Journal of SMT Article

SURFACE MOUNT MULTILAYER CERAMIC CAPACITORS FOR HIGH VOLTAGE MEDICAL APPLICATIONS

Authors: J. Bultitude, P. Gormally, J. Rogers, and J. Jiang
Company: Vishay Vitramon Inc.
Date Published: 7/7/2006   Volume: 19-3

Abstract: External Defibrillators and many other types of medical device equipment often must deliver high voltages or have provisions to isolate the high voltage from the lower voltage electronics. Typically leaded through-hole type capacitors or an over coating is used in the high voltage sections of the board to avoid arc over but this makes it difficult for designers to reduce the circuit board real estate. This presentation describes the performance of more reliable higher voltage surface mount capacitors that will allow further reductions in board space.

High voltage multilayer ceramic capacitors (MLCCs) rated for use at 500Vdc or higher, and having dielectric withstanding voltages above 1000V, have traditionally been manufactured with thick actives to increase the average voltage breakdown and achieve reliable performance in applications such as portable defibrillators and medical diagnostic equipment. When a high voltage potential is applied, typically over 1000V, an arc-over between the terminals may result so larger case sizes with more separation between terminals have been used to prevent arcover occurrence.

In an effort to decrease the case size of higher voltage MLCCs the voltage breakdown performance of improved 1206 and 1812 capacitor designs was measured in air and inert fluid. New designs yielded significant improvement in arc-over suppression and average voltage breakdown levels.

These results are presented together with the withstanding voltage for lightning surges. Parasitic measurements of ESR, impedance, capacitance and series inductance of the improved and standard designs are also compared.

The reliability of the improved designs was verified by life testing. The improved performance allows smaller case size capacitors to be used in high voltage applications. The improved designs will reduce board space requirements by up to 50% whilst not compromising breakdown voltage.

Key words: high voltage, MLCCs, arc-over.



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