Basics of Tantalum Capacitors

Tantalum Capacitors
Tantalum Capacitors

Capacitors are among the most vital components of any circuit board. You can find them next to microchips in most power circuits. They are often used to decouple AC signals for extra stability, clean up DC power into chips, filter out unneeded frequencies, and bypass AC noise to mitigate the effects of the inductance of conductors.

As systems and devices got smaller, capacitors became a limiting factor since specific sizes were required to meet capacitance needs. All this changed, however, after the introduction and adoption of tantalum capacitors.

What Are Tantalum Capacitors?

These are a special kind of electrolytic capacitor made of a metal called tantalum. This metal acts as the anode, with an oxide layer covering it to serve as the dielectric, and a conductive cathode surrounding it to complete the setup.

Tantalum is an excellent choice of metal since it allows for thinner dielectric layers. The benefits of a thin dielectric layer include:

  • Stellar stability over time
  • Frequency characteristics superior to other kinds of capacitors
  • Increased capacitance value per unit

These capacitors often come polarized, meaning that you may only connect them to a DC supply so long as you observe the appropriate terminal polarity. Arguably, the biggest drawback of using these capacitors is their unforgiving failure mode that may cause fires, small explosions and thermal runaways. However, you can prevent such adversities by using external failsafe devices, e.g., thermal fuses and current limiters.

Courtesy of technological advances, these capacitors are usable in a broad range of circuits, with the most common being in the shape of SMD’s (Surface Mounted Devices), e.g., in the automotive industry, in laptops, cell phones and many other devices. These surface mount capacitors consume less space on printed circuit boards compared to other capacitors while allowing for higher packing densities.

Characteristics

General

The capacitance values of a tantalum capacitor range from as little as 1nF to as much as 72nF and are significantly smaller than most aluminum electrolytic capacitors of similar capacitance. These capacitors have impressive voltage ratings ranging from 2V to upwards of 500V.

Their ESR (Equivalent Series Resistance) is ten times less than that of most aluminum electrolytic capacitors, allowing them to pass larger currents through the capacitor while generating less heat. Besides, their capacitance hardly changes as they age, and they provide greater stability over time, especially when pitted against aluminum electrolytic capacitors. With proper handling, you can find exceptional reliability in these capacitors and enjoy a virtually unlimited shelf life.

Polarity

Like aluminum electrolytic capacitors, tantalum capacitors are exceptionally polarized. While their aluminum counterparts are capable of surviving short bursts of reverse voltage, tantalum capacitors are very susceptible to reverse polarization. Applying a reverse polarity voltage to these capacitors causes the dielectric oxide to break down, which may lead to a short circuit.

Short circuits are dangerous since they may cause thermal runaways or even destroy the capacitor in the future. It is worth noting that these capacitors often have markings for their positive terminals, and like aluminum electrolytic capacitors that typically have markings for their negative terminals on the casing.

Failure Mode

As mentioned earlier, a significant drawback of these capacitors is their failure mode. Their failure mode can be potentially dangerous during voltage spikes, especially if the tantalum anode touches the manganese dioxide cathode in the presence of sufficient energy, starting a chemical reaction.

The resulting chemical reaction following a voltage spike usually generates heat, can sustain itself, and, if severe enough, may produce a flame and smoke. To prevent such potentially dangerous thermal runaways, always use external failsafe circuitry like thermal fuses and current limiters together with these capacitors.

Applications

Most applications that rely on tantalum capacitors prefer them for their high capacity, low leakage current, reliability and long-term stability. For instance, S&H (Sample and Hold) circuits that require low leakage current use these capacitors for their long hold duration abilities.

Also, courtesy of their long-term stability and small size, they are commonly used to filter power supply in cell phones and computer motherboards, usually as SMD’s (Surface Mount Devices). Their wide range of operating temperatures and impressive tolerance of relatively harsh conditions have also made them a popular choice for military applications in the form of MIL-SPEC (Military Specific) versions.

What makes a tantalum capacitor a superior alternative to an aluminum electrolytic capacitor for military applications is its resistance to drying out and consistent capacitance over time. Lastly, medical electronics and audio amplifiers rely on capacitors made of tantalum thanks to their high stability.

Benefits

Tantalum capacitors have many benefits over other kinds of capacitors. Their useful properties have seen them rise in popularity over the years, making them a staple in many forms of electronic equipment. Here are some of the benefits of these capacitors have to offer.

Volumetric Efficiency

Volumetric efficiency refers to the capacitance that a capacitor can provide within a specific unit volume. Tantalum capacitors offer greater volumetric efficiency, i.e., capacitance for each unit volume compared to most electrolytic capacitors.

Reliability

Unlike other kinds of capacitors, you will hardly ever go wrong with a tantalum capacitor. The only condition is that you operate them within their recommended ratings. If well operated, you can enjoy a virtually unlimited shelf life with these capacitors since their capacitance value hardly changes over time.

Broad Range of Operating Temperatures

These capacitors are very versatile when it comes to operating temperatures since they can function between -67°F and 257°F. Having such a wide range of operating temperatures makes these capacitors an excellent choice for equipment used in extreme environmental conditions.

Frequency Characteristics

Capacitors made of tantalum have a good frequency response, making them superior to their electrolytic counterparts. Good frequency characteristics make them a better choice for applications where electrolytic capacitors are not practical.

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Suitability for Modern Production Techniques

Modern production methods usually involve heating an entire assembly with infrared heat during soldering, thus exposing components to abnormally high temperatures. Using traditional leaded components only makes the board surface heated, meaning that the heat they conduct is usually insufficient.

Tantalum, on the other hand, is a good conductor of heat, and capable of withstanding the high temperatures used in SMT production. This property makes capacitors made of tantalum suitable for many modern electronics designs.

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