Niobium oxide capacitors outperform aluminium

Today's consumers demand electronic goods that perform to the highest levels, are reliable and cost-effective, says Tomas Zednicek.

Today's consumers demand electronic goods that perform to the highest levels, are reliable and cost-effective.

This is placing different demands on component engineers who must now consider not only cost, but also other factors.

Take, for example capacitors.

Where previously aluminium electrolytic devices were deemed adequate and chosen mainly for cost reasons, new high end consumer markets demand much more in terms of reliability and performance - yet cost is always a major consideration.

With a reliability of between 1000 and 5000 hours MTBF (mean time between failure), aluminium capacitors present considerable limitations for applications such as LCDs and PCs, and have raised concerns in the desktop industry.

Dry-out (a condition which occurs as a result of a leaking electrolyte), which typically occurs at continuous operating temperatures between 40 and 85C, has resulted in ESR and DSL instability and caused many desktop computers to fail.

The use of lead in aluminium capacitors also presents difficulties.

Under European Union legislation due in July 2006, no PCB with lead solder can be sold on the European market.

The use of lead-free solder alloys requires an increase of peak reflow temperature to 255-260C.

Aluminium capacitors withstand 1x reflow profile to 250-260C and are therefore unable to comply with JEDEC 020C.

The limitations caused by aluminium capacitors can be overcome by a new technology developed by AVX.

OxiCap niobium oxide capacitors are lead and halogen-free, environmentally friendly and provide a high level of safety and security due to self-healing and self-arresting mechanisms.

The parts offer an MTBF in the range of 200,000 to 500,000 hours, performing 100 times better than aluminium electrolyte capacitors.

They do not suffer from the dry out condition.

Furthermore, OxiCap capacitors withstand a 3x reflow profile up to 260C, complying with JEDEC 020C lead-free requirements.

Such capabilities enable mass production of advanced PCBs including rework.

Additionally, unlike other capacitor technologies, niobium oxide is a readily available material and OxiCap devices can be manufactured on existing standard tantalum processing lines.

AVX's NOJ series capacitors offer capacitance values from 4.7 to 1000uF and a rated voltage from 1.8 to 10V.

This voltage range, while fulfilling most demands, may be the only limitation of niobium oxide capacitors in a face-to-face comparison with aluminium electrolytic devices.

However if a cost analysis is performed, taking into account OxiCap's surface mount processing capability, the increased manufacturing yield and resultant reduction in customer complaints, the niobium oxide technology provides some very significant advantages.

NOJ OxiCap capacitors operate between -55 and +105C.

Lower ESR NOS series devices offer performance down to 35mohm (such as the latest 330uF 4V D case), and a temperature rating up to 125C.

Small and low profile case sizes (2, 1.5 and 1.2mm) are also available for space-constrained applications in SMD E case sizes.

Parts can be used up to 80% of rated voltage.

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