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72 FLEX007 MAGAZINE I APRIL 2019 design was to understand how these different materials and components would behave once they were put together, stretched to a three- dimensional form, and ultimately injection- moulded into a single unit. Because IMSE enabled electronic functionality to be integrated into three-dimensional surfaces and in space-limited locations, there was enormous scope for innova- tive design, and decorative surfaces could be made functional without changing their mechanical struc- ture. Further, conventional elec- tronic assemblies could be substan- tially reduced in thickness, weight, and complexity. An example demonstrated by Rytky and passed around the audi- ence was a typical automotive over- head control panel. In its conven- tional form, it was a bulky structure, 45-mm thick, and weighing up to 1.4 kg with 64 individual mechani- cal parts, and its assembly required 30 separate operations. In terms of durability and reliabil- ity, the structure was fully encapsulated and protected from debris and moisture, and fully functional over a -40°C to +80°C temperature range. In another automotive example, touch- sensitive illuminated seat controls had been integrated within a real-wood door trim and the overall thickness was only 3 mm. Electronic functionality could even be inte- grated into fabrics for wearable electronics, and a fully encapsulated smart connector had been developed that could withstand more than 10,000 twists and bends and more than 50 cycles of machine washing. Clearly, traditional electronic and mechani- cal design rules and guidelines were generally not applicable to the design of IMSE where an entire design team could be working in par- allel to define the layout of the thermoplastic film, which carried the user-interface graphics, the part geometry, and the electronics. It had been necessary to collaborate with suppliers of familiar design tools to create add-ons specific to its features and characteristics. And because the full film assembly—including its electron - ics—would subsequently be thermoformed and injection-moulded. Additional challenges had been overcome in the simulation of elec- tromagnetic performance, thermo- forming, and injection-mould flow. Rytky handed over to Tuomas Heikkilä to discuss the IMSE elec- tronics design flow and review the main design-for-manufacture differ- ences comparing IMSE with tradi- tional PCB technology. Apart from the obvious dissimilarities in the nature of the substrate—because the conductors were composed of silver flakes and polymers rather than solid copper—their dimen- sions and current-carrying capaci- ties followed completely different design rules. Dielectric bridges had to be designed in at conduc- tor crossovers and components carefully placed to avoid areas that would be significantly stretched during the process of forming from two-dimen- sional to three-dimensional. Using the automotive overhead control panel as his example, Heikkilä identified the prin- cipal electrical and mechanical features, and explained how the stackup had been created and the layout defined, design-rule checked, and simulated before the output of the tooling and fabrication files. Although TactoTek had the in-house capabil- ity to design, develop, and validate products according to customer requirements, they were also prepared to licence design and manufac- turing expertise to enable customers to exercise their own creativity with proven technology. As the closing slide of the presentation declared, "This is not the future; this is today!" FLEX007 Pete Starkey is technical editor for I-Connect007. Based in the UK, Starkey has more than 40 years experience in PCB manufacturing technology, with a background in process development and technical service. To contact Starkey, click here. Sini Rytky Tuomas Heikkilä