Homebrew_PCBs

twb8899 wrote:

> 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
>

7000 gallons (26500 liters) down to 75 gallons (280 liters) is a
massive saving !!
Had you thought about using "counter flow" rinse systems or
sometimes called cascaded rinse. This system is suppose to be
most efficient, and the more tanks you have chained together the
more efficient. The price is longer rinse times because of the
multiple dip & drip cycles. For example 4 cascaded rinse tanks
with a fixed ratio of water flow volume to drag in volume of 10:1
will theoretically dilute the concentration by more than 10000
times. In other words the concentration ratios of solution
wetting the PCB before and after rinsing is 1/10000 and you only
need to use 100 ml of rinse water for a typical 12"x12" PCB
wetted with 10 ml of liquid.

http://www.finishing.com/135/03.html

Adam

> 7000 gallons (26500 liters) down to 75 gallons (280 liters) is a
> massive saving !!
> Had you thought about using "counter flow" rinse systems or
> sometimes called cascaded rinse. This system is suppose to be
> most efficient, and the more tanks you have chained together the
> more efficient. The price is longer rinse times because of the
> multiple dip & drip cycles. For example 4 cascaded rinse tanks
> with a fixed ratio of water flow volume to drag in volume of 10:1
> will theoretically dilute the concentration by more than 10000
> times. In other words the concentration ratios of solution
> wetting the PCB before and after rinsing is 1/10000 and you only
> need to use 100 ml of rinse water for a typical 12"x12" PCB
> wetted with 10 ml of liquid.
>
> http://www.finishing.com/135/03.html
>
> Adam

Hi Adam,

We looked at every type of rinse system we could find. The cascaded
rinse tanks are a great way to go but we didn't have the floor space
and our main goal was to have zero discharge. The POTW sewer plant we
discharged to in turn discharged to what they called a "small stream"
so our limit was 1 ppm copper by EPA regulations. Our average copper
discharge was around .6 ppm. The regulations were getting very strict
so we went with cutting the flow and evaporation. I still use a small
evaporator that will blow off about 10 gallons per hour which is way
more than I need now days.

Btw, the tanks I made took up a 4' x 8' area and would run twice the
volume as the old system which was 5' x 40'long. We salvaged all of
the heaters and controllers from that old electroless line, cut it up
with a sawsall and junked it. I was glad to see it go.

You can get these tank systems for free if you look around. Lots of
PWB shops are going out of business and there is all kinds of
equipment available for cheap prices and sometimes free.

Tom