Flexible 2-Layer Paper Printed Circuit Board Fabricated by Inkjet Printing for 3-D Origami Electronics

Transcription

1 INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING-GREEN TECHNOLOGY Vol. 5, No. 3, pp JULY 2018 / 421 REGULAR PAPER DOI: /s ISSN (Print) / (Online) Flexible 2-Layer Paper Printed Circuit Board Fabricated by Inkjet Printing for 3-D Origami Electronics Mingyu Kang1,2 and Kyung-Tae Kang1,# 1 Korea Institute of Industrial Technology, 143, Hanggaul-ro, Sangrok-gu, Ansan-si, Gyeonggi-do, 15588, Republic of Korea 2 Program in Nanoscience and Technology, Department of Transdisciplinary Studies, Graduate School of Convergence Science and Technology, Seoul National University, 1, Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea # Corresponding Author / ktkang@kitech.re.kr, TEL: ORCID: KEYWORDS: 3-D printed electronics, Paper electronics, Metal printing, Inkjet, Origami Inkjet printing has advantages to be easy to use, environmentally benign and adaptable for flexible electronics manufacturing. Also, paper is an emerging potential substrate due to extremely cheap price and its abundance. We used inkjet printing on a paper to make inexpensive flexible 3-D origami electronics. We printed two pads of 2 2mm 2 and the metal lines between pads that had the width of 0.2 mm and the length of 5 mm on the paper. Repetitive printing methods reduced the resistance value of metal lines. The measured resistance values of metal lines printed on a chromatography paper ten times repeatedly were less than 10 ohms. We confirmed that the metal lines printed on both sides of the paper were not connected and could be connected through the printed via without holes. The inkjet-printed metal lines on paper were successfully used to construct the simple PCB with LED. We also tested bending test and confirmed lighting the LED. In order to prevent that metal lines were broken during folding the paper PCB, both sides of the folding point were additionally printed such as via. As a result, the metal line was not broken even when folded. Manuscript received: December 3, 2016 / Revised: March 9, 2017 / Accepted: June 5, Introduction Recently, flexible elctronics has gained attentions due to it esiness of be carried or worn. However, flexible electronics needs to new set of manufacturing methods due to the flexibililty of its substrates. 1-3 In flexible electronics or printed electronics, one of a variety of purposes is to make the low-cost device. The price of polyethylene terephthalate (PET) and polyimide (PI) as substrate are about 2 cent dm -2 and 30 cent dm -2 respectively. On the other hand, paper is suitable to replace expensive substrate for disposable devices due to the extremely low price ( 0.1 cent dm -2 ) of paper. 3,4 Nowadays paper is studied as a substrate for flexible electronics in thermochromic displays, 5 disposable radio frequency identification (RFID) tags, 6 antenna 7-9 and so on due to its advantages that are inexpensive, lightweight, and easy to use. But photo paper is mostly used to make electronics using paper substrate due to permeation of other papers such like office paper or chromatography paper. In the case of disposable microfluidic and diagnostic devices, the highly absorbent paper is suitable. 10,11 Inkjet printing, 12,13 one of direct writing technologies, has also many advantages that include low-cost manufacturing and lowtemperature micro-fabrication on flexible substrates. Moreover, this printing method can reduce the ink consumption due to drop-ondemand process that allows for the delivery of a precise amount of inks. Bu when metal lines were printed on various paper using an inkjet printing, the chromatography had a higher resistance and a worse dimensional accuracy of the width of printed lines than photopaper. 14 In this work, we made flexible electronics using chromatography papers. Inkjet printing and papers were used to make the low-priced device in all experiments easily. We investigated making flexible double layer paper electronics and method for increasing conductivity. 2. Experimental 2.1 Methods The goal of this experiment is to produce a two-layer PCB using only paper and ink-jet as shown in Fig. 1(a). Since the paper has a property to absorb inks, sufficient thickness of the paper is required to KSPE and Springer 2018

