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What is a Tantalum Capacitor?

Author: Apogeeweb
Date: 28 Apr 2021
 3574
Construction of Tantalum Capacitor

Catalog

Ⅰ What is a Tantalum Capacitor

Ⅱ Construction and Properties of Tantalum Capacitor

Ⅲ Characteristics of Tantalum Capacitor

  3.1 General Characteristic

  3.2 Polarity

  3.3 Failure Mode of Tantalum Capacitor

Ⅳ Tantalum Capacitor Classification

  4.1 Leaded Tantalum Capacitors

  4.2 SMD Tantalum Capacitors

Ⅴ Applications for Tantalum Capacitor

Ⅵ Difference Between Tantalum and Ceramic Capacitor

Ⅶ FAQ

 


Ⅰ What is a Tantalum Capacitor

Tantalum capacitors have a tantalum anode and are electrolytic capacitors. They're polarized capacitors that have excellent frequency and stability. Electrolytic capacitors with tantalum as a component are known as tantalum capacitors. They're made of tantalum metal, which serves as an anode, with a layer of oxide acting as a dielectric and a conductive cathode surrounding it.

Tantalum is used to create a very thin dielectric layer. As a result, the capacitance value per volume is higher, the frequency characteristics are superior to many other types of capacitors, and the capacitor has excellent long-term stability. Tantalum capacitors are usually polarized, which means they can only be connected to a DC supply if the terminal polarity is maintained.

 

The disadvantage of using tantalum capacitors is that they have an unfavorable failure mode, which can result in thermal runaways, fires, and minor explosions. This can be avoided by using external failsafe devices such as current limiters or thermal fuses.

 

Tantalum capacitors can now be used in a wide range of circuits, including computers, automobiles, cell phones, and other electronic devices, most commonly surface-mounted devices (SMD). These surface-mount tantalum capacitors take up significantly less space on the printed circuit board, allowing for higher packing densities.

 

It's worth noting that, like resistors, there are both fixed and variable capacitors. Capacitors with fixed values are classified as either non-polarized or polarized capacitors, depending on their polarity. The three most common capacitor types are represented by electric symbols in the figure below.

Tantalum capacitor-capacitor symbolsTantalum capacitor-capacitor symbols

 


Ⅱ Construction and Properties of Tantalum Capacitor

Tantalum (Ta) is a silver-gray metal with the atomic number 73. When looking at a cross-sectional view of a tantalum capacitor, such as a standard SMD tantalum electrolytic chip capacitor with solid electrolyte shown in the Figure below, the positive (anode) terminal is tantalum powder pressed and sintered into a pallet. The dielectric is formed by an insulating oxide layer covering the positive (anode) terminal, and the negative (cathode) terminal is formed by a solid manganese dioxide electrolyte.

 

Tantalum capacitor-construction of tantalum capacitorTantalum capacitor-construction of tantalum capacitor

 

In the case of solid tantalum capacitors, the electrolyte is added to the anode through pyrolysis. To create a manganese dioxide coat, solid tantalum capacitors are dipped in a special solution and baked in an oven. The procedure is repeated until the pellet has a dense coating on both internal and external surfaces. Finally, to ensure a strong cathode connection, the pellet used in solid tantalum capacitors is dipped in graphite and silver. Wet tantalum capacitors, unlike solid tantalum capacitors, use a liquid electrolyte. The anode is dipped into a liquid electrolyte inside an enclosure after it has been sintered and a dielectric layer has been grown. In wet tantalum capacitors, the enclosure and electrolyte serve as the cathode.

 

Tantalum capacitors have a high capacitance per volume and weight due to their thin, high permittivity dielectric sheet, which sets them apart from other electrolytic capacitors. Tantalum electrolytic capacitors are also ideal for passing or bypassing low-frequency signals and storing significant quantities of electric energy due to their large capacitance.

 


Ⅲ Characteristics of Tantalum Capacitor

3.1 General Characteristic

Tantalum capacitors have capacitance values ranging from 1nF to 72mF and are significantly smaller than aluminum electrolytic capacitors of the same capacitance. Tantalum capacitors have voltage ratings ranging from 2V to more than 500V. They have a ten-fold lower equivalent series resistance (ESR) than aluminum electrolytic capacitors, allowing for higher currents to pass through the capacitor while generating less heat. As compared to aluminum electrolytic capacitors, tantalum capacitors are very stable over time and their capacitance does not change significantly with age. When handled properly, they are extremely dependable, and their shelf life is nearly limitless.

3.2 Polarity

Tantalum electrolytic capacitors have a very high polarization. Although polarized aluminum electrolytic capacitors can survive a brief reverse voltage, tantalum capacitors are extremely sensitive to reverse polarization. When a voltage of the opposite polarity is applied, the dielectric oxide breaks down, resulting in a short circuit. This short circuit could lead to thermal runaway and the capacitor's destruction in the future.

