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JANUARY 2019 I FLEX007 MAGAZINE 87 and CVL thickness, RA copper foil has a lower surface roughness (Rz = 1.3) than ED copper foil (Rz = 2.7). IL measurements are shown in Figure 10. RA copper foil has a lower IL owing to its lower surface roughness. Conclusion Due to the dielectric characteristics, test traces with the same line widths and pitches have different impedances on different sub- strate materials. This would increase the IL measurement error. Described in this article is a standardized differential microstrip that enables us to achieve equal impedances for all materials by adjusting line width and pitch, and thus excludes parameters unrelated to materials for the IL measurement. Our measurement data clearly indicates that using an LCP as a dielectric leads to the lowest insertion loss. Modified PI (doped with other species) also leads to a lower IL than tradi- tional PI. For each dielectric, a thicker dielec- tric layer produces a lower IL. Furthermore, RA copper foil having a lower surface roughness provides a lower IL because of the skin effect at its surface. FLEX007 Yi-Chun Liu is director at the Research and Development Center of Uniflex Technology Inc., a flexible printed circuit design and manufacturing company based in Taiwan. Figure 9: IL dependence on dielectric thickness. Figure 10: ILs of RA copper foil and ED copper foil. A technique that enables biologically active enzymes to survive the rigors of inkjet printing presents a promis- ing alternative to routine blood screening exams faced by diabetic patients. The KAUST-led team used this approach to make disposable devices that can measure glucose concentrations in human saliva. Researchers are now working to create paper sensors that quickly indicate disease biomarkers. The key to this approach is replacing traditional electronic circuitry in the sensors with low-cost plastics that can be manufactured quickly and in large quantities. The team used inkjet technology to produce sensors sensitive to small sugar concentrations in biofluids. Utilizing a commercial ink made from conducting polymers, the team printed microscale electrode patterns onto glossy paper sheets. Next, they printed a sensing layer containing an enzyme, glucose oxidase, on top of the tiny electrodes. The biochemical reaction between available glucose and the enzyme creates electrical signals easily correlated to blood sugar levels. Experiments showed the top coating gave the sensor an unprecedented shelf life; the enzyme could be kept alive and active for a month if stored in a sealed bag. These results are encourag- ing the team to expand the capabilities of this approach by incorporating different enzymes into the sensing layer. (Source: KAUST) Paper Sensors Remove the Sting of Diabetic Testing