Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "twb8899 <twb8899@y...>"
<twb8899@y...> wrote:
> Adam,
> 
> Wow, you are quite a researcher and experimenter. I never did try out 
> the blackhole process. They had some trouble in the early days with 
> innerlayer voids on multilayers and we couldn't take a chance. On two 
> layer boards the blackhole process has always been excellent. It 
> could possibly be the way to go for home experimenters. If I remember 
> right, you needed an agitation pump to keep the carbon dispersed in 
> the solution and an oven to bake the panels after processing. After 
> drying the panel you must sand the carbon off of the copper leaving 
> just the holes coated. If thats the case, then this could be the way 
> to go. Just fire it up and run it when you need boards. 
> 

That's kind of correct. The boards are drilled and then immersed in to
a conditioner solution A monolayer of long chain molecules are
adsorbed to the surface of the epoxy surface and act to improve the
adsorption of the following stage, the carbon black dispersion. The
boards are immersed into a suspension of carbon black particles and
coagulate or adsorb tn the surface of the holes (and the copper foil).
The board is removed from the dispersion and put through a an air
knifed to remove excess liquid from the holes. The panels are then
baked at about 60 to 80°C to completely dry the carbon. The carbon is
now firmly packed and adhered to the surface. The carbon on the copper
is then removed by immersion in ammonium persulfate to lightly etch
the copper and at the same time take with it any carbon. The panels
are finished with rinsing and drying. As far as I am aware the
Blackhole SP is Macdermids latest process which I think began around
1996. It is frequency used to in manufacture of 16 or more layers
boards. The carbon bath does coagulate over time, but I've heard the
bath is maintained with regular additions of dispersion concentrate,
and the entire bath is replaced every 1 to 2 years. Carbon aggregates
will simply settle to the bottom of the tank. There is no continuos
pump in Blackhole, you might be thinking of a competing process call
Shadow by Electrochemicals Co, which run the bath through a high shear
pump to keep the graphite dispersed. Graphite particles have much
lower surface are to volume ratio that carbon black and so do not
normally behave as stable colloids.




> You can use a five gallon bucket for the electroplating part. The 
> copper anodes must have some phosphorus in the alloy or it won't work 
> properly. You will find these anodes marked "cu-phos". Plain copper 
> anodes are used in a cyanide bath but the high pH of that chemistry 
> will strip off your photoresist so it's no good for pc boards. When 
> the solution is adjusted properly the plated boards will look like a 
> copper mirror. Acid copper plating baths must be air agitated for 
> proper plating. The solder plating tank can be set up the same way 
> but doesn't require the air agitation.
> 

Its interesting you mentioned solder plate. Is that how most people do
it ? I am using tin plate mainly because a stannous sulfate/sulfuric
acid bath is less toxic than the fluroboric acid/fluroborate tin/lead
bath commonly used to plate solder. One big advantage of solder plate
is the ease of selectively etching the copper. With tin metal resist,
I'm forced to use alkaline ammonical etching solution, which need a
special tank in order to contain the ammonia gas. I'm now wondering if
solder plate is the better way to go. Is a solder plating bath very
difficult to control and too toxic to setup in ones home workshop ?

Adam