Homebrew PCBs

----- Original Message ----- 
From: "lcdpublishing" <lcdpublishing@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Saturday, October 25, 2008 1:21 AM
Subject: [Homebrew_PCBs] Dry film, photo resist - progress and question...


> Hi guys,
>
> I got a chance to do some more experimenting with the dry film photo
> process.  I did a "step" test doing various exposure times and found
> out that the UV lamp I bought for this purpose simply isn't powerful
> enough.  I have a regular light bulb of the right color range and
> tried that with much better results - exposure time through
> transparncy of only 3 minutes.  I have much more experimenting to do
> to get it better, but was able to make my first board all the way
> through the etching process.
>
> A couple of questions...
>
> 1) When I used to have a black and white dark room, I discovered
> that the developer would last a long time and could be reused over
> and over again.  I realize the developer for negative resist film is
> much different than photographic developer, but suspect that the
> chemical will stay "active" and as such, I could be reusing it.  Has
> anyone tried this?

NaOH developer can be reused many times. NaCO3 is probably similar, as it 
forms a weak solution of NaOH which actually does the development..

>
> 2) While doing the exposure / developer tests, I realized very
> quickly just how tough this resist is.  I was scrubbing with a
> scotch brite pad vigorously without removing the resist. This leads
> me to the next question. Should the resist be removed or can it be
> left on the copper?  If you have to remove it, how do you do it?

It can be soldered through, but it's best to remove it. Iso-propyl alcohol 
works very well for positive resist - I rub it with a moistened paper towel. 
It probably works for negative resist, as well.

Leon