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Determination of extrinsic (early) failure density

IP.com Disclosure Number: IPCOM000131669D
Published in the IP.com Journal: Volume 5 Issue 11B (2005-12-10)
Included in the Prior Art Database: 2005-Dec-10
Document File: 2 page(s) / 98K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

During reliability investigations an intermixture of intrinsic and extrinsic failures is often observed (see Fig. 1). For the intrinsic properties of devices many experimental setups, test structures and evaluation models are generated to determine the failure rate at product conditions. The extrinsic failure rate, which is the main cause for field returns, is determined by a bimodal fit of the intrinsic and the extrinsic mode. The extrinsic density is then defined as the intersection point of those two fits. This method is based on a sufficient statistics in both failure modes, which allows a precise fit. Since the requirements in respect to early fails become more and more stringent, i.e. only very few such fails are allowed in typical reliability investigations, this method does no longer work in a stable mode. For the determination of extrinsic (early) failure density two steps are necessary: First an appropriate measurement setup, and second a stable procedure to distinguish between such early fails and regular intrinsic ones.

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Determination of extrinsic (early) failure density

Idea: Dr. Rainer Duschl, DE-Munich

During reliability investigations an intermixture of intrinsic and extrinsic failures is often observed (see Fig. 1). For the intrinsic properties of devices many experimental setups, test structures and evaluation models are generated to determine the failure rate at product conditions. The extrinsic failure rate, which is the main cause for field returns, is determined by a bimodal fit of the intrinsic and the extrinsic mode. The extrinsic density is then defined as the intersection point of those two fits. This method is based on a sufficient statistics in both failure modes, which allows a precise fit. Since the requirements in respect to early fails become more and more stringent, i.e. only very few such fails are allowed in typical reliability investigations, this method does no longer work in a stable mode.

For the determination of extrinsic (early) failure density two steps are necessary: First an appropriate measurement setup, and second a stable procedure to distinguish between such early fails and regular intrinsic ones.

The core of the new method is the precise determination of the intersection point of mixed statistical distributions, based on the fit of the major distribution, calculation of a confidence interval for this distribution and a successive elimination of the events of the minor distribution(s), followed by a recalculation of the remaining main distribution until all remaining data points stay within the confidence interval.

The method is based on the separability of intrinsic and extrinsic failures, i.e. the independence of the two different modes responsible for the failures. In the transition range the intrinsic distribution is strongly affe...