• unlimited access with print and download
    $ 37 00
  • read full document, no print or download, expires after 72 hours
    $ 4 99
More info
Unlimited access including download and printing, plus availability for reading and annotating in your in your Udini library.
  • Access to this article in your Udini library for 72 hours from purchase.
  • The article will not be available for download or print.
  • Upgrade to the full version of this document at a reduced price.
  • Your trial access payment is credited when purchasing the full version.
Buy
Continue searching

Flexography printing of silver based conductive inks on packaging substrates

Dissertation
Author: Ramesh Chandra Kattumenu
Abstract:
Printing technologies for the production of flexible electronics have gained much interest due to its potential as a means to reduce the complexity and costs of present technology. High volume printing techniques like flexography are of great importance in order to produce rolls of flexible electronics printed directly on paper substrates. The proposed research will be focused on RFID components being in-line printed using flexography printing as the manufacturing platform. The properties of substrates and inks and printing process parameters are evaluated to study their effect on printed traces and RFID antenna. It was found in the study that properties of substrates like surface roughness, surface energy have an impact on the ink film thickness of the printed trace. The variation in ink film thickness and line width had a profound influence on sheet resistance. To achieve good printability and conductivity of printed traces variables like substrate roughness, surface energy, porosity, cell volume of anilox roll, printing speed, drying capabilities of press and ink flow characteristics have to be optimized and matched.

TABLE OF CONTENTS ACKNOWLEDGMENTS ii LIST OF TABLES viii LIST OF FIGURES xi CHAPTER 1. INTRODUCTION 1 2. LITERATURE REVIEW 4 2.1 RFID Technology 4 2.1.1 Introduction 4 2.1.2 Radio Frequency Identification Tag 4 2.1.3 RFID Tags - Classification 6 2.1.4 Choice of Operating Frequency 8 2.1.5 Markets for RFID Technology 10 2.1.6 RFID Benefits 11 2.1.7 RFID Drawbacks 12 2.1.8 Considerations for Item - Level Tagging 14 iv

Table of Contents—continued CHAPTER 2.2 Printed Electronics 15 2.2.1 Introduction 15 2.2.2 Material Aspects..... 18 2.2.3 Printing Processes and Their Potential for RFID Printing 21 2.2.4 Printing Technologies 23 2.2.5 Flexography as a Manufacturing Platform for Printing Electronics 28 2.2.6 Basic Principle of Flexography Printing 30 2.2.7 Substrates for Electronic Printing 32 2.2.8 Conductive Inks 33 2.2.9 Printing Plates for Flexography 35 2.2.10 Anilox Roll 38 3. PROBLEM STATEMENT 45 4. DESIGN OF EXPERIMENTS 49 5. MATERIALS AND PROCESSES 52 5.1 Substrates 52 5.2 Properties of Substrates 53 v

CHAPTER Table of Contents—continued 5.2.1 Roughness and Compressibility of Substrates 53 5.2.2 Porosity and Permeability Coefficient 54 5.2.3 Mercury Intrusion Porosimetry 56 5.2.4 Contact Angle and Surface Energy 60 5.3 Conductive Inks 63 5.4 Print Trials - Flexography 65 5.4.1 Trial -1 65 5.4.2 Trial - 2 72 5.5 Characterization of Printed Samples 76 5.5.1 Print Quality Evaluation 76 5.5.2 Ink Film Thickness 78 5.5.3 Electrical Characterization of Printed Resistors 78 5.5.4 Printed Antenna Radio Frequency Testing 83 6. RESULTS AND DISCUSSIONS 87 6.1 Data Analysis Procedure 96 6.2 Analysis of Printed Traces on Paper Substrates 97 6.2.1 Effect of Different Factors on Sheet Resistance 99 vi

