- an overview, information or tutorial about the basics of the tantalum capacitor: its construction, properties and the uses of tantalum capacitors.
Tantalum capacitors are widely used in electronics design these days. Tantalum capacitors offer a form of capacitor that provides a very high capacity density.
As a result this form of capacitor has found widespread use in many areas of electronics. In view of its size and the attainable levels of capacitance, these capacitors are widely used in many mass produced items of electronics equipment.
The tantalum capacitor is similar to the electrolytic capacitor, but using tantalum within the construction of the capacitor it is able to offer extremely high levels of capacitance for any given volume.
As such tantalum capacitors are widely used in electronics equipment where there is a need for small size and a high level of capacitance. In view of its advantages, the tantalum capacitor is used in large volumes within the electronics manufacturing industry.
Types of tantalum capacitor
While tantalum capacitors are widely used, it is not so well known that there are three types of tantalum capacitor that are available:
- Tantalum foil electrolytic capacitor: The tantalum foil capacitor was introduced around 1950. It was developed to provide a more reliable form of electrolytic capacitor without the shelf life limitations of the aluminium electrolytic capacitor. It was able to be developed as a result of the availability of high purity tantalum foils and wires. Initially plain foil variants were introduced, but this was quickly followed by etched variants.
The purity of the materials used plays a major part in determining the leakage current of this type of tantalum capacitor.
These tantalum capacitors have a higher capacitance density than their aluminium electrolytic counterparts. They can often operate at temperatures up to about 120°C and therefore they are often used in equipment used in extreme conditions.
- Tantalum capacitors with porous anode and liquid electrolyte: This form of tantalum capacitor is also known as the wet tantalum capacitor and it was the first form to be introduced. It still offers the best space factor.
A variety of electrolytes can be used within this form of tantalum capacitor. Those using sulphuric acid as the electrolyte have excellent electrical characteristics and the maximum working voltages that are manufactured tend to be a maximum of about 70 volts.
Basically this type of capacitor consists of a sintered porous anode of tantalum power. This is housed in a silver or silver plated container. The porous anode is made by pressing high purity tantalum power into a cylindrical body and then sintering in a vacuum at about 2000°C.
These wet tantalum capacitors are very much more expensive than their newer brothers and as a result they are not as widely used.
- Tantalum capacitors with porous anode and solid electrolyte: This variant of the tantalum capacitor family is also known as the solid tantalum, and it is the variety that is most commonly used. Many millions of them are sued each day, and they can be found in many items of consumer and commercial electronic equipment.
The capacitor was developed by the Bell Telephone Laboratories by using a porous anode and then replacing the liquid electrolyte with a solid semiconductor. This overcome the problem od requiring a vent that is common to all other forms of electrolytic capacitor.
These capacitors are superior to electrolytic capacitors in many ways exhibiting excellent temperature and frequency characteristics. They are also smaller than their aluminium electrolytic counterparts. However they are not able to handle high levels of current or voltage spikes. They are also damaged almost instantaneously by reverse polarity - usually exploding quite nicely.
Leaded tantalum capacitors
The most common form of leaded tantalum capacitors in use today are the "solid" tantalum capacitors. They offer particularly small package sizes and as a result they have been widely used in many areas of electronics.
Leaded tantalum capacitors (solid tantalum variety) are generally small and encapsulated in epoxy to prevent damage. The capacitor marking may be written directly onto the encapsulation as figures, although many used a colour coding system.
Warning: - In view of the nature of these capacitors, great care should be taken not to stress these capacitors. The polarity should not be reversed, nor should they be exposed to over-voltage conditions - even spikes. If they are exposed to these conditions then they may fail, sometimes exploding.
Tantalum SMD capacitors
Tantalum SMD capacitors are widely used to provide levels of capacitance that are higher than those that can be achieved when using ceramic capacitors. The capacitor technology that is used within SMD tantalum capacitors is based on the solid tantalum capacitor technology. This is robust and enables very small capacitors to be made.
For many years tantalum capacitors were used in SMD applications because electrolytic capacitors were not able to survive the high temperatures of the soldering process. Now that electrolytic capacitor technology has been developed to withstand the soldering process, these capacitors are now also widely used. Despite this, the other advantages of tantalum capacitors are employed in many circuits, and they are still used in vast quantities.
Tantalum SMD capacitors
As a result of the different construction and requirements for tantalum SMT capacitors, there are some different packages that are used for them. These conform to EIA specifications.
|Size A||3.2 x 1.6 x 1.6||EIA 3216-18|
|Size B||3.5 x 2.8 x 1.9||EIA 3528-21|
|Size C||6.0 x 3.2 x 2.2||EIA 6032-28|
|Size D||7.3 x 4.3 x 2.4||EIA 7343-31|
|Size D||7.3 x 4.3 x 4.1||EIA 7343-43|
Tantalum capacitor markings
There is a variety of different markings that are used with tantalum capacitors to indicate their value, working voltage and possibly other parameters.
The coding or marking system used will depend upon the type of capacitor, whether it is leaded or SMD and also the manufacturer, magnitude of the value, size of the component, etc.. To check out the systems used and the marking systems available read about capacitor marking & coding systems
Tantalum capacitor advantages and disadvantages
tantalum capacitors offer many advantages over other types of capacitor. This has meant that their use has risen considerably over the years, and now they are widely used in all forms of electronics equipment. The advantages of tantalum capacitors can be summarised:
- Volumetric efficiency: Tantalum capacitors offer a very high level of volumetric efficiency - much greater than many other types. In particular they are better than electrolytic capacitors which are their main rival.
- Good frequency characteristics: The frequency response of tantalum capacitors is superior to that of electrolytic capacitors. This means that they are more suitable for use in a number of applications where electrolytics could not be used.
- High reliability: Tantalum capacitors are more reliable than many other forms of capacitor. Provided they are operated within their ratings they are able to provide an almost unlimited life. Their use is not time limited as in the case of electrolytic capacitors.
- Wide operating temperature range: Tantalum capacitors are able to operate over a very wide temperature range. They are often specified for operating over the range -55C to +125C. This makes them an ideal choice for use in equipment for use in harsh environmental conditions.
- Compatibility with modern production methods: Modern production techniques often expose components to high temperatures during soldering as the whole assembly is heated by infra-red heat. Using conventional leaded components only the board surface was heated and the amount of heat conducted by the leads was usually insufficient to damage the components. Tantalum capacitors are able to withstand the temperatures of SMT production and are there fore ideal for use in many new electronics designs.
Tantalum capacitors have a number of disadvantages, and these need to be considered when using them in new designs.
- Low ripple current ratings: It is hardly surprising in view of their size, that tantalum capacitors do not have a high ripple current rating. They should not normally be used in areas that require any levels of current to be passed.
- Not tolerant to reverse or excess voltage: Tantalum capacitors do not like reverse or excess voltage. Even spikes can destroy them. If they are exposed to excess or reverse voltages then they can explode.
- More expensive than other types: Tantalum capacitors are more expensive than many other forms of capacitor. As a result their cost should be considered during the design phase as the other benefits may outweigh any increased costs.
By Ian Poole
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