The development of a digital laser printing process should make it possible to improve the performance of electronic boards on flexible substrates by increasing the number of integrated functions while maintaining low production costs.
The objective of the COPPRINT project is to design, realize and validate with an industrial partner a digital laser printing system for interconnexion in microelectronics. Such applications are currently achieved by inkjet technology by printing metallic nanoparticles inks. Improving the performance of electronic cards on flexible substrates requires an increase in the number of integrated functions while maintaining low production costs. The «LIFT double pulse« system developed within the framework of this project has made it possible by printing conductive structures with a better resolution than the inkjet method and by eliminating the annealing step. This new process should enable the production of cards with more sensors and better performance, which could be widely deployed in fields such as health and safety.
The reduction of the width of the interconnection lines of an electronic board allows to gain space to add other components and new functions. However, this reduction must be correlated with an increase in their thickness to avoid limitation of the current flow. The digital techniques currently used do not allow to reach these objectives. Laser printing allows to transfer liquid drops or solid pixels on a wide range of substrates from a donor film. The innovation developed in this project consists in using two laser pulses to transfer the material in liquid phase from a solid donor film. This process allows the use of stable and inexpensive donor films and the reduction of the size of the printed structures to a few micrometers.
The prototype designed and built in the framework of the COPPRINT project allowed to optimize the liquid metal printing process and to print conductive structures such as RFID antennas with a resolution and minimum dimensions never achieved to date by a digital technique. This work has been promoted by the OPTITEC and SCS competitiveness clusters. They are continuing in the framework of the 3DNanoLIFT project, financed by AMIDEX, to reach sub-micrometer dimensions.
From a scientific point of view, the results obtained have allowed the understanding of the physical mechanisms underlying the laser printing of metal in liquid phase. They have led to three publications and the implementation of new research on nano-printing. However, the electrical performances of the printed structures at high speed do not allow to consider an industrial application of the process in this field of applications.
The work carried out within the framework of this project corresponds to the first scientific study on laser transfer of liquid metal. It has been published in several international journals, especially to explain the ejection dynamics ('Dynamics of double pulse laser printing of copper microstructures', Applied Surface Science 471, pp. 627-632 (2019)), to present the printing of 3D structures ('Jetting regimes of double-pulse laser-induced forward transfer', Optical Materials Express 9 (8), pp. 3476-3486 (2019)) or to review laser printing techniques ('Digital laser micro- and nanoprinting', Review article, Nanophotonics 8 (1), pp. 27-44 (2019))
The potential applications of printed electronics are extremely important and have attracted an ever growing interest in the industrial community. The main application areas are health, personalized services, home automation, transportation, and distribution ... Despite strong investments, this industry has still difficulties to reach the market level corresponding to its potential. The development of printed electronics, and electronics on flexible substrates, requires the implementation of reliable digital printing systems to print 2D structures with a resolution compatible with the targeted applications, and that in industrial environment.
The purpose of this project is to design and implement a digital laser printing prototype that meets the requirements of printed electronics. The validation of this process will be done by the realization of copper interconnections. To date, the main digital technology used to print these conductive lines relies on the transfer of silver or copper nanoparticle inks by inkjet. This process yielded interesting results but has some drawbacks that limit its use in industrial context. These limitations are mainly related to the requirement of using metal nanoparticle inks which are very expensive and of low viscosities, and moreover, the technique requires a post-process annealing step to reach a good conductivity. That prevents the printing of thick lines for high current applications, or the achievement of line width smaller than twenty micrometers, even fifty in industrial conditions. In addition, the annealing step prevents the use of low cost substrates.
LP3 laboratory has developed a laser printing method that was used to transfer a large set of materials in solid or liquid phase and to print devices such as organic thin film transistors. Some drawbacks have been identified when printing in solid phase and very good results were obtained for the transfer in liquid phase. In particular, the printing of silver nanoparticle inks allowed the realization of conductive lines of 20µm width at a velocity of 17m/s. However, this approach does not eliminate the annealing step and still requires the use of metal nanoparticle inks.
In this project, we will develop a new approach for printing copper in liquid phase from a solid thin film of copper. This process will allow the transferring low cost materials, compared to inks, getting rid of the annealing steps, to print thick lines to drive higher current, and preserving the high resolution obtained when printing in liquid phase. The development of this technique relies on an innovative laser irradiation approach and the control of the phase change of the copper film.
The different steps of this project are: 1. The control and the optimization of the mechanisms of the laser-induced ejection of pure copper in liquid phase; 2. The implementation and the optimization of the laser printing prototype; 3. The realization and the characterization of copper conductive structures; 4. The printing of test circuits in order to validate the process with an industrial end user.
This project brings together three partners with specific expertise that are mandatory for its successful achievement: the LP3 laboratory for the process development, ARMINES-CMP which will perform the chemical, electrical and mechanical characterizations of the printed materials and structures, and Gemalto company for the definition of the technical goals with respect to its applications and it will also validate the process by manufacturing and testing printed smart cards.
Monsieur Philippe Delaporte (Centre National de la Recherche Scientifique délégation Provence et Corse - Laser, Plasmas et Procédés Photoniques (LP3))
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
CNRS DR12 - UMR7341 LP3 Centre National de la Recherche Scientifique délégation Provence et Corse - Laser, Plasmas et Procédés Photoniques (LP3)
Help of the ANR 464,041 euros
Beginning and duration of the scientific project: November 2016 - 36 Months