Capacitors tantalum

Solid-state welding Solid tantalum capacitors Solid waste disposal Soliton... 

Electrolytic Capacitors. Tantalum, because of its high melting point of 2850°C, is produced as a metal powder. As such, it is molded, sintered, and worked to wire and fod, and used to budd certain types of tantalum capacitors (51). Other capacitors are made by compacting and sintering the tantalum powder. 

The dramatic reductions in alkaUes and carbon concentrations have led to significant improvements in the electrical quaUty as measured by the performance of tantalum capacitors. 

The first commercial use of tantalum was as filaments ia iacandescent lamps but it was soon displaced by tungsten. Tantalum is used ia chemical iadustry equipment for reaction vessels and heat exchangers ia corrosive environments. It is usually the metal of choice for heating elements and shields ia high temperature vacuum sintering furnaces. In 1994, over 72% of the tantalum produced ia the world went iato the manufacturiag of over 10 x 10 soHd tantalum capacitors for use ia the most demanding electronic appHcations. 

Fig. 6. A chip-type surface mount soHd tantalum capacitor.

Sohd tantalum capacitors have a high volumetric capacitance which makes them attractive for use in miniaturized electronic systems like cellular telephones, hand-held video cameras, and personal computers. The insensitivity of their capacitance to temperature and their abiUty to operate at temperature extremes explains why these devices are used in such harsh environments as automobile engine compartments. Sohd tantalum capacitors are extremely rehable and, therefore, are often the capacitor of choice in critical appHcations like spacecraft electronics, pacemakers, and safety equipment. 

Wire. Tantalum wire is used primarily as the anode lead wire in soHd tantalum capacitors. Since the 1970s, the average weight of tantalum in a sohd tantalum capacitor has dropped from several hundred milligrams to less than 50 mg but the consumption of tantalum powder for capacitors has remained relatively constant because of the dramatic increase in the number of capacitors manufactured. The weight of wire per capacitor has remained relatively constant and thus wire consumption has increased steadily. 

I will be using a surface mount tantalum capacitor because they typically exhibit about 50 percent of the ESR of electrolytic capacitors. I will also derate the rating of the candidate capacitors by 30 percent at -i-85°C ambient temperature. 

There are very few surface mount capacitors with the desired value, voltage rating, and low ESR all in one part. It would be more conservative to parallel two capacitors of no less than one-half the desired capacitance value. This allows many more second sourced capacitors to be used and lowers the ESR. Lets use two 330 pF, 10 V tantalum capacitors in parallel. The Candidates now become ... 

The major consumer of tantalum is the capacitor production industry. About 60% of the total amount of tantalum currently produced is in the form of fine, agglomerated high purity powder of capacitor grade. Tantalum capacitors have high volumetric efficiency and reliability. A basic description of tantalum capacitor technology is presented in overview [19]. 

Tantalum production has increased steadily and strongly since 1993. An optimistic forecast regarding the strongly increasing demand for tantalum capacitors caused excessive demand for tantalum powder in 2000, when the overproduction of capacitors led to a sharp shortage in tantalum powder. It is still difficult to predict when the electronics industry will return to balanced condition. 

In the second part of the 20th century, the tantalum capacitor industry became a major consumer of tantalum powder. Electrochemically produced tantalum powder, which is characterized by an inconsistent dendrite structure, does not meet the requirements of the tantalum capacitor industry and thus has never been used for this purpose. This is the reason that current production of tantalum powder is performed by sodium reduction of potassium fluorotantalate from molten systems that also contain alkali metal halides. The development of electronics that require smaller sizes and higher capacitances drove the tantalum powder industry to the production of purer and finer powder providing a higher specific charge — CV per gram. This trend initiated the vigorous and rapid development of a sodium reduction process. 

The extraction technology is applied for scrap recycling of tantalum and niobium and for the treatment of related materials. Recovery of tantalum and niobium from secondary material, such as Sn slag, Ti slag, W slag, catalyst wastes, used cemented carbide and used tantalum capacitors was reviewed by Dai, Zhong, Li and Li [483]. 

The main reason for the tantalum industry s drive toward the sodium reduction process is an increasing demand for tantalum powder by tantalum capacitor manufacturers. The modem tendency of the electronics industry to miniaturize their components calls for the improvement of tantalum powder... 

Rare earth metals, as well as alkali earth metals, can be used as oxygen getters in the purification of tantalum powder. Osaku and Komukai [608] developed a method for the production of tantalum and niobium metal powder by a two-step reduction of their oxides. The second step was aimed at reducing the oxygen content and was performed by thermal treatment with the addition of rare metals. The powder obtained by the described method is uniform, had a low oxygen level and was suitable for application in the manufacturing of tantalum capacitors. 

Most of the evaluation boards of such ESR-sensitive parts are shipped out to customers with only aluminum electrolytic or tantalum capacitors at their outputs. But what really happens is that the customer happily connects the eval board (rather expectantly) into his or her system, and completely forgets there are a bunch of ceramic capacitors all over the system board (for local decoupling at different points). In effect, the switcher can lose that valuable zero in its control loop and break into oscillations (see Figure 3-5). More so if the connecting leads are short. 

Anodic oxidation is a very common process in the electrochemical industry, used for example in the manufacture of aluminum and tantalum capacitors. The anodic oxidation of silicon is not of comparable importance, because the electrical properties of anodic oxides are inferior to those of thermal oxides. 

The remarkable stability of the capacitance of the SIKO against variations in bias, temperature, frequency and time of operation is a consequence of the superior properties of its ONO dielectric. In contrast to aluminum and tantalum capacitors, the SIKO is a symmetrical device. It shows no significant voltage dependence of the capacitance, as the high s ceramic capacitors do. Only polymeric capacitors show a lower dependence of capacitance on bias than a SIKO. 

They are several concerns when designing an EMI filter. The parameters of the EMI filter examined in this book reflect these concerns. If the EMI filter is to be used on a converter, the input impedance of the converter must be greater than the output impedance of the filter at all frequencies. It is good practice to allow 6 dB of margin for this parameter. If the output impedance of the filter gets too close to the input impedance of the converter, there can be problems with the stability of the converter. It may be important to note here that this output impedance is sensitive to the effective series resistance (ESR) of the output capacitors. For the hardware data taken for this unit, tantalum capacitors, which have unspecified ESR, were used. The ESR of a similar capacitor was measured for the simulations. 

The actual SPICE model of this circuit is shown in Fig. 10.2. Note that there are two resistors in series with each of the capacitors, Rl and R2. These resistors model the approximate equivalent series resistance (ESR) of the tantalum capacitors in the circuit at the switching frequency. 

This circuit was built in the lab using 1N4002 1A 100V rated diodes with 1 /U.F tantalum capacitors. The input pulse was a square wave from -3 V to +3 V, with a frequency of 5 kHz at a 50% duty cycle. The PULSE statement in the SPICE model is shown below ... 

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