I think the fuser scraped the toner off because the board couldn't heat fast enough to fuse it. I've destroyed a couple of printers doing these tests but I think I understand what has to be done to make it work. Stefan has suggested that the charge on the board may be insufficient to attract enough toner to act as a resist, but visually it looks okay to me. I have to add a small mcu to simulate some of the printer's functions to test this further, but I plan to do some printing and etching tests next week. If necessary, I could either tweak the paper charge voltage a bit or add an external high voltage power supply, But I'm not at all sure it will be necessary. I also think the drum is somewhat tougher than Stefan thinks it is, and in any case it is easily replaceable if it gets damaged. An external smooth carrier might be necessary to mitigate this problem, but I think it is doable.
I should also add that the toner seems very well adhered to the board as it comes out of the printer. I can turn the board over and even blow on it without disturbing the toner. Once it is "cooked" in the oven, it seems very hard, though I have not etched a board yet.
Mark
-----Original Message-----
>From: James Newton <jamesmichaelnewton@...>
>Sent: Mar 14, 2009 9:11 PM
>To: Homebrew_PCBs@yahoogroups.com
>Subject: [Homebrew_PCBs] Re: Direct Laser PCB's (not TT)
>
>--- In Homebrew_PCBs@yahoogroups.com, Mark Lerman <mlerman@...> wrote:
>>
>> 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'm not sure I understand why nothing printed here...
>
>
>> 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.
>>
>
>That is very interesting... Why did removing the fuser cause it to print?
>
><SNIP>
>
>> If anyone is interested in more details, I am happy to share.
>>
>> Mark
>>
>
>
>I would be VERY interested in pictures, and descriptions of the modifications you made.
>
>--
>James Newton
>http://techref.massmind.org/techref/pcbs.htm
>
>
>
>
>------------------------------------
>
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>