 

In comparison to aluminum electrolytic capacitors, which have their negative terminal marked on the casing, tantalum capacitors typically have their positive terminal marked.

3.3 Failure Mode of Tantalum Capacitor

According to a paper published by ASM International, the Tantalum capacitor failure mode is divided into three major groups. 

• High Leakage/Short

High leakage currents may result from applying reverse voltage, which is common during troubleshooting, malfunctions, and/or bench testing. Since the hotspots formed during crystallization heat the cathode, tantalum capacitors with crystallization cause short circuit failure. 

 

• High Equivalent Series Resistance (ESR)

When a capacitor is exposed to board mounting, pick-and-place, reflow, and operation lifetime, the mechanical/thermomechanical has a significant impact on its ESR. External and/or internal relations are often harmed as a result of this form of stress, resulting in a high ESR.

 

• Low Capacitance/Open

The failure is uncommon since the capacitance of a Tantalum capacitor does not shift under normal operating conditions. A Tantalum capacitor's lower capacitance in any application may indicate a shorted capacitor, while an open failure can be caused by a damaged positive lead and wire link.

 

Tantalum capacitors, as we all know, have a potentially dangerous failure mode. The tantalum anode may come into contact with the manganese dioxide cathode during voltage spikes, and if the energy of the spike is adequate, a chemical reaction may start. This chemical reaction generates heat and is self-sustaining, as well as the possibility of smoke and flame. External failsafe circuitry, such as current limiters and thermal fuses, should be used in combination with tantalum capacitors to avoid thermal runaway.

 

 


Ⅳ Tantalum Capacitor Classification

4.1 Leaded Tantalum Capacitors

To avoid damage, leaded tantalum capacitors are usually packaged in a small epoxy box. Tantalum bead capacitors are the name given to them because of their shape.

 

Although a color-coding scheme was common at one time and some capacitors still use it, the capacitor markings are usually written directly onto the encapsulation as figures.

Leaded tantalum capacitorsLeaded tantalum capacitors

 

4.2 SMD Tantalum Capacitors

Tantalum capacitors with a surface mount are commonly used in modern electronics. When designed with enough margins, they provide dependable service and allow for high capacitance values to be achieved in the small package sizes needed for modern equipment.

 

Due to their inability to withstand the temperatures needed for soldering, aluminum electrolytes were not initially available in surface-mount packages. As a result, tantalum capacitors that could withstand the soldering process were nearly the only choice for high-value capacitors in surface-mount assemblies. Despite the availability of SMD electrolytic, tantalum remains the capacitor of choice for SMD due to its excellent cost, size, and performance parameters.

SMD tantalum capacitorSMD tantalum capacitor

 

• SMD Tantalum Capacitor Markings

SMD tantalum capacitors usually have three numbers on their markings. The major figures are the first two, and the multiplier is the third. Values are in picofarads. As a result, the SMD tantalum capacitor's value is 47 x 105pF, which equals 4.7F.

As seen in the illustration below, values are often marked more directly. The markings indicate the value.

SMD tantalum capacitor markingsSMD tantalum capacitor markings

 


Ⅴ Applications of Tantalum Capacitor

Tantalum capacitors have many advantages and are used in a variety of applications, including modern electronics, where they provide higher stability over a wide range of temperatures and frequencies, long-term reliability, and record-high volumetric efficiency.

 

Tantalum capacitors are used in applications because of their low leakage current, high capacity, and long-term stability and reliability. They're used in sample and hold circuits, for example, where a low leakage current is needed to achieve a long hold duration. Due to their small size and long-term reliability, they are often widely used for power supply filtering on computer motherboards and mobile phones, most commonly in surface-mount form.

Applications of tantalum capacitors

Applications of tantalum capacitors

Military standards (MIL-SPEC) tantalum capacitors are also available, with tighter tolerances and a wider operating temperature range. Since they do not dry out or change capacitance over time, they are a common substitute for aluminum electrolytic in military applications.

 

Tantalum is also used in medical electronics because of its high stability. Tantalum capacitors are often used in audio amplifiers where stability is important. A tantalum capacitor is a complex component used in cardio implants to detect irregular heartbeats and deliver an electric countershock in a few seconds. Medical, telecommunications, aerospace, military, automotive, and computers are only a few of the industries that use this capacitor.

 


Ⅵ Difference Between Tantalum and Ceramic Capacitor

Tantalum capacitors are used in a wide range of circuits, although they usually need an external failsafe system to prevent issues caused by their failure mode. PCs, laptops, medical equipment, audio amplifiers, automotive circuitry, mobile phones, and other surface-mounted devices are only a few examples (SMD). Tantalum electrolytic is a common alternative to aluminum electrolytic in military applications because it does not dry out or change capacitance over time.

