Understanding Conductive Polymer Capacitors

Advances in conductive polymers over the past several decades have opened the door to an array of new capacitor choices. Among these options are conductive polymer solid electrolytic capacitors, a technology that offers groundbreaking improvements in areas ranging from performance and flexibility to reliability and safety.

Conductive polymer capacitors mark a radical departure from traditional electrolytic capacitors, utilizing polymer electrolytes rather than liquid or gel electrolytes. Employing a solid electrolyte eliminates the risk of electrolyte dry-out, an issue that restricts the usable life of ordinary electrolytic capacitors and typically leads to circuit failure.

Although different in design and construction from conventional electrolytic capacitors, and offering significant improvements in several key areas, polymer capacitors can be used in much the same way as their older counterparts. In fact, in most applications, polymer capacitors can serve as direct replacements for electrolytic capacitors as long as the maximum rated voltage isn't exceeded.

Polymer capacitors are available with capacitances spanning between 10µF and 1mF, and typical voltage ratings ranging from 2.5 V to as high as 125 V. Like conventional electrolytic capacitors, polymer capacitors are usually polarized.

 

Key benefits

Conductive polymer capacitors offer a wide array of benefits for an almost endless number of applications. Leading advantages include—depending on the specific application—long life, high capacitance in a small package, high reliability and a number of other appealing electrical characteristics, such as higher energy density, a reduced need for voltage derating, high volumetric efficiency (high capacitance/voltage per cc) and excellent mechanical robustness. Additionally, polymer capacitors are non-ESD sensitive devices and, as such, don't require anti-static or conductive tape and reel packaging. The technology also exhibits low inductance, particularly with facedown/undertab termination designs.

A leading conductive polymer capacitor attribute is its excellent high frequency performance, including low impedance and equivalent series resistance (ESR). Using a capacitor with low ESR is preferable in many applications in order to improve power efficiency and to increase safety in the event of overload and overheating.

Conductive polymer capacitors can be used to smooth the voltage sent from a power source to a critical circuit, reducing power noise. When applied to this task, conductive polymer capacitors can provide a substitute for conventional electrolytic capacitors, as long as care is taken to keep the operating voltage sufficiently low.

A high ripple current capability, another key benefit provided by conductive polymer capacitors, is leading to its widespread use in computer workstations, servers, computer graphic accelerator cards and similar high-end systems and devices. Conductive polymer capacitors exhibit almost no change in capacitance (typically <1%) with applied AC ripple voltage.

Excellent low frequency/acoustic noise performance is an important conductive polymer capacitor attribute that's useful in many applications, particularly in the elimination of the acoustic noise created by ceramic capacitors. Conductive polymer capacitors exhibit negligible piezo noise (a notable characteristic of Class II ceramic dielectrics, which can cause an audible hum at low frequency or spurious voltage spikes under shock or vibration conditions). As a result, conductive polymer capacitors are an ideal choice for low distortion applications in audio/video circuits and also LED backlighting.

 

Reliability and efficiency

When it comes to stability, conductive polymer capacitors stack up well against ceramic capacitors. Ceramic capacitors exhibit capacitance drifts in response to temperature changes and DC bias. Conductive polymer capacitors are immune to drift and remain stable over time. Stability is particularly important in industrial and automotive applications, which tend to experience wide fluctuations in operating temperatures.

Conductive polymer capacitors can tolerate a wide operating temperature range—typically from -55° C to +105° C, and even as high as +125° C or more in some cases. High altitudes, low atmospheric pressure and even vacuum operation also have no impact on the function of conductive polymer capacitors. Nevertheless, attention must be paid to the power dissipation in environments with only limited convectional air cooling. It's important not to exceed the recommended maximum self-heating body temperature increase of 10° C by RMS current. Conductive polymer capacitors are also not sensitive to radiation exposure.

