Homebrew PCBs

On 8/07/2013 2:12 p.m., tda7000 wrote:
>
> Washing Soda does work, I have been using it since Day 1 with the 
> photo-resist process as it was the cheapest and easiest for me to get. 
> (And with the blue Chinese resist from eBay, too!)
>
> If you have problems with resist staying on between traces, check your 
> mask is dark enough, and you have your printed side right up against 
> the resist etc.
>

Ah right on. Careful examination of the negative show mottling in the 
black (I'm using artist's tracing paper in a Kyocera FX720 laser but 
I've also tried over-head projector transparency film). The mottling 
corresponds to the unexposed(?) resist left behind. I guess my next 
question is how do you get really black black on transparent film using 
a laser?

>
> It sounds like your LEDs are quite powerful - mine with LEDs takes 
> about 6 minutes - perhaps this is causing an overexposure problem?
>
> I usually take the board out of the solution and rub it with my 
> finger\soft toothbrush to speed things up too
>
> --- In Homebrew_PCBs@yahoogroups.com 
> <mailto:Homebrew_PCBs%40yahoogroups.com>, Leon Heller <leon355@...> wrote:
> >
> > On 07/07/2013 12:31, Kerry Koppert wrote:
> > > I am trying to produce a small PCB for a SMD pic16f628a-i/so using
> > > chinese blue dry film photoresist. The exposure seems to work fine 
> using
> > > a bank of uv leds and the photoresist turns a nice darkish blue around
> > > 30-45 secs of exposure. I am trying to develop using washing soda (I
> > > forget the exact strength but I think it was 200g in litre of 
> water). I
> > > am having difficulty getting this process right. Either some of the
> > > unexposed photoresist does not come off (particularly between close
> > > tracks) or some of the exposed photoresist lifts if I leave it longer.
> > > Anyone having experience with this process willing to comment on 
> what I
> > > may be missing.
> >
> >
> > I don't think that washing soda (sodium carbonate) will work, you 
> sodium
> > hydroxide. That's what I use - 2 teaspooons per litre.
> >
> > Leon
> > --
> > Leon Heller
> > G1HSM
> >
>
> 



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