CMM Magazine caught up with the CEO of Horizon Microtechnologies, Andreas Frölich to discuss the work the company undertakes in the field of micro-AM. Horizon has a set of proprietary coating processes that add functionality to plastic micro-AM parts, which when combined with the company’s expertise in design for micro-AM opens up the use of AM in numerous application areas for which it has had limited use until now.
CMM Magazine. Can you explain what it is that Horizon Microtechnologies does as you work at the intersection of micro manufacturing and 3D printing?
AF. In a nutshell, we have developed a number of proprietary so-called HMT coating technologies which can add functionality to 3D microstructures. The demand for such coatings is being driven by the rapidly evolving area of micro additive manufacturing (micro-AM), which today has the ability to repeatably make micro parts and components or parts with micron features repeatably. Such technologies today are realistically being looked at as viable production technologies, and are no longer the expensive and slow processes of a decade ago. Typically, however, the parts are made from plastic. Horizon allows the exploitation of polymer micro-AM produced 3D microstructures for hitherto unserved areas of industry by adding functionality to the microstructure through its coatings. This is a real game changer for industry.
The coatings we have developed remove or at least reduce the materials vs functionality vs manufacturability tradeoffs that currently impact design decisions in the manufacturing of precision- and microfabricated parts. Our customers can receive parts from us with the functionalities of the coating but are also able to exploit the design freedom, precision, and resolution achievable through micro-AM. We can work with customer supplied parts as well as parts made in-house, the latter case often giving the highest added value since the production process is completely controlled by us. That way, interfaces between different suppliers and external influences are eliminated and repeatable outcomes are achieved easily.
Horizon is positioned to work with customers at various stages in the product development cycle. We are vertically integrated, and have the in-house infrastructure to act as an end-to-end product development and contract manufacturing partner. This means that we are able to influence the design of micro AM parts to optimise them for end-use functionality and for the application of our proprietary coating technologies.
The use of micro-AM allows the integration of geometrically very different micro-elements like spirals, bars, and sockets with each other without any additional process overhead. Copper coating via Horizon’s HMT-Metal coating process adds functionality.
CMM Magazine. What coatings can Horizon provide?
AF. As we stand today, we have three coatings. Our HMT-Metal process applies copper films with >25% of the bulk copper conductivity on complex shaped parts. The process can either coat the entire part’s surface — including internal channels and undercuts — or be applied selectively. This coating process is ideally suited for those applications where the use of bulk copper is not required and would be impossible or uneconomic. Using this process in combination with 3D printed photopolymer parts, for example, previously unmanufacturable mm-wave components with sub-µm smooth surfaces can now be made, and it opens the design freedom of AM to applications where CNC machining or bulk metal 3D printing can’t deliver. For example, we have successfully printed and coated extremely thin-walled (100 microns) parts several millimetres wide which would have torn or collapsed when being machined out of solid metal. When the metallization is applied selectively, several independent metal features (lines, areas, tunnels) for interconnects, vias, or similar applications can also be created.
The HMT-Protect coating process we offer is used to hermetically encapsulate parts in order to protect them from the environment or, vice versa, to protect the environment from the part as would be the case in microfluidics if there is a risk that liquids might take up traces of the polymer. Parts can therefore be made compatible with aggressive chemical environments and will in some cases display increased resistance to high temperatures and mechanical loads or abrasion. The coating process’ ability to reach even deep recesses, undercuts, and the inside of long, bending channels is extremely important. In combination with 3D printed parts this allows, for example, for the fabrication (with extreme design freedom) of nozzles and monolithic 3D nano-/microfluidics for high flow rates, high pressure drops, aggressive solvents and certain acids and bases.
Finally, our HMT-Conductive coating process can deposit transparent non-metallic conductive layers with tailorable sheet resistances between 100 Ohm/sq and a few kOhm/sq onto virtually any part shape. The resulting film will have a near-constant thickness, and does not add more than one µm of thickness, unless desired. In combination with 3D printed micro-geometries, this allows for the manufacture of nozzles that won’t suffer from electrostatic discharge, freeform embedded resistors and conductive traces, as well as free-form electrodes. The coating’s transparency is useful, amongst other things, in opto-electronics applications like optogenetic devices or microfluidic devices with integrated electronics and optical readout. As with our HMT-Metal coating, importantly, the HMT-Conductive coating can be applied selectively to properly designed parts.
A high frequency D-band horn antenna made via micro-AM and coated with Horizon’s HMT-Metal copper coating.
CMM Magazine. Are there other technologies available that add metal to 3D microstructures or indeed make 3D metal microstructures, and how does Horizon’s HMT-Metal process stack up against these alternatives?
AF. First of all, it’s important to understand why in some application areas it is advantageous to use a metal coating rather than make a micro metal part. First, coating a given microstructure with metal allows for precise and controlled deposition of the desired material on the desired areas, enabling the post-production modification of the microstructure with almost no change to its dimensions and without needing to adapt the underlying microfabrication process. Hence, this approach offers additional flexibility and opens up customization options. Additionally, coating microstructures with metal can be more cost-effective than bulk metal micromachining, as it minimizes material waste and often reduces production time compared to traditional metal part manufacturing which, in addition, often subjects the parts to significant mechanical stresses that make it hard or impossible to achieve features such as thin, freestanding walls/fins that would tear when produced subtractively but can be relatively easily 3D printed in polymer. By applying metal coatings to microstructures, companies can achieve desired performance characteristics while maintaining the bulk properties of the original substrate material such as (in the case of polymer) lower density, and higher flexibility.