Conductive polymer capacitors' benign failure mode protects equipment from physical harm, thanks to a self-healing capability that eliminates the possibility of destructive failure. Incidentally, conventional electrolytic capacitors feature either vented casings or casings with a pre-scored surface that's designed to quietly rupture in the event of a runaway pressure build up to vent hot internal gases in a safe way, preventing an explosion. Conductive polymer capacitors don't need vents or scores, since there's never any pressure buildup during failure.

 

Multiple applications

Thanks to their excellent performance and reliability characteristics, conductive polymer capacitors have become a mainstay technology for engineers working on projects in a wide range of fields covering many different types of applications. Conductive polymer capacitors are, for instance, now the preferred choice in an array of switching, filtering, coupling/decoupling, timing and back up circuits, thanks mostly to the technology's reliability and parametric stability characteristics. Conductive polymer capacitors are also particularly favored for use in systems that require high capacitance with minimal piezo effects, improved capacitance and temperature stability.

Besides finding a home on an increasing number of high-end computer motherboards, conductive polymer capacitors are also being used to improve the lifecycles and reliability of various types of IT equipment, such as network switches, hubs, routers and modems used by offices, industrial facilities, data centers and the military. Additionally, as conventional hard drives continue to be superseded by semiconductor-based solid-state drives (SSDs), reliable and high-performance conductive polymer capacitors are beginning to replace the supercapacitors and aluminum capacitors used to help clear the SSD write cache during a sudden power loss.

The growing use of electronics systems designed for use at industrial sites, including Internet of Things-connected controllers and monitors, has also created a need for more robust and dependable capacitors. Such demanding systems often operate in unforgiving environments and are, therefore, not friendly to conventional capacitor technologies. Conductive polymer capacitors provide an effective and cost-friendly solution to this challenge.

Conductive polymer capacitors are also finding a home in a rapidly growing number of automotive electronic applications, where they are valued for their stability, durability and performance. The components have become the preferred choice for engineers designing many different types of vehicle entertainment, information, monitoring and management systems.

 

Types of conductive polymer capacitors

Conductive polymer capacitors have been in production for nearly three decades, and while the underlying technology remains the same, specific devices continue to arrive and evolve, both in terms of size and electrical characteristics.

Targeted at both general and specific market needs, AVX conductive polymer capacitors are available in a wide variety of designs, including:

 - EIA standard, TCN and F38 miniature and low-profile molded body case sizes
- Face-down/undertab and ultraminiature TCN and F38 series
- TCJ series Designs for high density circuit assemblies
- Multi Anode TCM series for extended capacitance
- Extended voltage ratings (TCJ series up to 125V)
- TCM Multi-anode series for ultra-low ESR
- J-CAP series for high energy density (Joule/cc) applications
- TCQ Automotive (AEC-Q200) series
- TCB and TCS Professional Grade and COTS-plus series for specific market needs

The AVX advantage

AVX is on the forefront of polymer capacitor technology, offering both the highest energy and smallest case-size conductive polymer capacitors.

The F38 Series, for example, provides the same footprint as 0402, 0603, and 0805 ceramics, enabling engineers to design-in noiseless and stable capacitance polymers without altering the board layout footprint. The J-CAP Series is designed to satisfy the needs of demanding SSD storage applications. AVX also offers the highest energy density in a given package.

AVX is the only supplier of hermetically sealed SMD polymers for space applications.

                         
 

Summary

Conductive polymer capacitors are the fastest growing segment of the tantalum-based capacitor technology market. This is mainly due to the technology's extremely high reliability and suitability for a wide range of applications as well as their low ESR, more benign failure mode, higher rated voltage availability and lower voltage derating requirements.

AVX's products provide the best choice for applications with low ESR requirements, such as DC-DC converters in notebooks, mobile phones, telecom devices and other demanding applications. Recent advances in AVX conductive polymer technology offer a significantly improved voltage rating capability—up to 125V—while providing enhanced robustness in high humidity environments, further expanding the application range.