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:
- the ASIC
- other active components in the circuit around the ASIC
- passive components in the circuit around the ASIC
- circuit interconnect
- operation of the circuit with the ASIC outside of specified operating conditions of voltage, current, temperature, etc.
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:
- Verify the failure.
- Determine failure mode (i.e., the symptoms or the way a part has failed).
- Diagnose the failure mechanism (i.e., the physical cause of the failure).
- Design stress conditions to perform a simulation (i.e., a reproduction of the failure), if needed.
- Suggest corrective actions to prevent or minimize the possibility of similar or like failures.
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:
- failure confirmation
- nondestructive (parts are not physically altered)
- semidestructive (parts that are physically altered, but should still function)
- destructive (parts are physically altered and will no longer function)
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
- Part Failure History: The F/A group carefully reviews all information associated with the failed part and how it failed prior to the examination and testing of the part.
- External Visual Examination: The identification markings and any package discrepancies on the suspect part are recorded and photographed as needed.
- Electrical Characterization: This includes curve tracer measurements, functional tests, parametric tests, or any environmental tests as required to verify the reported failure.
Nondestructive Examinations And Tests
- Radiographic Examination: Two X-ray views of the package are taken for possible internal anomalies and for assisting in opening of the package.
- Hermeticity Tests: Gross and fine leak tests are conducted to check the package seal integrity.
- Particle Detection Test: The particle impact noise detection (PIND) test is performed when particle(s) is suspected.
Semidestructive Examinations And Tests
- Package Gas Analysis: This test qualitatively and quantitatively analyzes the gaseous components in the package cavity and especially the water-vapor content.
- Package Opening and Internal Examination: Delidding of the package and internal optical and scanning electron microscopic (SEM) examinations are performed to identify any physical symptoms of the failure or any manufacturing defects.
- Emission Microscope Test: The emission microscope for multilayer inspection (EMMI) locates failure sites having current leakages down to 0.5 microamps (MA).
- Electromechanical Probing: This technique isolates the failure area when none of the other techniques (e.g., the emission microscope, the liquid crystal or the SEM voltage contrast) have been successful in locating the failure site.
Destructive Examinations And Tests
- Material Analysis: The SEM energy dispersive spectroscopy (EDS) performs qualitative and quantitative elemental composition analysis of contaminants or any suspect materials. EDS provides a hard copy listing of all analytical findings and/or photographs with elements identified by individual colors.
- Removal of Layers: Chemical etching or dry plasma etching are used to remove layers (e.g., glassivation, metallization, oxide) in order to uncover the failure site obscured by these materials.
- Cross-Sectioning: This technique exposes the interior of a suspect solid material for further examination and tests.
- Mechanical Tests: Destructive or nondestructive wire bond pull tests, or die shear tests, are performed as needed for failure (or defect) identification.
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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Last Revised:
February 03, 2010
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