Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Why not try etching with a sulfuric acid and hydrogen peroxide
mixture? We used this for years in a commercial shop with excellent
results. The solution makeup is easy, 15% technical grade sulfuric
acid, 10% hyrogen peroxide (35% grade), 75% water. This solution can
be heated to 100 to 120 degrees F. and it's ready to use.

One way to remove copper is to plate it out. This is called
"electrowinning". Use lead plates for anodes and stainless steel
sheets for the cathodes. The plated copper will peel off the
stainless sheet if the edges are masked off with plating tape. The
tape keeps copper from plating around the edges of the stainless
sheet. After plating just flex the sheet and the copper peels off.

My electrowinning tank had three lead sheets as anodes with two
stainless steel sheets in between as cathodes. A 500 amp rectifier
was used with the positive connection to the lead plates and negative
connection to the stainless steel plates. A much smaller system could
be made for hobby use.

We transferred the solution to this tank on Friday afternoons and let
it plate all weekend. On Monday we transferred the plated out
solution back to the etching tank and started over. When using this
method only the hydrogen peroxide had to be replenished to bring the
etching rate up to speed.

This seemed like a lot of work so after a while we went back to
simply cooling off the working solution and letting the copper fall
out. Copper will drop out as copper sulfate crystals when the
solution is cooled to around 60 degrees F.

We sold these crystals to a chemical recycler and never once
generated any waste from this process. The same working solution was
used for over seven years without replacement and etched many
thousands of square feet of boards.

All tanks, racks and hardware can be made of stainless steel, PVC,
polyethylene or polypropylene plastic. Don't use nylon or delrin as
they fall apart after a short time.

I made all of our tanks from PVC plastic using a hot air plastic
welding torch. My torch was made by Seelye Electric Company and was
expensive but I see a direct copy of this torch being sold by Harbor
freight for around $40. You also need a very small air compressor.
The welding pressure used is around 2 psi or less. Air is used for
PVC but nitrogen must be used for most other plastics.

Analysis is by titration, however, in all the years we ran this
process we never once analyzed the working solution. After dropping
out copper sulfate crystals we just added some sulfuric acid and
hydrogen peroxide until the etch rate was correct. We used a scrap
piece of laminate and timed the etch rate. It was real easy to run
this etching system with minimal problems.

For a hobby system I would just use a plastic bucket and glass
aquarium heater. When the solution is saturated the copper sulfate
crystals will drop out and can be collected for resale or used as
make up salts for a copper electroplating tank etc.

Tom