Thermal Management
material. This energy loss is linked to heat generation caused by molecular motion, which impacts the efficiency of power delivery. Excessive heating of the dielectric material beyond its thermal capability ultimately leads to failure due to dielectric breakdown. Lower loss materials are desired to mitigate such an occurrence, especially for high frequency applications where heat generation is of great concern. Referring to Figure 1, ranges where Dk maintains a flat response and Df is near a minimum are optimal for achieving peak capacitor performance. The effect of operating temperature on electrical losses with respect to frequency is demonstrated here for the new class of thermally stable ultra-thin polymer films.
Dielectric constant Dk and loss factor Df characterization The dielectric constant Dk and the dissipation factor Df are determined from the capacitance equation for a solid body and lumped impedance equation, respectively,
Corresponding performance of the dielectric constant Dk is shown in Figure 3. ELCRES HTV150A ultra-thin dielectric film is made of an advanced engineering thermoplastic material that is amorphous in nature, with Tg of 205°C. The film displays an electrical loss profile where the dissipation factor Df decreases at higher temperatures; Df drops by about 40 per cent from 0.0047 to 0.0027 at 150°C. This is likely related to the shift in the and relaxation states to a higher temperature. At some temperature between these two transition states, a minimum in electrical losses will be observed. This minimum happens to fall within the temperature range of interest for AC DC inverters using new MOSFETs such as SiC, where operating temperatures reach 150°C. Low losses at high temperatures are desirable in a few adjacent applications. These include, but not limited to, on-board chargers, fast chargers, alternative energy (wind and solar), industrial drives, deep-well drilling, SMD capacitors, and mass transportation. Dk for ELCRES HTV150A is stable over the frequency range, with only a minor drop
when the temperature changes from room temperature to 150°C, (Figure 3). Understanding the impact of temperature on electrical losses at high frequencies is critical for film performance in intended applications. Capacitors constructed from polymers where Df increases with
temperature can further generate heat under operation causing excessive energy losses and could be prone to thermal runaway, which may ultimately lead to catastrophic failure of the dielectric film.
where Cp is the measured capacitance of a metallized sample in Farads (F), Rp is measured resistance in Ohm, t is the thickness of the measured sample in metres (m), A is the contact area (m2) of the electrodes delivering an electric field, f is the frequency, and 0 is the permittivity of free space or vacuum, a constant of 8.854 x 10-12 (F/m). The test setup conforms to the ASTM D150 standard and comprises a parallel plate fixture that sandwiches the film sample between two electrodes to form a capacitor. An LCR meter is used to measure the capacitance created in the fixture. To measure the electric field at elevated temperatures, a custom test fixture was used. Both surfaces of each sample were metallized by depositing approximately 50nm of aluminum using a benchtop Physical Vapor Deposition equipment. Capacitance was recorded at a given temperature while a frequency sweep was performed. Measurements were also performed on PEN samples for comparison. Dissipation losses, represented by Df, as a function of temperature and frequency for ELCRES HTV150A film are depicted in Figure 2.
www.cieonline.co.uk.
Operating at higher temperatures beyond the 105°C limit of incumbent biaxially oriented polypropylene film (BOPP) has been an ongoing industry and academic challenge. Specialty high heat films, such as PEN films can withstand higher temperatures. However, Df experiences a large increase at 150°C, exceeding the industry limit of 0.01. To avoid the excessive losses, the designer is forced to limit the maximum operating temperature to around 125°C.
Figure 2: Dielectric Loss (Df ) vs Temperature and Frequency for HTV150A
SABIC has been developing new materials for potential use in ultra-thin film dielectric applications with operating temperatures upwards of 150°C. A new amorphous high heat engineering thermo- plastic material has been identified for use, subject to user testing, as the dielectric material in ELCRES HTV150A ultra-thin films having advantageous electrical properties for DC Link capacitors requiring high operating temperatures. ELCRES HTV150A film has a stable dielectric constant, Dk up to 150°C. Moreso, the dissipation factor Df exhibits a decrease of about 40 percent as temperature increases from 25°C to 150°C at high frequencies of up to 100kHz.
For more information
Additional key features and benefits, typical properties and potential applications for SABIC’s ELCRES HTV150A film portfolio can be found in SABIC’s new brochure.
Figure 3: Dielectric Constant (Df ) vs Temperature and Frequency for HTV150A
https://www.sabic.com/en/products/ documents/sabic-elcres-htv150a-film- flyer/en
Components in Electronics July/August 2023 49
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