Homebrew PCBs

On 8/07/2013 1:06 a.m., Duane C. Johnson wrote:
>
> Leon Heller 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 teaspoons per litre.
>
> > Leon
> > Leon Heller
> > G1HSM
>
> I agree, the bath must be alkaline and a common
> and convenient alkaline bath is "Sodium Hydroxide".
> I get mine at the local hardware store where
> plumbers use it as a drain cleaner.
>

The stuff sold as developer by the chinese supplier is anhydrous sodium 
carbonate (washing soda). The solution I'm using is 20g/L which is the 
strength recommended by the supplier. I really should use a stronger 
solution since the washing soda available in the supermarket is not 
anhydrous i.e. it has some water in the crystal Na2CO3.5H2O rather than 
Na2CO3.

> Note! This stuff has no shelf life. And the plastic container
> doesn't deteriorate, unlike the metal Lewis Lye did.
>
> Another use is to clean out cast iron solder pots.
> Especially when switching to ROHS lead free solders.
>
> However, it is used in some "Illicit drug manufacturing" and my
> hardware guy says it probably will go on the drug "precursor"
> list shortly which will make it harder to get.
> Stock up now, actually it is pretty cheap anyway.
>
> Just saying!!!
>
> Duane
>
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