Hi Robert,
I'm using a precision focused opto reflector - angled beam and receiver. I could use a split board with a slit to precisely detect the edge of the board, but there are other problems. The laser printer does not work like an inkjet. The rollers start moving, but the paper isn't pulled from the tray till the drum is charged. Then the paper is pulled, goes into the drive rollers, then hits the edge detector that starts the printing. I have to wait for a "beep" that represents the solenoid that originally pulled the paper from the tray, then I have a few seconds to hand feed the board into the rollers and release it. Too long and it doesn't print and goes into error mode. It's important that the rollers keep the speed constant as it prints to avoid distortion.
It's much easier to just make two boards (or print both sides on one sheet of pcb), then use registration holes to align and glue them together.
The whole process, from printing through etching, takes much less than 10 minutes, mostly for etching.
Mark
-----Original Message-----
>From: listgroups08@...
>Sent: Apr 2, 2008 9:14 PM
>To: Homebrew_PCBs@yahoogroups.com
>Subject: Re: [Homebrew_PCBs] Direct Toner - First Try Results
>
>Hello Mark,
> That is great to here!
>
>I can't immediately think what is causing the pitting to be in lines or
>streaks. If would have been great if you took a high resolution scan and put
>it somewhere where it can be downloaded. I have web space if you need.
>
>As for the opto sensor and registration, it may be worth mentioning that all
>opto sensors are not created equal. The worst problem with the mechanical
>flag type setup is that variations in movement from one activation to the
>next is the main cause. A direct opto sensor setup without the pivoting
>actuator is hundreds of times better.
>
>The common garden variety sensor used most in domestic electronics is a
>0.5mm. In other words the optical path is 0.5mm wide. These may be fine for
>some boards but if you are working down to 2mil resolution then they may not
>be so good.
>
>Physically and electrically identical opto sensors are available that only
>differ in optical path width. These go down to 0.01mm. If you can tell me
>approximately where you are then I will find a supplier close to you.
>
>You can get more registration reliability from the more common sensors by
>reducing the influence of optical and electrostatic noise and bias. Just put
>it in a metal shield to block out electrical interference and ambient light.
>The darker the sensors environment the more consistent it will be. As the
>actual sensor part of it is a semiconductor (photo transistor) it can also
>be influenced by electrical noise.
>
>The split board method will always solve this problem but I feel that it
>causes unnecessary work. In my project (inkjet direct etch resist) I will be
>drilling two registration holes in the board to clip onto pins in a truly
>flat bed printer.
>
>I am looking at my old laser printer now and wondering if I should bother to
>buy a new inkjet printer. Perhaps after your success I should go directly to
>laser direct etch resist.
>
>I looked in the shed the other day and I have quite an amount of single side
>laminate that is about 0.2 - 0.3mm thick along with plenty of single sided
>FR4. Perhaps I should try the thinner laminate in the laser.
>
>I have a spare image drum to, so perhaps my laser printer should be getting
>nervous.
>
>Keep up the good work, your getting excellent results, well capable for SMD
>work.
>
>My hobby work is digital so I need good resolution as well.
>
>Thanks, Robert.
>
>----- Original Message -----
>From: "Mark Lerman" <mlerman@...>
>To: <Homebrew_PCBs@yahoogroups.com>
>Sent: Thursday, April 03, 2008 9:31 AM
>Subject: Re: [Homebrew_PCBs] Direct Toner - First Try Results
>
>
>Robert,
>
>My second try was MUCH better. I noticed that the pitting was
>actually more like streaks, all going in the same direction. Perhaps
>caused by the gel?? Or not enough fusing?? Anyway, this time I used
>no gel, then ran it through the laminator 4 times, once in each
>direction. I etched it, and the results seem about perfect. No
>pitting, no smearing. The 2 mil traces are perfect! I suspect I can
>get them closer together than the 10 mil centers I am using now, but
>these are pretty fine traces and more than adequate for what I usually do.
>
>I used a precision optical sensor to find the leading edge of the
>board as it enters the printer. I wonder if I can make double sided
>boards with adequate registration? For now I think I'll stick with
>what I have. A double sided board can easily be made using thinner
>board and gluing two boards together using registration holes and pins.
>
>Mark
>
>
>
>At 06:59 PM 4/2/2008, you wrote:
>>Hello Mark,
>> An afterthought or two.
>>
>>I find that when I have to visually examine something in fine detail, it is
>>easier to scan it on my scanner at maximum resolution and then scroll
>>through the image on the PC screen. Perhaps you can do this with the fuser
>>PCB to look for clues.
>>
>>If the problem is air pockets then it may pay to go over the PCB with very
>>fine sand/emery paper (1200) before printing.
>>
>>Robert.
>>
>>----- Original Message -----
>>From: "Mark Lerman" <mlerman@...>
>>To: <Homebrew_PCBs@yahoogroups.com>
>>Sent: Thursday, April 03, 2008 7:16 AM
>>Subject: [Homebrew_PCBs] Direct Toner - First Try Results
>>
>>
>>I just made my first (single sided) board using my modified laser
>>printer that deposits toner directly on the board. A few observations
>>and questions:
>>
>>1- I used the Eagle Demo2 board, but inserted four 2 mil traces
>>between 2 of the dip pads, each connecting to one of 4 adjacent pads.
>>These are 2 mil traces on 10 mil centers, with the traces on the
>>sides being 7.5 mils from the pads.
>>
>>2 - I used some of Dave's gel on the 1/32 inch thick board - will try
>>without it later.
>>
>>3 - I then ran the board through a laminator once - no carrier.
>>
>>4- I etched using muriatic acid / peroxide, room temperature, a
>>little agitation by hand rocking the board.
>>
>>The board came out okay, but there is some pitting that I am not
>>happy with. All four 2 mil traces are intact, none of them are
>>shorted. Questions:
>>
>>1 - Should I have run the board through the laminator more than
>>once? I bought the laminator at Staples, no model number on the box,
>>but I believe it is one of those recommended on the laminator link.
>>I'll have to measure the temperature sometime. Any other thoughts re
>>the laminator?
>>
>>2 - Would I be better off using an oven or hotplate to fuse the
>>toner? I can control the temperature quite well, but will the toner
>>fuse well without the pressure?
>>
>>3 - What causes the pitting? Too long in the etchant? Toner not
>>completely fused? All the traces and pads seem equally pitted, so I
>>don't think it's the trace width.
>>
>>Lots of questions, but I realize that I am on somewhat uncharted
>>territory here. It's going to take time and experimentation to work
>>it all out, but I'm excited by the possibilities of this technique.
>>
>>Mark
>>
>>
>>------------------------------------
>>
>>Be sure to visit the group home and check for new Links, Files, and Photos:
>>http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>>
>>
>>
>>
>>------------------------------------
>>
>>Be sure to visit the group home and check for new Links, Files, and Photos:
>>http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>>
>>
>>
>
>------------------------------------
>
>Be sure to visit the group home and check for new Links, Files, and Photos:
>http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>
>
>------------------------------------
>
>Be sure to visit the group home and check for new Links, Files, and Photos:
>http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>