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Second, although self-healing does occur in the conductive polymer due to degradation of the polymer's conductivity at high temperatures, this self-healing mechanism is not thought to be as effective as the self healing mechanism of MnO2-based tantalum capacitors. Decomposition of the conductive polymer is thought to leave behind Water Damage Restoration For Electronics carbonaceous residues which retain some conductivity.

And carbon touching the dielectric's surface is known to enhance the conductivity of tantalum pentoxide dielectric by the mechanism of direct electron injection. No Exothermic Ignition Mechanism Although the absence of readily available oxygen in the Water Damage Restoration For Electronics conductive polymer may work against realization of reliable high-voltage tantalum polymer capacitors, it is certainly a benefit during capacitor failure.

When MnO2-based tantalum capacitors fail, Water Damage Restoration For Electronics it is not uncommon that sufficient heat is produced at the failure site to release substantial local oxygen. This oxygen can combine chemically with the tantalumsubstrate in an uncontrolled exothermic reaction which causes catastrophic instantaneous ignition of theMnO2-based tantalum capacitor.

The dividing line between controlled, successful self-healing and catastrophic ignition is not clearly drawn.But generally speaking, Water Damage Restoration For Electronics MnO2-based tantalum capacitors made from higher CV/gram powders and those with only lightly sintered connections between their tantalum particles appear to be more susceptible toignition. 

Also, Water Damage Restoration For Electronics capacitors used in low impedance, high-current circuits are more susceptible to ignitionrather than self-healing in response to dielectric faults.This uncontrolled ignition mechanism does not occur in tantalum polymer capacitors because there is noplentiful supply of oxygen adjacent to the dielectric. 

However, tantalum polymer capacitors do fail in the short-circuit mode, and if the available current from the circuit is substantial, Water Damage Restoration For Electronics it is possible to achieve sustained combustion of the capacitor and of the surrounding circuitry simply due to the substantial heatgenerated by the high fault currents. Materials and Processing In principle, the processing of tantalum polymer capacitors is quite similar to the processing ofconventional MnO2-based tantalum capacitors. 

The major change is the substitution of conducting polymerfor the MnO2. But other small materials changes may be made to optimize ESR reduction Water Damage Restoration For Electronics and reduce sensitivity to reflow conditions. These smaller changes are of no more significance than the typicalvariability seen between different manufacturers of a generically similar product. 

So the focus of thissection will be on materials Water Damage Restoration For Electronics and processes unique to the manufacture of tantalum polymer capacitors. A variety of materials are available to replace MnO2 as the solid electrolyte in a tantalum capacitor. Four possible materials will be described: tetracyano-quinodimethane (TCNQ) salts, polyaniline (PANI),polypyrole (PPY), and polyethelyne-dioxythiophene (PEDT). 

Other conductive polymers exist that havethe necessary conductivity to replace MnO2, Water Damage Restoration For Electronics but they have not been successfully employed in capacitor manufacturing because of a variety of shortcomings such as poor stability. Two examples are poly phenylene vinylene (PPV) with conductivity of 10-16 S/cm and iodine-doped polyacetylene with conductivity of 100 S/cm. 

TCNQ The first material, tetracyano-quinodimethane (TCNQ) is not strictly a polymer, Water Damage Restoration For Electronics but rather a charge-transfersalt that forms linear chains of molecules which are stacked in layers. Highly polarizable donor moleculescontribute electrons that provide conduction along the chains. One such donor molecule is N-methylphenazinium (NMP).

TCNQ salts made with NMP have been reported to have conductivity exceeding 100 S/cm. This is muchhigher conductivity than MnO2, Water Damage Restoration For Electronics which is generally considered to have conductivity in the neighborhood of 0.1 to 1 S/cm. However, the conductivity of TCNQ is typically in only one dimension (along the chain), so structures that depend on three-dimensional conductivity must rely on compositions that consist of shorter chains in random orientation and effective electrical communication among the chains. 

This Water Damage Restoration For Electronics generally reduces the effective conductivity of the material for capacitor applications. TCNQ is commonly used in wound aluminum foil electrolytic capacitors for power supply applications.There has been good success with this application. Typical ESR performance of these devices is roughly20-30 mΩ. 

The salt is melted and drawn into the pores of the etched aluminum foils and the separatormaterial and allowed to cool. Sanyo is a major supplier of these devices (OS-CON).TCNQ has not found much use in porous tantalum slugs, Water Damage Restoration For Electronics likely because of difficulties impregnating themuch deeper porosity of tantalum anodes and temperature limitations. 

While common aluminum foil is only etched to depths of roughly 30 microns, porous tantalum slugs have pores which reach to their core.These pores are 10 to 50 times deeper and present a more formidable challenge for complete impregnation. Finally, Water Damage Restoration For Electronics there is very little separation between the temperatures needed to melt and impregnate the TCNQsalt and temperatures that begin to decompose the material. 

Capacitors made with TCNQ are not generally stable above roughly 85oC, Water Damage Restoration For Electronics a temperature that would be too limiting for capacitors made from relatively expensive metal tantalum. But this temperature limit is frequently acceptable for less-expensive aluminum capacitors in less-demanding applications. PANI Polyaniline (PANI) is the most thermally stable conductive polymer but is easily de-doped in the presence of water. 

Conductivities up to 10 S/cm have been reported which are high enough to provide a substantial advantage over MnO2, Water Damage Restoration For Electronics but sensitivity to moisture discourages use of PANI in tantalum capacitors. Higher molecular weight dopants are being investigated to overcome the moisture limitation, but at the presenttime, PANI is not used in any commercially available tantalum capacitors. 

However, the material hasfound application in double-layer super-capacitors and other electronic applications. Another concern isthe possible generation of carcinogenic byproducts upon decomposition. PPYPolypyrole (PPY) is the first intrinsically conductive polymer successfully used to manufacture bothaluminum and Water Damage Restoration For Electronics tantalum capacitors. 

The basic raw materials are commonly available Water Damage Restoration For Electronics and relatively inexpensive. Aluminum capacitors based on PPY are manufactured by Panasonic (SP Cap), Rubycon, andothers. Tantalum capacitors based on PPY are manufactured by NEC and Sanyo (POS-CAP). PPY is suitable for both chemical polymerization and electro-chemical polymerization in tantalum capacitors. 

In the chemical polymerization process, the porous element is alternately dipped in monomerand oxidizer solutions with appropriate drying steps between. Contact between the monomer Water Damage Restoration For Electronics and oxidizer initiates polymerization. Afterwards, excess non-reacted materials must be washed out of the porous slug.

A suitable dopant material is added either to the monomer or oxidizer solution to enhance electrical conductivity by providing free electrons. The basic materials are highly reactive and Water Damage Restoration For Electronics care must be taken to control the reaction in order to deposit meaningful amounts of polymer inside the porous slug. Other factors that control the conductivity and morphology of the resulting polymer are temperature and pH.

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