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IEC TR 62240: Semiconductor Devices Outside Specified Temperature Range for Avionics
Process Management for Avionics — Qualification, Reliability, and Extended-Temperature Design
Scope and Purpose of IEC TR 62240
IEC TR 62240 (Technical Report, first edition, 2005) provides guidance on the process management for avionics concerning the use of semiconductor devices outside manufacturers’ specified temperature range. This technical report addresses a critical challenge faced by avionics designers: semiconductor components qualified for commercial (0 °C to +70 °C) or industrial (-40 °C to +85 °C) temperature ranges must often operate in avionics environments that expose them to -55 °C to +125 °C or beyond.
The central premise of IEC TR 62240 is that using a device outside its specified temperature range is permissible provided that the user performs adequate characterisation and reliability assessment to demonstrate that the device meets the application’s requirements. This is fundamentally different from “derating” — derating involves operating within specified limits at reduced stress, while this report addresses operation beyond those limits entirely.
The technical report applies to all categories of semiconductor devices used in avionics systems, including microprocessors, memory devices, FPGAs, linear and mixed-signal ICs, power devices, and discrete semiconductors. It covers both hermetically sealed and plastic-encapsulated packages, although the guidance differs significantly between these two packaging technologies due to their different failure mechanisms at temperature extremes.
| Temperature Class | Standard Range | Extended Avionics Range | Key Risk Factors |
|---|---|---|---|
| Commercial | 0 °C to +70 °C | -55 °C to +125 °C | Electromigration, hot carrier injection, latch-up |
| Industrial | -40 °C to +85 °C | -55 °C to +125 °C | Parameter drift, solder joint fatigue |
| Automotive | -40 °C to +125 °C | -55 °C to +150 °C | Package stress, wire bond fatigue |
| Military (883) | -55 °C to +125 °C | Within spec (no extension needed) | N/A (qualified for full range) |
Qualification Methodology
IEC TR 62240 outlines a structured qualification process that must be followed when a semiconductor device is to be used beyond its rated temperature range. The methodology consists of three phases:
Phase 1 — Characterisation: The user must characterise the device’s electrical parameters across the extended temperature range. Critical parameters include propagation delays, output drive strength, input threshold voltages, leakage currents (particularly important at high temperature), and supply current. Characterisation must be performed on a statistically significant sample (typically 25-50 devices from at least 3 different manufacturing lots) to capture process variation.
Leakage current is the parameter most sensitive to temperature. CMOS devices typically exhibit a doubling of leakage current for every 10 °C increase above 85 °C. At 125 °C, the leakage current can be 10-20 times higher than at 85 °C, which has direct implications for power supply design and thermal management in avionics LRUs (line replaceable units).
Phase 2 — Reliability Assessment: Accelerated life testing is used to estimate the device failure rate at the extended temperature conditions. The report recommends using the Arrhenius model with an activation energy (Ea) of 0.7 eV for most silicon-based failure mechanisms. The acceleration factor between the rated maximum temperature and the extended temperature is calculated, and the required test duration at elevated temperature is determined to demonstrate the equivalent of the target service life.
| Failure Mechanism | Typical Activation Energy (eV) | Acceleration from 85 °C to 125 °C |
|---|---|---|
| Electromigration | 0.5 – 0.7 | 8x – 20x |
| Time-dependent dielectric breakdown (TDDB) | 0.6 – 1.0 | 12x – 50x |
| Hot carrier injection | -0.2 to -0.4 (inverse) | N/A (worse at low temperature) |
| Negative bias temperature instability (NBTI) | 0.3 – 0.5 | 4x – 8x |
| Moisture/contamination (plastic packages) | 0.8 – 1.1 | 24x – 60x |
Phase 3 — Application-Specific Verification: The device must be tested in the actual system configuration under extended temperature conditions. This includes functional testing, timing margin analysis, and power consumption measurement at both temperature extremes. Special attention must be paid to start-up behaviour at low temperature (-55 °C) where oscillator circuits may fail to start and power supply sequencing may be affected by changed threshold voltages.
A practical approach is to apply a temperature margin of 15 °C beyond the intended operating range during characterisation. For example, if the application requires operation to +105 °C, characterise the device to +120 °C. This provides design margin and accounts for temperature gradients across the circuit board that may result in local hotspots exceeding the ambient temperature specification.