CHAPTER Table of Contents—continued 6.2.2 Effect of Different Factors on Line Raggedness 102 6.2.3 Effect of Different Factors on Line Width 105 6.3 Analysis of Printed Traces on Paperboard Substrates 108 6.3.1 Effect of Different Factors on Sheet Resistance 108 6.3.2 Effect of Different Factors on Line Width 112 6.3.3 Effect of Different Factors on Line Raggedness 115 6.4 Ink Film Thickness Analysis 116 6.5 Printed Antenna Radio Frequency Testing 117 6.5.1 Trial -1 117 6.5.2 Trial - 2 120 6.6 Simulation Results 123 7. CONCLUSIONS 127 8. REFERENCES 130 vii

LIST OF TABLES 1. Active and Passive Tags 7 2. RFID Frequency Ranges and Application 8 3. RFID Global Sale Forecasts (2005 - 2015) 11 4. Comparison of Traditional Printing and Electronics Printing 17 5. Comparison of Conventional and Printed Electronics Processes 21 6. Specifications for Major Printing Process 24 7. Contact Pressures for Printing Processes 25 8. Markets that use Flexography Printing 29 9. Printing Application and Appropriate Line Screen and Volume 39 10. Project Flow Chart 47 11. Design Matrix Determining the Order of Experiments 49 12. Substrates used for Printing 52 13. Properties of Paper and Paperboard 55 14. Parameters Measured with MIP 58 15. Contact Angle and Surface Energy of Substrates 63 16. Conductive Inks used for Printing 63 viii

List of Tables—continued 17. Properties of Silver Inks 64 18. Dryer Temperature at the Print Stations 68 19. Print Trial Summary 69 20. Symbols used During Print Trial 70 21. Print Trial - 2 Summary 74 22. Substrate Surface and Physical Properties 87 23. Characterization of Printed Traces 88 24. Calculated Resistance and Sheet Resistivity of Printed Traces 89 25. Best Subsets Regression Analysis for Ink Film Thickness 92 26. Factors for ANOVA Analysis 96 27. Results Obtained for Traces Printed with WB Ink 98 28. Results Obtained for Traces Printed with SB Ink 98 29. Analysis of Variance for Sheet Resistance 100 30. Tukey's Pair Wise Comparison Test - Sheet Resistance 101 31. Analysis of Variance for Line Raggedness 103 32. Analysis of Variance for Line Width 106 33. Tukey's Pair Wise Comparison Test - Line Width 107 34. Factors for ANOVA Analysis 108 ix

List of Tables—continued 35. Analysis of Variance for Sheet Resistance 109 36. Tukey's Pair Wise Comparison Test - Sheet Resistance 110 37. Analysis of Variance for Line Width 113 38. Tukey's Pair Wise Comparison Test - Line Width 114 39. Analysis of Variance for Line Raggedness 115 40. Alien Printed Antenna Performance with IC 119 x

LIST OF FIGURES 1. Inductively Coupled and Microwave Transponders 6 2. Simple Band Picture of Insulator, Semiconductor and Conductor 19 3. Applications of Conducting Polymers in Microelectronics 20 4. Comparison of Conductivity of Different Materials. 20 5. Overview of Printing Technologies 23 6. Printing Unit Cylinders with Flexible Layers 26 7. Diagram of a Flexographic Plate Image 31 8. Operating Principle of Flexography Process 31 9. Rubber Plate Making Process 36 10. Laser Engraving of a Rubber Plate 37 11. Comparison of a Photopolymer and Laser Engraved Plate 38 12. Dot Gain and Ink Film Thickness Based on Anilox Cell Volume 39 13. Percentage Film Transfer Versus Film on Plate 43 14. Cumulative Intrusion Curves for All Substrates 59 15. Pore Size Distribution of Paper Substrates 59 xi

