Components that Can Handle Harsh Environments: The Latest Research
Given that CARTS International 2013 was held in Houston, TX, a key center for energy exploration, it should come as no surprise that a number of papers presented discussed parts that can operate reliably in harsh environments, with particular emphasis on technologies and passives that can handle extremely high temperatures for the down-hole applications found in the gas and oil industries.
Applications such as gas and oil drilling require electronic component operating temperatures above 200°C. These applications also involve strong vibration and shock, so mechanical robustness must be on the list of required specs in addition to the ability to operate at high temperatures. Traditional high-pressure/high temperature (HPHT) wells, which have been characterized as having bottom well pressures up to 69MPa and temperatures of up to 177°C, have now been expanded to what is being characterized as "extreme high-pressure/high-temperature" (xHPHT) or "ultra HPTH," with pressures up to 138 MPa and temperatures of up to 204°C.
Can caps handle these extreme environments? Based on the papers presented at CARTS the answer seems to be an emphatic "yes". For example, in the paper "Film Capacitors for High Temperature, High Voltage and High Current," KEMET's (Bologna Italy) Luca Caliari et al. (six other co-authors are cited, which is not unusual for a research paper. To spare you, dear reader, from an endless list of names I will mention only the first author cited. At the end of this article I will provide a URL where you can go to download the complete text of the papers referenced here), noted that over the years R&D activities focusing on automotive and other markets' needs, have made it possible to increase the working temperature of film capacitors up to 170°C. Based on the last fifteen years of reliability data, 170°C is a temperature at which film capacitors can be considered to perform extremely well and be a safe component, the authors wrote, adding that temperature is clearly the most challenging parameter when looking at the design of film capacitors for drilling and aviation applications, where the maximum temperature exceeds 200°C, and reaches up to 220°C.
KEMET, the paper noted, recently has designed a film capacitor series using PEN to address high working temperature, voltage and current. The aim of their paper, the authors wrote, was to show designers that film capacitors can be utilized for extremely harsh environment applications like down-hole drilling, jet engines, industrial and automotive applications, where their typical working temperature range reaches (or will soon reach) temperatures around 220°C.
The paper reports that PEN film capacitors were tested from the physical, chemical, electrical and environmental points of view, in order to highlight any anomaly to working temperatures up to 220°C. "Each data and test has not confirmed any critical aspect on working at such temperatures, for a time frame up to 1,000 h," the authors wrote, adding that "The film is physically stable, the capacitance deviations reach equilibrium levels, the tg delta (dissipation factor) decreases after 160°C, reducing further temperature increase (self-heating), which might determine avalanche phenomena."
PEN film capacitors, either in SMD or radial technology, the authors concluded "can therefore be a choice for working temperatures up to 220°C."
In another KEMET (Simpsonville, SC) paper, titled "High Temperature Ta/MnO2 Capacitors," Y. Freeman, et al. presented results on high temperature stability of tantalum capacitors with MnO2 cathodes (Ta/MnO2 capacitors). The authors showed that replacing silver in the top coating with electrochemically plated nickel provided a substantial improvement in the high temperature stability of the Ta/MnO2 capacitors. The authors concluded that work on further boosting the operating temperatures of Ta/MnO2 capacitors as well as their longevity and operating voltages is in progress, including the technological means to suppress degradation mechanisms inherent to these capacitors such as oxygen migration and crystallization of the dielectric as well as forming a dense and uniformly thick cathode and a top coating on the external surface of tantalum anodes.
Addressing "High Operating Temperature Baseplate in Space Applications", Denis Lacombe of the European Space Agency (ESA, Noordwijck, The Netherlands) suggested that new demands including increased power and frequency bands will lead telecommunications satellite payload manufacturers to envisage modifications of the high power amplifier stage. An increase of the temperature is a necessary result with some consequences on passive components used in this equipment, he wrote.
