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Subject: Re: Etching!
Date: 23 Oct 2002 14:04:32 -0700
NNTP-Posting-Date: 23 Oct 2002 21:04:32 GMT
email@example.com (Bob Wilson) wrote in message news:...
> In article <3DB0977E.747EAFBB@earthlink.net>, firstname.lastname@example.org
> >"Märt Pikkani" wrote:
> >> Hi.
> >> I don't know if this is rihgt newsgroup to get my answer but i will try.
> >> not, then could anyone recomend me a newsgroup from where i could get
> >> answer.
> >> Here is what i did.
> >> I printed out my PCB on to a tranparency. Then used money detector as UV
> >> light an got tracks onto board. With NaOH (developer fluid) the tracks
> >> became clear and visible.
> >> Then used Fe3Cl to etch the Cu around the tracks.
> >> tracks are still with clear and visible but Problem is that Cu around the
> >> tracks changes its color( like Pink) but doesn't leave the PCB clear.
> >> Meaning that all the plate is still covered with Cu but little Cu has
> >> the PCB. I could feel the edge of the track with my finger.
> >> What is my problem?
> >> is it money detector (UV ligth), which I don't believe.
> >> Do I do something wrong?
> >> Is it problem of etching bouder?
> >> Märt Pikkani
> > You may have ruined the FeCl with the base; (1) do not use any base
> >for "developer".
> > The etching solution (a) did not work long enough, or (b) was "killed"
> >by the NaOH; you may have seen a "scum" on the surface, one indication
> >of the second possibility.
> > Add a very slight amount of acid (HNO3 is best, but use sparingly) to
> >prevent the FeCl from "turning".
> > FeCL etches perferentially on the Cu crystals, so the copper *will*
> >turn from bright copper to dull red (allowing you to "see" the traces);
> >ammonium perchlorate etches uniformly and the copper may seem to get
> >cleaner as it works.
> Ammonium Persulphate was abandoned in the PCB industry tens of years ago,
> because it creates excessive undercut, and holds relatively little copper in
> solution before it is spent. Ferric chloride is also never used in industry,
> but remains a useful hobbyist etchant.
> Small amounts of NaOH will NOT harm the ferric chloride in any way. It is
> typical to add an acid to ferric chloride to reduce ferrous hydroxide
> formation (the brown insoluable crud that forms upon oxidation), but nitric
> acid (HNO3) is NEVER used. What is used, is ordinary hydrochloric acid which
> is available at many hardware stores for use in cleaning bricks, and is
> often called "Muriatic Acid".
> Positive-working photoresists generally do not leave the sort of nearly
> invisible residue as negative resists (such as the old KPR series) tend to
> do (which causes spotty etching). Insufficient exposure of a positive resist
> can result in a thin layer of resist remaining where non is wanted. Increase
> your exposure times by 50% and try again. The problem may also be that the
> etchant is dead. Try a new batch of ferric chloride, and heat it to 50 or 60
I am new to etching. Got a few questions...What does shining UV light
through a transparency (containing a circuit diagram) do to the PCB?
It is to my understanding that the lines on the transparency will
block out the UV light and prevent the light from contacting the
copper (thereby forming lines), but what about the rest of the copper
that is exposed? Is there a chemical reaction?
If there is a chemical reaction, what is the purpose of using NaOH?
Does it adhere to the shadowed lines on the circuit board, thereby
protecting those lines from reaction to the acid applied onto the PCB
in the proceding step?
Or...is the tranparency somehow glued to the PCB, irradiated with UV,
then NaOH applied to it to remove the transparency??
Is the use of HCl the industry standard for etching purposes?
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