Electronics Guide

Failure Analysis Workflow

A systematic approach ensures thorough investigation and accurate conclusions:

• Problem definition: Clearly documenting the failure symptoms, operating conditions, and history of the failed device
• Information gathering: Collecting relevant data including field conditions, lot history, design specifications, and similar failure reports
• Non-destructive examination: Performing external visual inspection, electrical testing, and imaging techniques that preserve the sample
• Hypothesis formation: Developing theories about potential failure mechanisms based on initial observations
• Destructive analysis: Systematically deconstructing the sample to expose internal structures and validate hypotheses
• Root cause determination: Identifying the fundamental cause, not just the symptom, of the failure
• Corrective action recommendation: Proposing design, process, or material changes to prevent recurrence

Common Failure Categories

Electronic failures typically fall into several broad categories:

• Manufacturing defects: Issues introduced during fabrication or assembly, such as contamination, voids, or misalignment
• Design deficiencies: Inadequate margins, improper material selection, or insufficient consideration of operating conditions
• Overstress failures: Damage from electrical, thermal, or mechanical stress exceeding device limits
• Wear-out mechanisms: Gradual degradation over time from fatigue, corrosion, electromigration, or other cumulative effects
• Latent defects: Damage that does not immediately cause failure but reduces device lifetime or reliability
• Environmental damage: Failures caused by moisture, contamination, radiation, or other external factors

Failure Rate and the Bathtub Curve

Electronic component failure rates typically follow a characteristic pattern known as the bathtub curve:

• Infant mortality region: Early failures caused by manufacturing defects, screened out through burn-in testing
• Useful life region: Period of relatively constant, low failure rate representing random failures
• Wear-out region: Increasing failure rate as devices approach end of life due to cumulative degradation mechanisms

Understanding where failures occur on this curve helps determine whether the root cause is process-related, design-related, or inherent to the technology.

DPA Test Sequence

A complete DPA follows a prescribed sequence of tests and examinations:

• External visual inspection: Examining package condition, marking quality, and lead integrity under magnification
• Radiographic inspection: X-ray imaging to verify internal wire bonds, die attach, and absence of foreign material
• Particle impact noise detection (PIND): Acoustic test to detect loose particles inside hermetic packages
• Hermeticity testing: Fine and gross leak testing to verify package seal integrity
• Decapsulation: Chemical or mechanical removal of package material to expose the die
• Internal visual inspection: Detailed examination of die surface, metallization, and wire bonds
• Bond pull testing: Measuring wire bond strength by pulling bonds to failure
• Die shear testing: Evaluating die attach strength by shearing the die from the substrate
• Scanning electron microscopy: High-magnification imaging of critical features

DPA Standards and Requirements

Several military and industry standards govern DPA procedures:

• MIL-STD-883: Test methods and procedures for microelectronics, including Method 5009 for DPA
• MIL-STD-750: Test methods for semiconductor devices, including discrete components
• MIL-PRF-38535: General specification for integrated circuits requiring DPA
• JEDEC standards: Industry standards defining test methods and acceptance criteria
• Customer specifications: Application-specific requirements for critical programs

Sample sizes and acceptance criteria depend on lot size, component criticality, and applicable specifications.

Common DPA Findings

DPA frequently identifies workmanship and material issues:

• Wire bond defects: Heel cracks, ball lift, intermetallic voiding, or insufficient bond strength
• Die attach voids: Gaps between the die and substrate that can cause thermal issues
• Foreign material: Particles, fibers, or contamination inside the package
• Metallization defects: Scratches, corrosion, or incomplete coverage on the die
• Passivation cracks: Damage to the protective oxide layer on the die surface
• Package defects: Lid seal issues, lead frame problems, or molding compound voids

SEM Operating Principles

Understanding SEM operation helps analysts select appropriate imaging conditions:

• Electron source: Thermionic (tungsten or LaB6) or field emission sources generate the electron beam
• Electron optics: Electromagnetic lenses focus and control the beam diameter and position
• Scanning system: Deflection coils raster the beam across the sample surface
• Signal detection: Various detectors capture electrons and photons emitted from the sample
• Vacuum system: High vacuum maintains electron beam integrity and sample cleanliness

SEM Imaging Modes

Different detection modes provide complementary information about the sample:

• Secondary electron imaging: Provides topographic contrast, showing surface features with high resolution and depth of field
• Backscattered electron imaging: Generates atomic number contrast, distinguishing materials of different compositions
• Voltage contrast: Reveals electrically active regions by detecting voltage-induced secondary electron yield variations
• Electron beam induced current (EBIC): Maps junction locations and identifies defects in semiconductor devices
• Cathodoluminescence: Detects light emission from materials excited by the electron beam

Sample Preparation for SEM

Proper sample preparation is critical for obtaining useful images:

• Cleaning: Removing contamination that could obscure features or cause charging
• Decapsulation: Exposing internal structures through chemical, plasma, or mechanical methods
• Cross-sectioning: Cutting and polishing samples to reveal subsurface structures
• Conductive coating: Applying thin metal or carbon coatings to non-conductive samples to prevent charging
• Mounting: Securing samples to holders that provide electrical grounding and proper orientation

SEM Applications in Failure Analysis

SEM is invaluable for examining a wide range of failure modes:

• Fracture analysis: Examining broken surfaces to determine failure mode (brittle, ductile, fatigue)
• Contamination identification: Locating and characterizing foreign material on device surfaces
• Corrosion investigation: Analyzing corrosion products and attack patterns
• Electromigration damage: Observing metal migration, void formation, and hillock growth
• Wire bond evaluation: Examining bond interfaces, intermetallic formation, and failure sites
• Solder joint analysis: Investigating crack propagation, voiding, and intermetallic compound growth

EDS Operating Principles

EDS detection and analysis involve several key aspects:

• X-ray generation: Primary electrons eject inner shell electrons, and characteristic X-rays are emitted when outer electrons fill the vacancies
• Detector operation: Silicon drift detectors or lithium-drifted silicon detectors convert X-ray energy to electrical signals
• Energy resolution: The ability to distinguish X-rays of similar energies, typically 125-140 eV for modern detectors
• Detection limits: Generally capable of detecting elements present at concentrations above 0.1-1 weight percent
• Analysis volume: X-rays originate from a tear-drop shaped interaction volume, limiting spatial resolution

EDS Analysis Modes

EDS data can be acquired and displayed in several formats:

• Point analysis: Collecting a spectrum from a specific location to identify elements present
• Line scan: Acquiring spectra along a line to show compositional variations
• Elemental mapping: Creating images showing the spatial distribution of selected elements
• Quantitative analysis: Calculating elemental concentrations using standards or standardless methods
• Spectrum imaging: Collecting complete spectra at each pixel for comprehensive compositional mapping

EDS Applications in Failure Analysis

EDS provides critical compositional information for failure investigation:

• Contamination identification: Determining the elemental composition of foreign material
• Corrosion product analysis: Identifying elements involved in corrosion mechanisms
• Intermetallic compound characterization: Analyzing phases formed at solder joints or wire bonds
• Material verification: Confirming that correct materials were used in construction
• Diffusion studies: Tracking elemental migration across interfaces
• Plating thickness and composition: Analyzing coating quality and uniformity

EDS Limitations and Considerations

Analysts should understand EDS constraints for proper interpretation:

• Light element detection: Elements lighter than sodium are difficult to detect and quantify
• Peak overlap: Some elements have overlapping characteristic X-ray energies
• Matrix effects: Absorption and fluorescence can affect quantitative accuracy
• Surface sensitivity: Information depth of 1-3 micrometers limits analysis of thin layers
• Beam damage: Sensitive materials may be altered by electron beam exposure

FIB Operating Principles

Understanding FIB operation enables effective application:

