Electronics Guide

The Stress-Strength Relationship

Derating is grounded in the stress-strength interference model, which recognizes that both applied stress and component strength are statistical distributions rather than fixed values. Stress varies due to operating conditions, environmental factors, and system interactions. Strength varies due to manufacturing tolerances and degrades over time due to aging and wear-out mechanisms. When stress and strength distributions overlap, failures become statistically inevitable.

Derating reduces the mean and spread of the stress distribution, moving it away from the strength distribution and minimizing overlap probability. The degree of derating required depends on the width and shape of both distributions, the consequences of failure, and the target reliability. Critical applications requiring extremely low failure rates demand more aggressive derating than consumer products with shorter expected lifetimes.

Derating Factors and Ratios

Derating is typically expressed as a percentage of the maximum rated value or as a derating factor. A 50% voltage derating means operating the component at no more than half its rated voltage. A derating factor of 0.6 for power dissipation means limiting actual dissipation to 60% of the maximum rating. These factors are applied to the maximum ratings under worst-case conditions, not nominal or typical operating points.

Effective derating considers multiple stress parameters simultaneously. A component may require voltage derating, thermal derating, and current derating concurrently. The most restrictive derating for any parameter determines the allowable operating envelope. Comprehensive derating analysis examines all relevant stress factors and ensures adequate margin exists for each under worst-case combinations of operating conditions.

Derating Versus Overdesign

Derating should not be confused with simple overdesign or specification padding. Derating involves deliberate, quantified reductions in operating stress based on reliability physics and application requirements. Overdesign often results from arbitrary safety factors or component availability rather than systematic analysis. Effective derating provides known reliability benefits while overdesign may add cost without proportional reliability improvement.

The goal of derating is achieving required reliability at minimum cost, not maximizing component margins regardless of expense. Excessive derating wastes resources by using oversized components, while insufficient derating leads to field failures and warranty costs. Systematic derating analysis identifies the optimal balance point where reliability targets are met without unnecessary overdesign.

Semiconductor Derating

Semiconductor devices require careful derating of junction temperature, voltage, current, and power dissipation. Junction temperature is particularly critical because most semiconductor failure mechanisms are strongly temperature-dependent. The Arrhenius relationship indicates that failure rates approximately double for every 10 to 15 degree Celsius increase in junction temperature, making thermal derating highly effective for reliability improvement.

Typical semiconductor derating guidelines limit junction temperature to 110 degrees Celsius for commercial applications and 100 degrees or lower for high-reliability applications, compared to maximum ratings often exceeding 150 degrees. Voltage derating to 75% to 80% of breakdown ratings protects against transients and provides margin for voltage variations. Current derating ensures that power dissipation remains within thermal limits under worst-case ambient conditions.

Specific semiconductor types have particular derating considerations. Power MOSFETs require attention to safe operating area limits and gate voltage ratings. Bipolar transistors need derating of collector-emitter voltage to avoid secondary breakdown. Integrated circuits demand careful evaluation of supply voltage ranges and input/output voltage limits. Each device type has characteristic failure mechanisms that inform appropriate derating strategies.

Capacitor Derating

Capacitors exhibit strong voltage-dependent reliability, making voltage derating particularly effective. Electrolytic capacitors typically require derating to 60% to 80% of rated voltage depending on application criticality. Ceramic capacitors, especially high-dielectric-constant types, lose capacitance under DC bias and require both voltage derating and accounting for voltage coefficient effects.

Temperature derating is equally important for capacitors. Electrolytic capacitor life doubles for approximately every 10 degree Celsius reduction in operating temperature. Ceramic capacitor reliability degrades at elevated temperatures due to increased ionic mobility. Film capacitors generally tolerate temperature better but still benefit from thermal derating in demanding applications.

Ripple current derating prevents excessive internal heating in capacitors used for filtering and energy storage. Internal heating from ripple current adds to ambient temperature, effectively reducing the temperature margin. Ripple current ratings must be derated at elevated ambient temperatures to maintain acceptable internal temperatures.

Resistor Derating

Resistor derating focuses primarily on power dissipation and operating temperature. Standard practice limits power dissipation to 50% to 75% of rated values at 70 degrees Celsius ambient. Higher ambient temperatures require additional derating according to manufacturer power derating curves, which typically reduce allowable dissipation linearly to zero at maximum operating temperature.

