Ton,

The SLT refers to the silver colored modules that are on the boards. These were thick film hybrid circuits with aluminum covers. The modules were manufactured on an automated production line. Here is a reference: http://www.chipsetc.com/the-ibm-slt---solid-logic-technology.html.

I think the layout on the board was done to accommodate the SLT modules with their square shape.  The conductors on the board look something like a process that was used on some boards by the company I worked for. These were not etched conductors, but rather they were thin wires that were laid down on a layer of uncured resin. The way the wires were connected to the pads way by ending them in the area of the through hole, and when the hole was drilled and plated, the wires were connected together. I think the pads were plated on also. The wires were literally drawn by a pen like stylus that fed the wire through a center hole. Where there were crossovers, they wires look like they did on old schematics with their looped crossovers. These boards don't appear to use crossovers, probably because the crossovers are inside the SLT modules. I know we used those type boards for development, but I don't remember if we actually used them in production. These boards: http://www.hitachi-chemical.com/products_pwb_05.htm from Hitachi are similar to the ones we used, and the name Multiwire sounds familiar to me, we might have used the forerunners of this process.

Harvey

 

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

 

From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
Sent: Saturday, 7 October 2017 2:34 PM
To: Homebrew_PCBs@yahoogroups.com
Subject: [Homebrew_PCBs] Does anyone know the process that IBM used to make this PCB

 

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?