Electronic Restoration >> Tools For Restoring Water Damaged Electronics

The electrochemical process involves deposition of a suitable conductive seed layer inside the porous slug.This layer is electrically contacted and the slug is dipped in a doped monomer solution. Electric current is passed through the seed layer into the doped monomer solution stimulating the oxidation reaction that grows the doped polymer on the Tools For Restoring Water Damaged Electronics seed layer. 

A significant advantage of the electrochemical process is that it provides enhanced polymer thickness and Tools For Restoring Water Damaged Electronics uniform coverage on the edges and corners of the porous slug because of the enhanced electric field at these locations. A disadvantage is the relative difficulty getting the polymer to form inside the porous structure because of the limited electric field present there. 

PEDT Polyethelyne-dioxythiophene (PEDT) is the most popular conductive polymer for use in tantalum capacitors. It has high electrical conductivity (up to 300 S/cm) and Tools For Restoring Water Damaged Electronics is both thermally stable at fairly high temperatures (above 200oC in oxygen-free environments) and relatively insensitive to moisture. Another advantage is that the polymerization reaction is less aggressive which provides a wider processing window.

A variety of dopants are available and it is thought that PEDT's physical and electrical properties can beoptimized for specific dielectrics and Tools For Restoring Water Damaged Electronics operating voltages by judicious choice of dopant. One disadvantageis that while PEDT can be polymerized via the electrochemical process, little success has been achieved intantalum capacitors with this process. 

Another disadvantage is the relatively high cost of the raw materials.In the capacitor industry, PEDT is deposited in tantalum anodes by either the "two-pot" chemical polymerization method described above for PPY, Tools For Restoring Water Damaged Electronics or by a "one-pot" method. In the "one-pot" method,monomer, oxidizer, and dopant are combined in one container with additional ingredients that slow thepolymerization process. 

The porous tantalum slug is dipped in the solution and the polymerization reaction continues inside the slug. It is also possible to use both processes, Tools For Restoring Water Damaged Electronics i.e., internal polymerization via the"two-pot" method and external polymerization via the "one-pot" method.A variety of manufacturers use PEDT in tantalum capacitors. 

Among them are KEMET (KO-Cap), NEC(Neo-Cap), EPCOS (TOPcap), Vishay (255D), AVX (TCJ), and others.Construction DetailsTypical construction of tantalum polymer capacitors is best illustrated with pictures. Figures 6 through 14serve this purpose. It should be noted that the pictures were taken of samples that came from severaldifferent part types, Tools For Restoring Water Damaged Electronics so there may be small discrepancies from picture to picture that can be detected by theexperienced eye. 

Also, the samples were exposed to a good bit of incidental human handling and may not Tools For Restoring Water Damaged Electronics accurately represent optimum factory uniformity.Figure 6 is a magnified view of 50 kCV/g tantalum powder prior to being pressed into a porous tantalum slug. The powder particles typically stick together in porous bundles called agglomerates. 

The smallestagglomerates visible in the picture are roughly 5-10 µm in size and are made up of individual particles thatare roughly 0.1 to 1 µm in size. The powder is coated with an organic binder material that aids powderflow as it is dispensed into the presses that form the compacted, Tools For Restoring Water Damaged Electronics but still porous tantalum slugs. The binderalso provides lubrication during slug pressing. 

Figure 7 is a picture of a porous tantalum slug that has a tantalum anode wire pressed into it. The slug ofFigure 7 has been first heated in a vacuum to a temperature high enough (typically >200oC) to decomposethe organic binder, and Tools For Restoring Water Damaged Electronics then further heated to roughly 1,600oC to sinter the individual powder particlestogether. 

The objective is to form good mechanical connections between the particles and between theparticles and the anode wire without unnecessarily compromising the slug's porosity and Tools For Restoring Water Damaged Electronics internal surface area. The degree of sintering is controlled by time and temperature, and various properties of the finishedcapacitor can be fine-tuned during this process step. 

Figure 8 shows several tantalum slugs attached to a common conductive bar. The slugs have beenimmersed in a suitable electrolyte and dielectric has been "formed" on the exposed tantalum surface byelectrolytic anodization. During anodization, Tools For Restoring Water Damaged Electronics tantalum ions migrate from the surface of the tantalum metalto a point roughly halfway through the existing dielectric where they combine with similarly migratingoxygen ions that are supplied by the electrolyte. 

The result is partial Tools For Restoring Water Damaged Electronics consumption of the underlying tantalum metal and growth of the tantalum pentoxide dielectric on the remaining metal's surface. The color change is due to the refractive properties of the dielectric film which grows to a thickness consistent withroughly 20 angstroms per volt of applied formation voltage.

The peak formation voltage is usually about 3 to 4 times higher than the rated voltage of the finished capacitor. So for a 6.3 volt capacitor, Tools For Restoring Water Damaged Electronics 20V would not be an unusual formation voltage. 20V dielectric would be roughly 400 angstroms or 40 nm thick. For the smallest tantalum particles which could be 0.1µm or 100 nm thick, there isn't very much tantalum metal left after oxide this thick is grown. 

Indeed, atmuch higher formation voltages, Tools For Restoring Water Damaged Electronics oxide formation consumes enough of the tantalum metal in the smallerparticles to effectively disconnect them from the rest of the slug. The end result is reduced availablesurface area and less CV/gram than can be achieved at lower formation voltages. Figure 9 is a picture of tantalum slugs after dielectric formation that have been impregnated with conductive polymer. 

The color of this polymer lies somewhere between very dark blue and black. Theobjectives of this stage of the process are to create a uniform, highly conductive layer of polymer on all ofthe internal surface of the slug and then to create a uniform, Tools For Restoring Water Damaged Electronics dense layer of polymer on the outer surface ofthe slug. Electrically, the outer layer of polymer adds unwanted ESR to the finished device, but this is anacceptable tradeoff for the mechanical protection that the layer provides to the very thin dielectric that liesjust below it. 

Figure 10 shows the polymer coated slugs after addition of a carbon layer and a coating of conductivesilver paint. The carbon layer provides a good interface between the polymer and Tools For Restoring Water Damaged Electronics the silver flakes in thepaint. At this stage of processing, the capacitor elements are fully functional and have electrical propertiesvery similar to those of the finished capacitors. Initial electrical testing is done at this point to assess thequality of the elements before they proceed further in the process.

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