Voltage rating must also be considered for resistors, particularly high-value resistors where the power rating may be reached before the voltage limit. Voltage derating to 70% to 80% of maximum prevents dielectric stress failures. Pulse applications require separate evaluation of peak voltage and energy handling capability.

Different resistor technologies have different derating requirements. Wirewound resistors tolerate higher temperatures than thick film types. Thin film resistors generally exhibit better stability and may permit less aggressive derating in precision applications. Metal oxide and carbon composition resistors have technology-specific failure modes that influence appropriate derating levels.

Inductor and Transformer Derating

Magnetic components require derating of current, temperature, and voltage. Current derating ensures that copper losses remain within thermal limits and that core saturation is avoided with margin. Temperature derating accounts for insulation system limitations and core material property changes at elevated temperatures.

Saturation current derating typically limits peak current to 80% of rated saturation current to maintain adequate inductance and prevent core losses from excessive flux density. Temperature rise from internal losses must be added to ambient temperature when evaluating insulation system margins.

Transformer voltage ratings include insulation voltage withstand specifications that require derating for long-term reliability. Creepage and clearance distances may limit achievable voltage margins in physically constrained designs. High-frequency transformers require attention to skin effect and proximity effect losses that increase with frequency.

Connector and Switch Derating

Connectors and switches require current derating to prevent contact degradation from overheating. Contact resistance creates localized heating that can cause oxidation, material migration, and eventual failure. Current ratings are typically based on temperature rise limits that must be further derated in elevated ambient environments.

Voltage derating in connectors prevents arcing during mating and unmating operations. Arc suppression becomes increasingly difficult at higher voltages, and repeated arcing damages contact surfaces. Hot plugging applications require additional derating to account for arcing potential under load.

Mechanical derating limits insertion cycles and operational cycles to fractions of rated life for applications requiring high reliability over extended periods. Contact wear accumulates over cycles, and designs with limited margins may fail before reaching nominal cycle ratings.

Voltage Margin Requirements

Voltage margins protect against transients, supply variations, and unexpected overvoltage conditions. Systematic voltage margin analysis examines all voltage stress points in a design and compares actual maximum voltages against component ratings. Margin requirements vary by component type and failure consequence, with higher margins required for safety-critical functions.

Transient voltage protection requires careful attention to both magnitude and energy content. Voltage suppressors and clamps must be sized to handle expected transient energy while maintaining clamping voltages that provide adequate margin for protected components. The transient voltage after clamping, not the nominal supply voltage, determines the actual voltage stress on components.

Supply voltage tolerance must be included in voltage stress calculations. A nominally 12-volt supply with plus or minus 10% tolerance can reach 13.2 volts, which becomes the relevant stress for derating calculations. Worst-case analysis combines high supply tolerance with other factors that maximize voltage stress.

Current Limiting Design

Current limiting protects components from damage due to overload, short circuit, or fault conditions. Effective current limiting requires understanding both steady-state and transient current capabilities of protected components. The current limit must be set low enough to protect the weakest component in the current path while remaining high enough for normal operation.

Active current limiting circuits sense current and reduce it when thresholds are exceeded. Response time is critical for protecting against fast transients. Passive current limiting using resistors or positive temperature coefficient devices provides simpler but slower protection. The appropriate approach depends on the nature of expected overcurrent events.

Fuse selection for current limiting involves careful coordination between fuse clearing characteristics and protected component withstand capability. Time-current characteristics must be evaluated to ensure the fuse clears before protected components are damaged. Fuse voltage and interrupting ratings must also be adequate for the circuit.

Power Dissipation Management

Power dissipation management ensures that component temperatures remain within derated limits under all operating conditions. Power stress analysis identifies components with the highest thermal stress and verifies adequate heat removal. Thermal resistance from junction to ambient determines the temperature rise for a given power dissipation.

Worst-case power dissipation calculations must account for variations in supply voltage, load current, duty cycle, and efficiency. Components in power conversion circuits may experience higher stress at high or low line conditions depending on topology. All operating modes must be evaluated to identify maximum stress conditions.

Derating power components requires translating temperature limits into power limits based on thermal resistance. A device with 5 degrees Celsius per watt thermal resistance and a 50 degree temperature rise budget can dissipate 10 watts. Reducing thermal resistance through improved heat sinking effectively increases the allowable power within temperature derating limits.

