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M echatronic I ntegrated D evices I n M ould S tructural E lectronics This article discusses the new and related multidisciplinary technologies of Mechatronic Integrated Devices (MIDs) and In-Mould Structural Electronics (IMSE). Both techniques involve depositing metal tracks on three-dimensional plastic surfaces, with components soldered on top, but they are made differently. By Dr David Maddison, VK3DSM Photos above from top-to-bottom: an injection-moulded part prior to structuring laser activation and structuring of the part; visible conductive tracks added; the conductive tracks have been metallised; an SM4007 diode has been soldered to the conductive tracks. Source: LPKF – siliconchip.au/link/ac3x M echatronic Integrated Devices were known as Moulded Interconnect Devices until they were renamed in 2010. Mechatronic is a portmanteau of mechanical and electronics. They are devices with integrated mechanical and electronic functions, comprising an injection-moulded or 3D-printed plastic body (the “circuit carrier”) onto which are printed electrically conducting tracks, similar to those on a circuit board. Electronic components can then be soldered to those tracks. Also known as 3D-MIDs, these devices have been likened to three-­ siliconchip.com.au dimensional printed circuit boards (3D PCBs). By integrating both electrical and mechanical functions, space and volume can be saved. That’s especially useful in miniaturised devices like smartphones and tablets, mechatronic modules in motor vehicles (such as accelerometers) and medical devices (such as implantable prosthetics or hearing aids). The mechanical aspects of a 3D-MID relate to the moulded carrier substrate, which may form part of a connector, support structure for a high-powered LED, interconnector to another Australia's electronics magazine component, carrier for a specialised sensor or printed antenna etc. Examples of these will be given later. Apart from miniaturisation, additional advantages of MIDs include the integration of mechanical and electrical or electronic components into the one assembly and the possibility of new functionality not achievable in other ways. Almost any shape can be made. MIDs can provide a reduction in the number of parts required, a reduction in manufacturing cost, fewer materials required overall, reduced assembly cost and time, optimal placement of components and reductions in development time and ultimate weight. Related to 3D-MIDs are In-Mould Structural Electronics (IMSEs) or In-Mould Electronics (IMEs). With IMSEs, conductive tracks are incorporated into the item being fabricated at the time of moulding, typically using electrically conductive inks, rather than conductive metallic tracks being added after moulding, as with 3D-MIDs. Discrete electronic components such as LEDs, switches and capacitive controls can also be incorporated at the time of moulding. A typical application for this technology might be a control panel or a lighting panel such as in a car or aircraft (we’ll give examples of these later in the article). The history of MIDs & IMSEs 3D-MIDs were first developed in the 1980s, but they were not initially a success, perhaps because there was not a sufficient demand for the advantages they offered at the time. Also, the technology was not sufficiently well developed. Challenges included: • It was expensive. • It took a long time for a product to get to market. • Design changes were difficult due to tooling being hard to change. • There was a lack of production infrastructure. • There was a separation of specialists who did not work together, such as those working on electronics and those working on the moulded components and the metallisation aspects. • Engineers were not very familiar with the technology. Today, there is an increasing demand for 3D-MIDs due to their advantages. Those include more electronic packaging options and a greater April 2025  11 Fig.1: an example of IMD. Unlike IMSE, no electronic tracks are printed here (this was the predecessor of IMSE). The untrimmed film is on the left (note the print registration markings). On the right is the film after it has been moulded into a plastic body and trimmed. Source: www.dekmake. com/in-mold-decoration Fig.2: a 3D-MID antenna module made using laser direct structuring. The components are on the inside surface. Source: www.lpkf.com/en/ industries-technologies/electronicsmanufacturing/3d-mids-with-laserdirect-structuring-lds Fig.3: a 3D-MID from CIS containing a cell, ICs, capacitor, LED, resistors and switch. Source: https://cis.de/ en/products/electromechanicalcomponents-3/mid Fig.4: a 3D-MID component for a CCD sensor (left) and integrated into a system with standard PCBs (right) by Distant Focus