The following excerpt touches on applying electronics to a 3D surface (partially additive), in-mould electronics, and fully additive electronics.
Motivation for 3D electronics
While partially additive 3D electronics has long been used for adding antennas and simple conductive interconnects to the surface of 3D injection-moulded plastic objects, more complex circuits are increasingly being added onto surfaces made from a variety of materials by utilising new techniques. Furthermore, in-mould electronics and 3D printed electronics enable complete circuits to be integrated within an object, offering multiple benefits that include simplified manufacturing and novel form factors. With 3D electronics, adding electronic functionality no longer requires incorporating a rigid, planar PCB into an object and then wiring up the relevant switches, sensors, power sources, and other external components.
Applying electronics to a 3D surface
The most established approach to adding electrical functionality onto the surface of 3D objects is laser direct structuring (LDS). LDS saw tremendous growth around a decade ago and is used to manufacture hundreds of millions of devices each year, around 75% of which are antennas. However, despite its high patterning speed and widespread adoption, LDS has some weaknesses that leave space for alternative approaches to surface metallisation. Valve jet printing or termed dispensing, a technique enabling a wide range of materials deposition, is already used for a small proportion of antennas, and is the approach of choice for systems that deposit entire circuits onto 3D surfaces.
Aerosol jetting and laser induced forward transfer (LIFT) are other digital deposition technologies, which offer higher resolutions and rapid deposition of a wide range of materials respectively. Other emerging techniques such as ultra precise dispensing, electrohydrodynamic printing, impulse printing, pad printing, and spray metallisation enable new market potential of electronics on 3D surfaces. An advantage of digital deposition methods of the incumbent LDS technology is that dielectric materials can also be deposited within the same printing system, thereby enabling multilayer circuits. Insulating and conductive adhesives can also be deposited, enabling SMD components to be mounted onto the surface.
In-mould electronics
In-mould electronics (IME), in which electronics are printed/mounted prior to thermoforming into a 3D component, facilitates the transition towards greater integration of electronics, especially where capacitive touch sensing and lighting is required. IME offers multiple advantages relative to conventional mechanical switches, including reduction in weight and material consumption of up to 70%, and a much simpler assembly. The IME manufacturing process can be regarded as an extension of the well established in-mould decorating (IMD) process. Thus, much of the existing process knowledge and capital equipment can be reused.
IME differs from IMD through the initial screen printing of conductive thermoformable inks, followed by deposition of electrically conductive adhesives and the mounting of SMDs (surface mount devices, primarily LEDs at present). More complex multilayer circuits can also be produced by printing dielectric inks to enable crossovers.
Despite the wide range of applications and the advantageous reductions in size, weight, and manufacturing complexity, commercial deployment of IME integrated SMD components has thus far been fairly limited. This relatively slow adoption, especially within the primary target market of automotive interiors, is attributed to both the challenges of meeting automotive qualification requirements and the range of less sophisticated alternatives such as applying functional films to thermoformed parts. Along with greater acceptance of the technology, this will require clear design rules, materials that conform to established standards, and crucially the development of electronic design tools.
Fully printed 3D electronics
The least developed technology is fully printed 3D electronics, in which dielectric materials and conductive materials are sequentially deposited. Combined with placed SMD components, this results in a circuit, potentially with a complex multilayer structure embedded in a 3D plastic object.
The core value proposition is that each object and embedded circuit can be manufactured to a different design without the expense of manufacturing masks and moulds each time. Fully 3D printed electronics are thus well suited to applications where a wide range of components need to be manufactured at short notice. The technology is also promising for applications where a customised shape and even functionality is important. The ability of 3D printed electronics to manufacture different components using the same equipment, and the associated decoupling of unit cost and volume, could also enable a transition to on-demand manufacturing.
The challenges for fully 3D printed electronics are that manufacturing is fundamentally a much slower process than making parts via injection moulding, since each layer needs to be deposited sequentially. While the printing process can be accelerated using multiple nozzles, it is best targeted at applications where the customisability offers a tangible advantage. Ensuring reliability is also a challenge, considering different material properties; additionally, with embedded electronics post-hoc repairs are impossible – one strategy is using image analysis to check each layer and perform any repairs before the next layer is deposited.
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