The Reliability Cycle?

DfR Solutions has published a white paper entitled The Reliability Cycle: Understanding the Booms and Busts of Reliability in Electronics. In the 1950s and 1960s, large OEMs built-up impressive reliability programs in response to numerous reliability problems. The thesis of the paper is that large OEMs are reducing reliability staffs to reduce overhead costs. The paper further statest that companies are now vulnerable to major reliability problems as component and contract manufactuer suppliers are entrusted with product reliabilty. After some major problems, the reliabilty cycle pendulum will swing back to the other side.

Certainly no one has a crystal ball in this area. While I do see increased vulnerability in depending on suppliers, the reliabilty cycle (?) will not swing back to the 1960s. The days of reliability predictions based on a generic formula are gone (limited usefullness). The days of standard reliability qualification testing for either parts or systems is also gone (can't get the product to market). Instead what is needed is knowledge - or as Edward Deming would say profound knowledge. The best way to proceed in these fast paced times is hire, develop, nurture reliability masters with a deep knowledge of the physics of components and failure mechanisms. This type of knowledge is more important than knowledge in traditional reliability statistics. From this profound knowledge come keen observations and indentification of tests pin-pointed to answer specific questions. Some of these tests are simply ad hoc tests for rapid asessments. Assessments come in a timely manner. Useless tests can be ignored. Where to find these individuals? Since this specialty area is not taught in schools, first look for the old timers - those who have seen many failures. Secondly, start a mentoring program for the younger engineers who want this to be their life's work. Avoid those who are the fast track to management and will quickly leave the field. Also, encourage networking in professional organizations so that we can all learn from other's experience. The old does sometimes cycle back but it usually returns in a different form.

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