What Is Burn In?

Burn in is a reliability screening process in which electronic components or assembled systems are subjected to elevated temperature, voltage, or combined electrical and thermal stress for a specified duration before delivery to a customer or integration into a larger system. The purpose is to accelerate the failure of components that carry latent manufacturing defects, thereby removing so-called infant mortalities from the population before field deployment. The resulting survivors exhibit a substantially reduced early-life failure rate, which corresponds to the declining portion of the classic bathtub reliability curve. Burn in is applied across semiconductor devices, integrated circuits, laser diodes, and many categories of discrete components.

The technique rests on the empirical observation that failure rates in electronic components are not constant over time. A newly manufactured population contains a fraction of units with subtle defects, including voids in metallization, weak gate oxides, and marginal solder joints, that are not detected by standard functional tests at room temperature. Applying stress above the normal operating condition forces these weak units to fail quickly in a controlled environment, leaving the remaining population in a stable, low-failure-rate regime. Burn in is thus a screening tool, not a means of extending the intrinsic life of good devices.

The Reliability Screening Process

Burn in testing is conducted in ovens or on powered boards that simultaneously apply elevated temperature and operating voltage, often near or at the component's rated maximum. IEEE research on burn-in tests for reliability assurance of semiconductor devices in life-critical equipment characterizes both static burn in, where devices are unpowered in a thermal oven, and dynamic burn in, where devices execute functional patterns under power. Dynamic burn in is generally more effective because it creates the internal power dissipation and field gradients that exercise electrically sensitive defects. The duration ranges from a few hours for commodity devices to several hundred hours for components used in aerospace or medical-grade equipment, with the optimal duration determined by accelerated life modeling. Arrhenius relationships are commonly used to project from burn-in stress conditions to expected failure rates at normal operating temperature.

Hot Carrier and Oxide Degradation Mechanisms

Two degradation mechanisms are particularly central to burn-in physics: hot carrier injection and oxide reliability. In metal-oxide-semiconductor field-effect transistors (MOSFETs), carriers accelerated by high electric fields can gain enough energy to be injected into or through the gate oxide, generating interface states and causing parametric shift in threshold voltage and transconductance. Published IEEE work on hot-electron-induced MOSFET degradation established models relating device lifetime to the substrate current and drain current under stress, enabling designers to predict failure rates as a function of supply voltage. Hot hole effects produce analogous damage in p-channel devices. Oxide reliability, interconnect reliability, and insulator reliability are closely related failure paths, all of which can be exposed through burn in when the applied voltage creates localized high-field conditions that would otherwise take years to manifest.

Failure Modes and Reliability Metrics

The effectiveness of burn in is assessed through field failure rates measured in FITs (failures in time, defined as one failure per billion device hours) before and after the screen. Recoverable fails, meaning devices that restore function after stress is removed, are distinguished from hard fails that permanently degrade. A Springer chapter on burn-in as a reliability screening test discusses the trade-off between screen effectiveness and the accumulated aging damage applied to every unit in the population, including devices that would have operated reliably without screening. Excessive burn-in duration can shift the surviving population toward the wear-out portion of the bathtub curve, reducing long-term product reliability rather than improving it.

Applications

Burn in has applications in a wide range of fields, including:

• Semiconductor manufacturing, for screening integrated circuits and discrete transistors before shipment
• Aerospace and defense electronics, where field failure rates must meet stringent mission-reliability specifications
• Telecommunications infrastructure, for qualifying high-availability switching and transmission hardware
• Medical device manufacturing, to reduce infant mortality in implantable and life-sustaining equipment
• Automotive electronics, for components subject to harsh under-hood temperature and vibration environments