List of Figures—continued 16. Pore Size Distribution of Board Substrates 60 17. Change in Contact Angle of Substrates with Water 62 18. Change in Contact Angle of Substrates with Methylene Iodide 62 19. Printing Plate Design for Flexo Trial 1 67 20. Printing Plate Design for Flexo Trial 2 73 21. Dimensions of a Simple Bar for Calculating Sheet Resistance 80 22. Four Point Measurement Technique 80 23. Laboratory Antenna Measurement Range 84 24. Printed Line Traces on Substrates PL P2 and P3 89 25. Printed Line Traces on Substrates Bl, B2, B3 and B3bs 89 26. Scatter Plots - Ink Film Thickness, Roughness and Surface Energy 94 27. Printed Line Trace on Substrate B3bs 96 28. Main Effects Plot for Sheet Resistance 101 29. Interaction Effects Plot for Sheet Resistance 102 30. WB Traces on P2,15BCM Anilox, 80%, 90% and 100% Tone Step 102 31. Main Effect and Interaction Effect Plot for Line Raggedness 104 32. Main Effects Plot for Line Width 106 xii

List of Figures—continued 33. Interaction Effects Plot for Line Width 107 34. Main Effects Plot for Sheet Resistance 110 35. Interaction Plot for Sheet Resistance I l l 36. Main Effects Plot for Line Width 113 37. Interaction Effects Plot for Line Width 114 38. Main Effects and Interaction Effect Plot for Line Raggedness 115 39. Ink Film Thickness at 90% Tone Step with 18.6 urn Anilox Band 117 40. Alien Antenna Performance Data Set - Trial 1 119 41. Antenna Performance at 18.6 um Anilox Cell Volume 121 42. Antenna Performance for WB Ink 123 43. Simulation Resistance Results for WB Ink 124 44. Simulation Resistivity Result for WB Ink 125 xiii

CHAPTER 1 INTRODUCTION Printing technologies for the production of flexible electronics have gained much interest due to its potential as a means to reduce the complexity and costs of present solid state technology1. Both screen printing2 and inkjet printing3'4'56 have been explored but due to the limitation in speed and volume flexography and gravure, are currently being implemented. High volume printing techniques are of great importance in order to produce rolls of flexible electronics printed directly on paper substrates, resembling the newspaper production of the paper printing industry7, with the main idea of reducing the cost in addition to new applications that require large area and flexibility. This is mainly driven by desire to lower the cost of printed electronics including large displays, sensors and RFID (radio frequency identification). The direct printing of RFID tags onto paper substrates or packages directly would prove to be a great cost saving factor and would benefit the retail and supply chain management operations. 1

Printing techniques such as screen printing89'10 has been widely adapted for low resolution printing for switch pads. Offset lithography has been used to fabricate electronic components such as LED11, sensors12 and circuits13 using functional inks. Flexography14 and gravure15 printing have been used for sensors, solar cells transistors, and RFID system components, such as conductors or RFID tag antennae. Flexible polymer substrates, including polyester, polycarbonate and polyimide have been used for the high volume printing of electronic devices. The packaging sector is one of the main areas where the direct printing of RFID tags can provide a great cost advantage to retailers and supply chain management logistics. Due to the non-uniformity and hygroscopic properties of paper and paperboard, there are many challenges to yet be met for printing functional electronic devices to these materials. Hence, the requirements for printing electronics on paper are much higher than for conventional printing. However, in comparison to film, paper and board offer the benefits of opacity and stiffness. For conventional printing of the text and graphics, image quality must meet the optical requirements of an observer, while for printed electronics, although visually acceptable, may fail due to numerous problems 2

including open circuits, short circuits or inadequate overlapping areas or geometries. The components of an RFID tag antenna and circuit must be in proper registration to ensure required contact. Printed material gaps and line widths must be held to very close tolerances. The present work is divided into several chapters. At the beginning an introduction to RFID is presented with tag classification, choice of operating frequency, markets and price considerations. Various materials used in the manufacture of RFID tags and other printed electronics are discussed. The effects of various substrate and ink properties along with printing process parameters are considered in the analysis of printed traces. 3

