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Re: [Homebrew_PCBs] electroetch experiments => problem

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  • Adam Seychell
    ... Sounds like electrocleaning to me. Are there gas bubbles forming on the PCB copper surface when current is flowing ? If so then it could be one or more of;
    Message 1 of 6 , Jul 2, 2005
      mihai_hagianu wrote:
      >
      > 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. I have tryed toner, different
      > paints i've found here in the house(few oil based,acrilic,enamel), and
      > even sticky tape( :) ).I have also tryed different acid for
      > electrolite ( H2S04, HCl, acetic)in different concentrations, to see
      > any improuvement, but the result is the same:
      > -if I put the board, with the selected stencil in the acid,without
      > power connected to it, it lasts ok,
      >
      > - if I apply electricity to it, to start electroetching, it works ok
      > for a while, but after some time, the stencils are peeled off, for a
      > reson i do not undestand nor can prevent yet.
      >
      > - I have tryed to electroplate the board, to check if the peeling
      > happens, and of course it does not.
      >
      > - I have tryed different current densities, but the peeling still
      > happends...some times sooner, sometimes later.
      >
      > any ideeas what am I doing wrong ?
      >
      > thanx,
      > Mihai
      >
      >
      >

      Sounds like electrocleaning to me. Are there gas bubbles forming on the
      PCB copper surface when current is flowing ?

      If so then it could be one or more of;
      * Too high current density
      * low ionic concentration
      * missing ions that form soluble copper salts.

      H2SO4 is the stuff to use. The sulfate ion won't gas (unlike chloride
      ion in HCl). The copper must go into solution so it needs a soluble
      counter ion, and sulphate from H2SO4 is perfect for the job. your
      cathode (negative terminal) can be any piece of copper. If you want to
      reclaim the copper then the cathode should be a flat sheet with high
      surface area to keep current density to minimum. Keep PCB current
      density < 20mA/cm^2 and agitate with air bubbles for cleaner dissolution
      of the copper. This will need some experimenting, but start with 150g/L
      H2SO4 acid (1/2 strength car battery acid).

      Gas bubbles are used to advantage in electrocleaning as they scrub the
      surface and lift off any foreign material stuck to the surface. Usually
      done in alkaline solution so the metal to be cleaned cannot dissolve.
    • Earl T. Hackett, Jr.
      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%
      Message 2 of 6 , Jul 2, 2005
        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.

        [Non-text portions of this message have been removed]
      • Adam Seychell
        ... I ve never tried electroetching, but I m curious what the etch uniformity is like for a simple (homebrew style) electroetching setup ? With a conventional
        Message 3 of 6 , Jul 3, 2005
          Earl T. Hackett, Jr. wrote:
          >
          > 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.



          I've never tried electroetching, but I'm curious what the etch
          uniformity is like for a simple (homebrew style) electroetching setup ?
          With a conventional vertical bubble chemical etching tank, I found etch
          uniformity is the most serious factor effecting the minimum trace
          widths. For example, if one area of the PCB is etching twice as fast as
          another area (not uncommon in my experience) then the area with high
          etch rate is over etched by a factor of 2. Fine traces will become too
          thin. This gets worse for thicker copper foils.

          Obviously one still needs to keep his/her chemical etching tank, for the
          final removal of copper, but it should be a 2 minute job.

          Adam
        • James Newton
          ... setup ? This idea has been sticking in my mind as well.. The lack of lateral forces (I assume) makes it attractive for low cost CNC. As to the uniformity,
          Message 4 of 6 , Jul 4, 2005
            --- In Homebrew_PCBs@yahoogroups.com, Adam Seychell <a_seychell@y...>
            wrote:
            > I've never tried electroetching, but I'm curious what the etch
            > uniformity is like for a simple (homebrew style) electroetching
            setup ?

            This idea has been sticking in my mind as well.. The lack of lateral
            forces (I assume) makes it attractive for low cost CNC.

            As to the uniformity, it pops into my mind that low voltage, high
            amperage would result in a very short, but powerful spark which would
            only remove the copper very close to the electrode. A higher voltage
            spark would jump farther and potentially vary more. That is not based
            in experience, but just an educated guess.

            I'm trying to hint for a small welder to show up under the christmas
            tree at the end of the year, but I wonder what I could experiment
            with
            before that on a very limited buget. Any suggestions? Old car
            battery?
            I could use a car battery charger... Wonder if I could kill my
            alternator by playing about with the jumper cables? <GRIN>
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