Final Report Summary - LIGHT-ROLLS (High-throughput production platform for the manufacture of light emitting components)
Executive summary:
The European Commission (EC)'s LIGHT-ROLLS funded project, which took care of cost efficient production of light modules, started in July 2009 under the Seventh Framework Programme (FP7) (Grant Agreement No. CP-TP 228686).
The project focused on the development of modular based production line units applying three highly innovative manufacturing platforms for the seamless, high throughput manufacture of micro-structured systems (in particular LED-based lighting and display systems) for applications in automotive, consumer or life science. The scientific objective aimed to realise structures in the micron range and to integrate also dies to be assembled in high-speed and parallel by benefit of self-assembling. Nanoparticle dispersions used in fast conductive track printing technologies allowed the parallel generation of conductive lines. At project start the LIGHT-ROLLS manufacturing platform was based on:
1. RMPD-rotation, a patented process technology to generate three-dimensional (3D) polymer microstructures based on a fast additive manufacturing approach;
2. new chip assembly methods, originating from self-assembly methods;
3. high resolution - high speed conductive track generation and interconnection based on ink-jet and laser printing methodologies.
These three processes comprised the founding elements of the LIGHT-ROLLS technology platform with a roll-to-roll philosophy. The manufacturing modules were developed to be integrable, exchangeable, with mechanical, fluidic and Information technology (IT) interfaces, to make it easy and cost efficient to adjust the sequence of process steps for the product to be produced. Besides the translation of processes for high-throughput manufacturing, high yield was achieved by the application of Advanced process control (APC) and production IT methods.
Furthermore, a pilot line was set-up and tested for fabrication of flexible Light emitting diode (LED)-display systems. However, the manufacture of other components like lab-on-chip or integration of new micro-energy storage components will be also possible in the future to address needs of European industry. In this sense, LIGHT-ROLLS knowledge base for design for manufacturing was elaborated for future products.
The consortium of LIGHT-ROLLS was made up of 9 organisations from 8 different members and associated states (Germany, Romania, United Kingdom, Switzerland, Sweden, Italy, Austria and Spain) and has covered all different areas of the manufacturing technology aim of the project. This consortium has included:
- 6 Small and medium-sized enterprise (SME)s: microTEC Gesellschaft für Mikrotechnologie mbH, Microelectronica S.A. Design LED Products Ltd., Norbert Schläfli Maschinen Zofingen, XAAR Jet AB and ACP-IT GmbH.
- Research Institutes: Fraunhofer Gesellschaft (Fraunhofer IPA), Centro Richerche FIAT S.C.p.A. and PRODINTEC.
Project context and objectives:
Micro-products are nowadays used in a wide range of fields, for example medical, biotechnology, consumer and automotive. However, emerging micro-products as innovative display solutions, lab-on-chip systems, micro-energy supplies or light emitting panels, increasingly require the integration of different functionalities and present challenging demands in terms of high volume and low cost production.
Taking this into account, LIGHT-ROLLS project aimed to apply micro-fabrication basic research results to the development of new processes for the manufacture of micro-structured systems. Concretely, the project explored the following highly promising and innovative micro-fabrication technologies:
- RMPD, a patented process technology to generate polymer micro-structures by a fast photo-polymerisation manufacturing approach;
- self-assembly principles;
- ink-jet printing methodologies.
LIGHT-ROLLS aimed to provide new production solutions not only by the integration of these innovative micro-fabrication processes, but also by the development of APC and production IT to achieve quality control and high degree of automation. To demonstrate the feasibility of the new manufacturing concept, the ultimate objective of the project was the development of a new roll-to-roll production line for the seamless, high throughput manufacturing of micro-structured systems. The project intended to provide a flexible manufacturing solution. Therefore, the approach of LIGHT-ROLLS was based on a modular roll-to-roll philosophy, in such a way that the manufacturing modules are exchangeable to make easy and cost-efficient the adjustment of the sequence of process steps for the production of different products. So, although the pilot line was set-up and tested for the fabrication of flexible LED-display systems, other components like lab-on-a-chips or flexible solar cells, could be manufactured in future. Moreover, for manufacturing of future products, a LIGHT-ROLLS technology knowledge base about design and configuration of the line was developed within the project.
The arrangement of the LIGHT-ROLLS line is sketched below. A flexible polymer material ('web') is used as substrate. The substrate is provided on a roll, passing all processing modules and rolled up at the end.
The scope of LIGHT-ROLLS comprised the following detailed objectives:
1. Development of seamless micro-fabrication technologies:
- development of the RMPD-rotation based 3D micro-structuring unit for the production of microstructured polymer parts and microsystems;
- development of a die-placing module using the self-assembly effect for a massive parallel assembly of semiconductor dies;
- development of a self-assembly unit for positioning the smallest dies precisely on the substrate in a high volume process;
- development of a printing and sintering module for realising electrical tracks and interconnections, and also other microstructures, like coils, resistors, sensors, etc., for other future applications.
2. Development of high throughput roll-to-roll equipment platform
- development of integrable and exchangeable modules for the equipment platform, including the design of the required mechanical, fluidic and IT interfaces;
- development of an APC and a platform-based Manufacturing execution system (MES) to monitor and control de overall production line;
- enable high volume production;
- enable the integration of other micro-fabrication modules.
3. Development of knowledge base for LIGHT-ROLLS manufacturing
The aim of the knowledge base was to collect the expertise gained from the demonstration activities about the design, configuration and feasibility of the production line in order to promote LIGHT-ROLLS potential and facilitate its application to other future applications.
In order to fulfil the above mentioned objectives, the project was structured in six Work package (WP)s:
WP0 - Project management: This WP dealt with the daily management of the project and the consortium, the overall coordination of the WPs (including technical progress monitoring and quality assurance) and the management of the communication between all the stakeholders (also the communication with the European Commission).
WP1 - Micro-fabrication process elements: This WP was focused on the development and implementation of the 3 main units of the LIGHT-ROLLS manufacturing line (RMPD-rotation, self-assembly of small dies and ink-jet printing/sintering). The goal was to develop robust implementations of these technologies based on existing knowledge and integrate technical solutions as required.
WP2 - LIGHT-ROLLS manufacturing equipment: WP2 tackled the definition of the final platform specifications from the point of view of both hardware and software, as well as the integration of the manufacturing modules into the LIGHT-ROLLS platform. Thus, this WP has involved the definition of the interface specifications, the development of the full concept of the platform, the manufacturing and assembling of the modules and the development of the process control and production IT software solutions.
WP3 - Manufacturing of LIGHT-ROLLS products: WP3 has targeted the design and manufacturing of a LIGHT-ROLLS product accordingly with Light Rolls platform capabilities. Then, a first technology demonstrator was designed, developed and built to verify the feasibility of the three main technologies involved in the project and to address and avoid any possible risk before full integration into the manufacturing platform. Results obtained were used to adjust and design the final demonstrator product and to finally configure the line and their modular components.
WP4 - Demonstration of LIGHT-ROLLS manufacturing: The aim of this WP was to demonstrate the feasibility of the LIGHT-ROLLS concept and produce a demonstrator product. This experience was fed into WP5 to build up the knowledge base.
WP5 - Knowledge base for LIGHT-ROLLS LED products: In the framework of this WP the knowledge base necessary for the fast commercialisation of LIGHT-ROLLS equipment was created. Concretely, two tools were developed: 'Design for LIGHT-ROLLS manufacturing' to allow a fast design of new products, and 'Configuration of a LIGHT-ROLLS production line' to address the needs of the technicians for setting up and operating the line.
