Electro harmonics PCB design or any early etching for that matter HOW???

[Wild Zebra]

     Wasn't sure how to express this in a title, but a friend of mine was looking at an old EGO boost he had and asked how they made the PCBs back then and I really couldn't give him an answer.  You know the kind where it looks like they just hand drew some solder on the bottom and then drilled some holes.  So how did they do it back in the day???

[theehman]

I would suspect somebody just drew out a PCB design then transferred it to a screen for screen printing on the board.  After that, a little etching and drilling and Voila!

[Mark Hammer]

Look at those early Boss PCBs.  No straight lines there!  Same thing with MXR and especially with Japanese manufacturers like Univox/Shin-Ei.

At that time, what you would do is use the layout tape that was widely available (I may even have a small roll leftover somewhere).  You'd figure out where the holes needed to be and run the layout tape (which often curved very nicely) on a piece of onion skin paper or an acetate sheet.  Then you'd use rub-on transfers for the "donuts", and probably some IC-pad rub-ons (have a bunch of those too).  Much of this was easily available at Radio Shack.

Once you had a layout, you'd take a picture or make a photocopy to an acetate sheet, and use that to expose a photosensitive board.  If you were trying to be professional.  If you weren't trying to be professional, you'd try and copy the board with a Sharpie.  There WAS a DIY movement before PnP came along, you know.

[Wild Zebra]

Did they use a solder mask then also??

[R.G.]

Ah, one of the (few) advantages of being old - I remember how it was done.

Originally, draftsmen (that is, technical guys who were skilled at drawing with pen and pencil on real paper, then later plastic film) drew up the whole thing entirely on paper from scratch. When parts became somewhat standardized in shape, they made machine-printable paper-dolly representations of parts instead of drawing everything from scratch. Even later, the concept of a coordinate grid came about and the concept of putting all holes on a grid got started.

The process was well developed when I learned it in about 1974.
1. Get a light table. This is a drafting table with a glass top and fluorescent lights under it to shine through any transparent or translucent materials.
2. Obtain and place on the light table a transparent plastic sheet with an accurate grid on it, typically 0.1" or 0.05" between grid lines.
3. Lay a piece of translucent drafting mylar film on the grid. Draw the PCB outline on this at either 2x or 4x real size. In fact draw ALL mechanical details on this sheet. Each succeeding layer gets big target X's laid accurately on grid points to allow you to align them if they're moved.
4. Lay another sheet of clear mylar on the stack. Lay the component body paper-dollies on this one.
5. ... 'nother sheet, this one for placing black masking paper donut pads on
6. ... 'nother sheet, this one for drawing the bottom/copper side traces between pads
7. ... 'nother sheet, for top side traces...
8 - 20 - more sheets as needed for inner layers.

The stuff we think of as PCB layout today, placing parts and running interconnect traces were steps 4 thru 20, and were recursive. You iterated through placement and routing until you got it right.

Once you got the drawn traces right, you restacked only the outline/mechancal layer, pad layer, and colored-line trace layers and then made one new mylar layer per copper layer. On each copper layer, you laid black crepe drafting tape to cover that layer's colored line.

There were two main styles - long, loopy rounded traces and square-intersection traces like computers do now. The long loopy styles were frowned on because they easily pulled off the mylar. Stretching the tape as it was laid was a disaster, as it would relax and pull itself off the mylar.

Once all of the layers were taped, checked, checked, checked, checked and checked, they were taken to a drafting supplies place that had big lithographic cameras to make real-size photo negatives of each layer, including the alignment marks. Then a PCB etching company would use negative-acting photo resist to make the boards in a FeCl or Ammonium Persulphate etching cycle.

Some very simple boards were made by using the photo negatives to make screen printing masks and then the resist ink was printed on copper boards and the boards etched. Only the resist step was different.

Some boards were drawn in pen-and-ink directly instead of drafting tape, but it was exceedingly rare and only for trivially simple boards. It was just too difficult to erase mistakes in drafting ink.