• Ion source: Liquid metal ion sources, typically gallium, provide a bright, focused ion beam
• Ion optics: Electrostatic lenses focus the beam to spot sizes below 10 nanometers
• Sputtering: Ion bombardment removes material through physical sputtering
• Imaging: Secondary electrons generated by ion impact provide imaging capability
• Gas injection: Precursor gases enable selective deposition or enhanced etching

FIB Cross-Sectioning

FIB enables precise cross-sections at exact locations of interest:

• Site-specific sectioning: Targeting specific defects or features identified by other techniques
• High-quality surfaces: Producing smooth cross-section faces suitable for high-resolution imaging
• Real-time monitoring: Observing the cross-section as milling progresses to stop at the desired depth
• Minimal damage: Localized material removal preserves surrounding structures
• Three-dimensional reconstruction: Serial sectioning enables 3D visualization of internal structures

FIB Circuit Edit

FIB systems can modify integrated circuits for design verification or failure analysis:

• Metal cut: Severing conductors to isolate circuit elements
• Metal deposition: Creating new connections using tungsten or platinum deposition
• Via formation: Milling through dielectric layers to access buried conductors
• Design validation: Making design changes on silicon to verify proposed modifications
• Failure isolation: Systematically disconnecting circuits to locate failure sites

TEM Sample Preparation

FIB is the preferred method for preparing site-specific TEM samples:

• Lift-out technique: Extracting a thin lamella from a specific location for TEM analysis
• In-situ lift-out: Using a micromanipulator inside the FIB chamber
• Ex-situ preparation: Combining FIB with external sample handling
• Final thinning: Reducing sample thickness to electron transparency (less than 100 nm)
• Low-energy polishing: Minimizing surface damage and gallium implantation

Dual-Beam FIB-SEM Systems

Modern systems combine FIB and SEM capabilities in a single platform:

• Complementary imaging: SEM provides high-resolution, non-destructive imaging while FIB enables cross-sectioning
• Real-time monitoring: Observing FIB operations with the electron beam to control process endpoints
• Reduced damage: Using electron beam imaging minimizes ion beam damage to sensitive areas
• EDS integration: Combining compositional analysis with cross-sectioning capability
• EBSD capability: Electron backscatter diffraction for crystallographic analysis

Thermal Cycling Testing

Thermal cycling exposes products to repeated temperature transitions:

• Temperature range: Typically -55 degrees Celsius to +125 degrees Celsius for military applications, narrower ranges for commercial products
• Transition rate: Controlled ramp rates, usually 10-20 degrees Celsius per minute, that allow the product to reach thermal equilibrium
• Dwell time: Hold periods at temperature extremes ensuring complete thermal soaking
• Cycle count: Number of cycles depends on expected field life and acceleration factors
• Failure monitoring: Continuous or periodic electrical monitoring to detect intermittent or permanent failures

Thermal Shock Testing

Thermal shock provides more severe stress through rapid temperature transitions:

• Rapid transitions: Transfer times typically less than 10-15 seconds between temperature extremes
• Air-to-air chambers: Using hot and cold chambers with elevator or basket transfer
• Liquid-to-liquid systems: Immersion in hot and cold fluids for maximum heat transfer
• Higher stress levels: Rapid transitions create larger temperature gradients and higher mechanical stress
• Shorter test duration: More aggressive testing may reveal failures in fewer cycles

Thermal Expansion Mismatches

Understanding CTE mismatches helps predict failure locations:

• Silicon vs. organic substrates: Large CTE difference between silicon dies (2.6 ppm/degree Celsius) and FR-4 PCBs (14-17 ppm/degree Celsius)
• Ceramic vs. plastic packages: Different package materials create varying stress conditions
• Component body vs. leads: Differential expansion causes lead stress during thermal excursions
• Solder joint stress: Shear strain in solder accommodating CTE differences between component and board
• Distance from neutral point: Stress increases with distance from the center of the component

Thermal Fatigue Failure Mechanisms

Thermal cycling induces characteristic failure modes:

