LaserJet 6L Printer - Positive Films - A New Idea That Needs Guidance
idbruce
Posts: 6,197
Hello Everyone
As I am sure that many of you already know, I am performing some experiments with my new exposure box design and trying to obtain some very nice exposures. During some of these experiments, I have been using a LaserJet 6L and transparent overhead film to make my positive masks. After a lot of experimenting, I have come to the conclusion that I need a much better positive film to obtain better results, so I have spent an extensive amount of time researching the different methods that are available.
Creating inadequate positives for PCB photo-imaging is a common problem amongst electronics enthuiasts. I am sure there are several printers available that will print a nice transparency, as well as other solutions, but I want to attempt something new to try and resolve this problem. I want to create a photomask interface for my printer. The LaserJet 6L has a maximum density setting of Level 5, but somehow I want to surpass this density level with an electronic interface. I am certain there is a connection somewhere within the printer that can be seperated which controls the density of the toner. So I propose an interface that can be inserted between two connectors to control the density of the toner output. During normal printer operations, the interface is simply bypassed by the selection of a switch position, but by altering the switch position, the interface would allow fine tuning of the toner transfer, capable of surpassing the maximum factory level, for the purpose of creating purely opaque photo masks.
What do you guys think? Is this possible?
Bruce
As I am sure that many of you already know, I am performing some experiments with my new exposure box design and trying to obtain some very nice exposures. During some of these experiments, I have been using a LaserJet 6L and transparent overhead film to make my positive masks. After a lot of experimenting, I have come to the conclusion that I need a much better positive film to obtain better results, so I have spent an extensive amount of time researching the different methods that are available.
Creating inadequate positives for PCB photo-imaging is a common problem amongst electronics enthuiasts. I am sure there are several printers available that will print a nice transparency, as well as other solutions, but I want to attempt something new to try and resolve this problem. I want to create a photomask interface for my printer. The LaserJet 6L has a maximum density setting of Level 5, but somehow I want to surpass this density level with an electronic interface. I am certain there is a connection somewhere within the printer that can be seperated which controls the density of the toner. So I propose an interface that can be inserted between two connectors to control the density of the toner output. During normal printer operations, the interface is simply bypassed by the selection of a switch position, but by altering the switch position, the interface would allow fine tuning of the toner transfer, capable of surpassing the maximum factory level, for the purpose of creating purely opaque photo masks.
What do you guys think? Is this possible?
Bruce
Comments
-Phil
Given that cheap inkjet printers produce excellent transparencies, I don't see the point of messing about with a laser printer, which will probably never achieve the same quality.
With all due respect, you guys are not telling me what I want to hear
Bruce
Maybe you're asking the wrong questions.
-Phil
Perhaps, but it is just that endless problem solving quest that I have been on since birth. I simply can't help myself.
Phil is right on the reversed image, with direct contact to the pcb film.
I'm assuming this is some type of photosensitive film PCB overlay, correct ?
If so, then removing the cover sheet before exposure will generate finer lines with direct contact.
This will require about double the current exposure time, since the PCB film cover sheets constructively
add at the exposure wavelength. (reduced exposure time required with cover sheet on)
There was a product called 'Laser Buddy', mostly Methylene Chloride etc; that caused toner
to fuse (very slight swelling) better (chemically) for a improved contrast ratio on paper
but I expect that it would eat the transparency films.
That is what I use as a first step to make the first art phototools by camera and laserjet
at a 1.5 to 2X reduction of the laser prints to master films.
Then shoot the negs/pos from LPF films for the final exposure masks.
Most of this stuff is still available as Rapid Access (RA) process, by various makers.
It's about a buck a print for the RA films, and it will eliminate all your problems
on density (except for the pinholes that always creep in).
Most shops then shoot the master phototools (contact print) to Diazo
for the final tools (sacrificial after multiple uses) on production boards.
That brings up another interesting feature, that the Diazo masks are pretty
transparent, and mostly act as FILTERS at the exposure wavelength.
That speaks to Leon's point of making inkjet transparency exposures
that are FILTERS rather than the full spectrum blockage with toner.
Kick around the photo sites on books about inkjet films and inks for making exposure negatives
for making platinum and palladium prints and you will find certain inks that work best at filtering for UV.
Your next problem will be dimensional stability during the process use,
so use the thicker 7mil films for phototools and keep the process boards
and films <at room temperature> during all the process steps.
Or, you could bypass <all> of this and go to a focused dot UV direct write
and get single board exposures in about 5 minutes off a re-purposed flatbed plotter.
jr
I don't mean any offense by this, but this is not my first day at the rodeo
Yes, he is right, but I knew that
Yes, it is a positive acting photosensitive film. However, this film does not require UV lighting for exposure. It can be exposed with a standard incandescent bulb, and that is what I am using.
The internet has a lot of information pertaining to the subject of creating PCBs, especially with using laser printed transparencies as a positive film or mask. However, what these articles fail to mention is that if you want very fine detail with the photographic imaging process, you must have an opaque mask, otherwise you will never achieve fine detail. I can achieve 0.010" trace widths with no problem, but I am going after consistent 0.004" trace widths.
As mentioned in the original post, I am not the only person in the world who is having trouble creating a nice opaque positive, and I would like to attempt to achieve an economical solution for a lot of people. I am sure I can still find a print shop with a stat, floor, or vertical camera that can make a nice positive for me, but that does not help the poor guy that is fifty miles from the nearest print shop. Whereas slightly modifying the maximum density of the toner output on a cheap laser printer may be just the ticket for a lot of folks, instead of just me.