Frequency Derating Considerations

High-frequency operation introduces additional loss mechanisms and stress factors that require derating consideration. Switching losses in semiconductors increase with frequency, reducing efficiency and increasing thermal stress. Core losses in magnetic components increase approximately with the square of frequency for eddy current losses.

Capacitor effective series resistance increases at high frequencies due to dielectric losses, increasing self-heating for a given ripple current. Conductor losses increase due to skin effect, requiring larger conductors or alternative structures at high frequencies. These frequency-dependent factors must be included in derating analysis for high-frequency designs.

Component ratings are often specified at standard frequencies that may differ from application frequencies. Derating guidelines should account for frequency effects when components operate significantly above or below rated frequency conditions.

Temperature-Dependent Reliability

Temperature profoundly affects electronic component reliability through multiple mechanisms. Chemical reaction rates governing degradation processes increase exponentially with temperature following Arrhenius behavior. Mechanical stresses from thermal expansion induce fatigue at interfaces between materials with different expansion coefficients. Diffusion processes that cause parameter drift accelerate at elevated temperatures.

Activation energies vary by failure mechanism, resulting in different temperature sensitivities for different failure modes. Electromigration in metallization has activation energies around 0.5 to 1.0 electron volts, resulting in moderate temperature dependence. Corrosion processes may have lower activation energies and stronger humidity dependence. Effective thermal derating considers the dominant failure mechanisms for each component and application.

Temperature cycling introduces additional stress beyond steady-state temperature effects. Thermal expansion mismatches cause mechanical stress during temperature changes, with stress magnitude proportional to temperature range and material property differences. Solder joints, wire bonds, and adhesive interfaces are particularly susceptible to thermal cycling damage.

Junction Temperature Control

Semiconductor junction temperature is the critical thermal parameter for active devices. Junction temperature equals ambient temperature plus the product of power dissipation and thermal resistance from junction to ambient. Reducing any of these factors reduces junction temperature and improves reliability.

Thermal resistance minimization involves heat sink selection, thermal interface material optimization, and air flow management. Junction-to-case thermal resistance is a fixed device property, but case-to-ambient resistance can be reduced through design choices. Multiple thermal paths in parallel reduce effective resistance.

Junction temperature monitoring through thermal sensors or temperature-sensitive parameters enables active thermal management and protection against overtemperature. Thermal shutdown circuits prevent catastrophic failure by reducing power when temperatures exceed safe limits. These protection features complement but do not replace proper thermal derating.

Ambient Temperature Derating

Component ratings typically assume standard ambient temperatures, often 25 or 70 degrees Celsius. Operation at higher ambient temperatures requires derating to maintain acceptable internal temperatures. Derating curves provided by manufacturers specify allowable stress reductions as ambient temperature increases.

System thermal design must establish realistic ambient temperature specifications for each component location. Internal ambient temperatures within enclosures often exceed external ambient due to heat generation from other components. Localized hot spots near high-power components create elevated ambient conditions for nearby components.

Environmental extremes in the application must be included in ambient temperature specifications. Military and automotive applications commonly specify ambient temperatures from minus 40 to plus 85 degrees Celsius or higher. Industrial applications may encounter elevated temperatures from process heat or solar loading. The maximum ambient temperature, not typical operating temperature, determines required derating.

Thermal Margin Analysis

Thermal margin analysis quantifies the difference between actual operating temperatures and allowable limits under worst-case conditions. Positive margins indicate adequate thermal design; negative margins identify components requiring design changes. Systematic analysis evaluates all thermally critical components.

Worst-case thermal conditions typically combine maximum ambient temperature, maximum power dissipation, minimum air flow, and other factors that elevate component temperatures. Tolerance in thermal interface materials, heat sink mounting, and component power specifications contribute to thermal uncertainty that must be included in margin calculations.

Thermal simulation tools enable virtual evaluation of thermal margins before hardware construction. Computational fluid dynamics models predict air flow and temperature distributions. Finite element thermal analysis determines temperature gradients and hot spot locations. These tools support iterative thermal design optimization.

Vibration and Shock Margins

Mechanical stress margins protect against vibration and shock encountered during shipping, handling, and operation. Component natural frequencies, mounting strength, and fatigue life must all have adequate margin above expected stress levels. Mechanical failures often result from resonance amplification or cumulative fatigue damage.

