From: email@example.com (Bob Wilson)
Subject: Re: Etching!
Date: Fri, 25 Oct 2002 04:07:28 -0000
Organization: Your Organization
X-Newsreader: WinVN 0.99.9 (Released Version) (x86 32bit)
References: <3DB0977E.747EAFBB@earthlink.net> <3DB7523D.BC943100@rica.net>
In article ,
>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?
As I explained in a parallel post, positive resists have so many advantages,
and negative resists are so much less easy to work with (espeically the
aromatic solvent developers used) that although they were the first ones
used (e.g. Kodak's KPR, KPR2, KPR3, KOR, etc), they have been totally
supplanted by either positive resists (with their much better aquious
developers), ir photosensitive resist film (such as DuPont's Riston). Kodak
sold the line years ago and got out of the business.