2 422 / JULY 2018 INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING-GREEN TECHNOLOGY Vol. 5, No. 3 Fig. 2 Images of paper at different temperatures Fig. 1 Concept of 2-lyaer paper printed circuit board using ink-jet printing and design of (b) pads, metal line for measuring resistance and (c) via to connect unconnected metal lines on both sides make two-layer metal lines that are not connected. For this reason, a chromatography paper (Whatman cellulose chromatography papers 3 MM Chr sheets) with a thickness of the chromatography papers is 340 µm was chosen as a paper substrate. The FUJIFILM Dimatix Materials Printer (DMP-2831) as inkjet printing equipment was used to make two-layer PCB. This inkjet printing equipment can control the drop space that represents the distance of center between the drops and display the number of total droplets. In order to choose the silver ink, the chromatography paper was annealed in a convection oven for 30 min according to temperature. The chromatography paper becomes blacken or deteriorated above 200 o C as shown in Fig. 2. Low temperature sintered silver ink (Advanced Nano Products, DGP 40LT-15C) below 200 o C was selected to prevent the phenomenon of blacken or deteriorated chromatography paper. We printed 2 pads of 2 2mm 2 and 5 mm length metal line with 0.2 width between two pads to measure resistance value as shown in Fig. 1(b). Drop space of inks was fixed to 25 µm and metal lines were printed according to the repeating time and the number of repeating printing and on top of each other to penetrate silver inks less than half of chromatography thickness. In order to make vias which connect the unconnected metal lines on both sides, we printed it of mm 2 on both sides according to drop space to penetrate silver inks more than half of chromatography thickness. All printing processed at a substrate temperature of 60 o C that is the maximum substrate temperature controlled within the equipment. After printing, the silver ink printed on the chromatography paper was sintered at 150 o C for 30 min in a convection oven. Fig. 3 Image of (a) the printed lines and (b) cross-section of printed line according to repeat interval time of printing. (the number of printing at the same position: 10) (INT: interval time) To measure the penetration thickness of silver ink, the chromatography paper was cut with scissors after printing, and then the cross section was observed with a microscope. 2.2 Results The metal lines were printed on top of the each other 10 times repeatedly from 30 s to 5 min to verify the penetration thickness and the spread of silver inks according to interval time of re-print. Figs. 3 and 4 show the printed line and cross-section of printed line according to repeat interval time of printing. The width of printed metal lines was decreased to the average line width of 570 µm until the time interval of 180 s, but no significant decrease was observed thereafter. Although the penetration thickness of silver ink printed on chromatography paper was decreased until the time interval of 120 s, its thickness was measured more than half of the thickness of chromatography paper. The penetration thickness was

3 INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING-GREEN TECHNOLOGY Vol. 5, No. 3 JULY 2018 / 423 Fig. 4 (a) Line width and (b) penetration thickness of printed line according to repeat interval time of printing (the number of printing at the same position: 10) Fig. 6 (a) Line width and (b) penetration thickness of printed metal line according to the number of printing at the same position. (Repetitive printing interval time: 3 min) Fig. 7 Image of (a) the printed lines and (b) cross-section of printed line according to the number of repeated printing (dotted line: the portion of silver exposed on the chromatography paper surface) Fig. 5 Image of (a) the printed lines and (b) cross-section of printed metal line according to the number of repeated printing 150 µm which is less than half of thickness of chromatography paper at the time interval of 150 s and the penetration thickness was no significant decrease thereafter. This shows the penetration thickness can be reduced if printing repeatedly at the same position with enough time for drying the solvents of silver ink. To confirm the spread and penetration thickness according to the number of repeated printing, we printed metal line by ink-jet repeatedly from 1 to 10 at intervals of 3 minutes. Figs. 5 and 6 show the images of the surface and cross-section of printed metal line and line width of the printed metal line and the penetration thickness of silver ink according to the number of repeated printing at the same position. The line width of the metal line printed on chromatography paper gradually increased the number of repetition of printing 5 times, but thereafter, the average line width did not change significantly at 570 µm. Likewise, the penetration thickness of silver ink gradually increased the number of repetition of printing 5 times, but thereafter, the average penetration thickness of silver ink did not change significantly at 150 µm. Figs. 7(a) and 7(b) show the surface image of Scanning electron microscope (SEM) and silver on surface measured by energydispersive X-ray spectroscopy (EDS) after printing metal lines repeatedly 10 times at interval of 3 minutes on top of the each other. It is divided into a silver part exposed on the chromatography paper surface and a part where the solvent appears to spread as shown in Fig. 5(a) (R : 10). In the SEM image, only the portion of silver exposed on the chromatography paper surface is visible, but it is confirmed that the portion where the solvent spreads in the EDS measurement is also silver as shown in Fig. 7(b). Fig. 7(c) shows the cross-section image of SEM and measurement by EDS. The blue line in Fig. 7(c) is the intensity of silver measured by EDS. The penetration thickness of silver was half of the chromatography paper thickness. Fig. 8 shows the resistance value of metal according to the number of printing at the same position. As the number of repetitive printing increased, the resistance value decreased. Especially, when the printing was repeated 9 times or more, the value of 10 ohms or less was measured. Fig. 9 shows the ratio of D repeat x (the number of drop of printed silver ink) for D repeat 1 (the number of drop of printed silver ink about onetime printing) and the ratio of V repeat x (volume of printed line about line length of mm) for V repeat 1 (volume of printed line about onetime printing) according to the number of repeated printing. The printed volume as many as the number of used inks did not increase at the same rate. In the case of 10 re-printing, the used silver ink is 10 times larger than onetime printing, while the printed volume was only about