Engineering Design Insights
1. Hot Carrier Injection at Low Temperature: Counterintuitively, hot carrier injection (HCI) degradation is worse at low temperatures than at high temperatures. At -55 °C, carrier mobility is higher and mean free path is longer, resulting in more energetic carriers that can damage the gate oxide. Designers extending device operation to -55 °C must evaluate HCI lifetime using appropriate acceleration models that account for the inverse temperature dependence.
2. Plastic Encapsulation Considerations: Plastic-encapsulated devices (non-hermetic) present unique challenges at temperature extremes. At high temperature, moisture trapped in the plastic moulding compound expands and can cause “popcorning” or delamination. At low temperature, the thermal expansion mismatch between the silicon die and the plastic package increases, potentially causing passivation cracking or wire bond stress. The report recommends moisture sensitivity level (MSL) preconditioning and acoustic microscopy inspection for plastic devices used in extended-range applications.
3. Derating of Absolute Maximum Ratings (AMR): When operating a device outside the manufacturer’s specified temperature range, all other absolute maximum ratings (voltage, current, power dissipation) must be derated. As a rule of thumb, for every 10 °C above the maximum rated temperature, the maximum allowable junction temperature should be reduced by 5 °C through reduced power dissipation. This derating ensures that the device does not simultaneously operate at extended temperature AND maximum electrical stress, which would dramatically accelerate failure.
Never assume that passing functional tests at extended temperature extremes is sufficient for qualification. Functional testing only verifies that the device “works” at the moment of test. Long-term reliability mechanisms such as electromigration and TDDB can cause failures after hundreds or thousands of operating hours at extended temperature, even if the device functions correctly during initial testing. Accelerated life testing with appropriate sample sizes is mandatory.
Frequently Asked Questions
Q: Can IEC TR 62240 be used for commercial (non-avionics) applications?
A: The principles are applicable to any high-reliability application where semiconductor devices are used outside their rated temperature range, including automotive, industrial, oil and gas, and space applications. However, the specific qualification criteria and acceptance thresholds are tailored to avionics requirements and should be adapted for other sectors.
A: The principles are applicable to any high-reliability application where semiconductor devices are used outside their rated temperature range, including automotive, industrial, oil and gas, and space applications. However, the specific qualification criteria and acceptance thresholds are tailored to avionics requirements and should be adapted for other sectors.
Q: What is the minimum sample size for device characterisation at extended temperatures?
A: The report recommends a minimum of 25 devices from at least 3 manufacturing lots for initial characterisation. For production monitoring, a reduced sample size of 10-15 devices from a single lot may be acceptable, but the first article qualification must use the full sample size to capture lot-to-lot variation.
A: The report recommends a minimum of 25 devices from at least 3 manufacturing lots for initial characterisation. For production monitoring, a reduced sample size of 10-15 devices from a single lot may be acceptable, but the first article qualification must use the full sample size to capture lot-to-lot variation.
Q: How do I handle devices where the manufacturer explicitly prohibits use outside the rated range?
A: If the manufacturer’s datasheet or application note explicitly states that operation outside the specified range is not permitted, the device should not be used in extended-range applications, regardless of characterisation results. This is because the manufacturer may have application-specific knowledge about failure modes not covered by generic qualification. Seek alternative devices with appropriate temperature ratings.
A: If the manufacturer’s datasheet or application note explicitly states that operation outside the specified range is not permitted, the device should not be used in extended-range applications, regardless of characterisation results. This is because the manufacturer may have application-specific knowledge about failure modes not covered by generic qualification. Seek alternative devices with appropriate temperature ratings.
Q: What documentation is required for avionics certification authorities?
A: The qualification report must include: device identification and manufacturer details, characterisation data across the full extended temperature range, reliability assessment with acceleration model details and calculated equivalent service life, application-specific verification results, and a statement of limitations identifying any parameters that could not be verified. This report forms part of the overall equipment qualification package for DO-178C/DO-254 compliance.
A: The qualification report must include: device identification and manufacturer details, characterisation data across the full extended temperature range, reliability assessment with acceleration model details and calculated equivalent service life, application-specific verification results, and a statement of limitations identifying any parameters that could not be verified. This report forms part of the overall equipment qualification package for DO-178C/DO-254 compliance.
