Space Electronics
Space age capacitors
The essence of designing components for space applications is striking a balance between innovation and optimum reliability, as Steve Hopwood explains
D
esigning components for space applications has always been challenging. On the one hand the industry is highly conservative, selecting tried and tested solutions to ensure reliability. On the other, designers are constantly searching for something that will give them a performance advantage. The key is to strike the right balance between innovation and designing for optimum reliability. Typically, electronic components destined to be launched into orbit require an exhaustive specification, a lengthy qualification process and capability approval either by ESA, NASA or other national space agency. Eventually they are listed on the respective space agency QPLs (qualified parts lists).
Keeping these lists comprehensive and up to date however is not easy. It means that designers often wish to incorporate new devices that deviate slightly from the published specification. Variations may be contained in a smaller package, offering potentially valuable PCB real estate and weight savings which is a key consideration when the cost of launching a payload is in the region of $5000 - $40,000/kg depending on the type of launch vehicle and the height of orbit where the satellite is to be positioned. As yet unqualified components may provide greater design flexibility, performance and functionality or offer significant weight and size saving for the same performance level. However, it is possible to source unlisted components for space applications, providing strict guidelines are followed. The first stage is to ensure that the detailed specification of the chosen device is agreed between the manufacturer, the customer and, if necessary, the relevant space agency. Next, the part must undergo a stringent screening process, samples must be tested, and documentation produced. Syfer Technology have been supplying ceramic multilayer capacitors for space applications for over 20 years. The company’s MLCCs have been used in a number of high profile space projects in recent years, including being deployed in
16 September 2012
satellites and in space vehicles. MLCCs are typically used in power supplies for noise filtering and signal smoothing, and for filtering circuitry to protect against EMI and electrical noise.
Opportunities to supply screened MLCCs that were outside the scope included in the QPL have grown in recent years. The need to reduce size and weight has forced designers to look beyond the standard approved parts. One example of this is the use of smaller case size MLCCs such as 0603 which is outside the current ESA specification.
Syfer has specialised in producing devices for high reliability markets, using high quality materials, such as precious metal electrode (PME) rather than base metal electrode (BME) for capacitor electrodes. We were already supplying to hi-rel telecommunications and automotive markets, and therefore, in 2002, in response to growing demand, we developed the S02A-0100 screening process, based on ESCC/ESA Generic Specification 3009 requirements. This has allowed component engineers to choose over a much broader range of MLCCs with
the confidence that all required testing in accordance with 3009 has been undertaken. As a result, Syfer has developed a solid reputation as a supplier to the space sector.
Growth in non-European projects Initially business was established via European projects where European content was required. However, in recent years over half the business has been from non-European projects with USA, Russia, China and Japan being key markets. Meeting the space industry’s demand for special finishes, such as tin / lead or immersion gold rather than tin-plated terminations, is an additional factor in securing this specialist business. Still rather cautious of the risk of tin-whiskers creating short circuits and reliability issues, the space sector, along with the military/aerospace industry, remains exempt from the RoHS directive. The screening process includes 100%
burn-in and 100% detailed visual inspection. Although Syfer has been working on assessing the impact of even higher operating temperatures on capacitors, this is not typically required for space applications. However, if the electronics is not in a protected, temperature-controlled area of the space vehicle, it can be subject to extreme temperature fluctuations. Consequently, thermal cycling can be an important part of the screening process.
Interestingly, Syfer’s proprietary Flexi-Cap polymer termination technology is proving to demonstrate some useful advantages for space applications. It was originally designed to protect capacitors during the board assembly process by tolerating some flexing. This makes it ideal in applications where thermal cycling is experienced. The FlexiCap technology has already been shown to meet ESA outgassing specifications, and is expected to become more popular as its advantages become better known. After screening, samples from the batch
are subjected to further ‘lot-acceptance tests’ (LATs). There are three levels of LATs, including checks on solderability and accelerated life tests. Syfer’s comprehensive accelerated life testing programme includes 1000hours endurance testing at the maximum specified temperature of 125oC, at 2 times the rated voltage.
The final, and crucial, element of the
screening process is the correct documentation. Detailed documentation packs are prepared for every batch for every customer, according to ESCC requirements. Syfer also provides planar arrays which
are the key filtering element in connectors and has for many years provided parts for all the NASA programmes including the Space Station and has a well-established program of testing and quality procedures for these products as generally they are a bespoke design and therefore no generic space approval exists.
A specialist technical team is in place, working alongside the regular production and quality personnel, dedicated to the testing, qualification and documentation needs of the fast growing space application sector. In addition the company has made a significant investment in specialist test equipment. This includes a range of environmental test equipment, such as burn-in ovens, as well as a scanning acoustic microscope, to look for hidden defects in a non-destructive test. The market for space-qualified devices continues to expand, despite the turmoil elsewhere in industry. There are a growing number of long term projects, including satellites for communications, navigation, observation and exploration, as well as allied interests such as launchers and general space engineering.
Syfer Technology |
www.syfer.com
Steve Hopwood is Senior Applications Engineer with Syfer Technology
Components in Electronics
www.cieonline.co.uk
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