CHAPTER 2 LITERATURE REVIEW 2.1 RFID Technology 2.1.1 Introduction Radio Frequency Identification (RFID) is a technology that uses electromagnetic radiation in the radio frequency range to identify an object16. This is a wireless data transmission and identification technology that has been in use for many years and is a unique and powerful identification tool for a wide range of applications such as contact less payment, transportation, personal access, industrial and business applications17. Today, this technology has been catapulted into the technological forefront by integrating it into the field of supply chain management by providing improved speed, accuracy, efficiency and security of information sharing across the supply chain18. 2.1.2 Radio Frequency Identification Tag A basic RFID system consists of three main components19 • The transponder that is located on the object to be identified. 4

• A reader with an antenna that communicates with the transponder. • Network to analyze the transmitted and received information. An RFID tag, also called a transponder, is an object that can be attached to a product, animal or person for the purpose of identification using radio waves. The transponder consists of a coupling element or antenna and an electronic microchip carrying the data about the tagged item. Figure 1 shows two types of transponders- the inductively coupled transponder with loop antenna on the left and for higher operating frequencies and greater range of use, a dipole antenna on the right19. In passive RFID tags, the transponder usually does not possess its own voltage supply. When the transponder is within the interrogation zone of a reader it is activated and the power required for activation and operation is supplied through the wireless link to the reader. When not in the vicinity of an interrogation zone, a passive tag is inactive. 5

Coupling Element (Coil, Antenna^ Housing Chip J Figure 1: Inductively Coupled and Microwave Transponders19 An RFID reader contains a transmitter and a receiver. The transmitter sends out a wireless signal providing power and commands for a passive tag. When not sending commands, the receiver converts the radio waves returned from the tag back to a digital form, interprets the returned signal and has an additional interface to forward the information to computer systems for further processing20. There are several factors that determine the size and shape of an antenna such as the frequency range at which it operates the required read range and the product to which the tag will be applied21. 2.1.3 RFID Tags- Classification A common way of categorizing tags is by their source of power and is also one of the main determining factors for the cost and longevity of a tag22. Different types of tags are in use today and these include active, passive and semi-active tags. Active tags are powered by their own internal power 6

supply. These use an on-board battery to power communications, processor, memory and possible sensors. When a reader is querying information these tags transmit data and due to their on-board power supply the active tags are more reliable, can transmit at higher power levels allowing greater range and can transmit data in 'RF challenged' environments. These tags are typically larger and significantly more expensive than passive tags due to the presence of a battery on board. With the increase in size the capabilities of the tag increases23. Table 1 displays the advantages and disadvantages of active and passive tags24. Table 1: Active and Passive Tags Tag Active Tags Passive Tags Advantages Long read ranges Small size, long operational life, low cost Disadvantages Large size, limited operational life, high cost Short read ranges, more sensitive, close proximity needed Examples Intermodal transport containers, airport ground support equipment (GSE), highway toll tags Access control and security, library books, identifying widgets Passive tags do not have an internal power supply. The incoming radio frequency induces an electrical current in the antenna which is used to power 7

the onboard integrated circuit. Passive tag responses are transmitted by backscattering the carrier signal from the reader. Thus, the antenna of a passive tag is used to power up the circuit and transmit the backscatter signal. 2.1.4 Choice of Operating Frequency Based on the applications and the environment through which a RF signal must pass, different configurations and frequencies are employed. The frequency range in which an RFID tag operates is usually broken down into low, high, ultrahigh and microwave frequency ranges25 as shown in Table 2. Table 2: RFID Frequency Ranges and Applications Name Low Frequency (LF) High Frequency (HF) Ultrahigh Frequency (UHF) Microwave Frequency Frequency 30-300 kHz 3-30 MHz 300MHz- 3GHz >3GHz Read Range 50 cm 3 m 9m >10m Typical Applications Pet identification, items with highwater content Building access control Boxes and Pallets Vehicle identification 8

