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.
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
--
Home of the $35 Solar Tracker Receiver
http://www.redrok.com/led3xassm.htm [∗]
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