SEMICON Japan 2018 Printing pattern is formed in uneven and curved structures by modification of the screen printing

December 12-14, SEMICON Japan 2018 were held in Tokyo Big Site. Main topics of display in this exhibition are picked up.

SEL exhibits original OLEDs

Figure 1. Folderble 8-inch OLED (Semiconductor Energy Laboratory)

First of all, as concerns display, Semiconductor Energy Laboratory exhibited original OLEDs, which were 8.6-inch folderable panel (1200 × 1920 pixel) and 8.3-inch 8K panel.

The former is an RGB side-by-side color panel. It was fully flexible by making use of 2 plastic films as both substrates. For this reason, it's possible to bend at R＝3 �o.

By contrast, the latter is a white EL emission + micro color filter panel because of ultra-high resolution same as 1058 ppi. Concretely, it's composed of tandem units, which were Blue fluorescence emitting unit and Red/Green phosphorescence emitting unit.

By the way, original technologies such as OLED materials, CAAC-IGZO (C-Axis Aligned Crystal-In-Ga-Zn-O)-TFT were adopted for both panels.

Possible to print in uneven structure by a new screen printing method

With respect to manufacturing process, National Institute of Advanced Industrial Science and Technology (AIST) appealed an original printing method "the off-set screen printing method", and also, exhibited a die bond wiring sample, which was formed by this method.

Figure 2. Demonstration of the off-set screen printing (AIST)

As its name, this method is advanced model of the conventional screen printing method. As you know, in the screen printing method, a paste is directly printed on the substrate. By contrast, in this method, first of all, the paste is printed on PDMS (poly (dimethylsiloxane)) blanket. And then, this PDMS blanket is contacted with the substrate, as a result, ink pattern is transferred. In this time, it's possible to minimize bleeding of the paste in the transfer process, as a result, to enhance printing resolution because the PDMS blanket absorbs solvent in the paste.

Generally, resolution of the screen printing method is about 50 μm width for mass production, on the other hand, that of the offset screen printing method is W = 20 μm order. Furthermore, in this process, mesh mark of the screen mask does not remain on the substrate by existence of the PDMS blanket. Of course, it's easy to print thick film, too.

In this time, AIST pressed that it could be easily corresponded to 3D structure, curved surface, etc. As picture 2, Ag paste was printed on the IC chip at 50 μm width. As a result, it's possible to print Ag paste in side angle of the chip. In short, it can be corresponded to uneven surface easily. This is reason why PDMS blanket is changed by printing pressure, it is synchronized with shape of printing structure. For this reason, it's possible to transfer completely because of without change of ink.

High transparent and heat-resistance film appears

Figure 4. OLED using EXPEEK (Kurabo)

Figure 3. EXPEEK (Kurabo)

As regards material, Kurabo introduced a new PEEL film (EXPEEK) with high transparent and heat resistance property. Its transmittance and haze are 83 % and 4 % respectively. Furthermore, it has high heat resistance such as Tg = 320 ℃. For this reason, if this film is used as a substrate of a-Si TFT, organic-TFT, and so on, it can be corresponded to same annealing process of the conventional TFT with glass substrate. By the way, thermal expansion coefficient is not relatively low same as a few dozen ppm/℃. In the booth, a roll sample (520 �o width) and green OLED lighting device with EXPEEK made by Yamagata University were exhibited.