Ink-Free Digital Printing | Solder/Adhesive Free Die Bonding | Roadmap for 3DPE | HTL for High Performance OPV | OTFTs compatible with LCD ProductionHigh-Performance
Before delving into the details of the technology updates for this week, I would like to say that we very excited about our onsite event in Eindhoven, the Netherlands, on 12-13 OCT 2022. The exhibition is long sold out with a long waiting queue, the world-class agenda is announced, and there is very high demand for attendee tickets. You can see the full information here. This is the most important upcoming event in the industry.
Next, we will provide updates and insights on a few interesting developments in the world of additive electronics. We will cover (1) dry ink-free digital printing (2) HTL with deep work function (3) roadmap for 3DPE (4) direct die bonding on paper with solder or adhesives (5) liquid wire based on Ga-In-Sn conductive gels (5) OTFT backplanes compatible with LCD production and (6) key steps in printing sub 30um linewidths
A dry ink-free digital printing process to deposit multifunctional materials?
We recently came across this interesting system, developed by Masoud Mahjouri-Samani, PhD et al Auburn University. Here, as shown below, an excimer laser is focused by lens onto a target. The target is ablated, forming a plume of nanoparticles which then condense onto the substrate to form nanoparticles. The laser system can be used to in situ sinter and crystallize the structure.
This dry printing process thus involves no inks and can 'print' complex multifunctional materials like TiO2 or ITO, going beyond the capability of traditional digital ink printing. These researchers claim that this "new method allows the in situ and on-demand formation of various nanoparticle building blocks in atmospheric pressure and at room temperature. These nanoparticle building blocks can be directed toward the substrate through a nozzle forming a stream of nanoparticles that can be laser sintered/crystallized on various substrates in real-time."
Indeed, below you can see an example of the generated and sintered TiO2 nanoparticles. Furthermore, you can see examples of ITO and TiO2 circuits printed on SiO2 substrate using this process.
This is a novel, promising and innovative approach to direct digital deposition of a wide range of materials on various substrates. It may overcome some key limitations of ink-based wet printing techniques, especially in terms of possible material options. Of course, This is currently a small-scale lab operation and of course, as technology development advances more trade-offs will become known.
The technology is now entering the commercialization phase. Indeed, NanoPrintek (NanoPrintek, Inc.) has been recently set up to take this exciting approach forward.
New HTL materials enable bridging the gap between the latest lab-level and production-level printed OPV performance.
Below you can see the historical rise of OPV (organic photovoltaics) efficiencies from 2.5% in 2000 to >18% now, showing how evolution in materials has driven this rise.
(Material Evolution: P3HT: PCBM --> emergence of push-pull polymers (PPP) --> rise of non-fullerene acceptors (NFAs)---> novel PPP and NFA).
The chart below, by Nicolas Bouchard Brilliant Matters, also reveals the large gap between the best lab results and the best production level results with the highest industry-scale results being <8% !!
One key factor holding back the efficiency of production-level OPVs is the unavailability of a hole transport layer (HTL) compatible with the latest OPV donor and acceptor materials. This is because the latest novel donor and acceptor materials have wider bandgaps, thereby creating a large energy barrier with the common traditional HTL materials: PEDOT. This acts against charge injection and lowers efficiency.
Thus, to get the best from the latest PPPs and NFAs in industry-scale processes, one requires an HTL material in a non-halogenated solvent with a deep work function which can be printed in ambient conditions and which yields uniform thick (>100nm) layers.
Brilliant Matters has developed such a material. Here, it is shown how this novel printable deep HTL achieves results equivalent to MoO3 (best evaporated material) when used with PTQ10 and NFA.
This is an important step in the further development and industrialization of organic photovoltaics
You can see a short 5-min presentation by Nicolas Bouchard explaining this in good details here
Direct flip chip bonding on paper without adhesive or solder?
Ali Roshanghias et al Silicon Austria Labs (SAL) demonstrate an interesting approach in a recent publication, exploiting the unique properties of polypropylene(PP) coatings on paper.
Here, the bottom of the dies is coated with a sputtered lines of Cr(10nm)/Au (300nm) layers. The paper is coated with a thin 18-um PP layer through extrusion lamination. Ag tracks were R2R flexoprinted and dried. The dies are simply flip chip thermocompressed into the substrate.
The results - shown below- confirm that the bonding is formed without an adhesive or solder layer. Here, the PP layer is softerend at 150C and reflows locally at temperature of 162-165C during die bonding, allowing the bumps to penetrate and make contacts with the printed Ag lines. Upon solidification, the PP layer cirumpassed the contacts, acting essentially as a pre-applied adhesive and applying a compressive force to stabilize the electrical contacts.
This is an interesting advancement in the field and an alternative process to solder and ACFs. However, now, the burden is to apply a PP layer in advance. If the PP layer is essential in any case to planarize substrate and/or promote printability, then this step may simplify the process, removing an additional dispense/print step and removing the need for additional materials.
The future roadmap of 3D printed electronics in the medium (3-5 year) and long (5-10 year) terms?
In this short 5-min presentation, Dr. Martin Hedges shares his insights about the current status as well as medium term (3-5 year) and long term (5-10 year) development roadmap of the industry.