Long-run boards had photo-litho-negative shot onto glass plates, as glass is more stable than mylar. The working at 2x, 4x, or even 8x size let manual processes produce quality results when it was photo-reduced, reducing any placement inaccuracies by the same amount as the overall photo reduction

Drilling was done manually by people drilling out the centers of pads for simple boards. Later drilling was done with a drill microscope, and even later by CNC. The CNC machines then needed an Excellon-format drill tape - at the time, really a paper tape produced by a TTY machine you typed on. The coordinates were done by manually siting a crosshairs on the pads in a digitizer machine.

[Rodgre]

I guess I'm old as well. I took electronics in high school and that's how I learned to design PC Boards: draw it on paper, enlarge it 2X or 4X, and then cut it into Rubylith peel-away plastic film (which is also how I used to make masks for screen-printing), make a negative at the correct size reduction, and then use it as a photographic mask on pre-sensitized copper-clad board.

This was back in the mid-80s.

Roger

[Wild Zebra]

alright thanks for all the great info so far!!

[Mark Hammer]

Uh-huh.

This is also why, when you flip through old issues of Popular Electronics, Radio Electronics, et al., you will often see PCB layouts printed at half scale.  The tacit assumption was that you'd photograph them and enlarge them.

[SonicVI]

Funny you use the EGO boost as the example. It didn't have a pcb

[theehman]

Funny you use the EGO boost as the example. It didn't have a pcb

I wouldn't be surprised if it had a PCB.  Seems like I recall seeing some later boosters w/ PCBs.

[Mark Hammer]

The earliest EH units in those little teeny boxes that had a hard-wired phone plug sticking out the side were essentially terminal-less point-to-point on the inside.  Once EH made the switch to larger boxes, that sort of arrangement became untenable since no component leads could reach that far.

[SonicVI]

Funny you use the EGO boost as the example. It didn't have a pcb

I wouldn't be surprised if it had a PCB.  Seems like I recall seeing some later boosters w/ PCBs.

Even in the little boxes?  Hard to imagine one would fit, or at least a pcb made by EH

[Wild Zebra]

  I haven't seen it myself but it is an early one with plug attached ala dan armstrong, but my friend said it looked like a pcb and the underside had what looked like if you could draw solder on a piece of printed circuit material.  Curved lines not nicely laid out angles.  I'll have to take a pic next time.  He got an NOCS big muff, ego boost, screaming bird and a mic thingy.  He works in guitar restoration and they came as a trade.

[theehman]

The earliest EH units in those little teeny boxes that had a hard-wired phone plug sticking out the side were essentially terminal-less point-to-point on the inside.  Once EH made the switch to larger boxes, that sort of arrangement became untenable since no component leads could reach that far.

Are you sure about that, Mark?



Mid 70's Screaming Tree.  Yeah, crappy pic.  I need a better digital camera.
I'm checking to see if I have a booster w/ a PCB.

[theehman]

Funny you use the EGO boost as the example. It didn't have a pcb

I wouldn't be surprised if it had a PCB.  Seems like I recall seeing some later boosters w/ PCBs.

Even in the little boxes?  Hard to imagine one would fit, or at least a pcb made by EH

Ta-da!!!  Late 70's Muff Fuzz with a PCB:

[Mark Hammer]

Your reputation as all-knowing EH authority stands unchallenged, my friend!

I believe the proper response to both pictures is "Well, I'll be!"  On the other hand, the catch-as-catch-can nature of E-H in the earliest years leaves me a little unsurprised.  Still, how anyone  could think that the construction technique in that EGO boost would be sustainable for anything more complicated than that....

I've also tried sticking a board into the small box chassis that my old Muff Fuzz used to be in and it was tough slogging let me tell you (many of the "spider web circuit" parts are still around but the circuit in there now is a MosFET booster, and the onboard phone plug replaced with a jack).

[theehman]

Do I get a Guild Tri-Oct as a prize?

[Mark Hammer]

You most certainly will once the Canadian dollar drops again.

[SonicVI]

Funny you use the EGO boost as the example. It didn't have a pcb

I wouldn't be surprised if it had a PCB.  Seems like I recall seeing some later boosters w/ PCBs.

Even in the little boxes?  Hard to imagine one would fit, or at least a pcb made by EH

Ta-da!!!  Late 70's Muff Fuzz with a PCB:



Cool!

[Wild Zebra]

I talked to him last night it does not have a PCB another one he pulled open did.  Thanks y'all thanks for the pics and info