Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, Markus Zingg <m.zingg@n...> 
wrote:
> Hi folks
> 
> I'm still testing with water - the voltage regulator still get's too
> hot with low PCB motion speeds. Anyways, I created a little MPEG 
movie
> of the station in action for those interested. You find it on the
> bottom of the entry page.
> 
> http://www.myhome.ch/mzingg/pcbstuff/tps/
> 
> It's farily late now here again. I was busy all day with cleaning up
> my office to make room for the station et all. Then we also had
> guests. I studied the docs of the chemicals I got and - some one 
asked
> this - found info about the material the bag's around the anodes
> consist of. They are made of a polyprophylene tissue.

Markus,

That's an impressive tank system you made. I'm also interested in the 
chemistry you will be using. Please provide more information when you 
have time.

Many years ago I made a tank system for through hole plating in a 
commercial shop. This system had six tanks that were 25 gallons each.
Maybe this information will help those considering this method of 
processing.

Here is the process and details on that tank system:

Tank #1  Cleaner-conditioner, caustic soda based chemistry with 
surfactants. Stainless steel tank. 160 degree F operating 
temperature. 5 minute process time.

Rinse cycle
 
Tank #2  Micro-etch,  surfuric peroxide based. PVC tank operating at 
room temperature. 1 to 2 minutes.

Rinse cycle

Tank #3  Pre-dip,  proprietary chemistry. PVC tank operating at room 
temperature. 30 seconds to 1 minute dip. NO RINSE AFTER THIS STEP!!

Tank #4  Catalyst, proprietary activated palladium chemistry. PVC 
tank operating at 105 degrees F. 20 minute process time.

Rinse cycle

Tank #5  Accelerator, highly saturated solution of soda ash with 
about .5 gallons of copper sulfate solution added. It takes about 50 
to 60 pounds of soda ash to make up this 25 gallon bath. Stainless 
steel tank operating at 140 degees F. 10 minute process time.

Rinse cycle

Tank #6  Acid dip,  10% sulfuric acid solution. PVC tank operating at 
room temperature. 5 minute process time.

Rinse and dry.

The printed circuit panels are now conductive through the holes and 
across all exposed edges. An ohm meter connected across both copper 
planes will show 10 or less ohms depending on the number of holes.
The panels are now ready for electrolytic plating.

This system used the newer activated palladium chemistry with no need 
for electroless copper. Electroless copper is very difficult to run 
and needs constant attention. The palladium chemistry is a better 
choice for systems that are not run on a daily basis. Electroless 
copper is one of the major sources of pollution in a circuit board 
plant. You're better off if you never get near it.

Some thoughts about rinsing,  in our first system (using electroless 
copper)we had a 25 gallon flowing tank for each rinse cycle. Our 
small shop used over 7000 gallons of water per day with this rinse 
setup. This entire flow had to be waste treated which was a GIGANTIC 
headache. 

When I built the palladium based system we used a spray wand to rinse 
for about one minute into a trough that collected the spray water. 
Then the panels were dipped into a 25 gallon rinse tank that flowed 
about 2 gallons per hour after which the panels went on to the next 
process tank. The idea was to use a small amount of water as a spray 
to do 99% of the rinsing and then a quick dip into a slow flowing 
rinse tank caught anything else. Very efficient rinsing with very 
little water.

All of this rinse water was collected into a common holding tank that 
was fed into an evaporator system that boiled off the water at a rate 
of about 30 gallons per hour. We ran the evaporator tank several 
hours per day and had a ZERO DISCHARGE system with no connection to 
the sewer drain. Our only discharge was clean water vapor and we were 
able to reduce our water consumption to about 75 gallons per day. The 
savings were tremendous and it satisfied the environmental 
authorities as well.


Tom