Tuesday, December 05, 2006


Salt Water Etching

I just saw this item on Instructables. Step-by-step instructions on how to etch a PCB with salt water and electrolysis.

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Your link is broken and searching Instructables it appears that there are half a dozen PCB printing entries. Could you try to do the link to the one you saw again, please. :-)
Never mind, Steve. I dug the link out of the page source for your post. Here it is.


For some reason the formatting for the link had a misspelling in it. The formatting word href was spelled herf. That's weird since the formatting for links is done automatically.
Wow! He hand drew that circuit board. That's nasty looking. Still, the principle looks sound and it would be nice not to have a big pot of etch solution to get rid of legally.

I wonder, though. If you do it this way you'd get copper chloride, wouldn't you? That's poisonous, too. :-(
I wonder if you could use electrolysis again to recover the copper.
Wait a moment. It may be that the salt isn't getting into the process, in which case the excess copper will be deposited on the anode.
Humm, this is similar to how I used to make hydrogen as a kid. I was a bit more agressive with the voltage though! ;) I'd lately been thinking of revising this to make PCB. I guess the idea works. :)

One thing is that all the traces must be connected to the positive electrode. In other words, there must be no electrically isolated "islands" on the PCB design. That means you have to cut all those links in the circuit before you can use it. That could be minimized by sending more than one positive electrode into the tank.

Plaas, you might be right, I remember lots of deposits and discoloration...
Another option I've been thinking of testing is using standard etching procedures with Hotglue/Polymer as an etch resist.

As long as everything is calibrated and accurate, you'd just have to print the board, etch, and peel off the glue. (drilling holes either by hand or by reprap dremel mount)
reiyuki, that sounds workable, and quite ingenious too.
If you're going to dremel the holes anyway, could you also mill the copper plating? Not sure how thin the traces could be but it might do the trick for some layouts.
That question has also bothered me more than a little. Using a mounted Dremel with a bur tool would seem an obvious way of creating circuit boards that would avoid the whole nasty issue of chemicals.

I've also thought that PLA, if we can get it to extrude would be a nice substrate for circuit boards since it melts at temperatures considerably higher than that of lead/tin solder.
If I have time this weekend I'll try to pull off a test dremel etch on a simple circuit to see if it all lines up.

The power supply I'm using in my dremel-repstrap is a bit underpowered, so it's sticking every once in a while. If that gets fixed, or I overdrive my steppers, things should be good to go.
Now, if you could come up with a tool that could both cut copper and drill holes, you could do an entire board without human intervention. Something like a spiral cutting bit, possibly? Running the tip across the surface would remove copper plating. Pushing it into the board would drill a hole, the diameter of which could be controlled by making circular cuts.
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