Hello Mark,
Thank you for responding. Your advise is greatly
appreciated.
I had a look at the web site and method that you mentioned. I see two
distinct differences in your approach.
Firstly the web site shows a full contact method. The copper foil is coming
into full contact with the image unit, fuser and other less significant
parts.
I can see a number of problems with this -
1) The image unit is likely to be damaged, particularly where the edges of
the copper foil contacts the image unit. The same applies for the fuser
roller especially the more modern type.
2) There are safety issues as the foil is still in contact with the charged
image unit at the time that it is being handled by the operator.
3) The jell is coming into full contact with the image unit and fuser.
I doubt the jell is able to act as an insulator so I suspect the jell is
what is transferring the toner to the copper as the copper will be at the
same electrical charge potential as the image drum. It may also may be
increasing the thermal transfer from the fuser to the copper.
In your method you mentioned sparks so I assume the PCB has no physical or
electrical contact with the image unit? Normally I would expect the PCB to
float in voltage between the potential's of the image unit and charge wire.
The existence of sparks indicates that either it is static discharge in
which case there is not likely to be more than one, possibly two, sparks on
any print. Or the sparks are a result of a discharge path meaning that for
each obvious spark there is a corresponding spark from the copper to another
part of the printer.
Ideally (from a image point of view and not safety) the copper should be
electrically connected to the charge voltage or perhaps more appropriately a
division of the charge voltage.
I can see that you know what you are doing to a fair degree. I do not know
how experienced you are with electronics and more particular high voltage
electrostatics. I can provide some information that my assist you but I warn
that this information is provided in a context only suitable to qualified
technician such as myself. You may need to seek independent advice for
further explanation of safety procedures.
The HT generator in your printer is most likely a split rail generator. The
ideal voltage for the copper on the PCB (to prevent electrostatic discharge)
can be calculated this way -
((drum voltage)-(charge voltage))∗((distance from the PCB to the image
drum)/(distance from charge wire to drum))
On a single rail supply a divider can be made with resistors that or
normally used in the focus electronics of a television. These are available
for domestic electronic repair shops or a good electronics supplier. Normal
resistors are not at all useful.
If you are a technician (or have a technician friend) and know how to
measure the drum and charge voltages with respect the chassis ground then I
can tell you how to build a simple circuit to fix this problem and the
associated safety hazards. This however cannot be done with a simple
multi-meter and in fact it is downright dangerous to attempt to use a common
garden variety multi-meter without an external divider or HT probe.
I also need to know if there are two sparks for each flashover and where
they are located or if the is just one and where it is located.
I may be able to get some specs for your printer online but it is unlikely
with newer models.
Getting back to the web site mentioned -
At least this shows that a normal fuser will work. While you mentioned that
it is convenient to be able to blow away the toner on a poor copy, I expect
in the long run you will have consistent results and it may be more
convenient to use the fuser directly. If possible, this may not always be
the case for different fuser types.
The better short term solution would be an oven with good temperature
regulation. The closer you can get to the ideal (lower end) temperature the
longer the fusing will take. This gives the greatest margin for error in the
timing of the heating process. Obviously the board will have be handled very
carefully as even a breath to close to the board will disturb the toner
pattern.
I hope you don't feel that I am a "Nay sayer". I have confidence in your
project. I am happy to help if my 'opinion' is useful.
If you are a technician or you find my comments irrelevant than I am quite
happy not to bother you.
Thanks, Robert.
----- Original Message -----
From: Mark
I've spent the last month or so looking at all the discussions re direct
laser printing on boards. There are all sorts of warnings, nay sayers, etc
who say it can't work. Then I saw the post and site of laserpcb, where Dave
says (he has a patent)that he can print on copper foil using his special
"gel" then glue it to FR4 to make a PCB. So, if it is possible to put toner
on copper foil, it should be possible to put it on boards directly.
I took a Samsung ML-2510 and modified the paper path to be straight and
flat, and moved the feed sensor (also inverted it) then I simply ran a board
through. No problem. A few sparks, but the image seems very good, no
distortion, very crisp. I tried Dave's Gel (sorry Dave), but the image seems
identical with and without the gel.
I haven't finished experimenting, which is why I wanted the test pattern. I
seem to easily be able to print 1 mil traces, but I'm not sure yet of the
spacing I can use, though I would guess 5-8 mil.
The board comes out of the printer with the toner as powder
electrostatically stuck to the board, so it has to be fused. I am reluctant
to use the fuser on the printer for several reasons. One is that it is a
pain to move it to a flat path - I would have to move a gear, among other
things. Secondly, the speed might easily be too fast to fuse the toner.
Also, if the toner is smudged or not perfect, it is very easy to wipe and
reprint the board if it isn't fused.
An advantage of fusing it is that it (hopefully) will be stuck in place,
even if it isn't fused completely. Obviously there is a lot of work to do
here.
I think I have demonstrated that direct laser printing of pcb's is possible.
If anyone wants further information, I will be happy to share.
Mark