JDallas said:
...At this time printed circuit board layouts were still done by tape and mylar...
MattisLind said:
...It just have to take massive amount of time, right? Rip up and retry?...
Back then we had contractors that would do all our circuit board layouts. They'd use a large drafting table sometimes a light table with sheets of mylar onto which they'd add black tape and stickers special made for circuit board layout. The original were something like 8x the size of the board, so that it was easier to work with, except for flipping to layers of mylar. The final gerber prints were made photographically from the mylar and tape and reduced to actual size.
I only taped two small boards in those years and both at 1x instead of 8x size. One was a special keyboard layout for a control panel, with a 8048 I programed, for the Columbus Project at Johnson Controls where I worked as a co-op student during college (alternating semesters between full-time college and full-time work with night classes) and another for small board on a contract job-on-the-side.
Problems I've Had With PCB Layout Contractors:
I've done a lot of my own board design layouts in CAD since 1998. As I studied drafting in the mid 70s and did drafting work at Texas Instruments before going to college, its an easy thing for me and I can do it a lot faster and with less compromise than the PCB layout contractors I tried to use. I find that pcb layout contractors say something is "impossible" when they mean that wouldn't be easy and as profitable for them to do. That I did it anyway proves it wasn't impossible.
PCB Layout contractors also try to make each board of an assembly a separate contract - no way! Instead I bought PADs and did it myself with all the boards on the same panel with a snap-line to separate them AFTER SMT pick-and-place automated assembly, through-hole item insertion and wave-solder. The contractor's method would have also added extra labor hand-soldering the board connecting flex cables whereas my solution had it done in a single pass, tested, and *then* snapped apart and assembled onto the mechanical mounts.
In other words, all the flex cables were done by the single wave solder pass and the boards were all electrically connected allowing them to be tested before snapping them apart. My first board in PADs was a 6 layer panel with five snap-off boards, two or which were small external connector adapters. The prototype run included a test fixture card snap-off used to program the micro's firmware. I learned how to squeeze cost out of a design at Tandy.
Mylar & Tape Layout Methodology:
From what I saw of our mylar and tape pcb layout contractor back in 1982 doing board layouts on mylar and tape, it involved a lot of heuristics on what you do first and where you put certain traces on the board so that you minimized ripping up tape when you'd otherwise hit a dead-end. They'd sketch difficult traces through the layers before going back and taping it. They'd work over a grid behind the mylar and use registration marks so the mylar could be carefully aligned for vias (he may have used a thin punch or X-Acto blade point to tack a position through the mylar for aligning vias). Our boards didn't use wavy traces, they used 45 degree radials. This type of printed circuit board layout was fascinating to see, but it was a very slow process.
In contrast, the board I did at S.D.Systems was packed with chips... hardly any space between the sockets. Initially we used a contractor to do the layout by hand but after about 3 months (at least it seemed that long if it wasn't) he was stuck. To get a board we allowed him to put a patch of one of the planes on the back of the board and he delivered the entire power plane on the solderside - which under no circumstance would be acceptable. We punted that and had a 6 layer board (including the power and ground planes) done by CAD layout in Atlanta. They did a wonderful job.
Trinkets From The Age Of Hand-Layout PCBs:
I think I've got the prototype we built of the hand layout of the S.D.Systems board; someone did a full chip build of it anyway. I may have some of the final layout's 6x4 foot gerber prints of each layer too. I used to hang the set on the wall behind my desk as technology art.