Also as I previously mentioned, the LaserJet 6L has a maximum density level of 5, but the levels range from 1 to 5. Now this printer already comes close to an opaque image, but it is not completely light free. At this point, I can only imagine what it would look like if I could increase it to 6.
Bruce
They are fairly interesting <facts>.
The film may be broad in ability but if it has a cover sheet then it reacts
at a <specific> wavelength. (uv shorter wavelengths , means sharper images)
Physics isn't going to change to accommodate your budget.
I've always used florescent UV GERM lights, (short wavelength, intense output, cheap and available, lower heat transfer)
I don't see any real substitute if you are going for 0.004 l/s.
You're bombing the films with the broad spectrum lighting thinking that the opacity will solve
the problems, but you are <creating> the problem with the light source choice.
I didn't see any response to the FILTERS portion of the post and that's the key to your density problems
and a cheap and effective way of making the films by specific inkjet inks.
You can also pick up a thou or two in the post processing by proper dwell times
(a heat stabilization water soak, w/cover film removed) after exposure and before using soda ash
for development with direct impingement and mechanical agitation instead of diluted KOH developers.
KOH is only used as the final stripper.
But that's if you haven't already polymerized the films too much in exposure by the wrong type of light source.
good luck with that wheel, Buckaroo.
jr
the internet is filled with PCB voodoo, here's the facts.
Printed Circuits Handbook, 6th Ed. // Clyde F. Coombs, Jr.
( it's been torrented )
The Laserjet 6 series printers have a small wheel you use to set density, hidden somewhere under a cover.
(We mostly used the 6mp at the office, not the 6L)
I assume that this was connected to a variable resistor or something of that nature.
I would try to measure the resistance at both the high and low setting, ti find which way it 'dials'.
If its at 'high resistance' while at the '5' setting, it might be possible to increase the density by adding another resistor in series?
If it's at low resistance, you may have a problem...
Of course, figuring out how the resistor is wired into the system can be the real challenge.
I can't see you getting anything like 4 mil tracks with a laser printer and standard resist. I can just about manage 6 mil with my process and the etched tracks are very non-uniform. If you can create suitable transparencies you will need special high-resolution resist. Few commercial PCB suppliers offer 4 mil tracks, it needs special equipment and processing; 6 mil is the usual lower limit for standard processing.
jr,
Your comment about inkjet ink acting as a filter reminded me that some people on the Homebrew PCB group have tried different coloured inks. IIRC, yellow was best. I get good results with black ink, so I haven't bothered trying other colours.
Yea I was thinking almost exactly along those lines
@Leon
I am already getting 4mil tracks. I am just not getting them consistently.
Just to prove my theory, I will find a local print shop that can make me an opaque positive, but that will still not solve the problem for folks in rural areas.
Another reason for having the positive completely opaque, is that it also takes the positive image out of the equation for possible exposure problems. I won't have to think, "Well it could be because the positive is letting light pass through".
@jrjr and Leon
Unless you are creating half-tone etchings, I cannot see any possible reason for allowing any light to pass through wire trace areas, and wire traces were meant to be solid lines.
Besides the 4 mile tracks, I also want the periods (dots) to consistently show up in my web address. I would imagine they are 4 - 6 mil in diameter.
I would have to disagree. That is what most people settle for because of inadequate positives or negatives, incapable of achieving consistent 4 mil tracks.
Bruce
Okay Leon, I will retract some of my last comment. It is not very often that you will actually need a 4 mil track, but just in case it is necessary, I want a process that can achieve it.
Bruce
EDIT: Plus that will permit bragging rights
With the old exposure box approx. 50 mil, but with the new exposure box, I have not built any working circuts yet.
Bruce
Instead of wasting anymore valuable PCB material, my very next step is to make that opaque positive. That will eliminate all doubts pertaining to the positive mask. I truly believe that is my biggest problem. From there, at least I know the positive image will not cause me any unwanted grief.
Bruce
http://www.delorie.com/pcb/inkjet/
He's actually tried 4/4 mil, but it doesn't seem to have been successful.
I think he's mentioned that the film he is using is similar to the JetStar material I use.
To be perfectly honest, I have never liked inkjet printers or their quality of print, at least with the printers that I have seen and/or experimented with. I have a HP DeskJet 932C that I may have used to print perhaps 10 documents, which is practically brand new. I would not even consider attempting using it for my current experiments. Additonally, JetStar film is a UK remedy and the shipping could not be justifiable for a viable solution.
On the other hand, I have always been impressed with the output of laser printers.
Bruce
That was an interesting link. Just give me a bit more time, which will result in either glory or shame. I sincerely doubt that I could accomplish 4/4, but I believe 4/8 is possible.
Bruce
These excerpts are taken from the HP LaserJet 5L and 6L Printer Service Manual.
It helps to talk to the correct end of the horse when at the rodeo.
google : Stouffer Step Tab.
www2.dupont.com/Imaging_Materials/en_US/assets/.../tb9526.pdf
at 4/4 you will be making ADDITIVE circuits.
4/8 is what you make when the process is out of control.
spaces are equally important as traces.
read the Coombs book, 10 times.
there are bias tabs on the toner
cartridge that allow you to push
the HV for varying drum bias, It acts
as a range override to the density setting
for differing qualities of photosensitive drums.
You don't need a propeller to control it, a paper clip will do.
but none of this will help your problem.
jr
73
I could not agree more
I believe a Stouffer Step Wedge is for UV exposures. As I mentioned previously, I am using incandescent lighting for my exposures.
Here is something interesting, http://www.sandcarver.org/laserfilm.htm
Lucky for me, I have a graphics art supply house here in town. He just gave me a bunch of high resolution film and various other stuff for free.
Inkjets vary a lot, and must be used with the correct film. I get much better results than he gets with both printers.