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NOVEMBER 2019 I DESIGN007 MAGAZINE 105 Structural Electronics Technology Needs New Standards Current printed electronics standards lack in- formation that is important for structural elec- tronics. An example is a method for resistance- strain measurements. During thermoforming, 2D films with conducting layers are formed into 3D shapes. The films and conducting lay- ers deform plastically. Printed electronics stan- dards have some deformation related items [6–9] ; however, the deformations and stresses are in the elastic region only. For companies to design reliable structur- al electronics solutions, they must know how conductive layer resistance changes as a func- tion of plastic strain. This information is sel- dom available from ink suppliers. Moreover, there is no shared measurement or analysis methodology. Thus, results cannot be com- pared to ink suppliers. TactoTek made resis- tance-strain measurements for conductive inks in 2015, has continued developing the method since and is looking to refine it into an interna- tional standard. If a test method standard becomes an IEC or IPC standard, will the other standard organi- zation develop a similar one but with different test methods and requirements? TactoTek does not want this to happen. In a truly global indus- try, such as (structural) electronics, it would be a waste of effort to have overlapping work in two standardization organizations, with co-op- eration and similar standards being the goal. Conclusions Structural electronics use flexible plastic films as substrates. Thus, the standards that are based on typical PCB stiffness and temper- ature endurance are not applicable to structur- al electronics. In TactoTek's opinion, IEC de- vice embedded substrate standards have se- lected a good approach that does not hinder the utilization of new and evolving technolo- gies, which could be adopted in other standard documents. These standards allow the user and supplier to select temperatures that are rel- evant to the application environment. We wel- come this approach and hope to see it in other standards going forward. Acknowledgments The authors thank Tuomas Kallio, Antti Keränen, Pasi Korhonen, Dave Rice, and Jo- hannes Soutukorva for their much-valued con- tribution to this work. FLEX007 References 1. T. Simula, P. Niskala, M. Heikkinen, & O. Rusanen, "Component Packages for IMSE (Injection Molded Struc- tural) Electronics," NordPac Proceedings, 2018. 2. IEC Webstore, "IEC 62899," accessed June 2019. 3. IPC Online Store, "Printed Electronics," accessed June 2019. 4. IEC, "IEC Standard Development Working Groups," accessed August 2018. 5. IPC, "IPC Public Groups," accessed August 2018. 6. Standard IPC-4921, "Requirements for Printed Elec- tronics Base Materials (Substrates)." 7. Standard IPC-4591, "Requirements for Printed Elec- tronics Functional Conductive Materials." 8. Standard IEC 62899-201-2, "Printed Electronics—Part 201-2: Materials—Evaluation Methods of Stretchable Sub- strates." 9. Standard IEC 62899-201-4, "Printed Electronics—Part 201-4: Materials—Evaluation Methods of Stretchable Func- tional Ink (Conductive Ink and Insulator Layer)." This paper was first presented at the IPC APEX EXPO 2019 Technical Conference and published in the 2019 Technical Conference Proceedings. All of the authors are with TactoTek in Oulu, Finland. Outi Rusanen is senior interconnect specialist. Janne Asikkala is prinicpal research chemist. Mikko Heikkinen is chief engineer and co-founder. Paavo Niskala is VP of advanced engineering. Tomi Simula is principal integration specialist. Outi Rusanen Paavo Niskala Janne Asikkala Tomi Simula Mikko Heikkinen

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