4 424 / JULY 2018 INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING-GREEN TECHNOLOGY Vol. 5, No. 3 Fig. 10 Image of (a) the printed via and (b) cross-section of printed via according to drop space (DS) Fig. 8 The resistance value of metal line printed on chromatography paper according to according to the number of repetition of printing Fig. 11 The printed area and penetration thickness of silver ink of printed via according to drop space Fig. 9 The resistance value of metal line printed on chromatography paper according to according to the number of repetition of printing 2 times larger. This means that the amount of silver in the unit volume increases as the number of re-printing increases. As a result, as the repetitive printing at the same position was increased, the density of silver on the chromatography paper becomes higher and the resistance value becomes lower. The via was printed by changing drop space from 5 µm to 25 µm in 5 µm interval. Figs. 10 and 11 show the images of the surface and cross-section of printed via and the printed area and the penetration thickness of silver ink of the printed via according to drop space. The area of the printed via also increased as the amount of ink per unit area increased as the drop space decreased as shown in Fig. 11. For the drop space up to 10 µm, penetration thickness of silver ink was more than half of chromatography paper thickness. However, the penetration thickness of silver ink was less than half of chromatography paper when the drop space was more than 15 µm. In order to connect the unconnected metal lines printed on both sides, the penetration thickness of the via should be more than half of the paper thickness. Fig. 12 (a) surface and (c) cross-section image of SEM and silver measurement of (b) surface and (d) cross-section by EDS of two vias printed on both sides of the chromatography paper For this reason, two vias were printed on both sides of the chromatography paper with a drop space of 5 µm. Fig. 12 shows surface and cross-section image of SEM and silver measurement by EDS of two vias printed on both sides of the chromatography paper.

5 INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING-GREEN TECHNOLOGY Vol. 5, No. 3 JULY 2018 / 425 Fig. 14 Image of working blue LED on 2-layer chromatography paper PCB after (a) bending and (b) folding of 90 o C Fig. 13 (a) The design of 2-layer chromatography PCB to make a simple blue LED electronics. (b) Image of working blue LED on 2-layer chromatography PCB Fig. 15 The design of metal lines to prevent to break the metal line during folding Although printed via is divided into a silver part exposed on the chromatography paper surface and a part where the solvent appears to spread as shown in Fig. 10(a) (DS : 5 µm.), it is confirmed that the portion where the solvent spreads in the EDS measurement is also silver as shown in Fig. 12(b) like as metal line. It is confirmed that the two vias printed on both sides of the chromatography paper are connected by EDS measurement as shown in Fig. 12(d). To make the simple structure of one blue LED to see the potential of chromatography paper PCB, we printed pads, metal lines and vias on the front and the back of chromatography paper using inkjet printer as shown in Fig. 13(a). Figures in Fig. 13 show the printing order. The pads and the metal lines were printed 10 times repeatedly with drop space of 25 µm at interval time of 3 minutes on top of the each other and the vias were printed with drop space of 5 µm. Fig. 13(b) shows working the blue LED on 2-layer chromatography paper PCB after applying a voltage of 6 V. We tested bending and 90 o C folding test. In order to test the bending, 2-layer chromatography PCB was attached to the side of petri dish cover with a diameter of 57 mm as shown in Fig. 14(a). It was not changed before that the resistance value of the printed line. Also blue LED on 2-layer chromatography pater printed pad, line and via worked well. When the 2-layer chromatography PCB was folded inward of the printed metal line, the blue LED on PCB was worked well as shown in Fig. 14(b). On the other hand, when the 2-layer chromatography PCB was folded outward of the printed metal line, the resistance value of the printed line was not measured any value because it was broken. Finally, in order to prevent that metal lines were broken during folding 2-layer chromatography paper PCB, both sides of the folding point were additionally printed with drop space 5 µm such as via and length of 1.5 mm as shown in Fig. 15. Fig. 16 shows the resistance value of metal line according to the number of folding inward and outward of the printed metal lines about Fig. 16 The resistance value of metal line according to the number of folding inward and outward of the printed metal line about two samples two samples. Both resistance values of folding inward and outward of the printed metal lines were increased as the number of folds increased. The resistance value of folding inward of the printed metal lines was gradually increased compared to folding outward of them. Although the resistance value of the line was increased at the time of folding, the metal line was not broken even when the folding position was made to be connected with silver at all portions of the paper. 3. Conclusions We developed 2-layer flexible PCB using chromatography paper and inkjet printing to make inexpensive electronics. The

