KEMET SMD Film Capacitors for High Temperature Applications

Abstract

Trends of several applications like down-hole drilling, commercial aviation (e.g. jet engines), heavy industrial and automotive are challenging the capabilities of capacitors and other electronic components. The growing harsh-environment conditions for these applications are: high temperature, high voltage and high current. At the capacitor component level, required features are: very high reliability under mechanical shock, rapid changes in temperature, low leakage current (high insulation resistance), small dimensions, good stability with time and humidity, and high peak withstanding voltage. Capacitors for power-conversion circuitry must maintain a low AC loss and DC leakage at high temperatures. KEMET has recently designed film capacitor series using PEN to address the needs of the above mentioned circuits, in particular regarding the working temperature, voltage and current. This paper will cover technological advances in film capacitor technology to address harsh environment conditions needs, providing test results on temperature, voltage and thermal shock acceleration factor.

Polymer Capacitor Dielectrics for High Temperature Applications

“…As aircraft are becoming more electrified, new engine control systems require sensors/actuator and signal conditioning electronics to be located in or near aircraft engines where the operating temperature can be in range of 200–300 °C. Similar trends occur in the automobile industry with power electronics located in the engine compartment and near the wheels of hybrid and electric vehicles where the minimum temperature is 150 °C. − The introduction of wide bandgap semiconductors, e.g., silicon carbide, enables power electronics to operate at temperatures well above 150 °C; , however, unless capacitors are available that can operate in the same temperature range, such wide bandgap semiconductors cannot be employed efficiently. High temperature capacitors not only eliminate voltage derating but also ease thermal management as a result of the greater temperature difference between maximum device temperature and ambient.…”

“…The studies found that polymers with high ratios of carbon to (hydrogen + oxygen) tend to form greater amounts of free carbon for a given clearing energy. Table illustrates the chemical composition of various polymer dielectrics and the amount of carbon residue, both measured and calculated, based on comparison between amount of carbon in the gaseous byproducts and composition of the dielectrics. , Metallized paper clears well since cellulose contains a good balance among carbon, oxygen, and hydrogen. In contrast, polystyrene and poly­(phenylene sulfide), which contain aromatic rings and no oxygen, clear poorly, as does Kapton polyimide, which is used in the aviation industry as wire insulation and has a tendency toward carbonization (tracking). , Poor self-clearing can be mitigated to some degree by applying a thin coating of acrylate over the dielectric.…”

“…Poly­(ethylene terephthalate) (PET) has been available since the late 1950s and is often used for “general purpose” capacitors. Very thin film (presently ∼0.5 μm) can be manufactured with relatively high dielectric strength (∼500 MV/m) , and good self-clearing capability. ,,, In addition to these characteristics, which are superior to PC, PET also has a dielectric constant and operating temperature range similar to PC. However, PET is generally not the choice to replace PC because of its strong temperature dependence in both capacitance and DF (Figures and ).…”

“…Poly­(phenylene sulfide) (PPS) has been proposed as a substitute for PC in capacitors based on the similar dielectric properties between the two polymers, as illustrated in Figure . ,, This relatively new capacitor film was introduced in the late 1980s, initially for surface-mount capacitors which must withstand high temperature during wave soldering . PPS is a semicrystalline polymer with a crystallinity of 60 to 65% and crystalline melting temperature of 285 °C .…”

“…PPS is a semicrystalline polymer with a crystallinity of 60 to 65% and crystalline melting temperature of 285 °C . As a result, PPS capacitors can be used up to 150 °C with special design in some applications ,, even though its T g of 85 °C is lower than that of PC (150 °C) which is mostly amorphous…”