KEMET Adds AEC-Q200 Capability Plus Higher Breakdown Voltages for Polymer Electrolytic Capacitors
December 16, 2015 by John Day
By James C. Lewis, Technical Marketing Director, KEMET
KEMET has been working hard to meet the needs of automotive engineers in recent months. This resulted in several technology developments that will be of particular interest for design engineers involved with automotive electronic systems.
Firstly, the company made several key developments in polymer electrolytic capacitor technology. Temperature and humidity performance have been a problem for polymer electrolytic capacitors to the extent that they are still not widely used in automotive applications, despite their compact case sizes, high capacitance, and low ESR.
A technology breakthrough KEMET made last year opened up the automotive space for polymer electrolytic devices by giving them AEC-Q200 capability for the first time.
The breakthrough is based on a new packaging technology which limits the exposure of the cathode’s polymer material to oxygen; preventing oxygen from reaching the cathode inhibits its major failure mode under high temperature and humidity conditions.
Based on the KO-CAP® (KEMET Organic Capacitor) range of polymer electrolytic devices, combined with the new packaging, the T591 series was developed with an operating temperature range up to 125°C (see figure 1). This series is available with capacitances up to 330µF and it has been tested to 500 hours in 85°C with 85% humidity while voltage is applied, as per AEC-Q200 guidelines.
Significantly, a recent extension to the product range introduced options for up to 50V for both 12V and 24V power rails.
Figure 1. The T591 series of KO-CAP polymer electrolytic capacitors can now
meet automotive temperature requirements.
Following the release of the T591 series, polymer electrolytic capacitors with full AEC-Q200 qualification were not far behind. The T598 series was the first polymer electrolytic capacitor to meet all the requirements of the AEC-Q200 specification for passive components and gain full qualification. This series offers a new level of stability and endurance in extreme humidity and temperature environments, based on the T591 series but with some refinements in design, materials and manufacturing. This means they can bring the advantages of polymer electrolytic technology – saving space and reducing ESR – to automotive applications such as decoupling and filtering in DC-DC converters for infotainment and ADAS systems.
High Voltage MLCCs
In multi-layer ceramic capacitors (MLCCs), KEMET released the world’s smallest high voltage devices with internal arc protection – they are now available in EIA 0603 size with rating up to 1000V. High voltage MLCCs are typically limited by size due to the possibility of arcing, but KEMET’s devices feature our patented ArcShield™ technology, making them the physically smallest and highest capacitance arc-protected devices in the industry.
A typical way to try to prevent arcing is to use an external coating, which can be damaged during handling. KEMET’s ArcShield™ technology is an internal feature of the device and is not dependent on a coating; it uses an internal shield electrode structure that creates a partial Faraday cage inside the device, combined with a reliable base metal dielectric. Arc-over events can be effectively suppressed, meaning case sizes can be reduced while maintaining excellent lightning-strike performance.
For applications that are exposed to high levels of vibration in automotive systems, radial lead capacitors are a natural choice due to their strong wire lead termination system and versatile form factor. They can be weld or crimp mounted, which means they can be used without a PCB in applications where a PCB is not robust enough. Recent developments in this product group from KEMET include enhancements to the Goldmax radial MLCC range, shown in figure 5, including increasing the voltage rating to 630VDC. They are available in C0G or X7R dielectrics with operating temperature between -55 and 125°C.
Other options that meet AEC-Q200 include KEMET automotive grade film capacitors such as theF862 series. Design enhancements made by KEMET for this latest generation of film capacitors mean these devices can resist capacitance loss mechanisms, leading to high long term stability.
The F862 series is designed for harsh conditions and extreme environments as it’s made from metallized polypropylene film encapsulated in a self-extinguishing resin. These capacitors can be connected in series with the mains, or used for noise filtering and peak voltage protection in parallel with the mains; they are RFI Class X2 approved. They are durable enough for extreme temperature and humidity environments such as automotive applications, such as in-car PHEV chargers, but they also suit capacitive power supplies and energy meters.
The F862 series is rated to 310VAC at 50 or 60Hz with device values between 100nF and 4.7µF and devices are 100% screened at 1900VDC.
KEMET continues to develop and patent new technologies for automotive capacitors which are improving devices’ performance in these demanding conditions. New technologies, such as those we described above, result in better performance for space constrained applications, better energy efficiency, and better reliability for constantly evolving automotive electronics systems.