Subject: Re: Etching!
References: <3DB0977E.747EAFBB@earthlink.net> <3DB7523D.BC943100@rica.net>
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Date: Thu, 24 Oct 2002 17:44:50 GMT
NNTP-Posting-Date: Thu, 24 Oct 2002 10:44:50 PDT
Organization: EarthLink Inc. -- http://www.EarthLink.net
On Thu, 24 Oct 2002 01:51:57 GMT, John Popelish
>> 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.
Do they still use a negative images to make PCBs?