Failure-Mechanism-Driven Reliability Monitoring
(Revision of JESD659A, September 1999)
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JEDEC Standard 659B
FAILURE-MECHANISM-DRIVEN RELIABILITY MONITORING
CONTENTS Page Introduction 1 Scope 2 Terms and definitions 3 Process controls 4 Identifying failure mechanisms 5 When to establish a monitor 6 What a monitor includes 7 Control action system 8 Monitor optimization ii 1 1 3 3 4 4 5 6
Annex A (informative) Differences between JESD659B and JESD659A
JEDEC Standard 659B
FAILURE-MECHANISM-DRIVEN RELIABILITY MONITORING Introduction This standard presents a methodology for monitoring component and subassembly reliability. It can be of use to suppliers and users interested in known reliability as an attribute of the component through the production life. Under this standard, the suite of metrics is tailored to monitor the failure mechanisms which limit the reliability. This is distinguished from a stress-driven monitor approach in which a fixed suite of acceptance stresses or other testing are prescribed and applied without customization according the failure mechanisms for the component or subassembly.
JEDEC Standard No. 659B Page 1
FAILURE-MECHANISM-DRIVEN RELIABILITY MONITORING (From JEDEC Board ballot JCB-07-19, formulated under the cognizance of JC-14.3 Committee on Silicon Devices Reliability Qualification and Monitoring.)
This standard describes essential requirements for a reliability monitor for components and subassemblies based on the measurement of failure mechanisms which limit reliability. It applies through the postqualification production period. Both intrinsic (wearout and systematic) and extrinsic (defect-based) sources of failure are addressed.
Terms and definitions
For the purposes of this standard, the following definitions apply. Definitions marked by a asterisk (*) are taken from EIA-557-A, Statistical Process Control Systems. They are replicated here for
completeness. characteristic*: A distinguishing feature of a process or its output on which variables or attributes data can be collected. common cause*: A source of natural variation that affects all the individual values of the process output being studied. In control chart analysis it appears as part of the random process variation. control limits*: The maximum allowable variation of a process characteristic due to common causes alone. Variation beyond a control limit may be evidence that special causes affecting the process. Control limits are calculated from process data and are usually represented as a line (or lines) on a control chart. They are not to be confused with engineering specification limits. critical failure mechanism: In semiconductor devices, any potential physical failure mechanism that exhibits one or more of the following: intermittency (e.g., bond lifts), increasing failure rate (e.g., electromigration), and inconsistent or unpredictable failure kinetics (e.g., stress-induced metal voiding) extrinsic failure mechanism: (1) A failure mechanism caused by an error occurring during the design, layout, fabrication, or assembly process or by a defect in the fabrication or assembly materials. (2) A failure mechanism that is directly attributable to a defect created during manufacturing. failure: (1) The loss of the ability of a component to meet the electrical or physical performance specifications that (by design or testing) it was intended to meet. (2) A component that has failed. failure mechanism from fabrication processes: A physical failure mechanism in which all products with the same wafer fabrication process, design rules, and processing line are treated as a homogeneous population for the purpose of statistical reliability monitoring independent of package technology, material, construction, and type.
JEDEC Standard No. 659B Page 2
Terms and definitions (cont??d)
failure mechanism from assembly: A physical failure mechanism in which all products with the same assembly technology, including assembly material, assembly construction, and package type and built on the same assembly line are treated as a homogeneous population for the purpose of statistical reliability monitoring independent of the fabrication process and line. intrinsic failure mechanism: (1) A failure mechanism caused by a natural deterioration in the materials or the manner in which the materials are combined during fabrication or assembly processes that are within specification limits. (2) A failure mechanism attributable to natural deterioration of materials processed per specification. node*: A definable point in the process at which form, fit, or function of the product or service is altered. nonconformity*: A specific occurrence of a condition that does not conform to specification. Such an occurrence is sometimes called a
discrepancy. parameter: A measurable characteristic. physical failure mechanism: A physical or chemical process that ultimately results in failure. process*: (1) A combination of people, procedures, methods, machines, materials, measurement equipment, and/or environment for specific work activities to produce a given product or service. (2) A repeatable sequence of activities with measurable inputs and outputs. sample:* A set of individuals taken from a population. special cause; assignable cause:* A source of variation that is intermittent, unpredictable, or unstable, and affects only some of the individual values of the process output being studied. statistical reliability monitoring (SRM): A statistically based methodology for monitoring and improving reliability involving identification and classification of failure mechanisms, development and use of monitors, and investigation of failure kinetics, allowing prediction of failure rates at use conditions. statistical reliability monitor family (SRMF): A product or group of products whose process similarities make them a homogeneous population for the purpose of statistical reliability monitoring. A homogeneous population of product from one SRMF shall have similar propensity towards the physical failure mechanisms being monitored when that product is stressed by accelerated tests or operated in its intended system application. Each product in an SRMF will have the same failure rate for each mechanism only when the factors affecting a failure mechanism are identical for each product type. variables data*: A measure of a characteristic where every value within a given interval is possible.