Corporation. Source: https://3d-circuits.com/wp-content/uploads/2022/01/ Sensor-platform-for-a-large-format.pdf Fig.5: a 3D-MID sun sensor for an automotive climate control system. Source: HARTING; siliconchip.au/link/ ac3y Fig.6: a 3D-MID position sensor component for Adaptive Cruise Control (ACC) system from Continental AG. This version is smaller and cheaper than a PCBbased version and allows for the optimal location of components. Source: https://3d-circuits.com/wpcontent/uploads/2022/01/Positionsensor-for-adaptive-speed-control.pdf 12 Silicon Chip flexibility in design and miniaturisation of assemblies. The technology has improved with better materials, better processes, rapid prototyping and reduced development time due to CAD/CAM (computer aided design and manufacturing). It also helps that 3D printing has become commonplace and engineers are now more familiar with it. A major development in the field of 3D-MIDs was laser direct structuring (LDS), which enabled an electrically conducting track in any desired pattern to be created without contact using a laser beam. This process was developed by LPKF and will be discussed later. IMSEs are a newer but related technology to 3D-MIDs. They have their origins with in-mould decoration (IMD), a process introduced in the 1970s where a printed decorative pattern is incorporated into a moulded plastic part. With IMD, a carrier film with the desired pattern is put into a mould designed for plastic injection moulding, then plastic is injected into the mould. The pattern is incorporated into the moulded part (see Fig.1). The area of the mould where the pattern film is placed should be as flat as possible to avoid excessive distortion (we’ll have more details on this later). This process was rapidly adopted after its introduction. Then, with the mobile phone boom of the 1990s and the requirement to print keypads and buttons with labels moulded into them, its adoption was further expanded. An enhancement of in-mould decorating was to print the pattern with an electrically conducting ink, which enabled the direct moulded-in integration of electrically conducting tracks. Electronic components such as LEDs for lighting or backlighting could then be attached to these tracks. Thus, IMSE was born. Digital printing techniques further enhanced design possibilities. IMSE has become very popular since the early 2000s. Examples of 3D-MID and IMSE devices Fig.7: a light assembly with LED made using 3D-MIDs. Laser direct structuring was used to print the tracks. Source: LPKF; siliconchip.au/link/ac3x Australia's electronics magazine As few people are familiar with 3D-MID or IMSE technology, we will start by presenting a few examples. 3D-MIDs can have complex 3D shapes with extensive conductive siliconchip.com.au tracks on both sides of the device; for example, the antenna element shown in Fig.2. With regard to antennas, 3D design allows them to be optimised for beam pattern, gain, efficiency and for millimetre-wave frequencies, due to the small size possible and high-­ precision of the printed tracks and device shape. Another example is shown in Fig.3. Fig.4 shows a 3D-MID to mount a CCD (charge-coupled device) image sensor, while Fig.6 shows a vehicular cruise control component, Fig.5 shows a sensor for a vehicular climate control system and Fig.7 shows a light assembly. These examples demonstrate the versatility of this technique, and its ability to make components that would be difficult, expensive or impossible to create with other processes. It also allows miniaturisation compared to conventional methods. In Fig.9, the foreground shows the front and the background shows the rear of the panel with printed conductive tracks. The settings can be changed via touch and movement of the rubberised switch membrane. Touches are detected by capacitance changes in the printed tracks. Fig.8 shows a “smart surface” in the form of a panel for an aircraft cabin, while Fig.11 is an example of a control panel for an electric car and Fig.10 is a circuit board with 3D structure. Fig.8: an aircraft interior lighting and indicator panel ‘smart surface’ made with IMSE technology by Tactotek. Source: www.tactotek.com/ industry-aviation Fig.9: an example of a control panel made using IMSE. Source: www. eastprint.com/wp-content/uploads/InMold-Electronics.pdf Fig.10: an IMSE circuit board with 3D structure by DuPont, made using their thermoformable electronic inks and pastes to produce a 1.5mm-thick 3D plastic surface. Some small electronic components have been fitted. Source: https://semiengineering.com/getready-for-in-mold-electronics Making a 3D-MID The basic steps for making a 3D-MID are: 1. A computer-aided design (CAD) drawing is created of the plastic body and the conductive track layout. The section on Altium Designer below has more details on this. Also see Fig.12. 