Vibration derating involves ensuring that component and assembly natural frequencies are sufficiently separated from excitation frequencies to avoid resonance amplification. A common guideline requires natural frequency at least twice the highest significant excitation frequency. When this separation is not achievable, damping must limit amplification to acceptable levels.

Shock margins address the peak stress from impact events. Component mounting must withstand shock loads with margin for manufacturing variations and repeated exposure. Solder joints, wire leads, and mechanical fasteners all have shock withstand ratings that must exceed expected stress with margin.

Mounting and Attachment Stress

Component mounting creates stress from fastener torque, adhesive shrinkage, and constraint of thermal expansion. Excessive mounting stress can crack ceramic components, damage leads, or cause parameter shifts. Mounting designs must control stress while providing adequate mechanical security.

Large ceramic capacitors and resistors are particularly susceptible to mounting stress fractures. Compliant mounting using adhesive dots or flexible leads reduces stress transfer from board flexure. Stress analysis identifies components requiring special mounting attention.

Printed circuit board flexure during assembly, handling, and operation creates stress in surface-mounted components. Board stiffening, component placement away from high-flexure zones, and assembly process controls reduce flexure-induced failures. Strain gauges can measure actual board strain for comparison against component limits.

Lead and Termination Stress

Component leads and terminations experience stress from board flexure, thermal expansion mismatch, and handling damage. Lead forming and trimming operations must be controlled to avoid stress concentrations. Solder joint geometry affects stress distribution and fatigue life.

Through-hole component leads benefit from proper hole sizing and annular ring dimensions. Leads should be formed to minimize stress at the package interface. Lead cutting should be performed with sharp tools to avoid deformation.

Surface mount terminations experience shear stress from thermal expansion mismatch between component and board. Larger components require attention to this mismatch; very large ceramic capacitors may need underfill or strain relief to survive thermal cycling. Solder joint reliability depends on termination design, pad geometry, and solder volume.

Humidity and Moisture Effects

Humidity accelerates corrosion, promotes electrochemical migration, and can cause moisture-related failures in packaged components. Derating for humid environments involves reducing voltage stress to limit electrochemical migration potential, selecting moisture-resistant materials and components, and providing adequate conformal coating protection.

Conductor spacing derating for humid conditions exceeds dry environment requirements to prevent dendritic growth between conductors. Electrochemical migration of silver and copper can create conductive paths at voltages as low as a few volts in high humidity conditions. Spacing standards such as IPC-2221 provide guidelines for different pollution degrees and coating conditions.

Moisture sensitivity level ratings for surface mount components indicate their tolerance to moisture absorption during storage and exposure to reflow temperatures. Components that exceed floor life limits require baking to remove absorbed moisture before assembly. Proper handling and storage prevent moisture-related assembly defects.

Altitude and Pressure Effects

Reduced atmospheric pressure at altitude decreases the dielectric strength of air, requiring voltage derating to prevent arcing. Heat transfer by convection also decreases at altitude due to reduced air density, necessitating thermal derating. High-altitude and aerospace applications require specific attention to these factors.

Voltage derating for altitude typically follows the relationship between breakdown voltage and pressure described by Paschen's law. At 10,000 feet elevation, air breakdown voltage may be reduced by 25% compared to sea level. Hermetically sealed components maintaining sea-level internal pressure avoid this derating requirement.

Thermal derating at altitude accounts for reduced convection effectiveness. Forced convection systems may require increased airflow to maintain equivalent cooling. Natural convection designs may need design changes or component derating to accommodate reduced heat transfer.

Radiation Environment Considerations

Space and nuclear applications expose electronics to ionizing radiation that causes both temporary effects and permanent damage. Total ionizing dose causes cumulative damage requiring derating of device parameters over mission life. Single event effects require design techniques beyond simple derating.

Displacement damage from heavy particles degrades semiconductor performance, particularly affecting optical and solar cell devices. Derating for displacement damage depends on expected fluence and device sensitivity. Component selection focuses on radiation-tolerant device types.

Radiation derating guidelines specify end-of-life parameter values after expected radiation exposure. Designs must function correctly with degraded parameters, requiring additional margin beyond normal tolerances. Radiation testing characterizes actual component response to specific radiation environments.

Chemical and Contamination Exposure

Harsh chemical environments require derating of components and materials subject to chemical attack. Corrosive atmospheres degrade metallization and cause failures in unprotected components. Organic solvents can damage plastic packaging and conformal coatings.

