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AUGUST 2018 I DESIGN007 MAGAZINE 51 materials to have TCDk values of more than 300 ppm/°C. The general rule of thumb in the high- frequency industry is that the TCDk should not be greater than 50 ppm/°C, which is the TCDk value for the RO4835 laminate. Aside from the previously mentioned concerns, the tradeoffs between FR-4 and high-frequency materials often comes down to insertion loss dif- ferences. Some tricks can be done to get FR-4 to provide better loss performance at higher frequen- cies. One is to have the FR-4 laminate use a very smooth copper. The surface of the copper that is of concern is the copper surface roughness at the copper-substrate interface. Smooth copper at this interface will reduce the conductor loss, which is a component of the overall insertion loss. Also, if the FR-4 substrate is relatively thin, the con- ductor effects will be more significant, and the smooth copper will help improve insertion loss. The poor dissipation factor (Df) for FR-4 is really a big issue for insertion loss. In general, a high-Tg FR-4 substrate usually has Df values of 0.015 to 0.025 when tested at 1 GHz, as compared to the high-frequency material in these comparisons, which has a Df value of about 0.0025 at 1 GHz. Whether or not FR-4 is acceptable for insertion loss will need to be addressed by the PCB designer who is familiar with the limits of the loss bud- get. Remember that when dealing with the gray area between FR-4 and high-frequency laminates, another choice is available: mid-loss materials. These materials typically have a Df value of 0.005 to 0.015 at 1 GHz and their laminate costs are usually closer to the cost of high-frequency mate- rials costs than FR-4. The Rogers Kappa 438 lami- nate is considered a mid-loss material. It has a lot of the properties of high-frequency laminates, but it also has a Dk value that is closely matched to FR-4, with a much lower Df than FR-4 that is not as good as that of the RO4835 laminate. When it's time to move from FR-4 to a high- frequency material, keep in mind that you always have options. DESIGN007 John Coonrod is technical marketing manager of Rogers Corporation. To read his past columns or to contact Coonrod, click here. Smart Homes Open New Approaches and Business Models for Healthcare Delivery As healthcare shifts to proactive care, a huge market is opening for automation products that can help deliver health and wellness services through smart homes. The ubiquity of broadband connectiv- ity, development of smart sensors, and the decreas- ing costs of devices have already made it possible to offer aging-in-place, chronic disease manage- ment, and post-acute care services in smart homes. However, digital health vendors are striving to take telehealth to the next level by developing solutions that will allow care givers to check on the health of all the residents of the house, not just the patient's, monitor diet and nutrition, environment, and be inte - grable with existing and newer systems. "Patients are conscious of their health and want to be involved in the wellness and disease manage - ment," said Sowmya Rajagopalan, global program director, Transformational Health. "With consumer- ization of healthcare, enabling patients to clinically manage their disease at home has been of crucial importance for care providers and OEMs today as they have made this a reality with the launch of innovation in design, devices, services, and solu - tions." Frost & Sullivan's recent analysis, Vision 2025— Healthcare in the Smart Home, examines the con - cept of a smart home delivering healthcare. It seg- ments resident profiles and lists the individual needs that are relevant to healthcare delivery in the home. Source: Frost & Sullivan

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