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INTERCONNECTS Fig. 4: Cross section of laser cured Intrinsiq copper paste. CAD print head layout is shown in figure 1 and a detail of an imaged print head is shown in figure 2. Feature resolution in the ES JET is again much higher than in conventional inkjet due to the capability to deposit individual drops that are much smaller. Thus typical commercial printers provide individual drop volume in the region of a 5-90 Pico litres. With the ES JET printer, volumes as small as 0.001 Pico litres may be isolated and deposited on surfaces. The reason that these may be accurately printed onto surfaces is due to the fact that the droplet leaves the print head at a velocity of 50m/s, whereas again in commercial inkjet the velocity is typically only 2-6 m/s. The smallest feature printed with ES JET thus far is 900nm. A printed array of somewhat larger drops, having a mean diameter of 7.1μm, with a 1σ deviation of 0.2μm, is shown in figure 3. The print head is capable of printing inks over a vast range of viscosity; inks throughout the range 1 to 104centipoise having been demonstrated. The inks tested included aqueous solutions, high conductivity solutions up to 0.1S/m and inks without measurable conductivity. The adoption of this technology in the deposition of functional materials will result in a much broader design space to be accommodated for the formulation of functional inks, than is possible with conventional inkjet. Nanoparticle-based copper inks Intrinsiq’s copper inks and pastes are formulated using a patented nanoparticle functionalization technology. This allows the production of copper nanoparticles within a controlled structure and proprietary coating that protects the material from oxidation. By using nanoparticles rather than conventional micron particles as the basis for the ink, it is possible to use inkjet (and other) printing techniques and also sinter or cure the ink at much lower temperatures than would otherwise be possible After printing, an oxide free conductive copper track is produced via rapid thermal annealing of the deposited ink. Intrinsiq inks are specifically designed for photonic, or light based, curing in air via high intensity light sources such as flash lamp or laser, including Intrinsiq’s own LAPS laser curing systems, rather than standard oven-curing techniques. Fig. 6: Intrinsiq copper paste on a ceramic substrate for PVI automotive sensor application. This rapid (in the order of milliseconds), low temperature curing technique allows the use of a variety of low cost, low temperature, flexible, and other substrates including paper, PET , polyimide (Kapton), polyester, FR4, GX13 and glass. Conductivities of 20-40% of bulk copper are achievable and comparable to commercial silver inks. Although copper has been the mainstay of the traditional electronics industry, silver inks currently dominate the printed conductive electronics market. This is despite silver’s well known disadvantages: relatively high and volatile cost (around 100 x that of copper), migration of silver ions between conductive tracks which causes long term product stability issues, and environmental issues, in that silver exhibits antibacterial properties and its long term environmental effects are of growing concern. The reason that copper is not routinely used in printed electronics to date is due to its propensity to oxidize, resulting in poor conductivity. The technology overcomes the oxidation issue so that once the ink is deposited the coating is dispersed, exposing the highly reactive nanocopper which coalesces to form a continuous, highly conductive copper track. This is a key piece in the jigsaw of converging technologies which will see printed and flexible electronics becoming ubiquitous in the next 10 to 20 years, providing the products of the future from affordable solar cells and flexible displays to intelligent packaging and much more. To produce high purity, semiconductor grade nano-particles suitable for printed electronics, a “non-contact” plasma process is used to produce high purity (>99.99%), well controlled particle size distributions (5-50 nm) with controlled dopants to ppm levels to produce n-type and p-type structures. The high purity nano-particles produced from this process will enable improved semiconductor performance over state of the art technology, with target mobilities greater than 10 cm2/ Vs for printable nano-Si. Combining the expertise and facilities of IML and PVI allow the partnership to offer a range of services with device design and development as well as application development for automotive, LE D, medical devices, PV, displays and touch screens. It can also provide bespoke manufacturing of prototype and demonstrator circuits and devices such as sensors, RFID antennae and smart tags, etc, as well as the conductive inks and curing systems. Fig. 5: Intrinsiq LAPS-60 precision laser sintering system. 22 Electronic Engineering Times Europe September 2013 www.electronics-eetimes.com


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