Homebrew PCBs

I spent the last 2 months investigating the possibilities of directly 
depositing toner on copper clad boards. Some of my tests can be seen 
at <http://www.pbase.com/mark10970/galleries>. While I can claim some 
success, including clean 2 mil traces, results were inconsistent. My 
final thoughts are:

It can be done. I spoke with someone who is actually using this 
process in a commercial venture making boards for (mostly) hobbyists. 
I'm not mentioning his name because I'm not sure he wants to be 
identified, but he can chime in if he wants to. AFAIK he's the first 
to attempt this method in a serious way. He uses a proprietary method 
of externally charging the boards as they ride on a custom table 
beneath (I think) the printer.

The built in HV Transfer supply has a feedback mechanism to 
compensate for humidity caused leakage. Because of this, the voltage 
is constantly changing and is impossible to control. I ended up using 
an external supply and found that 2400 volts worked best for me. DO 
NOT play with this stuff if you're not familiar with high voltage 
safety requirements!!! It can kill you!! It might be possible to 
modify the internal transfer supply directly, but it is fed from a 
pwm signal from the processor, so I didn't bother. High voltage 
supplies are pretty cheap - see eBay.

Get a service manual for your printer! <http://www.smpcshop.com/> is 
a good source - mine cost about $10 USD. It has all the schematics as 
well as a lot of useful information.

I found that the transfer charge did not distribute evenly across the 
rubber transfer roller so that larger boards had uneven density. The 
boards are charged from the rear so that the pcb acts as a high 
voltage capacitor, further complicating things. Thinner boards work 
much better than thicker ones. Perhaps directly charging the board 
with a conductive roller might be better.

Make sure the edges and corners of the board are smooth - I gently 
filed the corners. This will protect the drum form mechanical damage.

I really stripped down the printer so that the board was only in the 
"printer" for an inch or so. This made for a very straight path.

A special thanks to Robert <listgroups08@... > for all the 
technical data on many of these issues. His long, detailed 
explanations were insightful and invaluable in this endeavor.

My main interest lies in using the boards for swarm robotics, not in 
pcb production. I have decided to abandon this approach and go to 
direct inkjet printing on boards as described by several people on 
this group. It seems easier, more reproducible, and less dangerous! 
Additionally, I am thinking that it should be possible to deposit 
conductive ink on the boards directly. I read a short summary of some 
work wherein they used a silver nitrate (?) solution to draw traces 
then ran a solution of Ascorbic acid (vitamin C) through the printer 
to convert it to silver. Lots of interesting things can be tried, 
without the high voltage.

If anyone has any questions, I will be happy to answer them.

Mark