Component manufacturers, handicapped by shortages of tantalum-chip capacitors for the past 18 months, are continuing to explore replacement alternatives, including the use of high-capacitance ceramic capacitors and aluminum electrolytic capacitors so they're not caught short again. New technologies such as the capacitive circuit architecture from X2Y Attenuators LLC (Erie, Pa.) and other materials such as niobium are also being considered as viable replacements for tantalum-chip capacitors.
Customers are using alternatives in whatever form suits their needs, said Sandy Beck, vice president of worldwide marketing at Kemet Corp. (Greenville, S.C.). Engineers have been using replacements for tantalum-chip capacitors for years but that practice has accelerated with the scarcity of tantalum capacitors, said Eric Pratt, director of information services at iSuppli Corp (El Segundo, Calif.). "There's nothing that forces the issue of alternatives quicker than when an engineer can't get a tantalum-chip capacitor," he added.
Many board manufacturers and designers are now setting up their pads to accommodate either a tantalum or ceramic-chip capacitor, which eliminates the conversion costs of shifting from one to the other, Pratt said. As tantalum-chip capacitors become more available in the smaller case sizes, some of the suppliers will convert back, he said.
Passive component manufacturers, meanwhile, are planning ahead for possible long-term shortages by strengthening their high-capacitance ceramic capacitor and surface-mount aluminum-capacitor lines so they can replace tantalum capacitors in some applications.
Before a conversion can take place, though, manufacturers must make sure that the replacement component offers capacitance that is high enough to meet the design engineer's requirements, said Frank W. Guiney, group product manager at Murata Electronics North America Inc. (Smyrna, Ga.). The recent shortage spurred numerous redesigns that required moving to ceramic capacitors, Guiney said.
Although base-metal multilayer ceramic chip capacitors have encroached on the 1- to 10-microfarad range of tantalum capacitors, the technical specs of the base-metal products are not as good as tantalum capacitors, particularly with regard to stability, said Glyndwr Smith, assistant to the CEO and senior vice president at Vishay Intertechnology Inc. (Malvern, Pa.).
If a design engineer has an option, he or she will use the product that is best suited for a particular circuit application, Smith said. Designers are evaluating each circuit to determine if using a replacement capacitor is appropriate. In general, though, they find that based upon the specs, a tantalum capacitor still offers the best functionality for its size, he said.
Still, ceramic capacitor manufacturers are moving ahead with the development of high-capacitance ceramic capacitors as viable alternatives to tantalum. Murata Electronics, for instance, doubled production capacity last year in Japan for its new GRM line of high-capacitance ceramic capacitors after realizing that these replacements for tantalum-chip capacitors are increasingly popular with cell phone and computer OEMs. These new capacitors can be used in several applications including coupling, decoupling, bypassing and signal smoothing.
Benefits of Murata's tantalum replacement devices include nonpolarization and low ESR. The high-capacitance ceramic caps offer a lower ESR value, typically 0.02 ohms compared with an average 1 ohm for tantalums.
The lower ESR allows a ceramic capacitor with a lower capacitance value to easily replace a tantalum capacitor without any loss of functionality, according to Murata.
Average lead times for the standard GRM Series of ceramic capacitors, which offers a capacitance range from 0.5 picofarad up to 47 microfarads, is about 10 to 12 weeks. The devices are available in various package sizes including 1210, 1206, 0805, 0603 and 0402.
The tantalum A-case size crosses to a ceramic cap in a 1206-size package and the B-case crosses to the 1210 ceramic equivalent. The parts are nearly dimensionally equivalent but are not necessarily drop-in replacements due to small dimensional differences as well as differences in electrical performance, Guiney said. C-case and D-case sizes do not have crossovers that have similar dimensions to ceramic capacitors, Guiney said.
For more information on test results comparing ceramic-chip caps with tantalum-chip caps, check out Murata's product brochure at www.murata.com/murata/weblibrary.nsf/pdf/c01/$file/tantalumalternatives.pdf.
Kemet Corp. also offers ceramic capacitors. The company is shipping ceramic-chip capacitors for the X5R dielectric up to 10 microfarads and up to 22 microfarads for the Y5V dielectric. Ceramic capacitors are probably the most frequently used substitute for tantalum-chip capacitors, VP Beck said.
Aluminum-electrolytic capacitors are also viable options in some cases, according to Rich Schuster, president of NIC Components Corp. (Melville, N.Y.).
