Homebrew PCBs

Greetings!

I have a question for everyone concerning the "wet method" of printed circuit boards. I was wondering what other types of etchants are available besides your basic ferric chloride, and sodium persulphate? I remember a while ago someone mentioned the use of sodium persulphate catalyzed with either hydrochloric acid or sulfuric acid. What does this mean and how can I do it? Basically I think it would be very interesting to experiment with high speed etching methods! 

Thanks!

-Randy Knutson



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Randy:

I'm no chemist, and I use Ferric Chloride, but I THINK the "other stuff" is 
AMMONIUM persulfate!  BUT...  For all I know, perhaps sodium- or 
potassium-persulfate would work, too.  I just do NOT know.

I bought some ammonium persulfate solids from Kepro about 20 years ago, and, 
either I didn't read all the instructions well, or "goofed", somehow, as it 
didn't work very well, at all.  (I only tried it once).  Then, not knowing 
it, the Ammonium persulfate is deliquescent, and it's HUMID here, so, the 
solids turned "gooey" all alone, THROUGH the plastic container they came in, 
and that ate THROUGH the plastic container, the bottom of my cabinet, onto a 
carpet, and, well...  I guess the Chinese are wondering what kind of 
kidney-trouble the American living below them has!  

And, though FeCl³ has a nasty staining color, it takes much less "Husbandry" 
to use with relative ease.  Which is too bad, as the former A-S stuff was 
CLEAR, if caustic!

Adding stuff "for speed" will get you in trouble, as that means HEAT, and 
heat will mess up the edges of even the BEST resist-patterns!  

Once, I was amazed to learn that, in professional etching, the holes are 
drilled FIRST, and then plating-through, if any, and then etching.  Logical, 
but I had never thought about it until I had reason to get a few boards done 
by a "professional PCB house".  The hole-pattern makes locating the 
negatives, if you are using photo-etch method, much more accurate, of course, 
and my "old idea" of using the etched pattern also as the "drilling pattern" 
was silly in several respects.  One learns as he ferments...  Uh, "ages"...

Randy,

You could also try using hydrogen peroxide and sulfuric acid as an 
etchant. The mixture is 10% hydrogen peroxide (35% grade) and 15% 
sulfuric acid (technical grade) with the balance made up of water. 
This mixture will heat up and be ready for use upon make up. You can 
replenish the etchant with small additions of peroxide when the etch 
time is too long. When the bath is saturated with copper let it cool 
down for a day or so and copper sulfate crystals will precipitate to 
the tank bottom. Scoop out the crystals, replenish the acid and 
peroxide and you can start etching again after heating the solution 
to 100-120 degrees F.

You will need a good ventilation system or do this outdoors since 
there will be some fumes produced. Also, the peroxide breaks down 
into water and most of this will leave the tank as vapor which is why 
you need the vent system. If solution growth becomes a problem, just 
turn up the heat for a while and the water will evaporate bringing 
the solution volume back down to normal.

The same solution can be used for many years without having to dump 
it. I used this method in a commercial shop and didn't change the 
solution for seven years. We processed many thousands of square feet 
through this tank and sold all of the copper sulfate crystals to a 
recycler for cash. If you are going to do lots of etching this is a 
good way to get the job done with a minimal investment.

Tom