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Discussion Starter #1
Hi all, I am brand new to screen printing (complete novice, just been learning off of videos and this forum). I'm actually pursuing a different avenue than most of you, I am working in a research lab and we are trying to use screen printing as a method of printing circuits (we have a conductive ink that we plan to use)

The circuits are on the micro-scale, so obviously we need extremely fine detail. We are using a 420 mesh count screen to try and obtain this.

Here's the thing: based on everything I'm reading, with a 420 mesh count I should expect to have to expose my screen for about 4 minutes (maybe more). However with this amount of time I can't wash out the image, maybe only bits and pieces here and there.

But if I reduce the time all the way down to 1:30, I get good details and no peeling. So I guess my question is, what am I missing here? I just want to make sure that this isn't going to cause any problems later (with inking or whatever), because 1:30 seems like a ridiculous time to me based on everything I've read

I coat the screen once on the shirt side and then once on the squeegee side. Let it out to dry overnight in a fume hood. Exposure table is an RXP exposure unit (25x36" Auto UV Screen Exposure Unit w/ Aluminum Compression Lid).

Thanks in advance for any information you might be able to provide, I'm trying to understand everything I can about this process so that I can adjust it as necessary for our needs
 

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The type of emulsion also affects the exposure time. I have never exposed with that type of bulb, but the metal halide exposure unit we use exposes screens in 20 seconds or less so 1:30 isn't unusual. You may want to pick up an exposure step scale to make sure you are using the correct exposure time.
 

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If the image area doesn't dissolve it was hardened

You didn't tell us anything about your ink or stencil, but most of the conductive ink I've printed was worth about US$1,000 per gallon. You're not print circuits with gentle plastisol. You need a completely cured stencil to resist the ink & cleanup solvents.


Exposure is easy, if the image area is 'crusty' and doesn't dissolve, it usually means your positive failed to stop invisible UV energy from reaching the image area like a bad raincoat or the image area is closing up because of light scatter & undercutting.

Positive comparison
Next time you expose any screen, test if your positive completely stops UV energy. Tape a dime (or any thin coin), or a piece of aluminum foil to the stencil.


No light will penetrate the dime and that area should wash out like a dream compared to your positive.

To measure stencil hardness (resistance to developing or cleanup solvents), I suggest a US$10 Stouffer 21 step gray scale to simulate 21 different exposures. This is a standard photographic darkroom test positive that's been used since the 1930's.

Exposure FAQ Screen Making Products how to measure exposure


As a novice, your dealer sold you an $880, low energy, multiple light source without any way to measure your exposure. If you told them your requirements and they accepted your money it's time for a discussion with them.

You will have a very hard time making fine line 420 mesh screens because of undercutting which is a built in part of a multi-light low resolution exposure unit. You can't make a hard sharp shadow with multiple lights.

Yes, it's less expensive a high resolution exposure unit. A fluorescent, low energy exposure unit is suited to large area low resolution images like signs. Textile printers buy them because the are the cheapest.

Amateurs will suggest underexposing your stencils as a method to prevent the fine lines from closing up.

The Great PositiveDave wrote a great article on undercutting which is the real cause of fine lines closing up.
http://www.t-shirtforums.com/t-shirt-articles/t108270.html
 
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as a newbee to this art I realize just that- it seems to be more of an art than science. your xposure paradox seems to prove this. I bought a system that told me the proper exposure for the emulsion, light, transparency and, etc,...was 12 minutes, 30 seconds. It never worked. NEVER. I read, reread, and experimented, changed my lighting, and now my exposure time is 3 minutes 15 seconds. is that a big difference? I am begining to think this process is as complex as the human body.
 

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BTW- I didnt read the above posts, so scold me if I have sinned. I must have missed a long time calculation the Myans created. Anyways, you came to the right site. I have learned more here than I could have expected. Now I just need to sell some shirts.
 

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Discussion Starter #7
Thanks all for your replies. My emulsion is CCI DXP dual cure emulsion, and the ink is bought from DuPont (http://www.tekra.com/products/conductive_inks/5000.pdf)

You mentioned that if the stencil is not completely cured, then it won't resist the ink or cleanup solvents. Is this true even if it has been allowed to completely dry out?

We have already ordered the 21step Stouffer scale, but it hasn't arrived yet and may not for a while
 

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Stencil for DuPont 5000 conductive ink

My emulsion is CCI DXP dual cure emulsion, and the ink is bought from DuPont ([media]http://www.tekra.com/products/conductive_inks/5000.pdf[/media])

You mentioned that if the stencil is not completely cured, then it won't resist the ink or cleanup solvents.

Is this true even if it has been allowed to completely dry out?
I see you searching for loophole shortcuts but, solvent resistance to your ink & ethylene diacetate cleanup solvent comes from cross-links, not whether the stencil is dry.

If strong solvents like ethylene diacetate come in contact with un-reacted (un-resistant) sensitizer, it forms a new UNBREAKABLE bond that stencil remover can't break.

YES, moisture in a stencil blocks the sensitizers from cross-linking so it's logical the the best cross-linking happens in stencils that are dry.

I am worried that you are printing the silver flakes in DuPont 5000 through a 420 tpi mesh instead of the recommended 195 tpi mesh.
 
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