2. Injection moulding or, in the case of low-volume or prototype devices, 3D printing is used to make the plastic body – see the lead images. 3. Structuring is performed, more specifically known as laser direct structuring or activation. This is the first part of the process by which conductive circuit traces are created. An infrared laser is used to write the desired pattern on the injection moulded part. Chemical additives which had previously been mixed with the plastic are activated by the localised heat of the laser, converting a non-conductive metal compound into isolated ‘islands’ siliconchip.com.au Fig.11: an example of a control panel for an electric car with touch-sensitive backlit switches and backlit indicators made using IMSE by SunChemical. Source: www.sunchemical.com/el/download-suntronic-for-in-mold-electronicsmaterials-brochure Australia's electronics magazine April 2025  13 of conductive metal, which become nuclei for the plating process in step 4. The traces can be quite fine. Harting (https://3d-circuits.com/en) states they can produce conductive traces down to 75µm (0.075mm) width and spacing. 4. Metallisation – the conductive metal track from step 3 has additional metal such as copper, nickel or gold (or a combination) added by an electroless method (no electrode), joining together the metal islands described in step 3. Additional metal can then be plated on using electroplating. This is a similar process to that of creating vias on a PCB. 5. Assembly – surface mount devices (SMDs) are attached to the conductive tracks by fully or semiautomatic processes. We will now discuss other process steps for making 3D-MIDs and IMSE devices in further detail. Design and prototyping Silicon Chip readers will be familiar with Altium Designer, both because we use it for our PCB designs and because we regularly review it as it is updated. Our last review, in the August 2024 issue (siliconchip.au/Article/16425) mentioned its new 3D-MID capability (on page 66). Altium Designer can now be used for the design of electronic aspects of 3D-MIDs and IMSE devices (Figs.12 & Fig.13). The mechanical components themselves are designed in a CAD tool for 3D mechanical design like SolidWorks. The Altium product is designed to integrate with such software. There is a video on this at https://youtu.be/c8Ld82LEHi8 LPKF ProtoLaser 3D The LPKF ProtoLaser 3D is an example of a machine for creating PCBs and 3D-MID prototype components using laser direct structuring to write conductive tracks onto plastic – see Figs.14 & 15. The ProtoLaser 3D can import designs from conventional layout software. The part might first be 3D printed. In 3D printing, a three-dimensional structure is built up one layer at a time. For prototyping and low-volume production, components can be produced by 3D printing and then processed to incorporate conductive tracks with laser direct structuring or by chemical means. LPKF is one company that offers technological solutions for this process. Once printed, the part is sprayed with LPKF ProtoPaint LDS. This paint contains additives to enable the LDS process. The paint is cured for three hours at 70°C, then the part is ready for LDS. Once the conductive tracks are written by the laser, the part is removed and the tracks thickened by an electroless plating process using LPKF’s ProtoPlate LDS solution. This machine and process can also be used for low-volume manufacturing of custom parts. For example, Boris Yasinov from Elcom Technologies said he could produce 500 custom filters in one week using this machine. Also see the video on the process at https:// youtu.be/THushdmY5Tc Note that normally, for mass production, the chemical components Figs.12 & 13: a 3D-MID being designed in Altium Designer and a rendering of an assembled 3D-MID. Source: www.altium.com/ altium-designer/features/ true-3d-circuit-design Fig.14: the LPKF ProtoLaser 3D for laser direct structuring. It can write conductive tracks onto prototype components. Source: www.lpkfusa. com/pls 14 Silicon Chip siliconchip.com.au ◀ Fig.15: the LPKF prototyping process for 3D-MID components. Source: www.lpkf.com/fileadmin/mediafiles/ user_upload/products/pdf/EQ/3DMID-LDS/brochure_lpkf_laser_ direct_structuring_en.pdf for LDS on 3D-MIDs are incorporated into the plastic feedstock for injection moulding and don’t have to be sprayed on. See below for further information on LDS. 1 2 3 4 5 6 5 Injection moulding Injection moulding is the process most used to fabricate 3D-MIDs and IMSE devices, except for prototyping or low-volume production runs. In fact, this is the most common method of mass production of solid plastic components of any kind. The process of injection moulding involves feeding