WP6 - Dissemination, exploitation, knowledge management: This WP involved dissemination, exploitation and knowledge management of project results.
Project results:
The ultimate result of the project was the development of a roll-to-roll production platform for the manufacturing of micro-structured flexible LED displays. To achieve this goal LIGHT-ROLLS tackled with the following challenges:
a) research and development on RMPD, self-assembly and ink-jet printing / sintering technologies to translate them into functional manufacturing solutions;
b) development of advanced control systems;
c) integration of process modules into a seamless equipment platform for a high throughput manufacturing of lighting and displays products.
Below we provide a description of the technical results that allowed overcoming each of these challenges. In the first chapter, an overall description of the LIGHT-ROLLS production line is detailed in order to facilitate the understanding of the concept developed. Subsequently, the main technologies involved in the project and the control systems developed are outlined.
An introduction to the LIGHT-ROLLS production line
The main result of the project has been the design, development and manufacturing of the LIGHT-ROLLS production line in order to manufacture flexible LED displays as a demonstrator of the feasibility of the LIGHT-ROLLS concept.
New micro-fabrication technologies have been developed or adapted for the integration into this module based production line. Each process module comprise:
- a core production element;
- a supporting frame;
- a controller unit for active control of the module;
- interconnection features for electrical, fluidic, mechanical and logical interfacing.
A flexible material ('web') is used as a substrate to build on. The substrate is provided on a roll, passing along all processing modules and rolled up at the end, all by means of the unwinding and winding cylinders located at the ends of the line. For LIGHT-ROLLS four different types of process modules have been defined: gravure printing, RMPD-rotation, self-assembly and Inkjet printing and sintering.
The gravure module (not foreseen in the initial configuration of the LIGHT-ROLLS line) is located at the beginning of the line and provides movement to the web by means of two rollers perfectly aligned. The gravure cylinder integrated on this module have an engraved mask according to the product to manufacture, and could be of course adapted to the desired final application. The objective of this engraved mask is to mark on the web with an adhesive material the specific places where the electronic components, LEDs in this case, have to be positioned. The gravure cylinder also prints on the web several predefined alignment marks that will play an important role for the operation of the line.
The second step consists on the self-assembly module. This is basically a system to deliver components onto the web with high precision. As explained before, in this application the self-assembly module will deliver LEDs on the previously printed adhesive material deposited by the gravure. The output of this module is then a range of LEDs correctly located on the web and ready to move to the next stage.
The next step consists on an RMPD-rotation module that lays a homogeneous thickness layer of a UV curable material over the web, and selectively cures it through the transparent zones of a patterned mask of a rotating glass cylinder. Where there is a transparent region the UV light passes through the glass and cures the underlying material into a solid polymer. The mask of this glass cylinder is designed to cover all previous components except for those areas to which the electrical connections have to be formed in next steps. In order to remove the non-cured material, the RMPD-rotation module also includes a cleaning unit and other additional elements to assure the integrity of the printing system situated just after.
The last step is the printing and sintering module, consisting of several inkjet printer heads, head controllers and a subsequent sintering system. The essential part of the printing module is the high precision machining and assembly of all these elements that allow a very precise orientation of the printing heads in direction and tilt angles, as well as in distance to the web. This complex configuration allows the module to perform the printing of the electrical connections in their correct position. A sintering post-process was also developed and adapted to the LIGHT-ROLLS production line in order to achieve an optimal cure of the specific ink used in the process.
For the operation of the LIGHT-ROLLS production line, a control system for the automatic aligning of the web in the transversal and longitudinal direction was developed. This control system is based on the identification of the predefined alignment marks printed by the gravure module by means of optical sensors located along the production line. Last but not least, it is necessary to highlight that the overall operation of the line is controlled by an APC application and a platform-based MES, specifically developed in the project.
Thus, although the LIGHT-ROLLS production line has been set-up and tested for the fabrication of flexible LED displays, the main goal of the project related to provide a flexible manufacturing solution has been achieved by the modular design. Thereof, the manufacturing modules are completely exchangeable, allowing to adapt the process steps to the production of different products, and also add any specific module if needed.
An overview of the technical characteristics of the LIGHT-ROLLS production line units is summarised in the table below in order to show the flexibility of the concept developed:
Technical characteristics LIGHT-ROLLS
Overall component size depending on the application selected, but for display applications foreseen:
- Width appr. 150 mm (max 200mm)
- Length approx. 300 mm
- Thickness min 0.240 mm
RMPD-rotation technology for the manufacture of polymer structures
- Line resolution ±10 µm ex substrate
- Registration <10 µm ex-substrate
- Minimum layer thickness per pass 50 µm
- Maximum layer thickness per pass ca. 100 µm - 150 µm depending on polymer and curing parameters
Self-assembly of Dies
- Die size down to 0.35mm x 0.,35mm
- Positioning accuracy on sub-carrier < 10 µm
- Thickness max 90 µm and min 50 µm
Conductive track generation
- Stable printing processes up to 100 µm line width
- Thickness 6 µm
High throughput equipment
- Roll-to-roll process
- Web speed 0.6 m / min - 1.0 m/min
- Operation at atmospheric pressure (air or inert gas).
LIGHT-ROLLS technologies
The design and developed of the three main units that integrate the LIGHT-ROLLS production line (RMPD-rotation module, self-assembly and printing / sintering) has involved the exploration of these promising and innovative micro-fabrication technologies to achieved their technical implementation. Thus, several possibilities were investigated and mock-ups for testing were produced to perform first experimental tests and optimise process parameters.
Below are detailed the main achievements that finally led to the modules implementation in the LIGHT-ROLLS production line.
RMPD-rotation module
RMPD-mask, microTEC's proprietary technology, is based on additive manufacturing methods and allows the high resolution, 3D production of microstructures based on UV curable materials. A Computer-aided design (CAD) system is used to design a three dimensional microstructure of almost any desired shape. This model is transferred to a mask, which is then produced and assembled on the manufacturing unit and the production process begins: a liquid monomer is cured through the mask layer by layer through a photopolymerisation process.
LIGHT-ROLLS research allowed the translation of the batch oriented RMPD-mask technology to a seamless roll-to-roll production method finally integrated into the LIGHT-ROLLS production line. Main advantages are larger areas of microstructures compared with the mask based process, cost efficiency and also an easier, seamless integration into production processes. The Rotation process also allows multi-material processing, i.e. different polymers can be integrated in one part.
As explained above, the developed RMPD-rotation unit lays a homogenous thickness layer of a UV curing monomer and selectively cures it through the transparent zones of an opaque mask on a rotating glass cylinder. The UV light which is holding inside the glass cylinder passes through the transparent region of the glass and cures the underlying monomer into a solid polymer. In the case of LED demonstrator, it was designed to cover two small areas on top of the LEDs' connection pads and separation areas between products.
A method to pattern the mask on top of the glass cylinder with resolutions down to one micron range was specifically developed for this project. The specific process to deposit coating layers onto the cylinder as well as the deposition of photo resins and the following etching steps on cylindrical surfaces were also developed.
Also remark that there is no physical contact between the web and the glass cylinder because the substrate moves on an air cushion, eliminating friction and, at the same time, maintaining the substrate at a proper distance of the glass cylinder. The air flow has to be adjusted depending on the density and thickness of the substrate.
Another element developed was the dispensing unit, fully integrated with the RMPD-rotation unit. Basic element is a spiral coater that applies a homogeneous thin film of the UV curing material on the substrate. Special spiral bars may be designed for different film thicknesses, starting in the one micron range.
