You have to watch the voltage and the solution conductivity and chemical makeup.
The solution should be sulfuric acid at a concentration somewhere around 10% with some copper sulfate dissolved in it. You want the acid to be as dissociated (broken up into ions) as possible. The conductivity of the solution must be as low as possible to allow maximum current. The cathode should be stainless steel, the board is the anode - just the reverse of a plating bath.
That's the easy part.
Now for the voltage part. When you apply a voltage to the board the system will conduct by shoving an electron into the solution at the cathode where either hydrogen will be released or if present, copper will be plated out. On the board side, an electron will be pulled away from the surface where you hope a copper atom will become an ion and dissolve into the solution. Unfortunately this isn't what happens - if it did the PC industry would long ago have dumped their spray etchers. The first few copper atoms dissolve, but very quickly the solution next to the anode is saturated with copper but the current is still flowing so since no more copper will dossolve, the next source of electrons is hydroxide ions. This releases oxygen which can either be emited as a gas or react with the copper surface to form a coating of copper oxide. Pull an anode out of a copper plating bath and you'll find it is covered with a slimy coating of copper oxide. If the voltage is too high you will have a lot of oxygen gas generated (just like in the high school electrolysis experiment. Gas generation at the edge of the resist will lift the resist and cause the circuit pattern to fail. Drop the voltage/current to the point where gas generation doesn't occur and the reaction will be unacceptably slow.
Many years ago we were trying to find ways to strip photoresist from overplated boards. I stuck a board on the cathode of a plating bath filled with a bit of ammonium chloride. The current generated a caustic solution at the surface of the board and the generation of hydrogen gas proved very effective at mechanically forcing resist out from under the over plate. Unfortunately this created quite an explosion hazard so we never commercialized it, but it demonstrated how effective gas generation is at removing materials from a board's surface.
----- Original Message -----
From: mihai_hagianu
To: Homebrew_PCBs@yahoogroups.com
Sent: Saturday, July 02, 2005 3:33 AM
Subject: [Homebrew_PCBs] electroetch experiments => problem
Hi guys,
i have tryed before, and restarted now to experiment with
electroetching, as an alternative method to FeCl3.
I and up with the same problem all the time. The electric courent is
peeling off any stencils i'm using.
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