plastic pellets from a hopper into a heated screw feed mechanism, which melts the plastic and injects the required amount into a mould (Fig.16). The mould is custom made for the required part (see Fig.17). A typical small injection moulding machine is shown in figure Fig.18. Two-shot injection moulding is a variation of injection moulding. A moulded part is first made as per the conventional injection moulding process. Then, the part is put into another siliconchip.com.au Fig.16: a simplified diagram of an injection moulding machine. The parts are: 1) screw feed with heated barrel to melt & inject plastic into mould, 2) hopper for plastic granules, 3) nozzle, 4) & 6) mould, 5) moulded part. Source: https://w.wiki/Cg6g section of the mould, which is a different shape to the first, into which additional material is injected to form the final shape of the part. The additional material may be the same type of plastic in a different colour, or a different type of plastic. For example, a rubbery compound can be added to the first part, as is commonly done with power tool housings. Those principles apply for all types of Australia's electronics magazine two-shot injection moulding, regardless of whether it is used for 3D-MIDs or not. One of the biggest costs for injection moulding is the cost of moulds, which are finely machined to high levels of accuracy and can come in complex shapes. Significant cost savings can be made by machining moulds from aluminium rather than stainless or hardened steel, but they have lower April 2025  15 Fig.17: the basic scheme of injection moulding. In this case, the charge of molten plastic is injected at the top into the mould P and two parts are produced simultaneously. Source: https://w.wiki/Cg6e charge nozzle durability, less longevity and worse dimensional accuracy. Nevertheless, aluminium moulds might be perfectly acceptable for many or most applications. Plastic choices sprue runner gates parts ejector pins A wide range of injection mouldable plastics are possible for 3D-MID, including: • acrylonitrile butadiene styrene (ABS) • polycarbonate • polyphenylene ether • polyetherimide • polybutylene terepthalate • polyethylene terepthalate (PET) • polyamide 66 (Nylon 66) • polyamide 6 (Nylon 6) • polyphenylene sulfide (PPS) • liquid crystal polymer • polyether ether ketone The specific choice of plastic depends on factors such as cost, thermal stability, mechanical properties, UV stability, chemical stability and compatibility with metallisation methods and additives. A variety of plastics are suitable for the fabrication of IMSEs, including polycarbonate, polyester, acrylic (Perspex), acrylonitrile butadiene styrene (ABS) and polyurethane. Metallisation methods for 3D-MID Fig.18: a typical small injection moulding machine. The cone-shaped hopper contains plastic granules. Beneath that is a horizontal screw feed. The mould goes inside the yellow cage and the product exits via the chute to the left of the yellow control panel. Source: https://w.wiki/Cg6h Fig.19: the process of laser direct structuring in which a laser creates metal particles by chemically transforming an additive precursor while also roughening the surface. Source: www.kyoceraavx.com/docs/techinfo/ Application-Based/LDSWorking-Principles-Benefitsfor-RF-Apps.pdf List of Important Acronyms (3D-)MID | (three-dimensional) Mechatronic Integrated Devices IM(S)E | In-Mould (Structural) Electronics IMD | In-Mould Decoration 16 Silicon Chip Australia's electronics magazine Metallisation of 3D-MIDs is generally done using laser direct structuring, but for two-shot injection moulding, it is done via chemical means. In LDS, the plastic compounds used in injection moulding have special additives of chemical compounds such that when a laser is directed at them, they undergo a chemical change to reduce them to pure metallic atoms, which are electrically conductive. These form a nucleation centre for additional subsequent metal deposition. In the case of 3D-printed prototypes or low-volume production, these can be instead sprayed onto normal plastic as a paint. This paint undergoes a similar chemical reaction when exposed to a laser beam, creating conducting pure metal atoms. The laser used in LDS is infrared and has a spot diameter typically of 50–100µm (0.05–0.10mm). Chemical additives typically used in LDS include cuprous oxide (Cu2O), cupric oxide (CuO) and copper chloride (CuCl2). These are reduced to siliconchip.com.au In-mould structural electronics (IMSE) Fig.20: two-step or two-shot injection moulding. The plastic to be metallised contains a special catalyst. Source: www.contag.eu pure copper nuclei by action of the laser, typically in the form of copper nanoparticles – see Fig.19. Other metal complexes can also be used. The