Homebrew PCBs

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. 

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.

A rectifier can be made from a car battery charger and a variac 
(variable transformer) on the 120 volt input. When plating with acid 
copper, the tank voltage will only be around 1.5 volts and solder 
plating is about 0.5 volts. Many shops have dumped the lead and just 
plate tin only. 

After the solder plating is completed, the photoresist is stripped 
from the panel with a 1% caustic (lye) bath and then etched. The 
solder or tin plating is the etch resist. The background copper will 
be etched and the tin or solder on the surface and in the holes will 
not be etched thus leaving your desired pattern. Ferric chloride 
can't be used for this type of etching unless your plated metal is 
gold. The best etchant would be ammonium or sodium persulfate since 
they are cheap and work good. We used a sulfuric acid - hydrogen 
peroxide etchant that was easily recycled but the fumes were hard to 
handle.

After etching the board is "reflowed" if it is solder plated. When 
solder is plated it goes onto the board as tin and lead but not as 
the original alloy. The reflow process melts the tin and lead back 
into a solder alloy as well as fusing it to the copper traces. The 
reflowing process can be done with a solder pot full of water soluble 
soldering oil. We used a modified donut fryer at 475 degrees F. The 
reflowed board is then cleaned with a soap solution, dried and cut or 
routed to size.

That is the basics of electroplating circuit boards. I'll post some 
more information on the sensitizing and electroless part later.

Tom


--- In Homebrew_PCBs@yahoogroups.com, "adam_seychell 
<adam_seychell@y...>" <adam_seychell@y...> wrote:
> Tom thanks for sharing this with the group. That is a fascinating
> story. I just blows me away when I hear how a common ingredient used
> in every day life can be so significant in a high tech processes 
like
> printed circuits, heck, lignin vanillin extract !!! It just shows 
how
> little the scientists understand electrochemistry and surface
> chemistry. Its true when people say its in an art not a science.
> 
> During my research into the carbon black method of making holes
> conductive I never came across Eric Harnden's invention. As far as 
I'm
> aware of there are four main (non-electroless) commercial processes
> for plating holes. This article gives a quick overview;
> 
> http://nr.stic.gov.tw/ejournal/ProceedingA/v23n3/365-368.pdf
> 
> I suspect Eric Harnden's super activate palladium chloride catalyst
> puts a very large amount of palladium inside the holes, so much so
> that copper can electroplate directly across the surface. I believe
> the palladium acts as a catalyst and dramatically speeds up
> electroposition of copper. The surface resistivity due to the
> palladium alone does not need to be low. The article above mentions
> Radovsky in 1969 discovering palladium inside holes being directly
> electroplated even with initial resistance of 80 Mohms. The carbon
> black process I am using reaches surface resistance of around 10 
Kohms
> for a unit square. This too uses an essential ingredient found in 
most
> home  kitchens, and that's eatable Gelatin derived from beef skin.
> There is already a patent on using Gelatin with carbon black
> dispersions. The trick with using carbon black is to modifying the
> carbon surface chemistry so it improves electrodeposition of copper.
> Many soluble organic dyes can adsorb on the carbon surface and also
> act as a catalyst in helping electrodeposition of copper. Palladium
> can also be loaded into the carbon to dramatically improve the
> plating, and I think that's what done with Blackhole(tm).
> 
> At the moment I'm working on trying to improve the Gelatin / carbon
> dispersion process. I've got holes plating, but there are too many
> variables and it takes long dwell times (30+ minutes) in the 
solutions
> to achieve reliable results. Its all just fun experimenting and
> discovery for me. I know that no money will be made from it because
> the ideas are already patented and I don't really want to get into 
the
> PCB manufacturing business.
>