[sdiy] Two more questions

[René Schmitz]

At 19:51 06.08.02 +0000, sbernardi at attbi.com wrote:

>I use the photo-etch process. Print the pattern on 
>transparency with a laser printer with fresh toner (con: 
>sometimes I still need to touch it up with a marker). I 
>buy presensitized PCB's from Circuit Specialists 
>http://www.web-tronics.com/, which I expose with a 
>flourescent light for about 10 minutes a side.  I etch 
>them in a etchant tank with Ammonium Persulfate (both of 
>which I also got from Circuit Specialists). 

I've done a number of PCBs that way. For getting a good exposure of the
PCBs a bit of experimentation needs to be done. I use a 1000W photolamp
(its a halogen lamp, so the glass doesn't filter UV). A simple way to
determine the right time for your light source / photo-lacquer / developer
combination is to cover a partof the layout with some cardboard, and
incrementally uncover half an inch every 30seconds or so, then develop
that, and see which exposure time gave the best results. You only need to
do that for the first time. After that and some more PCBs you'll have a
good feeling how long to expose.

Cheers,
 René
-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159