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From: John Popelish
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X-Mailer: Mozilla 4.7 [en] (Win98; U)
Subject: Re: Etching!
Date: Thu, 24 Oct 2002 01:51:57 GMT
NNTP-Posting-Date: Wed, 23 Oct 2002 21:51:57 EDT
> 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??
> Please help!
> Is the use of HCl the industry standard for etching purposes?
I buy presenstized boards that are coated with a positive resist.
This is a blue polymer coating that looses its resistance to
dissolving in NaOH when it is exposed to UV. After the exposure and
removal of the parts that had covered copper I intend ot remove, I
etch the board in ferric chloride solution. This leaves copper hiding
under the unexposed resist film, and removes any unprotected copper.
Then I drill and solder the board.
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