 

Ceramic capacitors are used in a wide range of applications, the most popular of which are personal electronic devices. MLCCs are the most widely used capacitors, accounting for around 1 billion electronic devices a year. Printed circuit boards (PCBs), induction furnaces, DC-DC converters, and power circuit breakers are some examples of applications. Since ceramic capacitors are non-polarized and come in a wide range of capacitances, voltage ratings, and sizes, they are often used as general-purpose capacitors.

 

Tantalum Capacitors vs Ceramic Capacitors

While tantalum and ceramic capacitors have similar functions, their construction methods, materials, and performance are vastly different. Tantalum and ceramic capacitors vary in a few main ways when it comes to performance:

 

• Aging

When it comes to capacitors, aging refers to a logarithmic drop in capacitance over time. Tantalum capacitors do not age, while ceramic capacitors do. There is no known wear mechanism for tantalum capacitors.

 

• Polarization

The majority of tantalum capacitors are polarized. This means they can only be linked to a DC power source while maintaining proper terminal polarity. Non-polarized ceramic capacitors, on the other hand, can be safely connected to an AC source. Ceramic capacitors have a higher frequency response because they are not polarized.

 

• Temperature Response

Tantalum capacitors have a linear capacitance change when exposed to temperature changes, whereas ceramic capacitors have a non-linear response. On the other hand, Ceramic capacitors can be made to trend linearly by narrowing the operating temperature ranges and taking temperature response into account during the design phase.

 

• Voltage Response

Tantalum capacitors have clear capacitance changes as a function of applied voltage, whereas ceramic capacitors do not. The permittivity of the dielectric shrinks inside the ceramic capacitor in response to higher applied voltages, causing capacitance changes. While most ceramic capacitor capacitance changes are linear and easily accounted for, some higher permittivity dielectrics can lose up to 70% of their initial capacitance when operated at rated voltage.

 

 


Ⅶ FAQ

1. What are the advantages and disadvantages of the tantalum capacitor?

The list of the advantages and disadvantages of a solid tantalum capacitor includes the following

The advantages are Long life, high-temperature resistance, excellent performance, high accuracy, efficiency in filtering high-frequency harmonics.

The disadvantages are: Having a very thin oxide layer that is not robust, cannot withstand voltage above limits, low ripple current rating.

 

2. When to use a tantalum capacitor?

When you need maximum capacitance in a small space like decoupling next to a microchip, excellent stability over a range of temperatures or voltages, and you are aware of their unique characteristics so they can be designed properly and not risk your system with a fiery failure.

 

3. What is surge voltage in terms of the tantalum capacitor?

A surge voltage is the highest voltage that can be applied to a capacitor for a shorter period in circuits that has minimum series resistance.

 

4. What is the difference between tantalum and electrolytic capacitors?

Electrolytic capacitors made with aluminum (or aluminum) are generally lower priced than those made with tantalum. Tantalum capacitors have higher capacitance per volume. Capacitors made with tantalum can be either polar and non-polar though the polarized form is more common.

 

5. Why do tantalum capacitors fail?

A transient voltage or a current spike applied to tantalum electrolytic capacitors with solid manganese dioxide electrolyte can cause some tantalum capacitors to fail and may directly lead to a short.

 

6. How long do tantalum capacitors last?

The capacitance stability achieved by polymer tantalum capacitors exceeds that of MLCCs over time, temperature and voltage. Whilst MLCCs are susceptible to aging, polymer tantalums achieve long-term stability over an operational lifetime of 20 years.

 

7. Are all tantalum capacitors polarized?

Tantalum capacitors are inherently polarized components. Reverse voltage can destroy the capacitor. Non-polar or bipolar tantalum capacitors are made by effectively connecting two polarized capacitors in series, with the anodes oriented in opposite directions.

 

8. What is a tantalum capacitor used for?

Applications using tantalum capacitors take advantage of their low leakage current, high capacity and long-term stability and reliability. For example, they are used in sample and hold circuits that rely on low leakage current to achieve long hold duration.

 

9. Can I replace a tantalum capacitor with an electrolytic?

A tantalum capacitor is also a type of electrolytic capacitor, however, due to low leakage, they are more accurate and reliable than the cylindrical electrolytic capacitor variants. If the leakage factor is not too critical then you can easily replace a tantalum capacitor with the other regular electrolytic capacitor.

 

10. What is a wet tantalum capacitor?

Wet tantalum capacitors are passive devices that provide capacitive reactance to circuits. They are electrolytic capacitors with a wet electrolyte, an anode and a cathode. They are used over other capacitor types due to superior characteristics including volumetric efficiency, high reliability, electrical stability over a wide temperature range and long service life. Wet tantalum capacitor technology is best suited for applications such as military, aerospace, satellites and heavy industrial application fields.

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