The cleaning unit integrated in the module to remove the remaining liquid material, which is not UV-cured through the cylinder mask of the RMPD-rotation process, has also involved important developments. Different solutions were studied, i.e. nebulisation of solvents and further drying. The solution finally implemented avoids the use of flammable substance since some potential substrates may cause important electrostatic charges. Thus, the solution developed consists on a hydrophobic absorbing tissue mounted on a supply roller with a friction brake, a traction roller to wind up the cleaning material and two spring loaded roller that effectively ensure the friction between the absorbing material and the substrate. Additional elements were also developed. For example, an open chamber to create a controlled atmosphere while curing the monomer in order to improve the flexibility of the system and allowing it to work with different materials. This chamber has internal channels designed to drive the main gas flow to the layer of monomer that is being cured. A second wide range UV post-curing has also been designed and situated after the cleaning unit in case that an additional curing is needed. This post-curing is also interesting to avoid contamination at further steps of the LIGHT-ROLLS manufacturing process.
Self-assembly module
Die self-assembling is a massively parallel approach to assemble micro-components on a substrate using self-assembly principles: freestanding micro-components assemble and bind to a location that has been patterned at the bottom of the binding sites. The self-assembly process is conducted in a fluid allowing the micro-components to move freely until they come into contact with the binding point in receptor sites, align in the right orientation and form a stable bond. The state of the art is to take the dies from the wafer by the sequential pick-and-place process. LIGHT-ROLLS approach brings the dies into a feeder unit and place many dies in parallel onto the seamless polymer interim substrate using the self-assembly effect for a precise and fast assembling, resulting in the integration of chip self-assembly methods into roll-to-roll production, which has not been implemented before.
To achieve this goal, LIGHT-ROLLS has focused on the research and development of solutions for:
- dispensing small volume of fluid on specific functionalised areas for the self-assembly process;
- developing solutions for feeding and transporting the chips;
- developing solutions for sorting the chips to detect their orientation and to discern whether they are in right position or not.
A novel process for feeding, transportation and sorting of the LEDs was designed and demonstrated at lab scale.
The feeding concept consists in a reservoir where the LEDs lie on the open surface of water. These LEDs have to be transferred to a channel system for position assessment and sorting. Thus, the reservoir is filled with water until it overflows into the channels filled or wetted with water. In a next step, the LEDs are 'poured' onto the surface of the water. The curvature of the surface causes the LEDs to move to the sides. Any overlying LEDs are separated from each other by vibration and subsequently placed in rows. Finally, the water is rapidly drained from the reservoir by suction. LEDs now lie in the channels and are ready for transportation.
A transportation concept was also developed and a method to produce channels and various geometries thereof were investigated with regard to flow characteristics. Additionally, problems related to flow behaviour in open micro channels were also studied. Different processes for machining the channels were tested and also different experiments were carried out in order to control the hydrophilic character of the surface of the channels. The sorting process developed is based on the use of image processing to recognise LEDs lying incorrectly. These LEDs are rejected and subsequently placed in awaiting magazines by a micromechanical feeder. LEDs lying correctly are further transported in the channel. Rejected LEDs are put back into the sorting process.
In the other hand, a novel wetting process solution combining offset printing technology and single droplet deposition was developed and adapted to the self-assembly process.
The self-assembly process developed and finally integrated in the LIGHT-ROLLS production line comprises one cylinder with an offset plate that is dependent on the application and has engraved marks according to the product design. The marks are hydrophilic surfaces, while the rest is a hydrophobic surface. The offset plate is fixed to a blank cylinder which is rotated by a motor. A water injector puts very small droplets of pure water on the hydrophilic marks on an offset plate. On the other hand, a vacuum gripper takes the LEDs from the magazine where they are stored. When the droplets reach the proximity of the vacuum gripper, the die is attracted and sticks to the water. Following the rotation of the offset cylinder the dies are placed exactly onto the adhesive marks previously printed on the web. The adhesion force is stronger than the attraction to the water droplet, so the die remains in place during the next steps of the manufacturing process.
These results achieved involve a major leap forward in the state of the art, breaking down the barriers to the implementation of this technology at industrial level.
Printing and sintering module
Ink-jet printing of conductive inks is a well-known process to provide electrically conductive tracks on flexible substrates and ink-jet print heads are now accepted as manufacturing tool in various industrial applications such as flat panel displays, electrical and optical devices, memories, as well as bio / pharma devices. The process comprises:
- ink-jet printing of an adequate conductive ink (a stable suspension able to be injected). Inks are normally formulated with nano-sized metal particles coated with polymeric shells that prevent agglomeration of the individual metal particles;
- post-process to destroy the polymeric shell and 'fuse' the metal particles;
- pre-treatment of the surfaces is sometimes also needed to increase adhesion on the substrate.
LIGHT-ROLLS project choses ink-jet technology to produce the electrical interconnection between individual electrical devices because it is easily integrated into a roll-to-roll environment, fast, flexible, and easy to configure for various applications. High tolerances when combined with production control systems and reduced waste are additional advantages considered to the selection of ink-jet as printing technique for conductive track generation.
The ink-jet process translation to LIGHT-ROLLS requirements has included the following tasks:
- Define specifications and select the appropriate conductive ink from a range of commercial products, checking material compatibility with substrate and other layers of the device.
- Select the inkjet print head considering line width and resolution to be printed and required process speed and throughput. Several models of piezo print-heads were evaluated. This kind of print-heads use electrical voltage signals to induce mechanical motion of the dividing walls between the individual ink channels. Several such two-directional wall movements result in the formation of an acoustical pulse within the ink channel, which is stepwise increased in amplitude by reflection at the open and closed ends of the ink channels and by further in-phase wall motions. Proper adjustment of amplitude and timing of the wall motion will cause the formation of a suitable acoustical pulse at the nozzle, which thus will cause the ejection of an ink drop from the nozzle.
Further wall motions are applied to create out-of-phase acoustical pulses in the channel, which are meant to eliminate the remaining acoustical energy in the channel after drop ejection so that the following drop formation process can start from well defined 'neutral' conditions.
- Develop the electrical driving waveform for optimum drop formation: The sequence of electrical voltage signals to cause the ejection of a drop and the elimination of residual acoustical energy is named the electrical driving waveform. Special equipment based on stroboscopic microscope was built within the project for the development of waveforms.
- Perform print tests on the different substrates to establish practical line width and thickness of the electrical tracks; define the x / y print resolution for optimum line shape and smoothness; introduce a pre-treatment if the surface tension of the ink and the surface energy of the substrate do not match sufficiently.
- Investigation of post process methods: Several sintering technologies such as convective oven sintering, Infrared radiation (IR), high power UV radiation, Rapid electrical sintering (RES), and broadband photonic sintering were studied considering compatibility with roll-to-roll process and dimensions to reduce the working chamber to a sensible module size. Photonic sintering was identified as the only technique able to perform appropriately in this roll-to-roll manufacturing line. Therefore, an exhaustive research work was performed on this novel technology to adapt it to the LIGHT-ROLLS production line. Below is schematically represented the final printing module designed and manufactured within the project. It integrates the units for both ink-jet printing of the conducting lines and for sintering the ink.
