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From: email@example.com (Bob Wilson)
Subject: Re: Etching!
Date: Sun, 20 Oct 2002 05:21:21 -0000
Organization: Your Organization
X-Newsreader: WinVN 0.99.9 (Released Version) (x86 32bit)
In article <3DB0977E.747EAFBB@earthlink.net>, firstname.lastname@example.org
>"Märt Pikkani" wrote:
>> 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
>> 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
> 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
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