surface of the plastic is also roughened by the laser, enhancing adhesion of the subsequent metallisation. The conducting pathways created by laser direct structuring are not thick enough to be used as-is; additional metallisation is required to thicken them and join the islands. Therefore, after the laser process, the components are dipped in a special chemical bath containing catalysts and a copper or other metallic compound. More copper (or another metal such as nickel, silver or gold) is deposited on the pathways modified by the laser, which contain the aforementioned metallic nanoparticles that act as nucleation centres for metal deposition. This process is purely chemical in nature and is referred to as ‘electroless’ (meaning that no electrode is required). After electroless deposition, electroplating of the tracks can also be performed if extra-thick tracks are required. This involves passing a current through a solution and the existing metal tracks, causing additional metal atoms to be attracted to the tracks, which are incorporated into them. LPKF report that they can achieve through-hole plating of 3D-MIDs using LDS, but they do not specify the process by which this is done. It is possible that they drill through-holes, then use a laser to perform LDS on the siliconchip.com.au exposed surfaces before the electroless and electroplating processes. Chemical process for two-shot injection moulding In the case of a 3D-MID made using two-shot moulding, metallisation is done via a chemical process rather than laser direct structuring. One of the plastics contains a catalyst that is metallisable, while the other does not contain the catalyst. The presence of the catalyst in one of the plastics causes metal deposition on that part when it is immersed in an appropriate chemical bath. Two examples are presented in Fig.20. On the left, the first material to be injected is metallised. On the right, the material that is injected second is metallised. 3D assembly Components have to be placed on 3D-MIDs and IMSE structures for soldering. This is done using 3D ‘pick and place’ machines, which can operate in three dimensions rather than just two as required for conventional PCBs. An example of such a machine is the Yamaha S20 – see siliconchip. au/link/ac3t With IMSE, the main circuit carrier component is mostly made in a single operation, unlike 3D-MID, which requires several operations. Electrically conductive tracks are incorporated at the time of moulding. Discrete electronic components, such as LEDs, can even be incorporated at the same time. IMSEs do have depth, but they tend to be flatter than 3D-MIDs in most applications. IMSEs typically start as 2D films, which may contain a printed design comprising artwork, labels for buttons or conductive or insulating tracks. Then additional plastics processing methods are used to convert them into more complex 3D shapes. The IMSE manufacturing process steps are: 1. The component is designed with appropriate CAD software. An example of one such CAD package is TactoTek IMSE Designer, which is intended for designing IMSE lighting devices for automotive applications (see siliconchip.au/link/ac3p). Another is Altium Designer, which was already mentioned. 2. Screen, inkjet printing or another form of printing is used on a plastic film. Decoration and/or labels are applied to a flat piece of plastic using a printing process; screen printing is the most common. This is followed by an additional printing process to apply electrically conductive tracks, similar to the tracks on a PCB. Special metal-laden inks are used – see Fig.22. 3. Components are placed onto the printed film using pick-and-place equipment. The components are attached with adhesive and electrical connections are made via conductive inks – see Fig.23. 4. The device is thermoformed using heat and an appropriate moulding to form the required 3D shape. WeLDS technology WeLDS is a technology developed by LPKF that combines LDS with laser plastic welding. It creates unique structures by welding 3D-MIDs to other plastic structures – see Fig.21. Australia's electronics magazine Fig.21: an example of WeLDS technology, with a device made by 3D-MID laser welder to another plastic structure. Source: www.lpkf. com/en/welds April 2025  17 Figs.22-25: (1) the tracks are laseretched onto a plastic film; (2) the components are then mounted around the periphery using a pick-and-place machine; (3) thermoforming is done to the part; (4) injection moulding seals the circuitry and gives extra structural rigidity. Source: www. tactotek.com/technology Within these structures, the typical layers of an IMSE part may include: ¬ A film on the top, bottom, or both. ¬ Electronics on the top (or bottom) film, or both. ¬ Injection moulding resin. IMSE