Homebrew PCBs

For anyone interested, there is absolutely no reason that laser 
printers cannot directly deposit toner on pcb boards. The practical 
problems are the fuser and the paper path. As a proof of concept, I 
took a Brother HL2140 laser printer that has a manual feed for 
thicker media and fed a sheet of thin (8 mil) laminate through the 
printer. Nothing printed.

I then removed the fuser, using appropriate resistors to simulate the 
correct fuser temperature and thereby fool the printer controller 
into thinking the fuser was still there. I ran the same test, and 
sure enough, it printed perfectly! Of course, the toner was only held 
to the board by electrostatic attraction, but I then put the board 
into my trusty toaster oven and "fused" it.

There are other practical problems, but these can be overcome with a 
little bit of work. A small mcu will be needed to simulate some of 
the feed sensors and the paper path will have to be changed, but my 
experiments show that these are (relatively) easily done.

I have used a datalogger to check the function of the three main 
sensors - paper feed, start print (rear register) and eject - and can 
simulate all of these and I have actually run the printer using an 
mcu instead of the sensors. However, the real problem is that the 
machine is not rugged enough to handle a lot of manipulation - the 
connectors break down easily and you end up with error lights that 
you have no idea how to fix, a tiny slip that causes a momentary 
short will sometimes blow a board, etc.

If anyone is interested in more details, I am happy to share.

Mark