Web alignment and synchronisation control system
Operation of the LIGHT-ROLLS production line has involved developing a control system to correct both the lateral and longitudinal displacement of the web. Without this control system it would be extremely difficult neither to put the electronic components in place nor printing precisely on the chip open pads. The solution finally chosen was a multivariable control system based on PC. This control system performs two tasks:
- An automatic alignment with the web of the modules, by means of micro-displacements in the transversal direction of the web travel axis.
- An automatic adjustment of rotation speed in the motors that produce the web linear movement in the longitudinal direction: Therefore, a uniform speed in all parts of the line is obtained.
- Servo motors and drives: The control system communicates with the drives so the rotational position and speed of these motors can be read and modified to obtain the required synchronisation between the processes in each module.
- Optical sensors: These sensors detect ink marks printed by the gravure module on the web, and generate digital signals that allow the control system to carry out the current position errors in lateral and longitudinal directions that affect the alignment and synchronisation of the line.
- PC unit: It runs the control strategy and communicates with the different motion control units of each actuator via RS232 or USB protocol.
- DAQ: A data acquisition system with digital and analogue inputs and outputs modules allows the control system to capture the digital sensor signals and, during the development and start-up of the line, allows the user to capture analog signal from these sensors and also to configure them. Analog outputs are used for controlling motor speeds in the synchronisation control loop.
- High precision motorised linear stages: These actuators generate linear displacements of modules in the transversal direction for obtaining the alignment between the web and them. Their resolution is below one micron.
Software for process and quality control
As mentioned before, LIGHT-ROLLS production line also involves the development of an ACP for the optimisation of the production process performed and a platform-based MES or production-IT to monitor and control the overall production line.
The ACP system implements elements as high speed process data collection, real time and offline visualisation of process data, workflow driven actions and process corrections, just-in-time data mining for correlation analysis, etc., in order to optimise the production process.
On the other hand, the production-IT prototype developed provides direct IT interfaces to process equipment as well as to the automation systems within the line. Some functionalities implemented are online monitoring of equipment within the production line, central recipe manager, equipment integration with the main modules, etc.
The MES is fully integrated with the production-IT prototype within the project in a three level scheme:
- Equipment level integration focuses on data collection aspects: Data collection comprises collection of parametric data as well as events and alarm groups. In addition it has to be considered that data might be provided either through messages or file-based. Active control of equipment is responsibility of the production-IT. Therefore this communication path is not topic of the integration between both systems.
- Application level integration comprises requests send from the production-IT to the APC system and events send in the reverse direction.
- User level integration enables integration of user interface components of both systems in one integrated client application frame.
Production-IT prototype is implemented as the primary source for incoming and outgoing data between the whole application and the equipment. Therefore on the equipment integration level there is only information flow from the production-IT prototype to the APC-system. On the application logic layer there are requests and transfer of master-data from the production IT prototype to the APC system. In the reverse direction events are transferred in order to notify out of control actions in the production-IT prototype. On the Graphical user interface (GUI) layer the mainframe is provided by the Production-IT prototype. Portions of the overall GUI are made up by the APC-system and are embedded into the production-IT prototype's GUI. In order to request appropriate content it is necessary that the Production-IT prototype provides information about the current context visualised in the GUI globally.
With regard to the user interface integration, the list of figures below show a Process Plan Editor from the Production-IT Prototype in conjunction with an embedded editor of Statistical process control (SPC) models.
Potential impact:
The main market addressed by partners focus on lighting applications. Thin 'light sheets' are very attractive in automotive applications or building lighting because they require little space, are potentially more reliable and cheaper, include several functionalities, and offer a high degree of freedom to fulfil designers' needs. Other applications with potential in other markets are possible, for example in the field of diagnostics or applications based on functional printing, as flexible active Radio-frequency identification (RFID) tags, flexible solar cells and batteries or simple consumer products.
a) Lighting
The move from using packaged LEDs and low precision screen printing methods for assembly and interconnection towards high-volume, low-cost application would push the commercialisation of LIGHT-ROLLS lines to new horizons.
One particular application which derives large cost/performance benefit from LED 'light where you want it' is retail lighting. To maximise customer experience, minimise power consumption and minimise unit cost, the light on the product should be directed to the front / middle of the shelf. Light weight, thin and mechanical flexibility makes for an easy install. Additionally, the generic benefits of LED technology are provided: long life-time, low voltage, custom colour temperature and high colour rendering index.
The LIGHT ROLLS technology can also be configured for backlighting, where the light source sits behind a graphic or diffuser in a Liquid crystal display (LCD) panel and provides a uniform and diffuser rectangle of light. The light extraction features can be patterned in 2-dimensions to vary the light output across the panel. An example of this concept using prisms is shown. In backlighting, the technology delivers high system efficiency with a thin system.
In automotive, LED for interior lighting and accessories lighting systems are taking retail shelf space away from traditional components (i.e. neon, inorganic emissive sheets) at an accelerated pace. The fastest growing segments are LEDs that replace the small filament bulbs found in tail lights and interior dome lights like courtesy lights or spot lights.
However, there are more applications with respect to lighting or even other applications where LIGHT-ROLLS solutions as a technology platform, may play an important role.
Also remark that the LIGHT-ROLLS technologies can also be exploited for the production of other automotive applications, regarding for example the trend to reduce the installation depth of car taillights or the production of complex components integrating different building blocks (lighting, electronic, photovoltaic modules and batteries for example).
b) Lifescience
Since the RMPD-rotation technology allows the manufacture of polymer microstructures and is able to use foils as a substrate, integrate electrodes, bab-on-a-chip, are potential candidates for future product development.
Several emerging applications that are particularly enabled by the use of thin foils are, for example:
- Temperature controlled biological reactions, such as the Polymerase chain reaction (PCR), take advantage of fast heat transfer through thin materials. In fact, heat transfer rate through a foil is inversely proportional to the square of its thickness as described by the diffusion equation.
- Applications, such as centrifugal microfluidics in which a microfluidic chip is accelerated can profit from low mass and thus low moment of inertia of foil cartridges.
- Foil-based lab-on-a-chip systems suit perfectly as disposable consumables because they only require a minimum of material volume.
With LIGHT-ROLLS concept it will soon be possible to realise a pilot-production-line for validation purpose, extend validation of developed lab-on-a-chip systems and identify low materials for cartridge.
c) Functional printing
Functional printing is a collective term for a platform of organic and printed electronics technologies based on the combination of new materials and cost-effective, large area - printing -production processes that open up new fields of application. Some of the key advantages that organic electronics can offer are thin, light-weight, flexible and environmentally friendly processes and products. It also enables a wide range of electrical components that can be produced and directly integrated in low cost roll-to-roll processes. Intelligent packaging, low cost RFID transponders, rollable displays, flexible solar cells, disposable diagnostic devices or games, and printed batteries are just a few examples of promising fields of application for organic and printed electronics based on new large scale processable electrically conductive and semiconducting materials. There are many other ideas like printed humidity sensors on a piece of paper to be placed in, e.g. cement bags indicating a wet-dry status, applications in smart packaging to support marketing to promote certain products.
The market for functional printing is still in its infancies. Flexible active RFID tags, flexible solar cells and batteries or simple consumer products and games are only a few examples according to OE-A roadmap, all of them potential applications of LIGHT-ROLLS technology.
In summary, the huge versatility of the LIGHT-ROLLS concept, based on its possibility of operate as a global line o through individual modules, allows its application to the manufacturing of high range of tech products as flexible displays, lab-on-a-chip devices or other microelectromechanical systems in a short period of time. These high tech fields will widen business opportunities of European industry to new and well known growing markets.