can be combined with IMD graphics for, say, a control panel. These are printed on a film which is then placed in the mould cavity and incorporated into the moulded part. A manufacturer in the field, Tacto­ Tek, has a theme of “smart surfaces” to describe their use of IMSE technology. Fig.8 is one example. Also see https:// youtu.be/eGxkby9MBIM Some advantages of IMSE products are said to be a reduced part count, higher durability, reduced assembly time, more simple assembly, weather resistance, reduced weight and thickness compared to other methods. It is also possible to build illumination into the product. Printable inks for IMSE Conductive inks for IMSE contain metal particles such as silver, which is quite expensive. SmartInk from Genes­ Ink (www.genesink.com/smartink) is an example of a silver-containing ink Thermoforming is a process that for IMSE applications. Another such involves heating plastic to its soften- ink is from Dycotec (siliconchip.au/ ing point and then moulding it into a link/ac3u). shape – see Fig.24. Some conductive inks contain Care must be taken in the design graphite or carbon. For transparent stage to ensure that deformation conductors, indium tin oxide (ITO) during the forming process is not so can be used. It is see-through and can great that it causes the printed tracks be ‘printed’ using physical vapour to be excessively deformed and they deposition, electron beam evaporation become non-conductive. This pre- or sputter deposition. cludes shapes with excessively sharp ITO is expensive, so alternatives angles or other areas of high deforma- such as aluminium-doped zinc oxide tion. Care must also be taken so placed (AZO), indium-doped cadmium components remain on flat sections. oxide and carbon-based materials like 5. The thermoformed component graphene and carbon nanotubes are from the previous step is placed in an being explored as substitutes. Carbon-­ injection moulding machine, where it containing inks can also be used for is overmoulded to seal the electronics static dissipation. and circuitry, and to give some strucDielectric inks are also used for tural rigidity – see Fig.25. insulation purposes. Other materials 6. The component is trimmed to used include electrically conductive remove excess material and bring it to adhesives. its final shape ready for use. Due to the high cost of silver, it is Typical examples of structural desirable to find appropriate substioptions with IMSE devices are: tutes. Substitutes that are being inves• A two-film structure with a film tigated are copper, aluminium and on top and bottom, and injection-­ nickel, of which copper is the most moulding resin in between. promising; it is only about 1% of the • A film on the top and injection cost of silver. It has been used to some moulding resin on the bottom. extent. • A film on the bottom and injection A major disadvantage of copper moulding resin on the top. is its tendency to oxidise over time. 18 Silicon Chip Australia's electronics magazine Approaches to improving the oxidation resistance of copper-containing inks include: • Coating copper micro and nanoparticles with various substances. • Using antioxidant additives. • Using copper nanowires. • Making mixtures of copper nanoparticles with other substances like carbon nanotubes. • Sintering copper powder or copper compounds using a laser or flashlamp to make a contiguous copper layer like on a PCB. Non-metallic conductive inks are also possible, such as those made with the conducting polymer poly(3,4-­ ethylenedioxythiophene) mixed with polystyrene sulfonate. This is referred to as PEDOT:PSS. 3D-MID vs IMSE 3D-MID and IMSE have their advantages and disadvantages. 3D-MID tends to be used when miniaturisation, high reliability and a 3D structure is required. IMSE devices tend to be flatter, although still three-dimensional, and are more suited to control panels and other human interface devices, including ‘smart surfaces’. Both technologies have many applications across aerospace, automotive, medical and consumer electronics. There are no hard and fast rules about which technology should be used where. It comes down to cost, designer intent, volume and complexity. SC Companies Celanese (www.celanese.com/ products/micromax) for inks Cicor (siliconchip.au/link/ac3v) Contag (www.contag.eu) Distributed Micro Technology Ltd (www.dmtl.co.uk) Dycotech (siliconchip.au/link/ac3u) DuraTech (www.duratech.com) Eastprint (www.eastprint.com/ in-mold-electronics) Essemtec (https://essemtec.com) GenesInk (www.genesink.com) Harting (https://3d-circuits.com). See their video on 3D-MID at https://youtu.be/DcjGGJlc81I LPKF (www.lpkf.com/en) Lüberg Elektronik (www.lueberg.de) Sun Chemical (siliconchip.au/link/ ac3w) for inks TactoTek (www.tactotek.com) siliconchip.com.au