It is crucial to choose the appropriate frequency to retain readability throughout the life of the product26. The useful carrier frequencies for RF tags range from a kHz to GHz. A robust frequency is 125 KHz which can be read through metal, water or practically any other surface but the read range is short. Such tags cost between 2 and 10 dollars per unit and therefore are typically only used on larger and more expensive items. An application example is in the automobile immobilizers where the car key has a passive RFID tag incorporated into it that the steering column authenticates27 reducing auto theft by as much as 50%28. The 13.56 MHz RFID tags are less expensive and have a smaller read range of about 3 feet. The most common frequency band that is being used today is 860-960 MHz, or UHF (Ultra-High Frequency) RFID. Active UHF tags can read at distances of up to 20 feet in open air; however, they can not operate in water or either on or through metal. These frequency ranges are currently being implemented by Wal- Mart29-30. RFID systems are regulated or restricted as radio devices and hence must follow governmental restrictions with other wireless applications such as amateur radio, radio station, emergency services or television transmissions. The different frequency ranges for RFID have different read range properties. 9

2.1.5 Markets for RFID Technology First patented in 1973 by Mardio Cardullo31 this technology has recently seen tremendous growth and is becoming commercially viable. Significant focus from the business world is due to mandates placed by Wal-Mart3233 and the United States Department of Defense (DOD)1334 requiring the use of passive RFID systems. The major emphasis placed by Wal-Mart is similar to the one it had on barcodes in 198412. The DOD is using RFID to trace military supply shipments. Active RFID tags have been placed on more than 270,000 cargo containers with passive RFID tags placed on packaged items inside the containers to track shipments throughout more than 40 countries35'36. The airline carrier, Delta Air Lines, intends to spend around $25 million to roll out an RFID system to track baggage, reduce loss and make it easier to route bags if customers change their flight plans37. In order to stop losses due to theft, RFID concepts are being used in corporate PCs, networking equipment and handheld devices. The use of RFID in these applications seems reasonable and non-intrusive. The credit card company VISA® is promoting contactless RFID enabled credit and debit cards to conduct transactions without having to use cash or coins38. The tire manufacturer Michelin has begun fleet testing of tires with RFID tags inserted into them with unique number that will be 10

associated with the car's VIN (Vehicle Identification Number) for tracking purposes39. But concerns regarding privacy issues are yet to be resolved. In addition to the above mentioned applications, consumer market RFID technology has attracted considerable interests from companies such as Gillette12'40, Georgia-Pacific41, Intel42'43and Texas Instruments44 to name a few. It is estimated that revenue generated with RFID tags will increase from $300 million in 2004 to $2.8 billion in 2009 according to a report by market research company In-Stat45. A recent market research report by IDTechEx showed that the market value of RFID tags by 2018 will be more than five times the current market value46. Table 3 below shows the trend for the increase in tag production from 2005-2015. Table 3: RFID Global Sale Forecast (2005-2015) Number (Billions) Item Pallet/case Other Total 2005 0.5 0.4 0.4 1.5 2010 27 30 5.7 62.7 2015 1000 35 12.5 1047.5 2.1.6 RFID Benefits While the bar code is prevalent, RFID offers benefits that exceed those of the barcode47. No physical contact or line of light is needed between the reader 11

and the tag. Due to this, the process of scanning is quicker and hence goods are able to move in and out through facilities faster, which increase productivity48. Industry experts have estimated that the distribution capacity can be increased by as much as 10 to 20 percent with RFID systems. RFID can be used to reduce the error rate in processes that are labor intensive. This would help in increasing the accuracy level from 90 to 100%49. In this regard, Delta Air Lines Inc implemented RFID to test 40,000 pieces of luggage from check-in to plane loading. They reported accuracy levels up to 99.9% illustrating the success of the RFID process50. An RFID system can be used to better monitor the expiration date of returns because the products are more transparent to the supplier. It can be used as an anti-counterfeiting measure in the pharmaceutical industry because it can be difficult to reproduce uniquely identified tags. Another benefit is fewer stock outs for retailers. Based on checkout data, retailers can replenish the shelves and inform the distribution and supply centers to replenish the inventory so that customers will be able to find what they want without needing to inquire. 2.1.7 RFID Drawbacks Apart from the various benefits of using RFID there are also several issues to be tackled for RFID implementation in the future. One drawback would be 12

