@drewfitz yeah, this design here is a two-layer one!
I'm not sure how you do that. I guess you just expose it twice, once on each side, and then do the etch step once?
The way this works: You have a blank PCB coated in a thin copper layer, and it's coated in a photoresist material. This material breaks down when exposed to light.
You then shine a bright (usually UV) light at it for a while, and the spots which got hit by light break down, while the other parts (which were in shadow) remain on the board.
You then use a corrosive chemical to etch away the copper layer, but it only etches away the parts that aren't covered in photoresist.
Normally you'd do this by printing or photocopying onto transparent paper, but I think they're saying you can just turn up your brightness/wait longer and blast the light straight through the paper.
And of course on one of the following pages, they had ads from companies who were happy to sell you the chemicals and equipment needed to make circuits this way.
The cool thing about this kind of photoresist PCB etching that may seem surprising if you know how circuit boards are designed today... you could totally do this without a computer.
Fundamentally you just need to come up with a photomask: that's some dark black ink on a transparency. You could use stencils and stickers and markers to make that, then turn it into a PCB. The only electronics you need is a bright light.
it's just neat to think that today PCB design is "you use this complicated program on a computer then send some files to a place that mails you back a bunch of PCBs", when 30 years ago it would be more "you carefully do some arts & crafts with stickers and then some chemical processes"
@foone that's still how most people do it though, usually you just send off for a more cleanly/professionally made one later. You can go to any microcenter and still buy coated PCBs and copper etchent. I always preferred the "iron on" process to the photoresist process though as it's a lot cheaper than buying the photoresist coated boards. (glossy paper, laser printer, toner transfer to the copper coated board with heat, then dip).
I just mill test boards now though, way easier/cheaper.
@vxo Did you ever see my Copy Pro Control board? I still made it in Kicad so I couldn't get to weird with it, but I did attempt to get as Weird as possible given the circumstances.
@foone iirc one of the tricks was to add some sort of clear oil (like baby oil) to stick it to the PCB, which made the white paper go kinda clear.
the actual home etching process is super messy though. ferric chloride stains eeeeeverything, it's bad for your skin, and you have to neutralise it before disposal which also creates a lot of mess. I used to own a kit and used it only a couple of times because the cleanup is horrible.
@foone although you can buy PCB etching tanks where you put the boards in a little carrier thing vertically (helps make the etch a bit more consistent) and some of them come with two separate compartments so you can have one with the ferric chloride and the other with water, and that makes things a lot less messy, since the ferric chloride is far less likely to splash and you're only moving the board a few centimeters to get it into the water tank.
@gsuberland@foone ferric perchloride is so old school and annoying. copper chloride is the way to go. in practice that just means hcl with a pinch of h2o2. when depleted it can be replenished with an air bubbler.
@foone I think I met something like this back in 1989 or 1990. A friend's dad was doing this with his own designs. He found that photocopies or laser prints on acetate weren't dense enough to block the UV properly, so you had to run it through the printer several times to get the ink density to make it work.
@foone He also had problems with drilling the holes in the board, so he was building an X-Y rig for a drill.
We spent a long night with an Acorn A440, me on the front end with the keyboard, him on the back end with the printer port and an oscilloscope, working out how to write a driver for this thing that ran off the !Draw files he'd use for the board designs, and would put the holes in the right place.
Add comment