| name | accelerated-life-testing |
| description | Accelerated life testing (ALT) — Arrhenius/Coffin-Manson/power-law models, acceleration factors, HALT/HASS, Weibull analysis, test planning, MIL-HDBK-781, IEC 60068. |
| metadata | {"priority":7,"promptSignals":{"phrases":["accelerated life testing","ALT","HALT","acceleration factor","Arrhenius model reliability","Weibull life testing","accelerated aging"],"minScore":3}} |
Accelerated Life Testing (ALT) — Complete Skill
Purpose and Approach
Goal: estimate product life at use conditions by testing at elevated stress (T, voltage, humidity, vibration, cycling) to precipitate failures faster
Key assumption: failure mechanism is the same at accelerated and use conditions (no new mechanisms introduced)
Output: acceleration factor AF → extrapolate test life to field life
Acceleration Models
Arrhenius Model (Temperature-Driven)
Applies to: chemical degradation, oxidation, corrosion, polymer aging, semiconductor wear-out
Failure rate at temperature T:
λ(T) = A × exp(-E_a / (k_B × T))
Acceleration factor (T_use vs. T_test):
AF = exp[(E_a / k_B) × (1/T_use - 1/T_test)] [T in Kelvin; k_B = 8.617 × 10⁻⁵ eV/K]
Activation energy E_a:
| Failure mechanism | E_a [eV] |
|---|
| Semiconductor electromigration | 0.7–0.9 |
| Corrosion (general) | 0.5–0.7 |
| Polymer oxidation | 0.8–1.2 |
| Solder joint fatigue | 0.3–0.5 |
| General electronics | 0.7 (JEDEC standard) |
Example:
E_a = 0.7 eV; T_use = 40°C (313 K); T_test = 125°C (398 K)
AF = exp[(0.7/8.617×10⁻⁵) × (1/313 - 1/398)] = exp[8121 × 6.83×10⁻⁴] = exp[5.55] ≈ 256
→ 1000 hr at 125°C ≈ 256,000 hr at 40°C field use
Coffin-Manson Model (Thermal Cycling)
Applies to: solder joint fatigue, thermal fatigue of metals
Cycles to failure ratio:
AF = (ΔT_test / ΔT_use)^m × (f_test / f_use)^n
ΔT = temperature cycle range [°C]; f = cycling frequency [cyc/hr]
m = 1.9–2.5 (solder); n ≈ 0.33 (frequency exponent; minor factor)
Modified Coffin-Manson (JEDEC JESD22-A104):
AF = (ΔT_acc / ΔT_use)^m × exp[E_a/k_B × (1/T_use_max - 1/T_acc_max)]
Combined temperature range + Arrhenius for time-dependent mechanisms
Power Law (Voltage/Electrical Stress)
Applies to: dielectric breakdown, electrostatic discharge wear-out
AF = (V_test / V_use)^n
n = 2–4 (oxide wear-out); n = 8–12 (ESD sensitive)
Example: V_use = 3.3 V; V_test = 6.6 V; n = 3
AF = (6.6/3.3)³ = 2³ = 8
Inverse Power Law (Mechanical Fatigue, Vibration)
Applies to: vibration-induced fatigue, wear
N₁ × S₁ᵐ = N₂ × S₂ᵐ (Basquin)
AF = (S_test / S_use)^m [S = stress amplitude; m = S-N slope; typically 3–10]
Humidity-Temperature (Peck Model)
AF = (RH_test / RH_use)^n × exp[E_a/k_B × (1/T_use - 1/T_test)]
n ≈ 2.7–3.0 (humidity exponent; empirical from corrosion data)
Combined Arrhenius + humidity power law
JEDEC JESD22-A101 (moisture sensitivity):
85°C/85% RH standard test; 168 hr or 240 hr depending on MSL
Combined Stress
Multiple stresses: multiply individual AFs (if mechanisms independent):
AF_total = AF_temp × AF_voltage × AF_humidity
Weibull Analysis for ALT Data
Weibull life distribution:
F(t) = 1 - exp[-(t/η)^β]
β = shape parameter (< 1: infant mortality; = 1: random; > 1: wear-out)
η = characteristic life (63.2% cumulative failures) [hours]
Accelerated analysis:
η(S) = η₀ × exp[E_a/(k_B × T)] (Arrhenius-Weibull model)
Fit using Maximum Likelihood Estimation (MLE) or least squares
Software: ReliaSoft ALTA, Minitab, JMP, R (ALTmodelR package)
Test Planning
Number of test units:
n ≥ [-ln(1 - C)] / [1 - (1 - p)^(1)] per stress level
Simplified: n ≥ 10–30 per stress level for adequate Weibull fit
Stress levels:
Minimum 3 levels to fit acceleration model
Level 1: T_use × 1.5; Level 2: T_use × 2.0; Level 3: T_use × 2.5
Upper bound: never exceed material capability (new failure modes)
Test duration:
t_test ≈ t_requirement / AF [hr; AF from acceleration model]
Confidence bound on life:
η_lower (90% confidence, 1-sided) from MLE ± 1.28 σ_ln(η)
HALT (Highly Accelerated Life Test)
Purpose: discover design weaknesses, not measure life
Protocol: step-stress (increase T, then vibration, then combined) until failure
Environment: rapid thermal cycling ΔT rate 60°C/min; random vibration 2–100 g_rms
HALT process:
- Cold step-stress: -10, -30, -50, -70°C (step until fail)
- Hot step-stress: +50, +70, +90, +110°C
- Rapid thermal cycling: ΔT = 60, 90, 120°C range at 60°C/min
- Vibration step-stress: 5, 10, 20, 40 g_rms (6-DOF vibration)
- Combined: all stresses simultaneously
Operating limit (OL): stress where DUT fails to function (reversibly)
Destruct limit (DL): stress where permanent damage occurs
Design margin: (DL - OL) / use_condition_stress; want margin > 2
HASS (Highly Accelerated Stress Screening)
Production screen (100% of units): brief exposure to stresses within HALT limits
Goal: precipitate infant-mortality failures before product reaches customer
Protocol (product-specific): typically ±60°C thermal cycling + 5–10 g_rms vibration for 2–10 cycles
Standards
| Standard | Scope |
|---|
| MIL-HDBK-781 | Reliability test plans; sample sizes |
| IEC 60068 | Environmental testing; temperature/humidity/vibration |
| JEDEC JESD47 | Stress-test-driven qualification of new ICs |
| JEDEC JESD22-A104 | Temperature cycling |
| JEDEC JESD22-A101 | Steady-state humidity/bias testing |
| MIL-STD-810H | Military environmental engineering |
Output
Provide: acceleration model type (Arrhenius/Coffin-Manson/power-law), activation energy E_a [eV] or model parameter m, acceleration factor AF at test conditions, test conditions (T [°C], voltage [V], humidity [%RH], vibration g_rms), test duration [hours], sample size per stress level, estimated field life at use conditions [hours or years] with 90% confidence lower bound, Weibull β and η parameters from fitted data, HALT operating and destruct limits, and applicable standard (IEC 60068, JEDEC JESD22, MIL-HDBK-781).