JEDEC Standard No. 659B Page 3
The supplier shall define a Statistical Process Control (SPC) system for all critical process nodes in accordance with EIA-557-A, Statistical Process Control Systems. This shall include establishing critical equipment capabilities, preventive maintenance, and calibration procedures. SPC metrics can intersect with those used for monitoring reliability, but are not required to do so. An SPC system alone might not address all requirements for a failure-mechanism driven reliability monitor program.
Identifying failure mechanisms
The supplier shall assess the failure mechanisms which contribute to the failure rate and institute respective monitors for those mechanisms. The identification of failure mechanisms may be based on mechanisms observed during development characterizing product sensitivities or process capabilities, mechanisms observed during qualification, mechanisms identified as part of Failure Mode and
Effects Analysis (FMEA), or mechanisms observed in previous test or field experience with products using like processes, materials set, or tooling and production facilities. JEP131 provides guidance on FMEA. Stress-driven qualifications (e.g., JESD47) and evaluations in which sampling is structured to show compliance to an acceptance criterion without generating failures will not provide an adequate basis for identifying the set of reliability-limiting failure mechanisms for a component. See section 6 regarding continuing acceptability to the original qualification criteria. The supplier shall be able to identify the rationale for the adequacy of the set of failure mechanisms identified for monitoring. The failure mechanisms requiring monitoring shall be reassessed for completeness and appropriateness when the process is changed or the product undergoes modifications which may alter its sensitivity to the existing process.
JEDEC Standard No. 659B Page 4
When to establish a monitor
A monitor for each failure mechanism which contributes non-trivially to the failure rate for the component shall be established. Non-trivial contributions shall be ascribed to critical failure mechanisms and systematic process risks as well as to extrinsic (defect-based) detractors that contribute significantly to the overall failure rate. Since extrinsic (defect-based) detractors may exist at trivial non-zero levels, a threshold of significant contribution at 10% of the overall failure rate expected in the field is recommended. Monitors may take any of several forms. Common forms are as in-process metrics and as product-level life tests or accelerated stress tests. Some monitors may be used to address more than one failure mechanism, e.g., a functional stress on an integrated product designed to monitor multiple extrinsic failure mechanisms. The vehicle for the monitor measurement shall be the product or another vehicle which shares the risk for this failure mechanism by similarity in process and construction (i.e., from the same SRMF).
What a monitor includes
For mechanisms needing a monitor (See Section 5), this section identifies features that monitor shall include. Sampling for the respective monitors shall be sufficient to allow the supplier to identify an excursion to the total component failure rate (driven by the composite of failure mechanisms). Sampling for any given monitor should be scaled to yield non-zero fallout (attributes monitors) or sufficient parametric shift for extrapolation to failure (variables monitors) as an opportunity for learning enablement and to validate the continuing presence, abatement, or elimination of particular
NOTE 1 To yield non-zero results at levels compatible with a component failure rate, monitors for intrinsic failure mechanisms typically will require smaller samples than those for extrinsic failure mechanisms do. As such, sampling for extrinsic failure mechanisms may require the aggregation of monitor data across broader sampling (especially in time). The aggregation of extrinsic data should be confined to no more than an annual basis; shorter periods are encouraged. NOTE 2 When a monitor is designed to measure well beyond the required minimum and no discernable failures (for attributes monitors) or shifts (for parametric monitors) are produced in a substantive sample history, it may be impractical to force non-zero data and unnecessary to do so for the purpose of measuring variations over time.
