed by placing the little modules and the passives, then taking out the lines they didn’t need.

The extra pads were left because ‘why not’ – it’s easier to leave them than to remove them (probably a standard mask) plus it makes rework easier.

I did come across a good website on these once that will probably show me how wrong I remember it, might see if I can find it.

Tony

Does anyone know the process that IBM used to make this PCB
http://www.learnmorsecode.com/3380/index.html

30 years ago I was a computer programmer on an IBM system 34.

IBM service technicians would sometimes open up the machine covers 
and I saw some really strange circuit boards inside.
They did not look like anything found in any other electronic appliances.
It looked like there was no etched traces on the IBM circuit boards that
had square blocks..and every square block had solder in them..regardless if
there actually was a component in the holes.
 All the components seemed to line up like houses on city streets.

Recently I stumbled onto an IBM 3380 disk drive analog servo board
and made these pictures with real up close details revealing what the strange boards
were really made of... sort of.
It turns out that the IBM PCBs had extremely thin traces on both sides of the PCB
and in some places there was 3 traces in the space between  the solder squares
and
that space was no wider than a penny.
These traces would terminate at solder pads but would disappear from view.....
never being actually visible touching a solder pad.
Does anyone know what process made this circuit board?