6 426 / JULY 2018 INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING-GREEN TECHNOLOGY Vol. 5, No. 3 chromatography paper PCB showed the potential of flexible electronics. In the case of printing more than 10 times at the interval time 3 minutes repeatedly, the sheet resistance values of metal lines with 5 mm 0.2 mm printed on a chromatography paper were less than 10 ohms. Although the metal lines printed on both sides of a paper was not connected due to penetration thickness, they are connected through the via that was made using inkjet printing only. In order to prevent that metal lines were broken during folding 2-layer chromatography paper PCB, both sides of the folding point were additionally printed such as via. As a result, the metal line was not broken even when folded. The metal lines printed by inkjet printing were on both sides of a paper which allow a wide variety of applications such as paper FPCB (flexible printed circuit board). The paper electronics can also be formed 3D shapes such as a cylinder, circular cone and so on by origami. ACKNOWLEDGEMENT This work was supported by the Global Leading Technology Program funded by the Ministry of Trade, Industry and Energy, Republic of Korea ( ). NOTE This On behalf of all authors, the corresponding author states that there is no conflict of interest. REFERENCES 1. Kim, S.-H., Lee, M.-Y., Woo, K., Youn, H., Lee, T.-M., et al., A Study on Thin Film Uniformity in a Roll-to-Roll Thermal Evaporation System for Flexible OLED Applications, International Journal of Precision Engineering and Manufacturing, Vol. 18, No. 8, pp , Yu, J. H., Rho, Y., Kang, H., Jung, H. S., and Kang, K.-T., Electrical Behavior of Laser-Sintered CU Based Metal-Organic Decomposition Ink in Air Environment and Application as Current Collectors in Supercapacitor, International Journal of Precision Engineering and Manufacturing-Green Technology, Vol. 2, No. 4, pp , Lab on a Chip, Vol. 9, No. 19, pp , Yang, L., Rida, A., Vyas, R., and Tentzeris, M. M., RFID Tag and RF Structures on a Paper Substrate Using Inkjet-Printing Technology, IEEE Transactions on Microwave Theory and Techniques, Vol. 55, No. 12, pp , Kim, S., Ren, Y.-J., Lee, H., Rida, A., Nikolaou, S., et al., Monopole Antenna with Inkjet-Printed EBG Array on Paper Substrate for Wearable Applications, IEEE Antennas and Wireless Propagation Letters, Vol. 11, pp , Shaker, G., Safavi-Naeini, S., Sangary, N., and Tentzeris, M. M., Inkjet Printing of Ultrawideband (UWB) Antennas on Paper-Based Substrates, IEEE Antennas and Wireless Propagation Letters, Vol. 10, pp , Cook, B. S. and Shamim, A., Inkjet Printing of Novel Wideband and High Gain Antennas on Low-Cost Paper Substrate, IEEE Transactions on Antennas and Propagation, Vol. 60, No. 9, pp , Martinez, A. W., Phillips, S. T., Butte, M. J., and Whitesides, G. M., Patterned Paper as a Platform for Inexpensive, Low-Volume, Portable Bioassays, Angewandte Chemie International Edition, Vol. 46, No. 8, pp , Lee, J.-C., Kim, W., and Choi, S., Fabrication of a SERS-Encoded Microfluidic Paper-Based Analytical Chip for the Point-of-Assay of Wastewater, International Journal of Precision Engineering and Manufacturing-Green Technology, Vol. 4, No. 2, pp , Xie, L., Mäntysalo, M., Cabezas, A. L., Feng, Y., Jonsson, F., et al., Electrical Performance and Reliability Evaluation of Inkjet-Printed Ag Interconnections on Paper Substrates, Materials Letters, Vol. 88, pp , Sirringhaus, H., Kawase, T., Friend, R., Shimoda, T., Inbasekaran, M., et al., High-Resolution Inkjet Printing of All-Polymer Transistor Circuits, Science, Vol. 290, No. 5499, pp , Joubert, T., Bezuidenhout, P., Chen, H., Smith, S., and Land, K., Inkjet-Printed Silver Tracks on Different Paper Substrates, Materials Today: Proceedings, Vol. 2, No. 7, pp , Lee, H., Lim, C. H. J., Low, M. J., Tham, N., Murukeshan, V. M., et al., Lasers in Additive Manufacturing: A Review, International Journal of Precision Engineering and Manufacturing-Green Technology, Vol. 4, No. 3, pp , Li, Y., Sun, H., Shi, Y., and Tsukagoshi, K., Patterning Technology for Solution-Processed Organic Crystal Field-Effect Transistors, Science and Technology of Advanced Materials, Vol. 15, No. 2, Paper No , Siegel, A. C., Phillips, S. T., Wiley, B. J., and Whitesides, G. M., Thin, Lightweight, Foldable Thermochromic Displays on Paper,