Back in the early 1970’s, when I started my PCB designcareer, every component package was through-hole. We manually sketched the padsand traces with red and blue pencils on vellum parchment paper using a 10^thinch grid pattern on a drafting table using a T-square and triangle and circletemplates. 

When the sketch was completed, the pencil drawing, and grid sheetwas placed on a flat light table. We overlaid a sheet of mylar on top of thepencil drawing and manually placed sticky donut pads, made by Bishop Graphicsand using an Exacto knife to create the Pad Master. Then a new sheet of mylar placedover the pad master and pencil sketches. We used 0.062” wide black tape and anExacto knife to create the traces for the top and bottom layers. All thedesigns were 2-layer boards that were laid out 2:1 scale and reduced to 1:1scale using a giant precision camera to create negatives of the outer layers. 

The pad master was over-exposed to create the solder mask swell. The PCB’swhere created using the negatives to apply a temporary mask that protects partsof the copper laminate from acid and leaves the desired pattern. This etchingprocess is still used today, but back in the 70’s it was a manual process usinggloves, tongs and timers. The solder mask was manually applied to the PCB usinga screening process. The primary goal of solder mask back in the 70’s was toprotect the bare copper traces from oxidation and the acronym SMOBC wascreated. The solder mask swell was between 0.20 mm (8 mil) and 0.25 mm (10 mil)annular ring. 

We were not concerned about solder bridging because the through-holecomponents were hand soldered. A manually sketched assembly drawing on mylarwas placed into an ammonia tube with blueprint paper to generate copies. The blueprintassembly drawing was used to indicate polarity and package part number or valueand was hung from a wire using alligator clips in front of the person doing thesoldering. All of the processes from schematic diagram to PCB layout tofabrication and assembly were all performed in the same building. 

The EEengineers would manually pencil sketch the schematic on paper and the PCBdesigner would use India ink on mylar using schematic symbol templates tocreate the master schematic. The Bill of Materials was manually created onpaper. There was no netlist and the PCB designer who drew the schematic had touse it to lay the PCB traces. The PCB holes were manually drilled using a drillpress and the holes were un-plated. The vias had to have a bare copper wire crimpedand soldered on both sides.