Electronic Restoration >> Tools For Restoring Fire Damaged Electronics

While the conductivity of some conducting polymers may be as much as 100 times higher than that of MnO2, the improvement in capacitor ESR is not this dramatic. What is typically seen is reduction of capacitor ESR by a factor of between 2 and 4. The discrepancy is due to several factors. First, Tools For Restoring Fire Damaged Electronics not all of the ESR of a tantalum capacitor comes from its electrolyte. 

There are other sources of resistance, including the resistance of the tantalum, carbon, conductive metal coat, termination metal, and Tools For Restoring Fire Damaged Electronics associated interfaces.There is even a component of ESR that comes from dielectric loss, but this is usually very small at higher frequencies. A second reason for the discrepancy is that creating conductive polymer inside a slug withfine pores is much more difficult that creating conductive polymer on the surface of a flat glass slide in thelaboratory. 

The polymer film inside the tantalum slug must be produced one thin layer at a time and theindividual layers must communicate well with each other electrically, Tools For Restoring Fire Damaged Electronics a difficult task. This process will bedescribed in more detail later.In spite of the current practical limitations of the technology, dramatically low ESR has been achieved intantalum polymer capacitors. 

Currently, single-anode capacitors with 100 kHz ESR under 7 mΩ havebeen manufactured, Tools For Restoring Fire Damaged Electronics and multiple-anode tantalum polymer capacitors have been made with ESR under 3mΩ. Such low ESR in combination with high capacitance makes the tantalum polymer capacitor the fastestgrowing segment of the tantalum capacitor industry.

Better High-Frequency PerformanceThe higher conductivity of the conductive polymer electrolyte improves Tools For Restoring Fire Damaged Electronics the high-frequency capacitance ofthese capacitors. Capacitance roll-off of tantalum polymer capacitors remains low until well above 100kHz. This characteristic substantially improves the filtering performance of these capacitors in DC-DC converters and other circuits that operate in this frequency range. 

The filtering characteristics of such circuits depend on both capacitance Tools For Restoring Fire Damaged Electronics and ESR, so filtering effectiveness improves more than would be anticipated by simply considering improvements in ESR alone. Typical MnO2-based tantalum capacitors could lose up to 50% of their capacitance at 100 kHz, while tantalum polymer capacitors typically retainmore than 90% of their capacitance at 100 kHz.

Superior Reliability for Lower Rated Voltages But low ESR in the absence of good reliability would not be very compelling. It turns out that almost all tantalum polymer capacitors have Tools For Restoring Fire Damaged Electronics better reliability than equivalent MnO2 tantalum capacitors. It is thought that the low-temperature deposition of the conducting polymer into the tantalum slug does less damage to the capacitor's dielectric than is done by the high-temperature conversion of manganous nitrate into MnO2.

Almost all of the polymer processing is done in the neighborhood of room temperature while MnO2generation is done at temperatures in excess of 250oC and typically involves more processing cycles. Thelow-temperature processing and Tools For Restoring Fire Damaged Electronics relative softness of the resulting polymer are thought to produce lessdamage to the dielectric than occurs from frequent thermal cycling of the tantalum slugs after the earlydeposition cycles of the hard, crystalline MnO2.

Two experimental observations support this hypothesis. First, Tools For Restoring Fire Damaged Electronics the ultimate breakdown voltages of capacitorelements impregnated with polymer are higher than those impregnated with MnO2 for similar dielectricthickness, and far fewer lifetest failures are observed under highly accelerated conditions (e.g., 1.5Vr @85oC) for tantalum polymer capacitors versus MnO2-based tantalum capacitors. 

Some Flies in the OintmentUnfortunately, not all the news is positive. Generally speaking, tantalum polymer capacitors are moresensitive to high temperature than are MnO2-based tantalum capacitors, their leakage current is higher, and Tools For Restoring Fire Damaged Electronics for the higher rated voltages, the breakdown and lifetest advantages disappear. 

No tantalum polymercapacitors are presently rated higher than 25V and Tools For Restoring Fire Damaged Electronics the reliability of those that are is less than spectacular. All conductive polymers appear to be inherently less thermally stable than MnO2. This is likely the resultof superior bond strength in the inorganic, crystalline MnO2 versus the bond strength in organic polymers.

Quantitatively, MnO2 begins to break down at temperatures above roughly 450oC while commonconductive polymers begin to break down at Tools For Restoring Fire Damaged Electronics temperatures closer to 200oC. It is also known that exposure to oxygen at temperatures much higher than 105oC can substantially increasethe resistance of the conductive polymers used in capacitors. 

For this reason, Tools For Restoring Fire Damaged Electronics capacitors advertised for use at 125oC are made with extra attention paid to careful sealing of the capacitor element within the protectiveepoxy case. It appears that the epoxy molding material captures the small amount of oxygen that diffusesthrough the case at 125oC before it can reach the conductive polymer within the capacitor element. 

But ifthe integrity of the case epoxy is disturbed by defects such as cracks or pin holes, ESR deterioratessignificantly over the course of 1,000 hours exposure to 125oC, a common lifetest duration. Also, Tools For Restoring Fire Damaged Electronics the DC leakage current of tantalum polymer capacitors is generally higher than that of MnO2-basedtantalum capacitors. 

The reasons for this higher leakage current are not fully understood, Tools For Restoring Fire Damaged Electronics but it is thoughtthat the higher leakage results from residues of the polymerization process, higher conductivity of thepolymer itself with respect to MnO2, and less effective self-healing properties of the conductive polymer.

Regardless of the reasons, the practical effect is that catalog leakage limits for tantalum polymer capacitors are typically 10 times higher than for MnO2-based tantalum capacitors, Tools For Restoring Fire Damaged Electronics and there isn't usually as much of a gap between actual leakage and the catalog limit as is common for MnO2-based tantalum capacitors.

Finally, the reliability of higher-voltage tantalum polymer capacitors is no longer superior to that of MnO2-based tantalum capacitors of similar rated voltage, Tools For Restoring Fire Damaged Electronics and in some cases it is inferior. The reasons for thereduced reliability of higher-voltage tantalum polymer capacitors are not precisely known, but it issuspected that at least two factors may contribute.

First, Tools For Restoring Fire Damaged Electronics the oxygen replenishment function that MnO2 performs is not present in the conductive polymer. It may be that this reliability-enhancement mechanism may simply be more important at higher voltages thanat lower voltages where the reliability of tantalum polymer capacitors is clearly superior to MnO2-basedtantalum capacitors.

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