• Solder joint cracking: Fatigue cracks initiating at stress concentrations and propagating through joints
• Wire bond heel cracking: Flexural fatigue at the weakest point of the bond loop
• Die cracking: Fracture of brittle silicon under excessive mechanical stress
• Delamination: Separation of package layers due to CTE mismatch and weak adhesion
• Plated through-hole failures: Barrel cracking from Z-axis expansion

Coffin-Manson Relationship

The Coffin-Manson equation relates thermal cycling parameters to fatigue life:

• Strain range dependence: Fatigue life decreases as cyclic strain range increases
• Temperature range effect: Larger temperature swings produce more damage per cycle
• Material constants: Fatigue ductility coefficient and exponent characterize material response
• Acceleration factors: Calculating equivalent field cycles from accelerated test conditions
• Life prediction: Estimating product lifetime based on expected field temperature profiles

Random Vibration Testing

Random vibration simulates the broadband excitation experienced in real environments:

• Power spectral density: Defining the test profile as power versus frequency
• Frequency range: Typically 20 Hz to 2000 Hz for most electronics applications
• GRMS level: Root-mean-square acceleration indicating overall severity
• Three-axis testing: Applying vibration sequentially in X, Y, and Z orientations
• Test duration: Determined by expected field exposure and acceleration factors

Sinusoidal Vibration Testing

Sine vibration characterizes resonant behavior and applies controlled stress:

• Resonance survey: Slowly sweeping frequency to identify resonant frequencies
• Sine dwell: Sustained excitation at specific frequencies to accumulate fatigue damage
• Sine sweep: Continuous frequency sweep at defined rate and amplitude
• Resonance tracking: Monitoring resonance shifts indicating structural degradation
• Transmissibility measurement: Quantifying amplification at resonant frequencies

Mechanical Shock Testing

Shock testing evaluates response to transient high-acceleration events:

• Classical shock pulses: Half-sine, sawtooth, and trapezoidal waveforms
• Shock response spectrum: Characterizing transient events by their effect on single-degree-of-freedom systems
• Drop testing: Simulating handling drops from specified heights
• Pyrotechnic shock: High-frequency, high-amplitude events from explosive separation
• Multiple axes: Testing in positive and negative directions of all three axes

Vibration Failure Mechanisms

Dynamic mechanical loading induces characteristic failures:

• High-cycle fatigue: Crack initiation and propagation from repetitive stress cycles
• Solder joint cracking: Fatigue failure of interconnections due to board flexure
• Lead breakage: Component leads failing from repeated bending
• Connector fretting: Contact degradation from micro-motion between mated surfaces
• Wire chafing: Insulation wear from contact with adjacent structures
• Fastener loosening: Loss of clamp force from vibration-induced rotation

Combined Environment Testing

Realistic stress combinations often reveal failures not found in single-environment tests:

• Temperature and vibration: Simultaneous application reveals synergistic effects
• Temperature, humidity, and vibration: Combined environments for accelerated testing
• Altitude and vibration: Reduced cooling effectiveness combined with mechanical stress
• Salt fog and vibration: Corrosive environments with mechanical loading
• Sequential versus simultaneous: Different failure modes may appear depending on test sequence

HAST Test Conditions

Standard HAST conditions provide aggressive acceleration:

• Temperature: Typically 110-130 degrees Celsius under pressure
• Relative humidity: 85% RH maintained at elevated pressure
• Pressure: 2-3 atmospheres to achieve target humidity at high temperature
• Test duration: Typically 96-264 hours depending on required acceleration
• Bias voltage: Optional application of operating bias to activate electrochemical mechanisms

Moisture-Related Failure Mechanisms

HAST accelerates several moisture-induced degradation processes:

• Corrosion: Electrochemical attack on metallization and bond pads
• Dendrite growth: Metal migration forming conductive paths between adjacent conductors
• Delamination: Moisture-induced separation at package interfaces
• Popcorn cracking: Rapid moisture vaporization causing package fracture during reflow
• Aluminum corrosion: Hydration of aluminum metallization on integrated circuits
• Mobile ion contamination: Activation of ionic contaminants affecting device parameters