privacy and security concerns. A tag on an item can be detected by other RFID scanners at other locations thereby giving a personal shopping history to the merchants51. This is similar to the current issue of consumer behavior tracking on the Internet using cookies, which tells subsequent sites visited by a user where the user has previously visited on the Internet. These security and privacy issues are more complicated in open-environments52 compared to closed environments where information is encrypted with some write-once only 'locks'. With packages traveling between two or more companies, encryption becomes even more difficult since the contents have to be read by the manufacturer, supplier and the retailer. Unified Global standards- A lack of uniform standards for RFID persists. It is difficult to understand how the standards will vary from one part of the world to another. Currently, United States and Europe operate in a similar segment of the UHF spectrum, however in other regions of the world, the UHF spectrum has been set aside for other uses such as mobile telephones. Although Electronic Product Code (EPC) global is a major player with respect to standards, the DOD has sought to follow the guidelines of the International Standards Organization (ISO)53. To date EPC global and ISO have proposed standards that are not compatible. 13

Tag Cost- One way for adopting RFID tags at item level is to bring the cost down to $0.01-$0.05 level. This can be achieved by permanently affixing RFID tags to goods for applications in logistics, anti-counterfeiting, transaction processing and brand protection. Hence, packaging manufacturers will be able to deliver these tags at much favorable prices than Consumer Packed Goods (CPG) firms buying millions of tags at a time. 2.1.8 Considerations for Item-Level Tagging Based on the above considerations, implementation of RFID technology at lower cost is realizable and can replace barcodes only when tags can be placed on individual items in a manner analogous to optically scanned barcodes. For such widespread use, tags must cost less than l-2 10(t. For item-level tagging, typical read ranges are expected to be less than l m. Hence, 13.56MHz or lower seems to be the "sweet spot" though there is a push for 900MHz frequency. The limiting factor that determines the operating capacity 14

at 13.56MHz is the antenna size. As a result, printed electronics may fit well into this from an economic perspective55. In the conventional approach silicon based tags in the form of small chips are connected to an external antenna using various attachment technologies (pick and place and lower cost technologies such as fluidic self-assembly56). As manufacturers are pushing towards higher frequencies and lower costs, conventional tags work well for pallet/case level tracking but are not suitable for item-level tagging in water or metal-contaminated environments. Using organic materials applied by vacuum sublimation, carrier mobilities greater than 10cm2/V-S have been realized resulting in circuits operating at several MHz57. Though the performance of devices by printing is still lower, progress is being made in this area. RFID tags by printing, an additive and high throughput process eliminates the need for photolithography, vacuum processing and hence is expected to be much lower in cost than silicon based techniques per unit area. 2.2 Printed Electronics 2.2.1 Introduction In the past, the growing need for low cost, high volume information led to the development of printing technologies such as the invention of a mold, 15

allowing the manufacture of movable type in the 1450s58. Printing processes could be efficient and cost effective ways of producing electronic components such as printed circuits (by printing conductive elements directly on the substrate without the etching stage), displays (such as Organic Light Emitting Devices), RFID antennas, batteries, etc. Robustness is an added advantage with printed electronics59. The trend is being driven by the demand for low cost, large area, flexible and lightweight devices. Organic and polymeric semiconducting materials have been widely used offering advantages of flexibility, compatibility with a wide variety of substrates, and ease of processing. These materials can be processed at a lower temperature (less than 120°C) compared to high temperature (900°C) and vacuum needed for inorganic semiconductors60. However, with the advantages of low cost printed electronic circuits, come challenges such as limited resolution, high registration requirements, and a high uniformity of the printed layers. Another challenging aspect is obtaining the proper ink characteristics for a desired printing process without reducing the functional properties of materials. Table 4 compares the requirements for traditional graphic printing to the requirements for printing electronics61. The unique benefits to printing electronics rather than using solid state technology are given below. 16

