Wear-out of MLCC?

Passive Component Magazine, March 2010, reported on the 2010 CARTS held in New Orleans on March 16. Clive Hendricks, Intel Corporation, is quoted regarding high value multi-layer ceramic capacitors from 2.2uF to 100uF. The dielectric thicknesses have decreased to sub-micron thickness.

Clive Hendricks - "Up until recently, failure due to dielectric wear-out was not a concern for the capacitors used to support CPUs, in fact, our reliability models showed that the capacitors could be used for thousands of years before the insulation resistance would begin to degrade ... in the last five years we have noticed a disturbing trend - as the capacitance density has increased, the usable life has reduced to hundreds, then tens and now even less than five years".

As the market is demanding more energy density in capacitors of all types, the result is decreasing margins for reliability. Historically, the multi-layer ceramic capacitor (MLCC) use-rating is 10% of the breakdown voltage to achieve a reliability margin. This means that the breakdown voltage must exceed 80V/um (ref. 1). As the dielectric spacings are reduced there will be pressure to reduce that reliability margin. At higher temperatures, the use-rating must be even more conservative. There is also a decreasing trend in the number of dielectric grains per layer (ref 1). Fewer grains per layer can result in increased probability of a defect which can bridge the internal electrodes. Reducing the grain size also reduces the K of the dielectric.

It is sometimes assume by the circuit designer that all the parts found in the supplier's catalog have equal probability of failures due to defects. It would be prudent however not to design-in the parts with the highest CV values as these parts are pushing the technology envelope.

With regard to inherent wear-out mechanisms, the same unsettling trends are also appearing in high density VLSI design as well PCB technology (the subject of the future blog entry). Only 10 years ago, electronic assemblies did not have any inherent wear-out mechanisms except in a few special circumstances such as power electrolytic capacitors and batteries or extreme environments. Now it appears that OEMs must pay more attention to wear-out mechanisms. The component suppliers will also be challenged to supply predictive reliability models along with the component. As these reliability concerns become more known, could we be seeing a renewed emphasis on reliability engineering within electronic design companies.

Reference 1: Thin Film MLCC, M. Randall, et al.,2007 CARTS Symposium Proceedings, March 2007