Martin is the CEO of Neotech AMT GmbH, a leader in the development of 3D printed electronics machinery, for both prototyping and volume production.
Current status: you can exampleds of (1) print on already 3D surfaces and (2) fully additive 3D printed electronics. In the latter, you can see an example of a filament (FFM) 3D printer building the mechanical part. The process is interrupted to automatically do SMT PnP and Ag metal jetting for building the conductive tracks. Here, multiple layers of interconnected electronics are created within the 3D structure, integrating parts such as LED, optics, waveguides, etc
Short term (3-5 year) roadmap: the industry should complete the first completely automated processing line based on digital 3D printing of electronics. Some degree of AI/ML will also be integrated for quality inspection and perhaps even auto correction. Furthermore, a wide range of functionalities, especially power electrodes, will be integrated, perhaps using cermaic structures, and the printed area/volume will also expand to form large 3D objects.
Long term (5-10year) roadmap: completely new product architectures will be enabled and the industry can start to move away from traditional etching-based PCB production techniques. Furthermore, automated recycling, repair and reuse will be possible
How to screen print sub 30um features?
Screen printing never ceases to advance and is entering into ultrafine line printing territory. This slideshow and short video considers what is required to reach sub 30um features in production:
Team effort: screen printing is a team effort, requiring close collaboration between paste maker, mesh and emulsion maker, printer, etc.
Black stainless steel mesh: conventional stainless steel meshes are reflective (10-15%). To achieve narrow and sharp openings in the high resolution photosensitive emulsion, random reflections from the stainless steel mesh- especially at 365nm and 405nm wavelengths- need to be minimized. This is why a black version is required
Narrow meshes: Asada Mesh is the master of making the most advanced stainless steel meshes. To achieve sub 30um, a mesh with a diameter of 11-13um with 55%-60% opening will be required. Asada Mesh is already pushing the performance envelope, offering even 9um meshes. This is an incredible advance, considering it takes around 3 years of intense developments to shave 1um from the diameter of the mesh
Substrate selection: depending on paste, substrate selection is key to balance surface tension/energy. The examples below, presented by FERNANDO ZICARELLI, show the outsize impact of substrate properties on on even 50um printed lines.
High-performance TFT backplanes printed at 80C and patterned using existing LCD equipment?
It is incredible to see the progress that organic semiconductors (OSC) have made over the past 15-20 years. SmartKem, Inc. is removing the long-existing barriers to adoption of OTFT technology. These are hard-won crucial and essential development steps to ensure commercial success, as technical progress alone in terms of mobility or stability will never suffice.
EDA tools: They have designed EDA tools enabling design and simulation of circuits using their OTFT circuits. This is an essential prerequisite for adoption which had been previously missing
Full portfolio of TFT materials: TFT is not just the semiconducting layer. All materials in a TFT stack must work together in an optimized way. Some 50M and ten years have been spent to develop a full portfolio of materials required to make an OTFT together with processing parameters including passivation layers, sputter resistant layer, base layer gate insulator, etc. This is incredibly important because all materials must work together and ensure compatibility with existing production processes.
Compatibility with existing processes: One can not expect display makers to reinvent the wheel and to adopt not just a new material but also a new process. Thus compatibility with existing processes is an absolute must-have. Smartkem has ensured that one can make OTFT backplane using its material set based on existing LCD equipment
Commercial partnerships across various display technologies: They have announced partnerships on AMOLED, QD-LCD displays, and mini-LED with RiT Display, Nanosys, and an unnamed Taiwanese player, respectively. This way they are covering multiple technology areas, and not chasing only a single target market. In the past, this error proved costly as most OTFT developers in the past only banked on low hanging fruit of e-papers!
It is a delight for us to see the progress of OTFT technology. The barriers to adoption are being cleared away. In the end, this technology proposes to offer the lowest processing cost for good enough displays, a prerequisite for the ubiquitous adoption of the emerging metaverse!
Watch a full 5-min presentation by Ian Jenks by clicking here
A full musculoskeletal kinematics platform using ultra-stretchable liquid metals?
Gallium-Indium-Tin is an interesting material for stretchable electronics. It can be formed into a non-toxic RoHS-compliant gel and applied to almost any substrate to form stretchable conductive metallizations and circuits.
It retains its limited liquidity, meaning that it can follow the form of the substrate as the substrate stretchec, provided the limits of its hysteresis are not approached.
In this presentation Jorge Carbo - innovator at Liquid Wire Inc.- shares data showing that they have approached 1M cycles of 100% stretch without any change in resistance- this is some benchmark to beat! In fact, most stretchable inks will struggle to match this performance (although they will likely offer higher conductivity).
Furthermore, They are developing a full platform based on its material. As can be seen, this platform integrates their stretchable interconnects together with microprocesses, strain gauge sensors, and other rigid ICs, showing that they can form fully-functional deformable silicone based novel sensor systems with embedded electronics.
The slides and the video below also outlines multiple examples of this technology, showing how this 'second skin' forms the basis of a platform technology that can be used in measuring athletic performance, in VR/AR gaming, clinical trials, etc.