Project website: http://www.LIGHT-ROLLS.eu
Email: info@LIGHT-ROLLS.eu
The European Commission (EC)'s LIGHT-ROLLS funded project, which took care of cost efficient production of light modules, started in July 2009 under the Seventh Framework Programme (FP7) (Grant Agreement No. CP-TP 228686).
The project focused on the development of modular based production line units applying three highly innovative manufacturing platforms for the seamless, high throughput manufacture of micro-structured systems (in particular LED-based lighting and display systems) for applications in automotive, consumer or life science. The scientific objective aimed to realise structures in the micron range and to integrate also dies to be assembled in high-speed and parallel by benefit of self-assembling. Nanoparticle dispersions used in fast conductive track printing technologies allowed the parallel generation of conductive lines. At project start the LIGHT-ROLLS manufacturing platform was based on:
1. RMPD-rotation, a patented process technology to generate three-dimensional (3D) polymer microstructures based on a fast additive manufacturing approach;
2. new chip assembly methods, originating from self-assembly methods;
3. high resolution - high speed conductive track generation and interconnection based on ink-jet and laser printing methodologies.
These three processes comprised the founding elements of the LIGHT-ROLLS technology platform with a roll-to-roll philosophy. The manufacturing modules were developed to be integrable, exchangeable, with mechanical, fluidic and Information technology (IT) interfaces, to make it easy and cost efficient to adjust the sequence of process steps for the product to be produced. Besides the translation of processes for high-throughput manufacturing, high yield was achieved by the application of Advanced process control (APC) and production IT methods.
Furthermore, a pilot line was set-up and tested for fabrication of flexible Light emitting diode (LED)-display systems. However, the manufacture of other components like lab-on-chip or integration of new micro-energy storage components will be also possible in the future to address needs of European industry. In this sense, LIGHT-ROLLS knowledge base for design for manufacturing was elaborated for future products.
The consortium of LIGHT-ROLLS was made up of 9 organisations from 8 different members and associated states (Germany, Romania, United Kingdom, Switzerland, Sweden, Italy, Austria and Spain) and has covered all different areas of the manufacturing technology aim of the project. This consortium has included:
- 6 Small and medium-sized enterprise (SME)s: microTEC Gesellschaft für Mikrotechnologie mbH, Microelectronica S.A. Design LED Products Ltd., Norbert Schläfli Maschinen Zofingen, XAAR Jet AB and ACP-IT GmbH.
- Research Institutes: Fraunhofer Gesellschaft (Fraunhofer IPA), Centro Richerche FIAT S.C.p.A. and PRODINTEC.
Project context and objectives:
Micro-products are nowadays used in a wide range of fields, for example medical, biotechnology, consumer and automotive. However, emerging micro-products as innovative display solutions, lab-on-chip systems, micro-energy supplies or light emitting panels, increasingly require the integration of different functionalities and present challenging demands in terms of high volume and low cost production.
Taking this into account, LIGHT-ROLLS project aimed to apply micro-fabrication basic research results to the development of new processes for the manufacture of micro-structured systems. Concretely, the project explored the following highly promising and innovative micro-fabrication technologies:
- RMPD, a patented process technology to generate polymer micro-structures by a fast photo-polymerisation manufacturing approach;
- self-assembly principles;
- ink-jet printing methodologies.
LIGHT-ROLLS aimed to provide new production solutions not only by the integration of these innovative micro-fabrication processes, but also by the development of APC and production IT to achieve quality control and high degree of automation. To demonstrate the feasibility of the new manufacturing concept, the ultimate objective of the project was the development of a new roll-to-roll production line for the seamless, high throughput manufacturing of micro-structured systems. The project intended to provide a flexible manufacturing solution. Therefore, the approach of LIGHT-ROLLS was based on a modular roll-to-roll philosophy, in such a way that the manufacturing modules are exchangeable to make easy and cost-efficient the adjustment of the sequence of process steps for the production of different products. So, although the pilot line was set-up and tested for the fabrication of flexible LED-display systems, other components like lab-on-a-chips or flexible solar cells, could be manufactured in future. Moreover, for manufacturing of future products, a LIGHT-ROLLS technology knowledge base about design and configuration of the line was developed within the project.
The arrangement of the LIGHT-ROLLS line is sketched below. A flexible polymer material ('web') is used as substrate. The substrate is provided on a roll, passing all processing modules and rolled up at the end.
The scope of LIGHT-ROLLS comprised the following detailed objectives:
1. Development of seamless micro-fabrication technologies:
- development of the RMPD-rotation based 3D micro-structuring unit for the production of microstructured polymer parts and microsystems;
- development of a die-placing module using the self-assembly effect for a massive parallel assembly of semiconductor dies;
- development of a self-assembly unit for positioning the smallest dies precisely on the substrate in a high volume process;
- development of a printing and sintering module for realising electrical tracks and interconnections, and also other microstructures, like coils, resistors, sensors, etc., for other future applications.
2. Development of high throughput roll-to-roll equipment platform
- development of integrable and exchangeable modules for the equipment platform, including the design of the required mechanical, fluidic and IT interfaces;
- development of an APC and a platform-based Manufacturing execution system (MES) to monitor and control de overall production line;
- enable high volume production;
- enable the integration of other micro-fabrication modules.
3. Development of knowledge base for LIGHT-ROLLS manufacturing
The aim of the knowledge base was to collect the expertise gained from the demonstration activities about the design, configuration and feasibility of the production line in order to promote LIGHT-ROLLS potential and facilitate its application to other future applications.
In order to fulfil the above mentioned objectives, the project was structured in six Work package (WP)s:
WP0 - Project management: This WP dealt with the daily management of the project and the consortium, the overall coordination of the WPs (including technical progress monitoring and quality assurance) and the management of the communication between all the stakeholders (also the communication with the European Commission).
WP1 - Micro-fabrication process elements: This WP was focused on the development and implementation of the 3 main units of the LIGHT-ROLLS manufacturing line (RMPD-rotation, self-assembly of small dies and ink-jet printing/sintering). The goal was to develop robust implementations of these technologies based on existing knowledge and integrate technical solutions as required.
WP2 - LIGHT-ROLLS manufacturing equipment: WP2 tackled the definition of the final platform specifications from the point of view of both hardware and software, as well as the integration of the manufacturing modules into the LIGHT-ROLLS platform. Thus, this WP has involved the definition of the interface specifications, the development of the full concept of the platform, the manufacturing and assembling of the modules and the development of the process control and production IT software solutions.
WP3 - Manufacturing of LIGHT-ROLLS products: WP3 has targeted the design and manufacturing of a LIGHT-ROLLS product accordingly with Light Rolls platform capabilities. Then, a first technology demonstrator was designed, developed and built to verify the feasibility of the three main technologies involved in the project and to address and avoid any possible risk before full integration into the manufacturing platform. Results obtained were used to adjust and design the final demonstrator product and to finally configure the line and their modular components.
WP4 - Demonstration of LIGHT-ROLLS manufacturing: The aim of this WP was to demonstrate the feasibility of the LIGHT-ROLLS concept and produce a demonstrator product. This experience was fed into WP5 to build up the knowledge base.
WP5 - Knowledge base for LIGHT-ROLLS LED products: In the framework of this WP the knowledge base necessary for the fast commercialisation of LIGHT-ROLLS equipment was created. Concretely, two tools were developed: 'Design for LIGHT-ROLLS manufacturing' to allow a fast design of new products, and 'Configuration of a LIGHT-ROLLS production line' to address the needs of the technicians for setting up and operating the line.