High speed and high volume Environment friendly Negligible waste Short time cycle from design to manufacturing Applicability in novel products Low end integrated electronics Flexible substrates Reduced logistic costs Table 4: Comparison of Traditional Printing and Electronics Printing' Requirement Resolution Register Edge Sharpness Layer Thickness Homogeneity Adhesion of Layers Solvents of Inks Purity of Solutions Visual Properties Electronic Properties Traditional 15um-100 um Low High High Not Important Important Cost Issue Not Important Very Important Not Important Electronics « 20um High Very High Less Very Important Important Functional Issue Very Important Not Important Very Important 17

Printed organic circuits require at least three functional components: a conductor, a semiconductor and a non-conductor (dielectric). A combination of these can be used to form capacitors, field effect transistors (FET), resistors etc. These components can be combined to form functional circuits and ultimately complete electronic systems. 2.2.2 Material Aspects The materials comprising the entire spectrum of conductivity, conductors, semiconductors and insulators are all needed for the processing of an integrated circuit. Conductors are used for device interconnection and contacts and as functional elements of inductors and capacitors. The electrical properties of a material arise from their electronic structure. Figure 2 shows the energy levels in the conduction and valence bands of an insulator, semiconductor and a metal. The energy spacing between the highest occupied molecular orbital called the valence band and the lowest unoccupied molecular orbital called the conduction band is called the band gap62. In metals atomic orbitals overlap with equivalent orbitals of neighboring atoms to form molecular orbitals. In a given range of energies, these molecular orbitals form a continuous band of energies making them conductive. In semiconductors 18

there is a small band gap that electrons may bridge the gap due to various forms of excitation (i.e. thermal, photon). Insulator Increasing energy Semiconductor Metal Wide Band Gap Narrow Band Gap No Gap Energy Levels in Conduction Band • Energy Levels in Valence Band Figure 2: Simple Band Picture of Insulator, Semiconductor and Conductor The most basic of all electronic components is the conductor which acts as a conduit for current through a circuit. For printed electronics, conductors are formed using inks. For field effect transistors conductive inks form the source, gate and drain electrodes. Conducting polymers are considered as an attractive option for printed electronics due to their unique combination of properties63 as shown in Figure 3. 19

Electrostatic discharge Electromagnetic ,, , „. ,. (ESD) interference Metallization , ,. /T^ m , . ,,. protection (EMI) shielding \ t / Lithography- x ' / e.g. charge < Conducting ^ Interconnection dissipators, Polymers ^ technologies/wiring conducting resists Corrosion D e v i c e s" protection e&>dlodes' of metals transistors Figure 3: Applications of Conducting Polymers in Microelectronics63 The conducting properties of different materials are shown in Figure 4 that range from quartz, diamond as insulators to copper, silver as very good conductors. s/m lO"16 Conductivity Quartz < Insulators io-12 10- Diamond Glass A Conjugated Polymers Semi-conductors 8 10-4 Silicon 10° Germanium > Metals 104 108 Copperilron/Silvei Figure 4: Comparison of Conductivity of Different Materials 20

Full document contains 157 pages
Abstract: Printing technologies for the production of flexible electronics have gained much interest due to its potential as a means to reduce the complexity and costs of present technology. High volume printing techniques like flexography are of great importance in order to produce rolls of flexible electronics printed directly on paper substrates. The proposed research will be focused on RFID components being in-line printed using flexography printing as the manufacturing platform. The properties of substrates and inks and printing process parameters are evaluated to study their effect on printed traces and RFID antenna. It was found in the study that properties of substrates like surface roughness, surface energy have an impact on the ink film thickness of the printed trace. The variation in ink film thickness and line width had a profound influence on sheet resistance. To achieve good printability and conductivity of printed traces variables like substrate roughness, surface energy, porosity, cell volume of anilox roll, printing speed, drying capabilities of press and ink flow characteristics have to be optimized and matched.