Reassuring reliability for chip capacitors in airborne applications

Syfer's Marketing Manager, Chris Noade, commented: “This range is aimed squarely at applications in aircraft, where much of the equipment is powered by lines running at 115Vac 400Hz.” The devices are designed to take into account associated voltage and frequency transients as specified in MIL-STD-704, Noade explained.

Multilayer chip capacitors are typically supplied with a dc rating only, such that the designer has to apply whatever he considers an appropriate de-rating. There are a number of factors to consider including reliability, the rms vs peak voltage trade-off and operating frequency.

Now Syfer has conducted reliability testing on its parts specifically to ensure the required performance in 115Vac 400Hz device applications. The higher frequency rating can lead to self heating due to losses in the capacitor, creating additional stresses on the parts. But Syfer's characterisation work shows the heating effects are limited to an acceptable level of a 25°C rise with neutral mounting at room temperature.

Accelerated life testing has also been carried out at maximum rated voltage and frequency, and at elevated temperatures, to ensure reliability. With the assurance of higher reliability, avionics designers today do not need to spend time establishing an equivalent dc working voltage for MLCCs but need only consider physical size, capacitance and dielectric type.

Syfer's avionics MLCCs are available in a choice of X7R or ultra-stable C0G dielectrics, with capacitance values from 4.7nF to 100nF and 330pF to 15nF respectively.

Package size, depending on capacitance required, ranges from 0805 to 2220. Termination options include nickel barrier for RoHS compliance and tin/lead for RoHS-exempt application where developers may be concerned about the possibility of tin whiskers, which can be regarded as possible cause of short circuits. FlexiCap™, Syfer's proprietary flexible polymer termination option, offers increased security against the possibility of cracking due to substrate flexing during board assembly, depanelisation or temperature cycling during operation.

The MLCCs are manufactured at Syfer’s Norwich, UK facility, and are readily available in production quantities on a standard lead time of 7 weeks.