WP6 - Dissemination, exploitation, knowledge management: This WP involved dissemination, exploitation and knowledge management of project results.
Project results:
The ultimate result of the project was the development of a roll-to-roll production platform for the manufacturing of micro-structured flexible LED displays. To achieve this goal LIGHT-ROLLS tackled with the following challenges:
a) research and development on RMPD, self-assembly and ink-jet printing / sintering technologies to translate them into functional manufacturing solutions;
b) development of advanced control systems;
c) integration of process modules into a seamless equipment platform for a high throughput manufacturing of lighting and displays products.
Below we provide a description of the technical results that allowed overcoming each of these challenges. In the first chapter, an overall description of the LIGHT-ROLLS production line is detailed in order to facilitate the understanding of the concept developed. Subsequently, the main technologies involved in the project and the control systems developed are outlined.
An introduction to the LIGHT-ROLLS production line
The main result of the project has been the design, development and manufacturing of the LIGHT-ROLLS production line in order to manufacture flexible LED displays as a demonstrator of the feasibility of the LIGHT-ROLLS concept.
New micro-fabrication technologies have been developed or adapted for the integration into this module based production line. Each process module comprise:
- a core production element;
- a supporting frame;
- a controller unit for active control of the module;
- interconnection features for electrical, fluidic, mechanical and logical interfacing.
A flexible material ('web') is used as a substrate to build on. The substrate is provided on a roll, passing along all processing modules and rolled up at the end, all by means of the unwinding and winding cylinders located at the ends of the line. For LIGHT-ROLLS four different types of process modules have been defined: gravure printing, RMPD-rotation, self-assembly and Inkjet printing and sintering.
The gravure module (not foreseen in the initial configuration of the LIGHT-ROLLS line) is located at the beginning of the line and provides movement to the web by means of two rollers perfectly aligned. The gravure cylinder integrated on this module have an engraved mask according to the product to manufacture, and could be of course adapted to the desired final application. The objective of this engraved mask is to mark on the web with an adhesive material the specific places where the electronic components, LEDs in this case, have to be positioned. The gravure cylinder also prints on the web several predefined alignment marks that will play an important role for the operation of the line.
The second step consists on the self-assembly module. This is basically a system to deliver components onto the web with high precision. As explained before, in this application the self-assembly module will deliver LEDs on the previously printed adhesive material deposited by the gravure. The output of this module is then a range of LEDs correctly located on the web and ready to move to the next stage.
The next step consists on an RMPD-rotation module that lays a homogeneous thickness layer of a UV curable material over the web, and selectively cures it through the transparent zones of a patterned mask of a rotating glass cylinder. Where there is a transparent region the UV light passes through the glass and cures the underlying material into a solid polymer. The mask of this glass cylinder is designed to cover all previous components except for those areas to which the electrical connections have to be formed in next steps. In order to remove the non-cured material, the RMPD-rotation module also includes a cleaning unit and other additional elements to assure the integrity of the printing system situated just after.
The last step is the printing and sintering module, consisting of several inkjet printer heads, head controllers and a subsequent sintering system. The essential part of the printing module is the high precision machining and assembly of all these elements that allow a very precise orientation of the printing heads in direction and tilt angles, as well as in distance to the web. This complex configuration allows the module to perform the printing of the electrical connections in their correct position. A sintering post-process was also developed and adapted to the LIGHT-ROLLS production line in order to achieve an optimal cure of the specific ink used in the process.
For the operation of the LIGHT-ROLLS production line, a control system for the automatic aligning of the web in the transversal and longitudinal direction was developed. This control system is based on the identification of the predefined alignment marks printed by the gravure module by means of optical sensors located along the production line. Last but not least, it is necessary to highlight that the overall operation of the line is controlled by an APC application and a platform-based MES, specifically developed in the project.
Thus, although the LIGHT-ROLLS production line has been set-up and tested for the fabrication of flexible LED displays, the main goal of the project related to provide a flexible manufacturing solution has been achieved by the modular design. Thereof, the manufacturing modules are completely exchangeable, allowing to adapt the process steps to the production of different products, and also add any specific module if needed.
An overview of the technical characteristics of the LIGHT-ROLLS production line units is summarised in the table below in order to show the flexibility of the concept developed:
Technical characteristics LIGHT-ROLLS
Overall component size depending on the application selected, but for display applications foreseen:
- Width appr. 150 mm (max 200mm)
- Length approx. 300 mm
- Thickness min 0.240 mm
RMPD-rotation technology for the manufacture of polymer structures
- Line resolution ±10 µm ex substrate
- Registration <10 µm ex-substrate
- Minimum layer thickness per pass 50 µm
- Maximum layer thickness per pass ca. 100 µm - 150 µm depending on polymer and curing parameters
Self-assembly of Dies
- Die size down to 0.35mm x 0.,35mm
- Positioning accuracy on sub-carrier < 10 µm
- Thickness max 90 µm and min 50 µm
Conductive track generation
- Stable printing processes up to 100 µm line width
- Thickness 6 µm
High throughput equipment
- Roll-to-roll process
- Web speed 0.6 m / min - 1.0 m/min
- Operation at atmospheric pressure (air or inert gas).
LIGHT-ROLLS technologies
The design and developed of the three main units that integrate the LIGHT-ROLLS production line (RMPD-rotation module, self-assembly and printing / sintering) has involved the exploration of these promising and innovative micro-fabrication technologies to achieved their technical implementation. Thus, several possibilities were investigated and mock-ups for testing were produced to perform first experimental tests and optimise process parameters.
Below are detailed the main achievements that finally led to the modules implementation in the LIGHT-ROLLS production line.
RMPD-rotation module
RMPD-mask, microTEC's proprietary technology, is based on additive manufacturing methods and allows the high resolution, 3D production of microstructures based on UV curable materials. A Computer-aided design (CAD) system is used to design a three dimensional microstructure of almost any desired shape. This model is transferred to a mask, which is then produced and assembled on the manufacturing unit and the production process begins: a liquid monomer is cured through the mask layer by layer through a photopolymerisation process.
LIGHT-ROLLS research allowed the translation of the batch oriented RMPD-mask technology to a seamless roll-to-roll production method finally integrated into the LIGHT-ROLLS production line. Main advantages are larger areas of microstructures compared with the mask based process, cost efficiency and also an easier, seamless integration into production processes. The Rotation process also allows multi-material processing, i.e. different polymers can be integrated in one part.
As explained above, the developed RMPD-rotation unit lays a homogenous thickness layer of a UV curing monomer and selectively cures it through the transparent zones of an opaque mask on a rotating glass cylinder. The UV light which is holding inside the glass cylinder passes through the transparent region of the glass and cures the underlying monomer into a solid polymer. In the case of LED demonstrator, it was designed to cover two small areas on top of the LEDs' connection pads and separation areas between products.
A method to pattern the mask on top of the glass cylinder with resolutions down to one micron range was specifically developed for this project. The specific process to deposit coating layers onto the cylinder as well as the deposition of photo resins and the following etching steps on cylindrical surfaces were also developed.
Also remark that there is no physical contact between the web and the glass cylinder because the substrate moves on an air cushion, eliminating friction and, at the same time, maintaining the substrate at a proper distance of the glass cylinder. The air flow has to be adjusted depending on the density and thickness of the substrate.
Another element developed was the dispensing unit, fully integrated with the RMPD-rotation unit. Basic element is a spiral coater that applies a homogeneous thin film of the UV curing material on the substrate. Special spiral bars may be designed for different film thicknesses, starting in the one micron range.
