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Fine line screen printing - applications

This text is auto transcribed and auto-summarized by AI:

  • Screen printing is becoming increasingly finer and smaller, and it is expected that within a few years we will be reaching 20 micrometer line widths and maybe even lower. The wafer per hour rate for the back end processes is also rising, and it is projected to rise to >10,000 wafers per hour by the next years

  • The state of the art for screen printing on solar cells is 19 micrometers and above, with an aspect ratio of 1818 micrometers. This is a relatively easy application, because the pictures are very wide and interrupted lines can be tolerated.

  • Micro-led displays are very hot display topic, and one of the key uniques of this display technology is that you can create bezel free displays. This means that you can create a larger display by putting together many kind of smaller tiles and building up the big display.

  • One way to create wraparound edge electrodes is to drill via into the glass, fill the field and feel the field through glass fires. But this is really not elegant, so a more interesting approach would be to create this so called wraparound edge electrodes.

  • Screen printing can produce very fine lines, but as micro led dyes shrink in size, the bond sizes and metallization lines will also get smaller, which means that if screen printing is to stay competitive in this technology, it also has to produce ever finer lines.

  • Applied Materials showed how they can print screen printed lines as fine as 15 micrometers, but the application is very challenging because it cannot tolerate broken interrupted lines and must have defect-free metallization on 90% of the tiles.

  • Samsung uses a PVD process developed by a Korean company, but if screen printing could produce fine lines, 15 micrometers or less without defects, maybe this could be with very little defect [ this is in our view too big challenge for screen printing]

  • Another application that I wanted to highlight is around flexible hybrid electronics, and I think many of the technology hurdles that have held back this technology are being cleared away now. And I think screen printing could also play a role here. The wiring lines can be screen printed, but the pins of the ICs are much narrower than the wiring lines. So one needs to have a fan out structure connecting the pins to the actual wiring.

  • Screen printing cannot do the wiring and the final structure just based on screen printing process, but if fine line screen printing would be further advanced, then this would be possible.

  • This image is from Nexflex, and I took some of these images from a presentation by Komori in Japan. It shows a very interesting application for Transparent Touch or HMIs, where one maybe does not need a protective layer.

  • The requirements for a transparent touch display are very different from the requirements for a transparent switch, so the line width needs to be a lot narrower. The line widths are generally sub four micrometers, and this shows you the requirement for this industry.

  • If screen printing could print ever finer lines, then it would stay relevant in this application and be very competitive process, and the requirements have also shrunk over time. So if screen printing is to stay relevant, it needs to target sub 15 or so, maybe at least sub 20 micrometer range.

  • Standard screen printing takes you down to 50-60 micrometers, but new screen printing technologies are taking you down to 20-15 micrometers [in lab conditions not production]. Then people start to use hybrid processes, such as screen printing plus laser plus photolithography.

  • We want to focus on alternative technologies, so we talked about photovoltaic metallization, microgrid, flexible hybrid electronics, transparent light switches, edge electrodes, and LTCCs. Before going to the alternative technologies, I just want to mention maybe a couple of applications which I admitted in my presentation but are very important.

  • In order to print very fine lines for 5G and LTCC, you need to have very good edge definition, so you need to be able to print lines as small as 15 micrometers

  • In this hybrid screen printing process, the ink itself contains a photosensitive material, so you don't need a photoresist. This allows you to get very fine lines, and the ink is compatible with peat substrates.

  • A hybrid screen printing process was developed by Kodak, where they created a metal mesh, and then used plating to thicken the layer and achieve bulk like bulk like conductivity. This process can go down to sub10 micrometers.

  • A Japanese company can print complex patterns with just 1.5 micrometer line with silver nanoparticles, and they can cure the ink at low temperature. If you want to go below that level and achieve kind of one micrometer, then the reverse offset process is interesting.

  • Reverse offset printing technique is very unique because you totally ink the roller mold, the ink semi absorbs into the mold material, and then the ink is transferred to the relief plate. This allows you to create metal meshes with just one micrometer line.

  • Here's another, I think, interesting technology, by Asahi Kasei in Japan. This one uses a seamless roller mold, which is patterned not using just laser, but with electron beam lithography, and it produces very fine lines with very well defined edges and just 300 micrometers wide.

  • Here you can see an application of printing aligned with a three micrometers for transparent RF ID on products without taking up real estate.

  • There are a lot of hybrid and road roll technologies, and Panasonic has developed a process that allows them to print two micrometer lines with a good aspect ratio and a good sheet resistance of two ohms per square

  • The main competition is photolithography, and Nippon Printing has achieved a line width of one micrometer in their products. This technology can be used for transparent displays, and the company is targeting the market of sub 40 inch displays.

  • We looked at applications for screen printed lines, photovoltaic metallization, microgrids, transparent capacitive type switches, edge electrodes in capacitive touch displays, and hybrid and direct printing techniques.


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