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View Full Version : Inkjet masks for PCB- small breakthrough


crossup
Dec 04, 2004, 04:55 PM
Since an inkjet printer was not only all I have but I dont have access to lazer toner unless I buy it, I decided to try it despite the info I could find here saying it doesnt work. Let me be clear, I talking sensitized photoresist here not plain board.
Anyway, I used my EPSON Color 880 printer with transparency film from Staples " 3M Multipurpose Transparency Film" to print a postive mask. Its designed for use in Inkjets, Lazers and copiers. Its basically dual sided, the inkjet side has some pretty serious texture perhaps 400 grit sized. It holds inkjet standard ink like a big dog!! I set my advance options for my EPSON to max brightness, contrast, saturation, maxed my CYM sliders and told it to print color, my black was like 2,2,2 which I did in Photoshop using the paint bucket tool, so that it printed in color rather than black cartridge. I also used the 2880 dpi resolution(Im sure thats a highly interperpolated mode but regardless, its prints detail beyond the resolution necessary here by a good margin). The result was opaque even to the sun, no light spots or pin holes and it was dry immediatedly.
So I did as Comatose suggests and used a quartz/halogen work light to expose my media using the mask made above and turned out that with a 250W bulb at 4" it takes 15 minutes to expose my Injecterall PCB. My first attempt kinda failed as the exposure process heats the pcb up to 150 deg F or so and dummy me just chucked it into the developer which stripped the resist off the hottest part of the board regardless of exposure :eek:
Next attempt I chucked the exposed board into the fridge for 5 minutes warmed with my body to ambient and then gave it 60 seconds of developer.
Etched it and she is BEAUTIFUL...definitely the equal to most commerical boards I see in quality stuff, and light years better than the cheap Chinese stuff common today. I forsee no problem with structure as fine as we we need for our most micro circuits. I made a JDM programmer board and 2 Linear Tech LiPo charger on chip boards on this test etch, they have traces only .010 aprart and the lines are perfect under the highest magnification I have. My guess is the resist is as much the limitation as the mask involved here.
FWIW, the temp did not seem to hurt the mask, it did not try to stick either.
For me this method is the bomb despite the $28 cost for 25 sheets of the tranparency film- so what if I have a life time supply?
Sorry for the crap webcam pics...file size limit here makes them worst then they have to be...mask, board with 3 etchings on it, developer ruined 1st attempt....
just realized someone here had giving me encouragement said it would take like 5-6 attempts to get what I want... its nice to be lucky and even nicer to be able to contribute here. Major ****e eatin grin here right now! So much fun and its even legal.
Oh yeah, the Linear Tech etchings are 20x35mm the JDM programmer, approx 35mm square to give you an idea of scale

crossup
Dec 04, 2004, 07:59 PM
Something else I've not seen mentioned: apparently the chemistry is pretty robust. I was able to expose a board, develop, etch THEN decide it wasnt developed right so I gave it more time in the developer then tried etching.
Still no good. Try AGAIN. Finally I mixed up some stronger developer(thought the orginal mix too fast at 60 seconds but diluted 50% then it was too weak to work much) and gave it a shot of stronger developer. Then back to etch... much better, it etched normally. :D

Marion
Dec 04, 2004, 08:32 PM
Nice work. Thanks for sharing it. Now I'll know how to make professional looking PCBs :D

crossup
Dec 04, 2004, 09:42 PM
It turns out I neglected to check the orientation of the LiPo Charger boards above and had to remake them mirrored, the new masks worked just like the old ones and I got another pair of super crisp boards. :D Time to print up the masks for Koichi Tanaka's pico IR Rx...

Comatose
Dec 04, 2004, 11:51 PM
Looks great. Transparency film is usually pretty remperature resistant: overhead projectors have pretty big bulbs too. Now you just need to make yourself a CNC drill. Excellon format is just a text file - easy enough to parse...

/ no I haven't made a CNC circuit drill yet. Yet...

Andrew0820
Dec 05, 2004, 12:00 AM
We have used dense resolution inkjet transparancies for some time to mask prototype boards for our robotics lab -- although we use a UV box for exposure. For one-ups, it's hard to beat and the boards are usually of top quality. I have found that the quality is quite superior to the laser offset/Press-n-Peel approach.

andrew

JMP_blackfoot
Dec 05, 2004, 03:01 AM
Something else I've not seen mentioned: apparently the chemistry is pretty robust. I was able to expose a board, develop, etch THEN decide it wasnt developed right so I gave it more time in the developer then tried etching.
Still no good. Try AGAIN. Finally I mixed up some stronger developer(thought the orginal mix too fast at 60 seconds but diluted 50% then it was too weak to work much) and gave it a shot of stronger developer. Then back to etch... much better, it etched normally. :D

I have found that warming the developer in the microwave for about 40 seconds helps a lot. I think the temperature to shoot for is about 50°C

crossup
Dec 05, 2004, 10:10 AM
In my short experiance with modern materials I find warming the etchant significantly increases the likely hood that the resist will be comprimised. Also if you use press-on resist you will loosen and wrinkle it as its seems wax based.
Be VERY CAREFULL heating etchant in microwave...I use small quantities...2 oz for 40 seconds would be boiling hot...40 seconds on a quart wont warm it too much. So THINK before you do it... for safety sake I warm my etchant in warm water and keep it below 100 deg F. Knock on wood, so far no spills or stains or misshaps.
Thanks JMP.. some day I hope to buy one or more of your excellent receivers

I have found that warming the developer in the microwave for about 40 seconds helps a lot. I think the temperature to shoot for is about 50°C

Norman Adlam
Dec 05, 2004, 10:45 AM
Crossup,

Yup! I've done this for somewhile - but use an Epson at 14400 dpi and printing black, onto Inkjet overhead transparencies. Note that one side is slightly rough, and this is the side to print the ink onto!

Works great for me! :D

Here's a hint. Print the word 'Bottom' onto the PCB mask (somewhere where it doesn't matter on the PCB). That helps reduce the confusion factor at exposure time!

Cheers,

Andrew0820
Dec 05, 2004, 11:07 AM
As an aside, for those of you that may not have PCB development software, Microsoft Powerpoint has fairly decent drawing capability. You can create a palette of shapes that may be dragged onto the surface; you can do overlays if you are etching both sides; with resizing, you can draw in a larger mode then reduce accordingly and finally, if you are producing multiple small PCB's, the copy and paste works very well to fully populate a 6x8 photoresist board with multiple PCB's. Adding witness marks to the edge of the original mask will also aid in alignment and shearing. Powerpoint is not a replacement for good design software, but it is almost always available on a machine you may have access to.

the "other" andrew

OzDragonFlyer
Dec 05, 2004, 10:51 PM
another tip.. print on the side that will be placed hard up against the face of the pcb.

If done the other way around, light will get under the design due to the thickness of the transparency and give fuzzy edges :)

I've been using this method with a laser printer for years and it gives excellent results.


BTW, a cheap light source can be had by scrounging for old EPROM erasers.. UV tube ,sliding drawer and timer built in :)