The cleaning unit integrated in the module to remove the remaining liquid material, which is not UV-cured through the cylinder mask of the RMPD-rotation process, has also involved important developments. Different solutions were studied, i.e. nebulisation of solvents and further drying. The solution finally implemented avoids the use of flammable substance since some potential substrates may cause important electrostatic charges. Thus, the solution developed consists on a hydrophobic absorbing tissue mounted on a supply roller with a friction brake, a traction roller to wind up the cleaning material and two spring loaded roller that effectively ensure the friction between the absorbing material and the substrate. Additional elements were also developed. For example, an open chamber to create a controlled atmosphere while curing the monomer in order to improve the flexibility of the system and allowing it to work with different materials. This chamber has internal channels designed to drive the main gas flow to the layer of monomer that is being cured. A second wide range UV post-curing has also been designed and situated after the cleaning unit in case that an additional curing is needed. This post-curing is also interesting to avoid contamination at further steps of the LIGHT-ROLLS manufacturing process.
Self-assembly module
Die self-assembling is a massively parallel approach to assemble micro-components on a substrate using self-assembly principles: freestanding micro-components assemble and bind to a location that has been patterned at the bottom of the binding sites. The self-assembly process is conducted in a fluid allowing the micro-components to move freely until they come into contact with the binding point in receptor sites, align in the right orientation and form a stable bond. The state of the art is to take the dies from the wafer by the sequential pick-and-place process. LIGHT-ROLLS approach brings the dies into a feeder unit and place many dies in parallel onto the seamless polymer interim substrate using the self-assembly effect for a precise and fast assembling, resulting in the integration of chip self-assembly methods into roll-to-roll production, which has not been implemented before.
To achieve this goal, LIGHT-ROLLS has focused on the research and development of solutions for:
- dispensing small volume of fluid on specific functionalised areas for the self-assembly process;
- developing solutions for feeding and transporting the chips;
- developing solutions for sorting the chips to detect their orientation and to discern whether they are in right position or not.
A novel process for feeding, transportation and sorting of the LEDs was designed and demonstrated at lab scale.
The feeding concept consists in a reservoir where the LEDs lie on the open surface of water. These LEDs have to be transferred to a channel system for position assessment and sorting. Thus, the reservoir is filled with water until it overflows into the channels filled or wetted with water. In a next step, the LEDs are 'poured' onto the surface of the water. The curvature of the surface causes the LEDs to move to the sides. Any overlying LEDs are separated from each other by vibration and subsequently placed in rows. Finally, the water is rapidly drained from the reservoir by suction. LEDs now lie in the channels and are ready for transportation.
A transportation concept was also developed and a method to produce channels and various geometries thereof were investigated with regard to flow characteristics. Additionally, problems related to flow behaviour in open micro channels were also studied. Different processes for machining the channels were tested and also different experiments were carried out in order to control the hydrophilic character of the surface of the channels. The sorting process developed is based on the use of image processing to recognise LEDs lying incorrectly. These LEDs are rejected and subsequently placed in awaiting magazines by a micromechanical feeder. LEDs lying correctly are further transported in the channel. Rejected LEDs are put back into the sorting process.
In the other hand, a novel wetting process solution combining offset printing technology and single droplet deposition was developed and adapted to the self-assembly process.
The self-assembly process developed and finally integrated in the LIGHT-ROLLS production line comprises one cylinder with an offset plate that is dependent on the application and has engraved marks according to the product design. The marks are hydrophilic surfaces, while the rest is a hydrophobic surface. The offset plate is fixed to a blank cylinder which is rotated by a motor. A water injector puts very small droplets of pure water on the hydrophilic marks on an offset plate. On the other hand, a vacuum gripper takes the LEDs from the magazine where they are stored. When the droplets reach the proximity of the vacuum gripper, the die is attracted and sticks to the water. Following the rotation of the offset cylinder the dies are placed exactly onto the adhesive marks previously printed on the web. The adhesion force is stronger than the attraction to the water droplet, so the die remains in place during the next steps of the manufacturing process.
These results achieved involve a major leap forward in the state of the art, breaking down the barriers to the implementation of this technology at industrial level.
Printing and sintering module
Ink-jet printing of conductive inks is a well-known process to provide electrically conductive tracks on flexible substrates and ink-jet print heads are now accepted as manufacturing tool in various industrial applications such as flat panel displays, electrical and optical devices, memories, as well as bio / pharma devices. The process comprises:
- ink-jet printing of an adequate conductive ink (a stable suspension able to be injected). Inks are normally formulated with nano-sized metal particles coated with polymeric shells that prevent agglomeration of the individual metal particles;
- post-process to destroy the polymeric shell and 'fuse' the metal particles;
- pre-treatment of the surfaces is sometimes also needed to increase adhesion on the substrate.
LIGHT-ROLLS project choses ink-jet technology to produce the electrical interconnection between individual electrical devices because it is easily integrated into a roll-to-roll environment, fast, flexible, and easy to configure for various applications. High tolerances when combined with production control systems and reduced waste are additional advantages considered to the selection of ink-jet as printing technique for conductive track generation.
The ink-jet process translation to LIGHT-ROLLS requirements has included the following tasks:
- Define specifications and select the appropriate conductive ink from a range of commercial products, checking material compatibility with substrate and other layers of the device.
- Select the inkjet print head considering line width and resolution to be printed and required process speed and throughput. Several models of piezo print-heads were evaluated. This kind of print-heads use electrical voltage signals to induce mechanical motion of the dividing walls between the individual ink channels. Several such two-directional wall movements result in the formation of an acoustical pulse within the ink channel, which is stepwise increased in amplitude by reflection at the open and closed ends of the ink channels and by further in-phase wall motions. Proper adjustment of amplitude and timing of the wall motion will cause the formation of a suitable acoustical pulse at the nozzle, which thus will cause the ejection of an ink drop from the nozzle.
Further wall motions are applied to create out-of-phase acoustical pulses in the channel, which are meant to eliminate the remaining acoustical energy in the channel after drop ejection so that the following drop formation process can start from well defined 'neutral' conditions.
- Develop the electrical driving waveform for optimum drop formation: The sequence of electrical voltage signals to cause the ejection of a drop and the elimination of residual acoustical energy is named the electrical driving waveform. Special equipment based on stroboscopic microscope was built within the project for the development of waveforms.
- Perform print tests on the different substrates to establish practical line width and thickness of the electrical tracks; define the x / y print resolution for optimum line shape and smoothness; introduce a pre-treatment if the surface tension of the ink and the surface energy of the substrate do not match sufficiently.
- Investigation of post process methods: Several sintering technologies such as convective oven sintering, Infrared radiation (IR), high power UV radiation, Rapid electrical sintering (RES), and broadband photonic sintering were studied considering compatibility with roll-to-roll process and dimensions to reduce the working chamber to a sensible module size. Photonic sintering was identified as the only technique able to perform appropriately in this roll-to-roll manufacturing line. Therefore, an exhaustive research work was performed on this novel technology to adapt it to the LIGHT-ROLLS production line. Below is schematically represented the final printing module designed and manufactured within the project. It integrates the units for both ink-jet printing of the conducting lines and for sintering the ink.
Web alignment and synchronisation control system
Operation of the LIGHT-ROLLS production line has involved developing a control system to correct both the lateral and longitudinal displacement of the web. Without this control system it would be extremely difficult neither to put the electronic components in place nor printing precisely on the chip open pads. The solution finally chosen was a multivariable control system based on PC. This control system performs two tasks:
- An automatic alignment with the web of the modules, by means of micro-displacements in the transversal direction of the web travel axis.