Component selection for chemical exposure focuses on materials compatibility. Metal finishes resistant to specific corrosive agents may be required. Hermetically sealed components provide protection against environmental contaminants. Conformal coatings protect assemblies from less aggressive environments.

Cleanliness requirements prevent contamination-related failures. Ionic contamination from flux residues or handling promotes corrosion and electrochemical migration. Particulate contamination can cause shorts or interfere with mechanical operation. Cleanliness testing verifies that contamination levels remain below thresholds that would require additional derating.

Application-Based Safety Factors

Safety factor requirements vary based on application criticality, accessibility for repair, and consequences of failure. Consumer products with short expected lifetimes and easy replacement may accept smaller safety factors than industrial equipment expected to operate reliably for decades. Safety-critical applications demand the highest safety factors regardless of economic considerations.

Failure consequence analysis informs safety factor selection. Failures causing safety hazards require higher margins than those merely causing inconvenience. Failures in inaccessible locations where repair is costly justify increased margins to reduce failure probability. Mission-critical applications where failure causes mission loss demand comprehensive derating.

Economic optimization balances component cost against failure cost. Higher safety factors increase initial cost but reduce failures. The optimum balance point depends on failure rates, failure costs, and the relationship between margin and reliability. This analysis should inform derating decisions for cost-sensitive applications.

Statistical Approaches to Safety Factors

Statistical safety factor determination uses probability distributions for stress and strength to calculate failure probability. The safety index relates the separation between mean stress and mean strength to the combined standard deviation. Higher safety indices correspond to lower failure probabilities.

Design to specified reliability targets involves determining the safety factor needed to achieve required failure probability. If stress and strength are normally distributed, standard reliability tables relate safety index to failure probability. More complex distributions require Monte Carlo simulation or other numerical methods.

Sensitivity analysis identifies parameters with greatest influence on reliability. Design efforts focus on reducing stress or increasing strength for parameters with highest sensitivity. Safety factors may be reduced where sensitivity is low without significantly affecting overall reliability.

Margin Allocation Strategies

Margin allocation distributes available design margin among various parameters to achieve overall reliability targets. Equal margin allocation assigns the same derating percentage to all parameters. Weighted allocation assigns more margin to parameters with higher uncertainty or greater impact on reliability.

System-level margin allocation ensures that subsystem margins combine to meet overall requirements. Series reliability models require each element to have adequate margin; parallel redundant elements may tolerate smaller individual margins. Allocation must consider both independent and common-cause failures.

Margin verification confirms that allocated margins are achieved in the final design. Analysis and testing verify that actual stresses remain within derated limits under worst-case conditions. Margin documentation enables future design changes to be evaluated for impact on reliability.

Military Derating Standards

Military standards define comprehensive derating requirements for defense applications. MIL-HDBK-454 provides general derating guidelines for electronic component applications. MIL-STD-975 specifies NASA standard electrical, electronic, and electromechanical parts. These documents establish minimum derating levels for various component types and application classes.

Military derating typically requires more conservative margins than commercial practices. Semiconductor junction temperatures are often limited to 110 degrees Celsius or less. Capacitor voltage derating of 50% to 60% is common. Resistor power derating to 50% at rated temperature is standard. These conservative requirements reflect the demanding environments and high reliability expectations of military systems.

Defense contractor-specific derating guidelines often exceed military standard requirements. Additional derating may be specified for particular failure-sensitive applications or based on experience with specific component types. Contract requirements may invoke specific derating standards that supersede general guidelines.

Aerospace Derating Requirements

Aerospace applications combine military-level reliability requirements with unique environmental challenges including launch vibration, vacuum operation, radiation exposure, and extreme temperature cycling. NASA-specific requirements add to military standards for space applications. Commercial aviation follows DO-160 environmental categories that influence derating requirements.

Space applications require particular attention to radiation effects and vacuum operation. Derating for radiation degradation ensures end-of-life performance meets requirements. Vacuum operation eliminates convection cooling and may limit voltage ratings due to reduced dielectric strength. Thermal design relies on conduction and radiation heat transfer.

Launch vehicle electronics experience extreme vibration and shock requiring substantial mechanical margins. Random vibration environments during launch may exceed 20 g RMS. Pyrotechnic shock events can reach thousands of g. Components and assemblies must survive these stresses while maintaining function.

