Tiny capacitors are more complex than they seem
By Bill Schweber -- EDN, December 17, 2004
The venerable capacitor, one of the oldest electronic components, has morphed into many special variations for various parameter combinations. A trio of new families from AVX clearly illustrates that engineers have choices and trade-offs. The OxiCap NbO (niobium-oxide) solid-electrolyte devices feature ESR as low as 55 mÙ. These lead- and halogen-free capacitors, which come in standard-EIA case sizes, are alternatives to tantalum devices, due to their electrical features and high volumetric efficiency. Prices are 30 cents to 40 cents (OEM volumes).
The tantalum 0402 TAC Microchip series has the highest volumetric efficiency along with low leakage, and delivers a variety of capacitance/voltage pairings, such as 10 ìF at 2V and 2.2 ìF at 6.3V. The –55 to +125°C devices, which sell for 45 cents to 55 cents (10,000), also feature capacitance-value stability over temperature. In addition, a proprietary “soft-termination” technology allows the capacitor to compensate for thermal mismatch between components and pc boards, a cause of solder-joint failure.
Also taking advantage of the volumetric efficiency possible with tantalum, the TCJ series uses a conductive-polymer cathode for low ESR and can withstand the multiple-reflow-cycle, 260°C solder temperature of some lead-free soldering processes. These devices are available in 4.7- to 150-ìF values at voltages of 4 to 10V; price is 25 cents to 35 cents (10,000) (Picture).
AVX Corp, www.avxcorp.com.