Monitors shall include targets which reflect acceptable levels. Ideally, these targets directly correlate to quantified failure rate levels. Regardless of whether they have an established correlation, the supplier shall provide for the quantification of the impact when the total component failure rate is in jeopardy for an excursion as signaled by the combined monitors. Regardless of the qualification approach used, targets for a qualified device shall be in compliance with the qualification acceptance criteria used or equivalent.
JEDEC Standard No. 659B Page 5
What a monitor includes (cont??d)
For failure mechanisms from fabrication processes that require a monitor, each wafer fabricator shall have its own monitor or SRMF. For failure mechanisms from assembly that require a monitor, each assembly site monitor or SRMF shall have its own monitor or SRMF. For mechanisms requiring a monitor and driven by the combined effects of wafer fabrication and assembly, each combination of fabricator and assembly site shall have its own monitor or SRMF.
Control action system
The supplier's control system shall address situations in which characteristics reach or exceed statistical warning limits or characteristics exceed the control limits. The supplier's control action system will: Document the definition of nonconformities as well as the procedure used to identify, verify, and determine the cause of nonconformities reported. Corrective actions shall remedy the situation causing the nonconformity without adversely affecting the reliability of the product/program. These corrective actions must be documented. Establish reasonable and effective time periods for responding to nonconformities. Evaluate the corrective actions for meeting response time, achieving scheduled completion of planned
activities, and bring the situation back into statistical control. Identify and disposition product affected by nonconformities. The supplier shall provide timely customer notification of significant changes in the monitor results and corrective actions being taken to minimize product jeopardy.
JEDEC Standard No. 659B Page 6
Where new failure mechanisms emerge or are spotlighted by customer experience, suppliers shall institute monitors to assure insight about the full complement of failure mechanisms. Deployed monitors may also be eliminated when ? ? ? The risk factor for a failure mechanism is eliminated (as by a materials or tooling change) Data shows a failure mechanism has become an irrelevant contributor to the component failure rate A substitute metric is deployed
If a supplier replaces a packaged device monitor with a monitor implemented earlier in the manufacturing process, objective evidence must be available which validates that the new monitor is equally or more effective in detecting the failure mechanism as the existing monitor.
NOTE It is understood that certain in-line monitor data may be proprietary and not shared with the general public.
If a supplier proposes to eliminate an existing monitor without a replacement, there must be objective evidence that the failure mechanism has also been reduced to a trivial level.
JEDEC Standard No. 659B Page 7
Annex A (informative) Differences between JESD659B and JESD659A This table briefly describes most of the changes made to entries that appear in this standard, JESD659B, compared to its predecessor, JESD659A (September 1999). If the change to a concept involves any words added or deleted (excluding deletion of accidentally repeated words), it is included. Some punctuation changes are not included. JESD659B is a significant rewrite and simplification. A top-level description of the substantive changes follows (relative to the 659B section numbers). 1. Scope Consolidated and simplified Purpose & Scope from 659B; narrowed scope to reliability monitor activity only 2. Definitions Removed uncited definitions; introduce extrinsic failure mechanism and intrinsic failure mechanism; include existing JEDEC definition for special cause 3. Process Controls This section is based on ??Critical Equipment and Facilities?? in 659A. Requirements are clarified and distinguished from reliability monitoring. 4. Identifying failure mechanisms In combination simplify, generalize, and reformat 659A content in ??General Requirements,?? ??SRM Family Selection,?? and ??Sampling Plans.?? 5. When to establish a monitor
See changes in 4. 6. What a monitor includes See changes in 4. 7. Control action system Groomed language and format of existing content. 8. Monitor optimization Provided more detail about the path to eliminating a monitor. 9. ??Self audit?? section of 659A eliminated.
JEDEC Standard No. 659B Page 8
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