The range of available polymer capacitors is both manifold and comprehensive.
It is not only since the widespread introduction of 5G that the demand for multilayer ceramic chip capacitors (MLCCs) has been growing. In addition to significantly intensifying MLCC market growth, applications in the field of consumer electronics, data processing, telecommunications, and many others have even led to an industry-wide shortage in recent years.
All these factors contributed to more and more OEMs starting to look for ways to replace MLCCs with alternative capacitor types. This was exacerbated by the anticipation of an increasing demand due to 5G.
Some appropriate MLCC alternatives can be found within Panasonic’s extensive industrial portfolio. As a leading manufacturer of polymer capacitors with a long design-in expertise, Panasonic’s SP-Caps and OS-CONs are as well worth a closer look, as are POS-CAP tantalum polymer capacitors, along with the manufacturer’s polymer hybrid aluminum electrolytic capacitor technologies.
For conductive polymer capacitors, the fields of application have broadened remarkably in recent times. Polymer capacitors (as well as conventional aluminum electrolytic capacitors) stand out with large capacitance figures and excellent bias characteristics that are clearly outperforming their multilayer ceramic chip capacitor counterparts.
MLCCs are surface-mounted, fixed-value capacitors with alternating layers of metal and ceramic serving as dielectric. MLCCs are used in a higher volume than any other type of capacitor, in everything from smartphones to electric vehicles.
Panasonic’s industrial polymer capacitors have already been proven as a highly relevant alternative for customers seeking to save printed circuit board (PCB) cost and real estate. These polymer-based devices offer a performance edge over conventional electrolytic and ceramic capacitors when it comes to the following:
- Electrical characteristics
- Stability
- Longevity
- Reliability
- Safety
- Life cycle cost
The various types of polymer and hybrid capacitors have very specific advantages and benefits in terms of their ideal voltages, frequency characteristics, operational conditions, and other application requirements.
If we include hybrid devices, there are basically four main varieties of polymer capacitors, each composed of different electrolytic and electrode materials and each offering different packaging and application targets. A brief overview is as follows…
SP-Caps: The new flagship of ultra-low ESR
Using a conductive polymer as the electrolyte and an aluminum cathode, the distinguishing electrical characteristic of these polymer capacitors is their extremely low equivalent series resistance (down to 3mΩ), which is among the lowest in the industry.
SP-Caps cover a voltage range from 2 to 6.3V and offer capacitances between 2.2 to 820μF. Packaged in molded resin as a compact surface-mount device (SMD), these layered polymer capacitors come in a low profile. As a result of their electrical and form factor characteristics, they suit a variety of handheld electronic devices or other applications that require a low-profile capacitor that will not interfere with a nearby heat sink.
OS-CONs: Large capacitances and long lifetimes
Like SP-Caps, OS-CON capacitors are also based on conductive polymers and aluminum, but they have a wound foil structure. These wound polymer capacitors cover a wider range of voltages and capacitance values than other types of polymer capacitors. Voltages extend from 2.5 to 100V, while capacitances run from 3.3 to 2,700μF.
In addition, their long lifespan is one of the factors that causes them to be preferred for use in servers and base stations. For example, with lifetimes of 20,000 hours at 105°C, the SVPT series offers a unique solution for such applications.
POSCAPs: The capacitors of choice for compact devices
These types employ a conductive polymer as the electrolyte and have a tantalum cathode. They span voltages from 2 to 35V and capacitances from 3.9 to 1,500μF. They also impress with a low ESR, with some of our POSCAP capacitors exhibiting ESR values as low as 5mΩ.
Packaged in a molded resin case, these tantalum polymer capacitors are among the most compact options available on the market. Having said this, although they are indeed compact, a wide range of sizes is available for this capacitor type.
Hybrid capacitors: The best of both worlds
Hybrid capacitors consist of a combination of a liquid and conductive polymer to serve as the electrolyte and aluminum as the cathode. The polymer offers high conductivity and a correspondingly low ESR. The liquid portion of the electrolyte, meanwhile, can withstand high voltages and provide higher capacitance ratings due to its large effective surface area.
These hybrid capacitors offer a voltage range from 25 to 80V and capacitances between 10 and 560μF. At 11 to 120mΩ, ESR values for hybrids are higher than other types of polymer capacitors, but still very low considering the higher power applications they address.
Advantages of polymer capacitors
Let’s take a closer look at polymer capacitors to see what makes them outperform MLCCs and other technologies.