HAST Equipment and Procedures

Proper equipment and procedures ensure valid test results:

• Pressure vessel design: Chambers capable of maintaining temperature, humidity, and pressure
• Temperature uniformity: Minimizing gradients across the test load
• Humidity control: Accurate measurement and control of moisture content
• Electrical connections: Hermetic feed-throughs for bias application and monitoring
• Sample preparation: Pre-conditioning and proper handling before testing
• Post-test evaluation: Electrical testing and physical analysis of stressed samples

Acceleration Factor Calculation

Relating HAST conditions to field exposure requires acceleration modeling:

• Temperature acceleration: Arrhenius relationship with activation energy specific to failure mechanism
• Humidity acceleration: Power law or exponential dependence on relative humidity
• Combined models: Peck model and Hallberg-Peck equation for temperature-humidity interactions
• Mechanism specificity: Different failure mechanisms have different acceleration factors
• Validation: Correlation with field data to verify acceleration assumptions

Electromigration Fundamentals

Understanding electromigration physics enables effective testing:

• Electron wind force: Momentum transfer from electrons to metal atoms causes directional atomic transport
• Diffusion paths: Atomic migration occurs along grain boundaries, interfaces, and through the bulk material
• Void formation: Atomic depletion creates voids that increase resistance and eventually cause opens
• Hillock formation: Atomic accumulation creates protrusions that may cause shorts
• Flux divergence: Failures occur where the atomic flux changes, such as at vias or grain boundary intersections

Electromigration Test Structures

Specialized test structures enable quantitative electromigration assessment:

• Straight line structures: Simple conductors for baseline characterization
• Via chains: Multiple vias in series to stress via interfaces
• Contact chains: Structures stressing metal-to-diffusion contacts
• Multi-level structures: Interconnect stacks replicating actual circuit configurations
• Kelvin structures: Four-point measurement for accurate resistance monitoring

Accelerated Electromigration Testing

Elevated stress accelerates electromigration for practical test durations:

• Current density: Typically 1-3 MA/cm squared, well above normal operating conditions
• Temperature: Elevated temperatures from 200-350 degrees Celsius depending on metallization system
• Black's equation: Relating median time to failure to current density and temperature
• Activation energy: Material-dependent parameter characterizing temperature sensitivity
• Current exponent: Power law exponent relating failure time to current density

Electromigration Prevention

Design and process techniques mitigate electromigration risk:

• Current density limits: Design rules limiting maximum current per unit width
• Redundant vias: Multiple vias in parallel to reduce per-via current
• Barrier metals: Refractory metal layers that block atomic diffusion
• Copper metallization: Higher electromigration resistance compared to aluminum
• Bamboo structures: Grain structures that span the conductor width, blocking grain boundary diffusion

TDDB Mechanisms

Several physical mechanisms contribute to dielectric degradation:

• Trap generation: Electrical stress creates defects within the dielectric that accumulate over time
• Percolation model: Random defect generation eventually forms a conducting path across the dielectric
• Anode hole injection: Hot electrons generate holes at the anode that damage the dielectric
• Hydrogen release: Bond breaking releases hydrogen that contributes to degradation
• Soft breakdown: Progressive increase in leakage current before hard breakdown

TDDB Test Methods

Accelerated testing characterizes dielectric reliability:

• Constant voltage stress: Applying fixed voltage until breakdown, measuring time to failure
• Ramped voltage stress: Increasing voltage until breakdown to determine intrinsic breakdown strength
• Constant current stress: Maintaining fixed tunneling current and measuring charge to breakdown
• Temperature acceleration: Elevated temperature reduces time to breakdown following Arrhenius behavior
• Voltage acceleration: Higher voltage exponentially accelerates breakdown

TDDB Test Structures

Dedicated structures enable statistical assessment of dielectric reliability:

