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.
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, 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
>