EC-25.5 Reliability: Wear-Out, Burn-In and Lifetime
You can name the principal wear-out mechanisms in a modern device and say what accelerates each, read a bathtub hazard curve and explain what burn-in removes, and use an acceleration model to convert a short stress test into a lifetime figure.
Before:PE1-1. VLSI TechnologyEC-8. Measurements, Instrumentation and Experimental MethodEC-21. Hardware Verification, FPGA and SoC Design
A part that passes every test on the day it is made can still fail after two years, and the mechanisms that cause that are physical, understood and predictable in aggregate. The whole of qualification rests on acceleration: stress a sample harder than the field will and use a model to convert the result. That model is where the argument usually is, and understanding its assumptions is what separates a qualification from a ritual.
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The hazard curve: infant mortality, useful life and wear-out
Failure rate is high at first, low for a long period and rises again at the end, and the three regions have entirely different causes. Quoting one failure rate for a product ignores which region it is in.
NPTEL: Introduction to Reliability Engineering (IIT Kharagpur) · CourseBurn-in: paying to remove the weakest parts before shipping
Running parts hot and biased for a period causes the marginal ones to fail in the factory rather than at a customer. It costs time and a little life from every part, so it is used where field failures are expensive.
NPTEL: Digital VLSI Testing (IIT Kharagpur) · CourseThe wear-out mechanisms, and what accelerates each
Oxide breakdown, hot-carrier damage, bias-temperature instability and metal electromigration are the main four, and each responds to a different combination of voltage, temperature and current. Which one dominates depends on the technology and the use.
NPTEL: Basic Overview of Semiconductor Device Processing and IC Fabrication (IIT Kanpur) · CourseAcceleration models, and turning a week of stress into ten years of life
A model relates failure time at a stress condition to failure time in the field, usually through an activation energy. The prediction is only as good as that constant, which is measured rather than derived.
NPTEL: Introduction to Reliability Engineering (IIT Kharagpur) · CourseLife distributions, and why the average is the least useful statistic
Failures cluster in a distribution with a shape, and the fraction failing by a given date is what a customer cares about. A mean lifetime tells you almost nothing about that fraction.
NPTEL: Introduction to Reliability Engineering (IIT Kharagpur) · CourseQualification: the stress sequence a new product has to survive
Temperature cycling, humidity, high-temperature operating life and mechanical stress in a defined sequence and on a defined sample size make up a standard qualification. Passing it is a condition of selling into most markets.
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