Commercial and Industrial Practices

Commercial electronics typically apply less aggressive derating than military applications, balancing reliability against cost competitiveness. Industry sectors have developed guidelines appropriate to their reliability requirements and operating environments. Telecommunications, medical, and automotive industries each have characteristic derating practices.

Telecommunications equipment guidelines emphasize long service life and high availability. Telcordia standards provide reliability prediction methods and implicit derating assumptions. Network equipment is expected to operate reliably for 20 years or more, justifying conservative derating despite commercial cost pressures.

Automotive electronics follow AEC component qualification specifications that define stress test requirements. Operating temperatures from minus 40 to plus 125 degrees Celsius are common requirements. Vibration and thermal cycling requirements exceed those of most other commercial applications. Automotive derating practices ensure reliability under these demanding conditions.

Medical device reliability requirements vary by device classification and risk level. Class III life-sustaining devices require comprehensive derating analysis. FDA quality system regulations require design controls that typically include derating documentation. IEC 60601 safety standards impose specific requirements for medical electrical equipment.

Consumer Electronics Considerations

Consumer electronics balance reliability against aggressive cost targets and short product lifecycles. Derating practices focus on achieving acceptable failure rates over expected product lifetime without excessive margin. Field failure rates inform derating adequacy assessments.

Warranty period reliability receives primary attention in consumer product derating. Products must survive the warranty period with acceptably low failure rates to avoid excessive warranty costs. Post-warranty reliability may receive less design attention due to product obsolescence and replacement cycles.

Consumer products often operate in uncontrolled environments with temperature and humidity variations. Design margins must accommodate these variations while meeting cost targets. Worst-case environmental assumptions balance the need for reliability against the cost impact of excessive derating.

Design Margin Verification

Design margin verification confirms that analysis predictions are achieved in actual hardware. Testing at worst-case conditions validates that circuits meet specifications with expected margins. Any deviations from predicted margins trigger investigation and potential design changes.

Parameter margin testing varies individual parameters to determine actual margins. Supply voltage, temperature, and load variations are applied independently and in combination. Measured margins are compared against requirements to verify design adequacy.

Limit testing determines actual failure points for comparison against predicted margins. Testing beyond specification limits, where safe, reveals actual margin rather than just confirming specification compliance. This information supports reliability assessment and identifies opportunities for cost reduction or reliability improvement.

Accelerated Stress Testing

Highly Accelerated Life Testing (HALT) applies progressively increasing stress to discover actual operating limits and destruct limits. The difference between operating limits and destruct limits indicates available margin for reliability improvement. HALT results inform derating adequacy assessment.

Step stress testing at multiple stress levels characterizes the stress-life relationship. Results enable extrapolation to normal operating conditions and comparison with derating assumptions. Acceleration factors validate or challenge assumed relationships between stress and failure rate.

Life testing at elevated stress levels verifies that derated designs achieve expected reliability. Test duration and sample size are selected to demonstrate required reliability with acceptable confidence. Results may lead to derating adjustments if actual reliability differs from predictions.

Environmental Margin Testing

Environmental testing verifies performance under extreme conditions specified in product requirements. Temperature extremes, humidity exposure, and mechanical stress testing confirm that design margins accommodate environmental variations. Test profiles represent worst-case combinations of environmental factors.

Temperature margin testing operates products at maximum and minimum specified temperatures while measuring critical parameters. Adequate margin exists when all parameters remain within specification at temperature extremes. Characterization across temperature reveals temperature coefficients for comparison with analysis assumptions.

Combined environment testing applies multiple stresses simultaneously to reveal interactions not apparent in single-stress testing. Temperature and vibration combined testing is particularly effective at revealing marginal designs. Combined stress profiles should represent actual use conditions to ensure realistic margin assessment.

Production Verification

Production testing verifies that manufacturing variations do not consume design margins. Statistical process control monitors critical parameters and identifies trends toward margin reduction. Out-of-specification results trigger investigation of root causes and potential margin erosion.

Sample testing at environmental extremes verifies ongoing margin adequacy as manufacturing processes evolve. Process changes require revalidation of design margins. Component substitutions must be evaluated for impact on stress and margin.

Field reliability data provides ultimate verification of derating adequacy. Failure rate tracking identifies products or components with inadequate margins. Failure analysis determines root causes and informs derating adjustments for current and future designs.