Homebrew PCBs

>From: "gmc_za" <gmc_za@...>
>Reply-To: Homebrew_PCBs@yahoogroups.com
>To: Homebrew_PCBs@yahoogroups.com
>Subject: [Homebrew_PCBs] Using Photoresist Spray
>Date: Mon, 04 Oct 2004 18:26:37 -0000
>
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>I've started fiddeling around with photoresist spray and developing it
>using caustic soda, and have a few questions as the board is still not
>coming out 100%
>
>
>1) How thick should the photo resist be sprayed on. After I've sprayed
>it on and its dried you can clearly see the purple film - there's no
>gaps.
>
>2) After you put the board in CS - how do you know when to take it
>out? I can see the tracks clearly but the pcb is still have a layer of
>the purple stuff on it. Should the purple film vanish completly
>(except for on the tracks)

All the resist should have disappeared where it was exposed to the UV.

>
>3) Which is a better etchent to use - Ferric Chloride (mine works
>really slowly even when heated up - like 30-40mins) or Hydrochloric
>Acid+Hydrogen Peroxide

Warm ferric chloride etches in less than 10 minutes for me with continuous 
agitation.

>
>I've done another board (etched) and the top half of it is perfect -
>nice clear tracks. But on the bottom half none of it is etched. If I
>leave it in too long it starts to eat away the tracks, but still
>doesnt touch the bottom section? Does this sound like too thick spray?

Make single-sided boards until you get the process right, then try 
double-sided ones.

Leon