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Re: [Homebrew_PCBs] Re: Etching woes: Press-n-Peel, Laminator, Etch Tank + Sodium Persulphate

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  • William Whyte
    (excess quoting trimmed by moderator - please trim!) Todd,  What are your ratios, particuly the sodium chloride(salt) ?
    Message 1 of 8 , Feb 20, 2013
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      (excess quoting trimmed by moderator - please trim!)
      Todd,  What are your ratios, particuly the sodium chloride(salt) ?
                                                     Ollie       k0lqk

      --- On Tue, 2/19/13, Todd F. Carney <k7tfc@...> wrote:

      From: Todd F. Carney <k7tfc@...>
      Subject: Re: [Homebrew_PCBs] Re: Etching woes: Press-n-Peel, Laminator, Etch Tank + Sodium Persulphate
      To: Homebrew_PCBs@yahoogroups.com
      Date: Tuesday, February 19, 2013, 11:21 PM

      Either ammonium persulfate or sodium persulfate is used by commercial pcb
      manufacturers. They do not use ferric chloride, not for decades. Only
      hobbyists use the stuff. I'm using a peroxide-muriatic acid-sodium chloride
      etchant. It's very cheap, and the chemicals are available either in a drug
      store or at places such as Home Depot (for the acid). I use it "one-shot."
      I use just enough to do the board I'm etching and then toss it away. It's
      that cheap. This way, It works the same way--etch times, etc.--every time I
      use it.

      73,

      Todd
      ------------------------------------------------------------------------------------
      K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
      ------------------------------------------------------------------------------------
      QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design

      (snip excess by moderator - please trim!)
    • Todd F. Carney
      ... Todd, What are your ratios, particuly the sodium chloride(salt) ? Ollie, I m actually no longer using the salt additive, just the muriatic (hydrochloric)
      Message 2 of 8 , Feb 20, 2013
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        On Wed, Feb 20, 2013 at 4:08 AM, William Whyte <olliewhy@...> wrote:

        > **
        >
        >
        Todd, What are your ratios, particuly the sodium chloride(salt) ?

        Ollie,

        I'm actually no longer using the salt additive, just the muriatic
        (hydrochloric) acid and peroxide. I wish I could find my link, but I think
        my original source used salt as a means of getting more chloride ions into
        depleted etchant without adding more acid. I tried it a few times when I
        was reusing the etchant and it did seem to shorten long etch times. Now
        that I use the etchant one-shot---a small amount that is then discarded---I
        don't need to refresh used etchant.

        My formula for the one-shot version is the typical 1 part ≈35% muriatic
        (hydrochloric) to 2 parts 3% hydrogen peroxide (the drug-store variety). I
        warm it a bit to ≈100°F (38°C), but since I use only about 6oz (170ml) of
        solution in a tray, it cools down fairly quickly. I use the foam trays that
        meat comes packaged with.

        I learned the one-shot method as an industrial photographer. Not reusing
        film (and paper) developer, but using small amounts one-shot, allowed for
        precise control that cannot really be had with reuse/replenishment schemes.
        Precise repeatability is possible with one-shot. It's not with reuse.

        Much of the need for repeatability, in my mind, is that we DIYers use some
        pretty dubious methods of applying etchant resist to our boards--toner
        transfer being the most common, it seems--I use it myself. This means using
        materials that are not optimum for the purpose and applying them with
        make-shift methods: cloths irons, etc. Combined with less-than-thorough
        surface preparation of the copper clad, all this means our resist patterns
        are fragile and cannot withstand long etch times with repeatable results.
        It's not just that the resists are probably not-all-that chemically
        resistant, but that their mechanical bond with the copper is weak and
        uneven. Flaking of the resist, or undercutting of it in long etch times, is
        an ongoing problem for many of us. Fast etch times and
        repeatably-predictable results can minimize these problems. Both point to
        one-shot etching.

        Now in my online poking around in the last few days on these issues, I am
        now persuaded that I need to be much-more careful in the disposal of my
        etchant--especially since I'm tossing out several ounces at a time for each
        board. To be perfectly honest, I used to just dump the stuff down the drain
        with plenty of running water. Bad news! So what I'm going to try is to dump
        it into a five-gallon bucket filled about 3/4 full of wood shavings. I have
        a whole bale of the stuff left from when we had hamsters (a rant for
        another occasion). Saw dust or even shredded paper might work just as well.
        I'll dump the spent etchant into the bucket, maybe stir the shavings around
        a bit (maybe not), and then keep the bucket open and outside (not
        inside!!!) but out of the rain. Before long, each dumping will dry in the
        bucket, sequestered (oh that word!) in the wood or paper fibers. I guess I
        should put a warning sign on the bucket. At some point I'll have to
        double-bag the shavings before tossing them in the land-fill garbage, but
        as I'm thinking now it might take many years before that will be necessary.
        It may never be necessary in my lifetime, so I'll have to leave disposal
        instructions in my will (wink wink).

        Best,

        Todd
        ------------------------------------------------------------------------------------
        K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
        ------------------------------------------------------------------------------------
        QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design


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