Tantalum capacitors are benefiting from many of the same advances experienced by other types of capacitors. Higher capacitance, higher temperature ratings, greater reliability, and smaller package sizes are some of the improvements in tantalum parts ranging from SMD chip capacitors used in consumer electronics, to wet tantalum capacitors used in high-reliability industrial and military/aerospace applications.
Tantalum capacitors are polarized capacitors that use a tantalum anode electrode with a thin insulating oxide layer as a dielectric, and a solid or liquid electrolyte atop the oxide layer that functions as the cathode. This construction enables tantalum capacitors to combine high capacitance per volume and low weight. Technical advances are enabling tantalum capacitor suppliers to squeeze more capacitance out of their parts, according to Dave Valletta, executive vice president of worldwide sales for Vishay Intertechnology.
Like other suppliers, Vishay has replaced manganese oxide with polymer material in its tantalum capacitors, which according to Valletta, enables the capacitors to operate at 80 percent of rated current as opposed to 50 percent.
“The polymer is more robust and was developed because of its higher degree of safety compared to traditional tantalum powder,” said Valletta.
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Vishay Intertechnology recently enhanced its T55 series of vPolyTan™ surface-mount polymer tantalum molded-chip capacitors (Figure 1) with eight new ratings in A, B, and T case sizes. The T55 series offers a capacitance range from 3.3 µF to 470 µF over voltage ratings from 2.5 to 10 V, with a capacitance tolerance of +/-20 percent. The operating temperature range is -55° C to +105° C. The capacitors’ polymer cathodes produce lower equivalent series resistance from 500 mΩ down to 25 mΩ at +25° C and 100 kHz. Ripple current ratings range up to 2.28 A IRMS.
Figure 1: Vishay’s T55 series vPolyTan™ tantalum capacitors. (Source: Vishay Intertechnology)
With miniaturization of electronics as a continuing trend, tantalum capacitor suppliers are tweaking their product designs to squeeze the performance of larger capacitors into smaller footprint parts.
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AVX has developed what it considers the smallest size polymer capacitors available. The F38 series (Figure 2) comes in case sizes of 0.063 L x 0.033 W x 0.031 H (in.) or 0.079 L x 0.049 W x 0.031 H (in.). The footprint is identical to 0402, 0602, or 0805 ceramic capacitors, which enables engineers to design in noiseless and stable capacitance polymers without changing the board layout footprint, according to Allen Mayar, Product Marketing for Tantalum Capacitors.
Figure 2: AVX’s F38 Series polymer capacitors. (Source: AVX Corporation)
KEMET has revised the anode construction methods on its tantalum capacitors, using what the company terms as a “facedown” technique, according to Ken Lai, director of program management for KEMET in Asia. This enables the company to produce capacitors with 1 mm heights and packages that are only 1.8 mm wide x 0.8 mm long.
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AVX is now packaging its high-reliability tantalum capacitors in moisture-barrier bags to minimize the impact of moisture absorption in non-hermetic epoxy packages, according to Lizzie Geismar, Product Marketing Manager for High Reliability Tantalum. This has reduced the level of capacitor fallout through customer reflow processing. The company recently introduced surface-mount, hermetically sealed packages for both polymer and manganese-oxide capacitors that allows use in high-reliability, high-temperature applications. The THH Series manganese-oxide capacitor can withstand operating temperatures to 230° C, which is ideal for down-hole drilling applications. The hermetically sealed TCH series polymer capacitor is designed for satellite applications.
New Applications
Tantalum capacitors are finding their way into a number of emerging product sectors, including enterprise solid-state devices (SSDs), mobile devices, and high-performance cloud appliances. According to KEMET’s Lai, polymer tantalum capacitors are being used in “hold-up” circuits to prevent data loss when the SSD loses power. Polymer capacitors offer long operating life, low height, and high-energy density for these applications.
Tantalum capacitors are also being used in FPGA or ASIC-based cloud appliances requiring high frequency decoupling and filtering, Lai added. Automotive electronics is another growing area. KEMET’s KO-CAP T591 series (Figure 3) is designed for decoupling and filtering of DC-to-DC converters in automotive infotainment and driver assistance applications, as well as industrial applications where harsh conditions such as high humidity and temperature are of concern.
The KO-CAP T591 is available in capacitances up to 220 microfarads and rated up to 10 volts. This series now features operating temperatures up to 125° C, but future versions will be available with rated temperatures up to 150° C and voltages up to 63 V.
Figure 3: KEMET’s T591 automotive-grade electrolytic tantalum capacitor. (Source: KEMET)
The red-hot field of medical devices is also a fledgling area for tantalum capacitors. AVX recently developed the T4J series of medical capacitors (Figure 4), which are designed for use in medical non-implantable applications. The T4J offers a capacitor range of 1.0 µF to 680 µF. It is available in voltages of 6.3, 10, 16, 20, 25, 35, and 50 V. Operating temperature range is -55° C to +125° C.
Figure 4: AVX’s T4J series of medical capacitors. (Source: AVX)
Wet tantalum capacitors, used in high-reliability applications, are also benefiting from performance improvements. Vishay now offers a wet tantalum capacitor approved to Defense Logistics Agency (DLA) drawing 15005, with a reverse voltage of 1.5 V at 85° C with the ability to withstand a thermal shock of 300 cycles. The device is initially being offered in an axial T4 case size with a capacitance rating of 1000 uF, capacitance tolerance of +/-10 percent and +/-20 percent, and voltage rating of 75 V. It can operate to 125° C with voltage derating.
Tantalum Powder Supply
Earlier in the decade, a shortage of tantalum powder created challenges for tantalum capacitor makers trying to keep up with demand. That is not the case now as tantalum powder supplies are steady, said Vishay’s Dave Valletta.
“Tantalum powder has fluctuated like any other material due to market demand,” Valletta said. “It is sometimes up and sometimes down. But demand always comes back; none of these supply fluctuations last that long.”
Capacitor suppliers are also tightening their supply chain to ensure that tantalum powder supplies are uninterrupted by political conflicts in the regions where tantalum originates. KEMET, for example, has developed a conflict-free, vertically integrated tantalum supply chain the company claims ensures a reliable supply of conflict-free parts to the global electronics industry. The supply chain covers all processes ranging from the mining of tantalum ore to capacitor manufacturing.