Schuster said he's noticing a trend where low-ESR and low-leakage surface-mount aluminum-electrolytic capacitors are being used in applications where space is not a critical factor. These devices typically have a much higher profile than tantalum capacitors. For example, the height difference may be as much as 2 millimeters.
There are other trade-offs, too, such as life cycle. Although tantalum caps may offer a longer life, aluminum-electrolytic capacitors offer a higher capacitance/voltage (CV) range.
Surface-mount aluminum-electrolytic capacitors have been available for several years. But once manufacturers recognized the opportunity to replace tantalum caps in some applications, they expanded into higher values and smaller packages as well as increased production capacity.
For more technical information on using surface-mount aluminum-electrolytic caps, visit NIC Components' Web page at www.niccomp.com/Products/tantalum.html-ssi. You'll find two papers: "Alternates to SMT Ta Chip Caps" and "Using SMT Aluminum E-cap on Existing SMT Ta chip E-cap Land Pattern."
Another alternative to using tantalum capacitors is solid polymer aluminum electrolytic capacitors. Although there are less than a handful of suppliers for these capacitors and very limited production capacity, some users nonetheless are designing in these devices. Kemet's low ESR AO-Cap devices are available in a capacitance range of 47 to 220 microfarads at 6 volts and less.
These polymer aluminum electrolytic capacitors can plug-in to replace low-voltage and low-ESR tantalum-chip capacitors, in appli-
cations where capacitance, ESR and voltages are suitable for power-supply decoupling, Beck said.
One of the most attractive features of polymer aluminum electrolytic capacitors is that they require less voltage derating than tantalum caps, Beck said. The typical industry-derating factor for a tantalum chip is 50 percent. An engineer, for instance, will typically use a 16-volt-rated tantalum capacitor for a 6-volt app.
Some up-and-coming technologies could also work as replacements for tantalum caps. A new capacitive circuit architecture from X2Y Attenuators seems poised to offer higher performance than current decoupling and filtering solutions. It offers low ESR and low ESL. The ultralow ESR characteristic makes them suitable as tantalum cap replacements, according to the company. For instance, a 100 nf x 2Y in an x7R dielectric has an ESR rating of 2.4 milliohms.
The 3-terminal capacitive X2Y component has an "x" decoupling capacitor and two "y" bypass capacitors, which means it performs two functions in a single package. The devices from X2Y reduce or eliminate supporting inductors, capacitors, resistors and other circuitry, which reduces component count and placement costs. The new architecture can be used to manufacture a variety of devices including capacitors, decouplers, transient voltage suppressors and filters.
The ceramic-chip version is available in EIA sizes from 0603 to 1206 and capacitance values ranging from less than 10 picofarads to 10 microfarads. The high-cap value chips can replace Ta capacitors, according to X2Y president and CEO Tony Anthony.
Another option that has gained momentum as a result of the tantalum-cap shortage is niobium. Using niobium as an alternative to tantalum is not a brand new idea; but it has gained credibility now that the capacitance of niobium powder is equivalent to 70,000 to 100,000 CV/gram. That matches the CV/gram values of state-of-the-art tantalum powders, said Bill Serjak, niobium product manager at materials supplier H.C. Starck Inc. (Newton, Mass.).
Two new developments in tantalum powder processing-the reduction of powder oxygen, and treatments that add nitrogen to the surface and bulk of the powder-have proved to be crucial factors in reaching capacitor-grade niobium powder, Serjak said.
Niobium caps can be made in the form of a surface-mount, solid-electrolyte chip capacitor that will provide better volumetric efficiency than aluminum electrolytic capacitors, Serjak said. Niobium caps could also be used as a substitute for OS-CON-type aluminum capacitors, and large niobium chip caps could replace some tantalum apps where capacitance is more critical than the low dc leakage provided by Ta caps.
H.C. Starck has sent niobium powder samples to several companies, and preliminary results indicate that manufacturers will be able to produce a capacitor whose qualities approach those of tantalum, Serjak said. However, leakage may not be as good and it's not clear how it rates in terms of long-term stability, he said.
While the jury is still out on niobium's technical specs, availability and pricing look good. The worldwide supply of niobium is almost unlimited, Serjak said, and it costs less than half the price of tantalum.
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Murata Electronics North America Inc.
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NIC Components Corp.
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Vishay Intertechnology Inc.
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