Electronic Restoration >> How To Troubleshoot Sensors On Circuit Boards

Solid-electrolyte tantalum capacitors were first developed and commercially produced in the 1950s. They represented a quantum leap forward in miniaturization and reliability over existing wound-foil wet electrolytic capacitors. While the solid tantalum capacitor has dramatically improved electrical performance versus wet-electrolyte capacitors, How To Troubleshoot Sensors On Circuit Boards especially at low temperatures.

Today's electronic circuits require even better performance.In response to this need, How To Troubleshoot Sensors On Circuit Boards steady improvements in the equivalent series resistance (ESR) of tantalum capacitors have been made. Low ESR is the most important attribute of capacitors used to filter and decouple power for high-speed digital electronics. 

While the first patented tantalum capacitor was claimed tohave ESR of roughly 2.0 ohms, How To Troubleshoot Sensors On Circuit Boards a similar capacitor today has ESR of about 0.1 ohms. Even so, today's digital electronics frequently require capacitors to have ESR in the low milliohms, a level that can be achieved with conventional tantalum capacitors only by connecting many in parallel.

A substantial fraction of the ESR of a tantalum capacitor comes from its solid electrolyte material,manganese dioxide (MnO2). While MnO2 is substantially more conductive than almost all wet electrolytes, How To Troubleshoot Sensors On Circuit Boards especially at low temperatures, capacitor manufacturers search for higher conductivity materials to replace MnO2. 

Today's solid electrolyte material of choice is the conductive polymer PEDT (polyethylenedioxythiophene) which has up to 100 times MnO2's conductivity and has generally acceptable compatibility with tantalum pentoxide, the tantalum capacitor's dielectric.With the introduction of conductive polymer electrolyte, How To Troubleshoot Sensors On Circuit Boards remarkable improvements in capacitor ESR arepossible. 

But ESR isn't the only capacitor performance characteristic to benefit. For lower-voltagecapacitors, improved dielectric strength and long-term reliability are also observed. Also, How To Troubleshoot Sensors On Circuit Boards substantially more capacitance stability with frequency is observed. But there are also limitations to the technology including marginal material stability at elevated temperatures, muted self-healing capability, and reduced dielectric reliability at high rated voltages.

This document briefly describes the origin of MnO2-based solid tantalum capacitors, their methods ofprocessing and How To Troubleshoot Sensors On Circuit Boards construction, and their defining electrical characteristics versus the wet electrolytic capacitors they replace. The case for improved electrolyte conductivity is briefly presented and conductivepolymer is identified as the candidate material of choice to replace MnO2 in the solid tantalum capacitor.

The defining electrical characteristics of capacitors made with conductive-polymer solid electrolyte aredescribed. Typical processing options How To Troubleshoot Sensors On Circuit Boards and material issues related to conductive polymer electrolyte are identified.Details of the step-by-step processing of typical tantalum polymer capacitors from tantalum powder toassembled and encapsulated devices are photographically presented. 

The electrical performance, dielectricrobustness, reliability, and environmental stability of tantalum polymer capacitors are discussed in some How To Troubleshoot Sensors On Circuit Boards detail. Competitive testing of these capacitors will occur during the FY06 task. Results of this competitiveevaluation will be published in FY06 as the phase two deliverable of this project. 

Whether tantalum or aluminum, How To Troubleshoot Sensors On Circuit Boards these first-generation metal-foil electrolytic capacitors all employed wet electrolytes to make the electrical connection from the circuit to the negative side of the capacitor's dielectric. The positive electrical connection was made directly to the metal foil upon which the metaloxide dielectric was grown by electrochemical anodization. 

The foil was typically chemically etched prior to anodization to increase its surface area How To Troubleshoot Sensors On Circuit Boards and thereby increase the capacitance of the finished capacitor. One consequence of making the negative connection to the dielectric with a wet electrolyte is poor lowtemperature performance. This is true because electrolyte conductivity falls at low temperatures as chargecarriers become less mobile. 

Another problem is that the wet electrolyte can slowly escape from the capacitors, causing them to gradually go open-circuit. Though big improvements have been made over the last half-century, How To Troubleshoot Sensors On Circuit Boards these two problems still cause trouble for wet-electrolyte, wound-foil electrolytic capacitors.A New Kind of Capacitor

The scientists at Bell Labs realized that low-voltage transistorized circuits not only promised significant miniaturization, How To Troubleshoot Sensors On Circuit Boards but also promised higher reliability than was possible with vacuum-tube circuits. Theyalso saw the need for smaller, more reliable capacitors to complement the transistors. Their solution was acapacitor physically different from anything seen before.

This capacitor was made with tantalum instead of aluminum. But instead of chemically etching tantalummetal foil to increase its surface area prior to growing the insulating dielectric film on it, as is commonlydone with aluminum electrolytic capacitors, How To Troubleshoot Sensors On Circuit Boards the surface area of the tantalum metal was increased by adifferent method. 

The surface area was increased by compacting finely-divided tantalum powder into aporous slug and then carefully sintering the powder particles together at high temperature whilemaintaining much of the slug's porosity. After this sintering step, How To Troubleshoot Sensors On Circuit Boards the dielectric film was electrochemicallygrown on the porous slug's internal and external surfaces. 

The result was a compact element withdielectric grown on a remarkably high surface area, much higher than could be achieved in the samevolume by etching tantalum foil. This was the first substantial innovation of Bell Labs' capacitor, How To Troubleshoot Sensors On Circuit Boards but notthe only one. In conventional wound-foil electrolytic capacitors, the exposed negative-polarity surface of the dielectric iscontacted with a wet or gelled electrolyte which provides the electrical path from the dielectric to theexternal circuit. 

The electrical path the external circuit is completed via a nearby high-surface-area etchedfoil cathode that also contacts the electrolyte. It is possible to make the negative connection How To Troubleshoot Sensors On Circuit Boards to thedielectric of a porous-slug tantalum capacitor in a similar fashion using wet electrolyte and a high-surfacearea cathode. Indeed "wet" tantalum capacitors are made this way. 

However, How To Troubleshoot Sensors On Circuit Boards such construction does notsolve the problem of poor performance at low temperatures, or the possibility that the electrolyte mayescape from the capacitor over time (it should be noted that modern, hermetically-sealed wet tantalumcapacitors are very reliable and rarely leak, but they are also relatively heavy and expensive). 

Second substantial innovation of Bell Labs' capacitor was the use of a dry or solid electrolyte in place How To Troubleshoot Sensors On Circuit Boards of the wet electrolyte used in conventional wet electrolytic capacitors. The exposed negative surface of the tantalum capacitor's dielectric is contacted by coating it with the semi-conducting crystalline solid, manganese dioxide (MnO2). 

This is accomplished by dipping the porous slug into manganous nitrate To facilitate good internal coverage, the concentration of the manganous nitrate solution is kept low, and How To Troubleshoot Sensors On Circuit Boards many dip and convert cycles are usually required to adequately contact the dielectric. 

The endresult is a solid and dry functional capacitor element composed of tantalum metal as one electrode, highquality dielectric, and another electrode, MnO2, contacting the other surface of the dielectric. However, How To Troubleshoot Sensors On Circuit Boards MnO2 is not a material easily connected to external circuits, so a few finishing steps are needed to make apractical capacitor from the functional capacitor element.

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