NASA Office of Logic Design

NASA Office of Logic Design

A scientific study of the problems of digital engineering for space flight systems,
with a view to their practical solution.


The NASA ASIC Guide: Assuring ASICs for SPACE

Appendix Four: Failure Analysis

Objective:

To present the concept of failure analysis for ASIC work and for use as an example methodology.

Failure Analysis (F/A) takes place after you have discovered an ASIC-related failure. The failure may actually originate at any of the following places:

ASIC failure analysis determines the cause of the failure. Although the visible failure effect may be in the ASIC, the cause may be external to the ASIC. When verified within the ASIC, F/A continues on the device. If the device passes all specifications and the failure cannot be found in the ASIC, then failure analysis must focus on other parts of the circuit surrounding the ASIC. Formally stated: failure analysis examines electronic parts to determine the cause of performance variations outside previously established limits, for the purpose of identifying failure mechanisms and failure activating causes.

Because of the high cost, F/A usually cannot be performed on every failed part. In response, QPL and QML have devised a system to account for expected failures due to random process variations. Thus engineers need perform F/A only when the failure is most likely due to a systemic (i.e. recurring and correctable) problem. Failures assumed due to random errors are expressed as a percentage of parts from a given lot, called the lot tolerance percent defective (LTPD), and from a given screen, called the percent defective allowable (PDA). This approach saves significant money by foregoing F/A on statistically expected part failures that have no remedy, due to their random nature. However, some failures that forego analysis could result from subtle but correctable problems in the fabrication process if the LTPD and PDA are not statistically accurate. Therefore, determining when and when not to perform F/A calls for sound engineering judgment.

Major Tasks in Failure Analysis

F/A consists of logical and systematic examination of the failed part in order to identify and analyze the failure mode and mechanism and to recommend an appropriate corrective action to prevent recurrence of the failure. This procedure breaks into five major tasks:

FAILURE ANALYSIS LABORATORY WORK FLOW

Many examinations and tests are used to systematically deduce the cause of a failure. They can be broken into four types:

Examinations and tests used for each of these categories are outlined below, along with the contents of the F/A report.

Failure Confirmation Examinations and Tests

Nondestructive Examinations And Tests

Semidestructive Examinations And Tests

Destructive Examinations And Tests

FAILURE ANALYSIS REPORT

The failure analysis report, together with the analysis results and conclusions, will cover all significant measurements and data including optical and SEM photographs necessary to prove the determination of cause of failure. Recommendation for corrective action is the last significant part of the failure analysis report.


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