• Large area capacitors: MOS capacitors for intrinsic oxide characterization
• Transistor arrays: Parallel transistors providing area scaling
• Antenna structures: Structures sensitive to plasma-induced damage during fabrication
• Thin and thick oxide: Separate evaluation of different dielectric thicknesses
• Multiple dies: Large sample sizes for statistical confidence

TDDB Modeling and Extrapolation

Relating accelerated test results to operating conditions requires careful modeling:

• Voltage acceleration models: E-model, 1/E model, and power law relationships
• Temperature dependence: Activation energies typically 0.5-0.8 eV for thermal SiO2
• Area scaling: Larger areas fail sooner due to weakest-link behavior
• Statistical distributions: Weibull distributions characterize failure time variability
• Lifetime prediction: Extrapolating to operating voltage and temperature for reliability projection

High-k Dielectric Considerations

Advanced gate dielectrics present unique TDDB challenges:

• Different breakdown physics: High-k materials may have different degradation mechanisms than SiO2
• Interface quality: Defects at high-k/silicon interface can accelerate breakdown
• Polarity effects: Different behavior under positive and negative gate bias
• Reliability characterization: Developing acceleration models for new materials
• Process sensitivity: Strong dependence on deposition conditions and post-deposition treatments

Hot Carrier Injection Testing

Hot carrier effects cause transistor parameter shifts over operating life:

• Mechanism: High-energy carriers cause interface damage and charge trapping
• Test conditions: Maximum substrate current stress accelerates degradation
• Parameter monitoring: Tracking threshold voltage, transconductance, and drain current
• Lifetime projection: Extrapolating from accelerated stress to operating conditions
• Design mitigation: Lightly-doped drain structures reduce hot carrier generation

Negative Bias Temperature Instability (NBTI)

NBTI affects PMOS transistors under negative gate bias at elevated temperature:

• Threshold voltage shift: Progressive increase in PMOS threshold voltage magnitude
• Recovery effect: Partial reversal of degradation when stress is removed
• Temperature sensitivity: Strong Arrhenius temperature dependence
• Voltage acceleration: Higher gate voltage accelerates degradation
• Circuit impact: Timing degradation and reduced noise margins

Stress Migration Testing

Stress migration causes void formation in metal interconnects without applied current:

• Driving force: Mechanical stress gradients cause atomic diffusion
• Test conditions: High temperature storage, typically 150-200 degrees Celsius
• Vulnerable structures: Wide metal lines transitioning to narrow vias
• Void formation: Vacancies accumulate at stress concentration points
• Prevention: Proper via design and metal encapsulation

Latch-up Testing

Latch-up is a potentially destructive condition in CMOS devices:

• Mechanism: Parasitic thyristor structure becomes triggered and conducts high current
• Trigger sources: Overvoltage on I/O pins, ionizing radiation, or transient events
• Test methods: I/O current injection and supply overvoltage per JEDEC standards
• Pass criteria: No latch-up at specified current levels
• Design prevention: Guard rings, substrate contacts, and layout rules

ESD Qualification Testing

Electrostatic discharge testing verifies protection against static electricity:

• Human Body Model (HBM): Simulating discharge from a person touching the device
• Charged Device Model (CDM): Simulating discharge of a charged device to ground
• Machine Model (MM): Simulating discharge from manufacturing equipment
• System-level ESD: IEC 61000-4-2 testing of complete products
• Classification levels: Defining component handling requirements based on ESD sensitivity

Corrective Action Process

Effective corrective action follows a disciplined methodology:

• Problem containment: Immediate actions to protect customers from defective products
• Root cause analysis: Thorough investigation to identify fundamental causes, not just symptoms
• Corrective action development: Identifying design, process, or material changes that address root cause
• Implementation planning: Developing schedules, responsibilities, and resource requirements
• Verification testing: Confirming that corrective actions eliminate the failure mode
• Effectiveness monitoring: Tracking results to ensure sustained improvement

