Homebrew PCBs

----- Original Message ----- 
From: "patroclus04" <patroclus04@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Sunday, February 19, 2006 10:35 AM
Subject: [Homebrew_PCBs] Re: Photolithography


>
> Hi, thanks for your reply.
> I'm not sure if I understud. Should I use both a UV light tube and a
> fluorescent tube?

No, two UV tubes.

>
> Also, I would need developer, and I think that is.

Sodium hydroxide, about 12g/L. Two teaspoons is about right.


> After printing in trasparent paper, I need to fix it to the board in a
> dark room (using tape maybe?) and then put it into the light box for 5
> or 10 minutes.

You don't need a darkroom. I just put the transparency in contact with the 
board (print side down), make sure it is positioned correctly, and put the 
board and transparency on the glass. I then put a heavy book on top of the 
board to ensure it is pressed down. You have to experiment to get the 
correct exposure, it mainly depends on the distance from the lamps. I use 13 
minutes.

>
> Then go out, put it in developer a few minutes more, and then ferric
> clorhidre.

That's right. The unexposed resist goes purple in the developer so you can 
take it out and rinse it when all the purple has gone.

>
> More or less, is that it?

Yes


> Developer liquid can be stored and reused many times?

It can last a long time. As it's very cheap, I use fresh each time.

Once you get the process right, it's completely repeatable and gives 
excellent results. I don't have much trouble with 8 mil tracks and 0.5 mm 
lead spacing ICs.

Leon
--
Leon Heller, G1HSM
leon.heller@...
http://www.geocities.com/leon_heller 

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