Passive component--Tantalum Capacitor

2023-11-24

As one of the passive component, tantalum capacitor must be the important parts for the appliance, first we should know How to Identify Tantalum Capacitors.

Identifying tantalum capacitors can be crucial when dealing with electronic components. Here are a few pointers to help you recognize them:

• Sizing: Tantalum capacitors are usually smaller than their electrolytic counterparts, making them suitable for applications where space is limited.
• Markings: Tantalum capacitors are often labeled with their capacitance, voltage rating, and polarity markings, allowing for easy identification.
• Appearance: Tantalum capacitors are known for their distinctive metallic appearance and compact size, making them stand out from other types of capacitors.

A typical tantalum capacitor is polarized and has positive and negative poles. The component is usually yellow colored and is designed to be surface mounted on the circuit board. On the surface of the housing, an end marked in-dash denotes the positive pole, and hence the negative pole is at the other end.

1. The basis of 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.

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.

2. 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.

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.

3. 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.

4. 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.

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 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.

No matter which series you choose, you can be assured of our commitment to providing only the highest quality products. Hongda capacitors undergo stringent quality control processes to ensure their performance and durability.

Thank you for considering our tantalum capacitors for your electrical projects. We look forward to serving you and exceeding your expectations.