Capacitance density and stability vs. DC bias: The MLCC exhibits strong capacitance dependence on DC bias due to the ferroelectric dielectric materials used for MLCCs.
By comparison, polymer capacitors have no such problem and remain stable over time. This specific advantage allows a significantly lower part count when using polymer capacitors instead of MLCCs, thereby saving precious PCB space, reducing steps during the production process, and lowering costs.
Stability vs. temperature: Typical temperature characteristics for MLCCs involve the curve changing in various ways within the tolerance range of each product. By comparison, in the case of polymer capacitors, the capacitance grows in a linear fashion in response to the increase of temperature.
The temperature characteristics of MLCCs differ according to the dielectric type, but all of them suffer aging failure by exhibiting temperature dependency and require lower operating temperature.
Ceramic capacitors are brittle and sensitive to thermal shock, so precautions need to be taken to avoid cracking during mounting, especially for high-capacitance large MLCCs. Typically, ceramic capacitors support a temperature range from –40°C to 85°C, while their capacitance varies about from +5% to –40%, being in the optimal range around a low temperature of 5 to 25°C.
Also, polymer capacitors have great development potential to achieve higher ratings in terms of density, field stress, and temperature (which is currently limited to 125°C) due to their working mechanism and dielectric materials advancement. Higher dielectric constant polymers enable a high energy density.
Piezoelectric effects: A MLCC deforms (contracts or expands) when exposed to voltage. This MLCC characteristic is called the “inverse piezoelectric effect” (the reverse of a piezoelectric effect).
The DC voltage output from an AC adaptor or switching power supply causes a ripple voltage in some cases. In the case of a MLCC capacitor, if the frequency of the ripple voltage is within the audible frequency range, the inverse piezoelectric effect may result in the emission of a screeching noise.
By comparison, a conductive polymer capacitor has no inverse piezoelectric effect and therefore does not cause any noise emissions or micro-vibrations.
Stability vs. frequency: Different technologies exhibit different change in capacitance profiles over a wide frequency range.
Unlike tantalum capacitors, polymer capacitors exhibit very similar frequency response performance to their MLCC counterparts.
Robustness: Cracks in ceramic surface-mount technology (SMT) components limits assembly reliability and yields. These cracks manifest themselves as electrical defects in the form of intermittent contacts, variable resistance, loss of capacitance, and excessive leakage currents. This is why MLCCs are exposed to different reliability tests including thermal shock, board flex (bending), and biased humidity tests, etc., depending on the targeted applications.
Among the various reliability tests, the board flex test evaluates the mechanical resistance to cracking when MLCCs are subjected to bending stress on the PCB onto which the MLCC is soldered. Such bending of the PCB can occur frequently during (and between) manufacturing steps and during operation under temperature variations.
Ceramics are strong in compression but weak in tension. Thus, when a soldered MLCC experiences excessive board flex, a crack is easily generated in the element. A flex crack can cause an electrical conduction between opposing internal electrodes. It is also possible that a fail-open can progress to a fail-short with continued product usage over time. If a crack on a capacitor element progresses to a short circuit failure, it may cause problems such as heat generation, smoking, or ignition. This means it is imperative to take counter measures against flex-induced faults, particularly in equipment where reliability is essential.
Safety: Most ceramic capacitors have a fairly high voltage rating. If the capacitor experiences a voltage between its terminals higher than its rated voltage, the dielectric may break down and electrons will flow between the thin metal layers inside the capacitor, creating a short.
Fortunately, most ceramic capacitors are built with a hefty safety margin and do not experience any sort of catastrophic failure (such as exploding). However, the generally accepted “rule-of-thumb” dictates that you should derate ceramic capacitors by 50%. This means that if you are expecting to have a maximum of 5V between the capacitor’s leads, then you should use a capacitor rated for 10V or more.
By comparison, no derating needs to be considered for polymer capacitors. Furthermore, these devices can usually withstand a 15 to 25% surge voltage.
Conclusion
The range of polymer capacitors that can be used as MLCC alternatives is manifold and comprehensive. There are specific types for specific requirements. What they all have in common, however, is that they are a contemporary choice in terms of electrical performance, reliability, durability, and safety, not least when looking at their overall lifetime cost.
To put things even more simply, polymer capacitors are not only a good alternative in case of supply shortages of other products, but are actually the first choice for the design process of many modern applications.