- An automatic adjustment of rotation speed in the motors that produce the web linear movement in the longitudinal direction: Therefore, a uniform speed in all parts of the line is obtained.
- Servo motors and drives: The control system communicates with the drives so the rotational position and speed of these motors can be read and modified to obtain the required synchronisation between the processes in each module.
- Optical sensors: These sensors detect ink marks printed by the gravure module on the web, and generate digital signals that allow the control system to carry out the current position errors in lateral and longitudinal directions that affect the alignment and synchronisation of the line.
- PC unit: It runs the control strategy and communicates with the different motion control units of each actuator via RS232 or USB protocol.
- DAQ: A data acquisition system with digital and analogue inputs and outputs modules allows the control system to capture the digital sensor signals and, during the development and start-up of the line, allows the user to capture analog signal from these sensors and also to configure them. Analog outputs are used for controlling motor speeds in the synchronisation control loop.
- High precision motorised linear stages: These actuators generate linear displacements of modules in the transversal direction for obtaining the alignment between the web and them. Their resolution is below one micron.
Software for process and quality control
As mentioned before, LIGHT-ROLLS production line also involves the development of an ACP for the optimisation of the production process performed and a platform-based MES or production-IT to monitor and control the overall production line.
The ACP system implements elements as high speed process data collection, real time and offline visualisation of process data, workflow driven actions and process corrections, just-in-time data mining for correlation analysis, etc., in order to optimise the production process.
On the other hand, the production-IT prototype developed provides direct IT interfaces to process equipment as well as to the automation systems within the line. Some functionalities implemented are online monitoring of equipment within the production line, central recipe manager, equipment integration with the main modules, etc.
The MES is fully integrated with the production-IT prototype within the project in a three level scheme:
- Equipment level integration focuses on data collection aspects: Data collection comprises collection of parametric data as well as events and alarm groups. In addition it has to be considered that data might be provided either through messages or file-based. Active control of equipment is responsibility of the production-IT. Therefore this communication path is not topic of the integration between both systems.
- Application level integration comprises requests send from the production-IT to the APC system and events send in the reverse direction.
- User level integration enables integration of user interface components of both systems in one integrated client application frame.
Production-IT prototype is implemented as the primary source for incoming and outgoing data between the whole application and the equipment. Therefore on the equipment integration level there is only information flow from the production-IT prototype to the APC-system. On the application logic layer there are requests and transfer of master-data from the production IT prototype to the APC system. In the reverse direction events are transferred in order to notify out of control actions in the production-IT prototype. On the Graphical user interface (GUI) layer the mainframe is provided by the Production-IT prototype. Portions of the overall GUI are made up by the APC-system and are embedded into the production-IT prototype's GUI. In order to request appropriate content it is necessary that the Production-IT prototype provides information about the current context visualised in the GUI globally.
With regard to the user interface integration, the list of figures below show a Process Plan Editor from the Production-IT Prototype in conjunction with an embedded editor of Statistical process control (SPC) models.
Potential impact:
The main market addressed by partners focus on lighting applications. Thin 'light sheets' are very attractive in automotive applications or building lighting because they require little space, are potentially more reliable and cheaper, include several functionalities, and offer a high degree of freedom to fulfil designers' needs. Other applications with potential in other markets are possible, for example in the field of diagnostics or applications based on functional printing, as flexible active Radio-frequency identification (RFID) tags, flexible solar cells and batteries or simple consumer products.
a) Lighting
The move from using packaged LEDs and low precision screen printing methods for assembly and interconnection towards high-volume, low-cost application would push the commercialisation of LIGHT-ROLLS lines to new horizons.
One particular application which derives large cost/performance benefit from LED 'light where you want it' is retail lighting. To maximise customer experience, minimise power consumption and minimise unit cost, the light on the product should be directed to the front / middle of the shelf. Light weight, thin and mechanical flexibility makes for an easy install. Additionally, the generic benefits of LED technology are provided: long life-time, low voltage, custom colour temperature and high colour rendering index.
The LIGHT ROLLS technology can also be configured for backlighting, where the light source sits behind a graphic or diffuser in a Liquid crystal display (LCD) panel and provides a uniform and diffuser rectangle of light. The light extraction features can be patterned in 2-dimensions to vary the light output across the panel. An example of this concept using prisms is shown. In backlighting, the technology delivers high system efficiency with a thin system.
In automotive, LED for interior lighting and accessories lighting systems are taking retail shelf space away from traditional components (i.e. neon, inorganic emissive sheets) at an accelerated pace. The fastest growing segments are LEDs that replace the small filament bulbs found in tail lights and interior dome lights like courtesy lights or spot lights.
However, there are more applications with respect to lighting or even other applications where LIGHT-ROLLS solutions as a technology platform, may play an important role.
Also remark that the LIGHT-ROLLS technologies can also be exploited for the production of other automotive applications, regarding for example the trend to reduce the installation depth of car taillights or the production of complex components integrating different building blocks (lighting, electronic, photovoltaic modules and batteries for example).
b) Lifescience
Since the RMPD-rotation technology allows the manufacture of polymer microstructures and is able to use foils as a substrate, integrate electrodes, bab-on-a-chip, are potential candidates for future product development.
Several emerging applications that are particularly enabled by the use of thin foils are, for example:
- Temperature controlled biological reactions, such as the Polymerase chain reaction (PCR), take advantage of fast heat transfer through thin materials. In fact, heat transfer rate through a foil is inversely proportional to the square of its thickness as described by the diffusion equation.
- Applications, such as centrifugal microfluidics in which a microfluidic chip is accelerated can profit from low mass and thus low moment of inertia of foil cartridges.
- Foil-based lab-on-a-chip systems suit perfectly as disposable consumables because they only require a minimum of material volume.
With LIGHT-ROLLS concept it will soon be possible to realise a pilot-production-line for validation purpose, extend validation of developed lab-on-a-chip systems and identify low materials for cartridge.
c) Functional printing
Functional printing is a collective term for a platform of organic and printed electronics technologies based on the combination of new materials and cost-effective, large area - printing -production processes that open up new fields of application. Some of the key advantages that organic electronics can offer are thin, light-weight, flexible and environmentally friendly processes and products. It also enables a wide range of electrical components that can be produced and directly integrated in low cost roll-to-roll processes. Intelligent packaging, low cost RFID transponders, rollable displays, flexible solar cells, disposable diagnostic devices or games, and printed batteries are just a few examples of promising fields of application for organic and printed electronics based on new large scale processable electrically conductive and semiconducting materials. There are many other ideas like printed humidity sensors on a piece of paper to be placed in, e.g. cement bags indicating a wet-dry status, applications in smart packaging to support marketing to promote certain products.
The market for functional printing is still in its infancies. Flexible active RFID tags, flexible solar cells and batteries or simple consumer products and games are only a few examples according to OE-A roadmap, all of them potential applications of LIGHT-ROLLS technology.
In summary, the huge versatility of the LIGHT-ROLLS concept, based on its possibility of operate as a global line o through individual modules, allows its application to the manufacturing of high range of tech products as flexible displays, lab-on-a-chip devices or other microelectromechanical systems in a short period of time. These high tech fields will widen business opportunities of European industry to new and well known growing markets.
Project website: http://www.LIGHT-ROLLS.eu
Email: info@LIGHT-ROLLS.eu