8D Problem Solving

The 8D methodology provides a structured approach to corrective action:

• D1 - Team formation: Assembling cross-functional expertise to address the problem
• D2 - Problem description: Clearly defining the problem using quantitative data
• D3 - Containment actions: Protecting the customer while permanent solutions are developed
• D4 - Root cause analysis: Identifying the fundamental cause using appropriate tools
• D5 - Corrective action selection: Choosing permanent solutions that address root cause
• D6 - Implementation: Executing corrective actions with proper controls
• D7 - Prevention: Modifying systems to prevent recurrence in similar products or processes
• D8 - Team recognition: Acknowledging team contributions and closing the investigation

Root Cause Analysis Tools

Various tools support systematic root cause identification:

• 5 Why analysis: Iteratively asking "why" to drill down from symptoms to root cause
• Fishbone diagram: Organizing potential causes by category (materials, methods, machines, manpower, environment, measurement)
• Fault tree analysis: Logical decomposition of failure into contributing events
• Failure mode and effects analysis: Systematic evaluation of potential failure modes and their effects
• Is/Is Not analysis: Distinguishing what the problem is from what it is not to narrow focus

Design Changes

Many corrective actions involve design modifications:

• Material selection: Choosing materials with better reliability characteristics
• Design margins: Increasing safety factors to account for process variation and aging
• Stress reduction: Modifying geometry to reduce mechanical, thermal, or electrical stress
• Redundancy: Adding backup elements for critical functions
• Design rules: Updating guidelines to prevent similar issues in future designs

Process Improvements

Manufacturing process changes often address reliability issues:

• Process parameter optimization: Adjusting settings to reduce defect formation
• Additional process controls: Implementing monitoring to detect drift before failures occur
• Equipment upgrades: Replacing or improving equipment capability
• Incoming inspection: Adding or enhancing verification of material quality
• Work instructions: Clarifying procedures to prevent operator errors

Verification and Validation

Confirming corrective action effectiveness requires appropriate testing:

• Accelerated testing: Demonstrating elimination of the failure mode under stress
• Comparative analysis: Testing before and after samples to verify improvement
• Field monitoring: Tracking reliability metrics after implementation
• Process capability: Verifying that process changes maintain or improve capability
• Documentation: Recording all changes and verification results

Weibull Analysis

The Weibull distribution is widely used for reliability data:

• Shape parameter (beta): Indicates whether failure rate is decreasing (beta less than 1), constant (beta equals 1), or increasing (beta greater than 1)
• Scale parameter (eta): Characteristic life at which 63.2% of units have failed
• Weibull plotting: Graphical technique for parameter estimation and distribution fit assessment
• Confidence bounds: Quantifying uncertainty in parameter estimates
• Mixed distributions: Identifying multiple failure modes with different characteristics

Acceleration Factor Estimation

Relating accelerated test results to field conditions requires acceleration modeling:

• Arrhenius relationship: Temperature acceleration based on activation energy
• Power law models: Voltage and current acceleration relationships
• Combined stress models: Eyring and other models for multiple stress factors
• Activation energy determination: Testing at multiple temperatures to estimate Ea
• Model validation: Comparing predictions with field data

Reliability Metrics

Key metrics quantify product reliability performance:

• Mean Time To Failure (MTTF): Average time to failure for non-repairable items
• Mean Time Between Failures (MTBF): Average operating time between failures for repairable systems
• Failure rate: Failures per unit time, often expressed in FITs (failures in 10^9 device hours)
• Reliability function: Probability of survival to a given time
• BX life: Time at which X percent of units have failed (e.g., B10 life)

Handling Censored Data

Reliability tests often end before all units fail, requiring special analysis methods:

• Right censoring: Units that have not failed when the test ends
• Interval censoring: Failures known only to occur within a time interval
• Maximum likelihood estimation: Statistical method handling censored data
• Kaplan-Meier estimator: Non-parametric survival analysis
• Sample size considerations: Larger samples reduce uncertainty from censoring