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Old 20th April 2012, 12:09 PM   #1
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Location: in a small town called Senlis, north of Paris
Default Mylar printing nt dark enough

Hi all
I usually print on my Mylar sheets to make PCB masks but out of a laser printer it comes out not dark enough.
Who knows about another way to print those, with enough black so the UV rays wont jeopardize the resin ?
Thanks
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Old 20th April 2012, 01:40 PM   #2
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Print 2 and overlay or try an inkjet. E
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Old 20th April 2012, 02:07 PM   #3
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I have tried printing two and overlaying but the result is blurred.
Inkjet ? I ll find an old one in my scrap and try.
is it efficient ?
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Old 20th April 2012, 03:22 PM   #4
Simon B is offline Simon B  United Kingdom
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Printing two and putting them one above another is unlikely to work well for anything with fine detail. The ink or toner needs to be in direct contact with the uv sensitive layer, unless you have a perfectly collimated uv source, which is unlikely.

I use ordinary A4 office paper, which seems to transmit about 30% of the uv hitting it, through a laserprinter. With my homebrew 196x uv led array that gives an exposure time of about 6 mins.
It works very well indeed. As always with photographic developing, do a test strip to determine correct exposure time.

If this seems just too easy to be true, and it did slightly surprise me, put draughtsman's tracing paper (about 60% uv translucency) through a laserprinter. You might notice that I keep saying laserprinter.

Also, be aware that the chemistry you use for developing the image has a big effect on the contrast of the final image, and here contrast is our best friend. This is a 1-bit colour depth image - copper, or not copper, nothing in between. I get much better results using a silicate developer than plain sodium hydroxide - it's a higher contrast developer.

For a more in depth treatment of this, on much the same lines, I recommend anyone to read this:

Making PCBs

I have this page stored on my offline machine with the words THIS IS IT at the end of the folder name. The rest of his site is quite fun too.

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Old 20th April 2012, 04:10 PM   #5
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Thank you Simon
Could you please develop about that silicate developper ? I never heard about it.
I use the usual NaOH but could not imagine there was a better developper.
thanks
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Old 20th April 2012, 05:26 PM   #6
Simon B is offline Simon B  United Kingdom
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Well it is in the link I gave above, here it is again:

Making PCBs

In case it's not working for you for some reason I'll quote the info, with apologies to Mike's Electric Stuff:

Take 200cc of "water glass", add 800cc of distilled water and stir. To this add 400g of sodium hydroxide (caustic soda).
Important safety precautions: The sodium hydroxide solid must NEVER be handled, use disposable gloves. When the sodium hydroxide dissolves in water it produces a great deal of heat so it must be added a little at a time and each portion allowed to dissolve before more is added. If the solution becomes very hot leave it to cool before adding more sodium hydroxide.
The solution is VERY caustic and it is particularly damaging to the eyes, use eye protection when making and handling it.
It also ruins clothing. Water glass is also known as "sodium silicate solution" and "egg preserver", It used in fire proofing fabrics, for waterproofing walls and making "chemical gardens". Caustic soda is used for clearing drains and available from any chemist. The solution cannot be made by dissolving solid sodium silicate.This solution will be the same strength as the concentrate, and so will need diluting - about 1 part concentrate to 4 to 8 parts water, depending on the photoresist used and temperature.


It does seem to be something available much more easily in Europe as a pcb product than in the US, though see later. The stuff that I use comes as a concentrate solution, no recipe attached, but warns that it contains NaOH and >5% silicates. Typical mealy mouthed euro-babble "safety" speak.

I don't understand the warning in the Mike's Electric Stuff recipe that it can't be made by dissolving sodium silicate in water - sodium silicate is water soluble, though there is a something of a family of related compounds, so some scope for confusion.

In the US, Web-tronics sell straight sodium silicate as pcb developer in tiny little 2oz bags.....:

Positive Developer

Read the MSDS sheet (the blurriest I've ever seen!) to find out what's actually in it:

http://www.web-tronics.com/pdf/POSDEV_MSDS.pdf

Sodium silicate, white powder, probably available from somewhere very close to you, very cheaply. Either the solid stuff, or "water glass". Add some NaOH, or don't add it. If you do do some home chemistry, I'd be glad to hear of your results.
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Old 20th April 2012, 06:17 PM   #7
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Got it Simon, easily found here in Frogland (the next to be communist country in teh world, aftter North Korea and Cuba), named 'silicate de soude' for water^proofing of cement.
It happens that I have some in my cellar.
I'll try.
keep you posted.
thanks for the info
best regards
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Old 20th April 2012, 06:41 PM   #8
Simon B is offline Simon B  United Kingdom
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If you possibly can, watch the pH, I think that it might well become much more corrosive as it becomes alkaline, ie its pH rises above 7. Corrosive both as in eats copper, and as in eats flesh.

If it isn't pokey enough to start with, maybe try adding a small amount of NaOH?

Haven't given much thought to the chemistry of this stuff's action on copper yet - hoping I can con someone else into working it all out for me!
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Old 20th April 2012, 07:52 PM   #9
AuroraB is offline AuroraB  Norway
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Location: Norway, -north of the moral circle..
I have used a product called Laserstar for several years in our proto lab at work. Never had a problem with even my first old laser printer almost 20 years ago.
Available here:
100062 - MEGA - LASERSTAR FILM, A4, 10 SHEETS | Farnell United Kingdom or here:
Mega-UK - Artwork Films

Developer for the more common positive resists these days is 14g of NaOH pr liter. I use standard caustic soda from the paint shop. Use at room temp or there abouts....... do not reuse, - discard after use.... it's cheap enough.....
There really is no need for any more or less strange additives. Use latex gloves if you feel for it. If the resist is somewhat old, out of date, a very light swipe with a cotton ball will help release the resist residues.
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Old 20th April 2012, 08:35 PM   #10
Simon B is offline Simon B  United Kingdom
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Well, good to know it's there if you do have to use film for some reason, though happily I don't. Even at 5 per 10 sheets (direct from Mega) it costs about 100x plain paper, from Farnell, 12 per 10. I'll stick with the paper.

As for developers, NaOH works, I just find silicate better. I expect that having a good setup of bubble tanks etc reduces the need for high contrast developer with wide developing time latitude. The stuff I'm using is from Mega, via Rapid, though I should think I'll be buying it from ebay once Billy starts flogging off that sack full in his basement

Probably a rarity nowadays, but photographic developing tongs are useful and cheap for handling purposes, and don't make those men from forensic science, who still won't go away, ask even more awkward questions.....

Last edited by Simon B; 20th April 2012 at 08:37 PM.
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