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54 DESIGN007 MAGAZINE I AUGUST 2018 where the environmental conditions are one consideration in predicting the long-term per- formance of the final product. The results from the test conditions ensure that the user can expect optimal performance from our products in a range of environments. Q. Which industries typically ask for resins that are designed to perform well in RF applications, and what is so special about these resins? A. Typically, the communications industry (manufacturers of mobile and fixed telecom- munications equipment) is most likely to specify a resin that is specially formulated to protect electronic assemblies that generate RF signals. However, many other companies are now adding Wi-Fi/Bluetooth functionality to a much wider range of products to facilitate easy communication between devices. Resins designed for RF applications do not contain fillers—particles that might otherwise cause RF signal scattering or attenuate the sig- nal altogether. In many cases the transmission power of devices utilising Wi-Fi/Bluetooth is quite low, so any intervening medium, such as a protective resin, which might reduce or scat- ter the signal strength, is a potential problem. Flame retardancy is often specified for RF applications but most flame-retardant resins will either contain halogens (which are now facing increasing regulatory restriction) or metal containing fillers (that scatter or attenu- ate RF signals). We have met this challenge with the UR5641/2/3 series of flame-retardant, filler-free and halogen-free resins that are suit- able for a wide range of RF applications. Q. When is it important to ensure that a resin's dielectric constant does not vary over the long term? A. Dielectric constant (also known as rela- tive permittivity) is an important parameter when resins are concerned. A resin with low dielectric constant, for example, will have min- imal impact on any electric field produced by a device and thus ensure maximum transpar- ency for any signals generated by that device. It is also important that the resin's dielectric con- stant remains low over the entire life of a prod- uct or system to which it has been applied. In the case of marine applications, for example, a resin's consistent long-term electrical per- formance may be critical, as having to replace units compromised by dielectric constant vari- ability is likely to be operationally costly, par- ticularly if those units are in difficult-to-access areas, such as the bottom of the ocean. Q. How does Electrolube measure thermal con- ductivity and why is the accuracy of the testing method so important? A. We have recently invested in some new thermal conductivity measurement equipment that uses the Modified Transient Plane Source method of measuring thermal conductivity, (an improvement upon the well-known Hot Disk Transient Plane Source method), which has been well established over the years. This enables us to obtain many measurements over a wide temperature range quickly and reliably. Direct measurements of a thermal paste or cured resin provide values for thermal con- ductivity that are very close to those experi- enced under real operating conditions; how- ever, there will always be some slight variation due to the nature of the design of the unit and the components used. Unfortunately, there are still cases where the thermal conductivity of a cured resin will have been calculated from the component parts, rather than having been obtained from a measurement of the material. Calculated values are generally far higher than those obtained from direct measurement of the materials in question. Q. When is it appropriate to consider using a single- vs. a two-component resin system? A. Single-component resins (or 1K resins) are generally used for adhesive applications such as a glob top, or for bonding components to a PCB or other substrates. A 1K resin does have its disadvantages, however. Viscosity is generally higher than that of its 2K counter-

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