Lacombe pointed out that ECSS-EST-31 standards used in European space projects defines the following temperature ranges:
- cryogenic below 200K
- high temperature above 470K
He noted, however, that this definition is inappropriate for electronic parts for which the temperature range defined by manufacturers usually stands between -55°C and 125°C. What may be considered as high temperature for these parts is temperature above 85°C, according to Lacombe. Below this temperature, the derating applied to a part will be less restrictive than above this temperature level.
Lacombe suggested potential payload evolutions may induce an increase of baseplate temperature up to 110°C. Current space qualified passive component are not suitable for these new constraints due to reliability issues. For the most part, Lacombe noted, passive component used today and in the past stay most of time safely under 85°Cin space applications with de-rating of 60% in voltage for ceramic capacitors.
In "High Voltage Multi-Layer Ceramic Capacitors for Use at High Temperatures", Jim Magee et al, (KEMET, Simpsonville, SC) addressed multi-layer ceramic capacitors (MLCC) rated to 200Vdc for use at 200°C developed using a high temperature C0G dielectric technology compatible with nickel electrodes. To meet the need for improved pulse detonator performance larger case size (2824 to 4540) capacitors rated to 2000Vdc at 200°C were then developed using this technology, the team reported. Furthermore, the growing demand for higher temperature electronics capable of exploiting new reserves of oil and natural gas led them to develop a range of smaller case (0805 to 2225), high voltage designs (> 500V to 2000V). The electrical characteristics of these surface mounted MLCCs, such as insulation resistance, voltage breakdown, impedance and ESR, were described in the paper. The authors report that a range of surface mountable, high voltage capacitors has been developed for use at 200°C using high temperature base-metal-electrode (BME) multilayer C0G technology that has stable capacitance with temperature and voltage, high insulation resistance and low dissipation factors. These capacitors have low ESR and impedance and passed life testing for 1000 hours at 200°C rated voltage, according to the authors.
MLCCs were shown to have a higher volumetric efficiency when compared to competitor leaded X7Rs rated at 500V so more capacitance can be achieved in a smaller space. This new range of high voltage MLCCs will allow designers of high temperature electronics to realize reliable, miniaturized circuit designs, the authors concluded.
Also at CARTS KEMET's (Simpsonville, SC) Reggie Phillips et al. took on the topic "High Temperature Ceramic Capacitors for Deep Well Applications."
Noting that: 1) increasing demand for oil and natural gas has driven the technology to deeper and deeper deposits resulting in extreme temperature environments-- up to 200°C and above; 2) developments in modern fracking and horizontal drilling also have increased the shock and vibration exposure to drilling tools; and 3) the increasing depths to which the electronic instruments are submerged have also increased the importance of minimizing the losses of the components, especially at higher and higher temperatures, the authors described a novel capacitor solution utilizing temperature-stable base-metal electrode capacitors in a molded and leaded package.
This paper focused on recent development of a range of high-temperature (200°C-rated) radial molded C0G capacitors. In recent years, the paper said, high temperature surface mount base-metal electrode C0G multi-layered ceramic capacitors have been developed for extreme operating conditions. These devices were characterized at high temperature and the authors compared them to existing industry standard X7R radial molded capacitors.
The C0G high-temperature radial-molded capacitor solution provided improved performance over traditional X7R capacitors by providing a predictable, stable capacitance over the -55°C to +250°C temperature range, according to the paper. The C0G has higher insulation resistance even at elevated temperatures (>200°C). Although the authors noted that the C0G capacitor size is smaller than the X7R alternatives, the available capacitance per unit volume at temperatures > 200°C and rated voltage was found to be comparable to that currently available. The paper concluded that Highly Accelerated Life Tests (HALT) as well as 200°C life testing proved the C0G capacitors have good reliability for long-term service.
ECIA (the Electronic Components Industry Association) makes its CARTS Digital Library available without charge to engineers. The CARTS Digital Library is a compendium of technical papers presented at the series of CARTS symposiums. More than 500 technical papers are searchable by Title, Abstract or Authors and can also be viewed as a directory of papers from each conference. Individual papers are available for download in pdf format. The library, including the papers mentioned in this article, can be found at http://ecadigitallibrary.com/.