Alternative coating technologies do exist like Atomic Layer Deposition (ALD), Chemical Vapour Deposition (CVD), Physical Vapour Deposition (PVD), electroless plating, and electroplating. Complete micro metal parts can be made via micro metal 3D printing machines (high cost and low resolution) and metal injection molding. All these processes struggle when working with complex, three-dimensional microparts or are considered slow or hard to control. Achieving consistent deposition on all part surfaces requires precise control over process parameters such as flow rates throughout the part or line-of-sight to the surfaces. Obviously, this can be particularly challenging when working with complex part geometries, and is an area where Horizon’s research and development has been consistently placed.
We have focused our initial efforts on copper metal coatings, as this opens up an array of application possibilities for companies wishing to add functionality to 3D microstructures and especially polymer micro-AM templates. Copper coatings can offer significant benefits for microstructures or micro-additive manufactured parts, but there are several challenges and problems associated with current coating solutions that Horizon has sought to address to ensure the successful application of the copper.
The company has carefully optimized the coating process, materials, and deposition parameters, and has largely overcome these challenges to harness the full potential of copper coating which can now be applied reliably, cost-effectively, and speedily, making it viable for a large range of applications.
Horizon’s copper coatings are typically in the 1-2 micron thickness range and reach conductivities between 10 and 16 MS/m, which is sufficient for many applications. Depending on the part geometry and a process-friendly part design, these values can be exceeded. Importantly, the company’s process can also coat internal channels and undercuts, the channel’s aspect ratio being the limiting factor now rather than the absolute length.
CMM Magazine. What application areas is HMT-Metal best suited?
AF. HMT-Metal is ideally suited to the very many applications where the use of bulk copper is not required and would be technically impossible or uneconomic. Making geometries via polymer AM not possible through the use of bulk copper, and then adding the functionality of a copper coating can therefore be highly disruptive. The most important use case for the coatings is when highly conductive surfaces are required. Horizon’s copper coating can be used not just to coat an entire micro-part, but also allow to selectively coat features on a part’s surface, creating several independent metal features like interconnects and vias. Copper coatings can also significantly improve the surface properties of micro fabricated parts by adding wear resistance, lubricity, and hardness.
The key application areas are those that require high precision, complex geometries, and advanced materials properties, such as high electrical conductivity. As such, opportunities exist in the production of micro-electronic devices such as free-form printed circuit boards, interposers and interconnects; micro-sensors; miniaturized biomedical devices (such as implantable sensors); drug delivery systems; lab-on-a-chip systems, micro-reactors, and microfluidic sensors; and MEMS actuators and transducers. Also, and importantly, mm-wave and RF components can be made using this approach which opens up the full design freedom of AM to RF-Designers. The additional degrees of freedom this offers are readily taken up by the antenna design community and have sparked a near-revolution in terms of new designs which optimize different performance parameters or greatly simplify the integration and assembly processes.
CMM Magazine. Has Horizon had any success in the area of mm-wave components?
AF. Yes, indeed. It was only a couple of months ago that we announced the results of rigorous functional testing proving the effectiveness of our HMT-Metal coating process for making high frequency D-Band horn antenna via 3D printing. From a commercial perspective, such components fit well with the use of micro-AM as they are typically in the cm size range, with sub-mm dimensions, and require the attainment of micron tolerances. The market demands such antenna and other mm-wave components to exhibit higher frequencies and connectivity for use in industrial measurement technology, sensor technology and communication applications with very low latencies. Being able to make such mm-wave components via micro-AM allows the production of smaller and lighter weight components, and also opens up the possibility of making them with properties and geometric features impossible using alternative fabrication processes.
We undertook a functional comparison of our copper coated micro-AM produced horn antenna with a traditionally produced commercially available antenna. Measurements were made of the radiation pattern (how much signal goes out of the antenna and in which direction) and the so-called S11 parameter (how much of the signal is reflected back from the antenna into the transmitter). The gain of the antenna (how much signal goes in the forward direction) and the S11 parameter were compared clearly and directly with traditionally produced antennas, and the test showed that the Horizon antenna had approximately the same gain and a better S11 parameter.
We were delighted to see that our micro-AM copper coated horn antenna performed as well as a conventionally built horn antenna, removing many of the reservations that 3D printed devices are often faced with. This opens up some very interesting opportunities as companies requiring horn antennas and other mm-wave components can now exploit the process advantages of micro-AM by partnering with Horizon as their development and manufacturing partner. We didn’t even perform full-blown dedicated additive design-thinking efforts for the antenna since we wanted to fabricate something emulating the conventional counterpart. Yet we have an antenna that weighs only a sixth of its conventional counterpart and takes up 15% less space. This is a powerful indication of the kind of benefits that dedicated AM-based component design-thinking could achieve.
Parts made on Horizon’s in-house micro-AM system.
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