Burn-in Testing
Burn-in testing is the process by which a system detects early failures in semiconductor components (infant mortality), thereby increasing a semiconductor component reliability. Normally burn-in tests are performed on electronic devices such as laser diodes with an Automatic Test Equipment laser diode burn-in system that runs the component for an extended period of time to detect problems.
A burn-in system will use cutting-edge technology to test the component and provide precision temperature control, power and optical (if required) measurements to ensure the precision and reliability required for manufacturing, engineering evaluation, and R&D applications.
Burn-in testing may be conducted to ensure that a device or system functions properly before it leaves the manufacturing plant or to confirm new semiconductors from the R&D lab are meeting designed operating requirements.
It is best to burn-in at the component level when the cost of testing and replacing parts is lowest. Burn-in of a board or an assembly is difficult because different components have different limits.
It is important to note that burn-in test is usually used to filter out devices that fail during the “infant mortality stage” (beginning of bathtub curve) and does not take into count the “lifetime” or wearout (end of the bath tub curve) – this is where reliability testing comes into play.
Wearout is the natural end-of-life of a component or system related to continuous use as a result of materials interaction with the environment. This regime of failure is of particular concern in denoting the lifetime of the product. It is possible to describe wearout mathematically allowing the concept of reliability and, hence, lifetime prediction.
What Causes Components to Fail During Burn-in?
The root cause of fails detected during burn-in testing can be identified as dielectric failures, conductor failures, metallization failures, electromigration, etc. These faults are dormant and randomly manifest into device failures during device life-cycle. With burn-in testing, an Automatic Test Equipment (ATE) will stress the device, accelerating these dormant faults to manifest as failures and screen out failures during the infant mortality stage.
Burn-in testing detects faults that are generally due to imperfections in manufacturing and packaging processes, which are becoming more common with the increasing circuit complexity and aggressive technology scaling.
Burn-in Testing Parameters
A burn-in test specification varies depending on the device and testing standard (military or telecom standards). It usually requires the electrical and thermal testing of a product, using an expected operating electrical cycle (extreme of operating condition), typically over a time period of 48-168 hours. The thermal temperature of the burn-in test chamber can range from 25°C to 140°C .
Burn-in is applied to products as they are made, to detect early failures caused by faults in manufacturing practice.
Burn In Fundamentally performs the following:
Stress + Extreme Conditions + Prolong Time = Acceleration of “Normal/Useful life”
Types of Burn-in Tests
Dynamic Burn-in : the device is exposed to high voltage and temperature extremes while being subjected to various input stimuli .
A burn-in system applies various electrical stimuli to each device while the device is exposed to extreme temperature and voltage. The advantage of dynamic burn-in is its ability to stress more internal circuits, causing additional failure mechanisms to occur. However, dynamic burn-in is limited because it cannot completely simulate what the device would experience during actual use, so all the circuit nodes may not get stressed.
Static Burn-in : Device under test (DUT) is stressed at elevated constant temperature for an extended period of time.
A burn-in system applies extreme voltage or currents and temperatures to each device without operating or exercising the device. The advantages of static burn-in are its low cost and simplicity.
How is a Burn-In Test Performed?
The semiconductor device is placed onto special Burn-in Boards (BiB) while the test is executed inside special Burn-in Chamber (BIC).
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Burn-in Chamber
A burn-in chamber is an environmental oven used to evaluates the reliability of multiple semiconductor devices and performs large capacity screenings for premature failure (infant mortality). These environmental chambers are designed for static and dynamic burn-in of integrated circuits (ICs) and other electronic devices such as laser diodes.
Selecting Chamber Size
The chamber size depends on the size of the burn-in board, the number of products in each burn-in board, and the number of batches required per day to meet production requirements. If the interior space is too small, insufficient space between parts results in poor performance. If it is too large, space, time and energy are wasted.
Companies that are purchasing a new burn-in set-up should work with the vendor to ensure the heat source has enough steady-state and maximum capacity to match the load for the DUT.
When using forced recirculating airflow, parts benefit from spacing, but the oven can be loaded more densely vertically because airflow is distributed along the entire side wall. Parts should be kept 2-3 inches (5.1 – 7.6cm) from the oven walls.
Burn-in Chamber Design Specs
Temperature Range
Depending on the requirements of the Device Under Test (DUT) select a chamber that has a dynamic range such as 15°C above ambient to 300°C (572°F)
Temperature Accuracy
It is important that the temperature does not fluctuate. Uniformity is the maximum difference between the highest and lowest temperatures in a chamber at a specified setting. A specification of at least 1% setpoint for uniformity and 1.0°C control accuracy is acceptable in most semiconductor burn-in applications.
Resolution
A high-temperature resolution of 0.1°C will provide the best control to meet burn-in requirements
Environmental Savings
Consider a burn-in chamber that has a refrigerant that has a zero ozone layer depletion coefficient. Burn-in chambers with refrigeration are related to chambers operating in temperatures below 0 degrees Celsius down to – 55°C.
Chamber configuration
The chamber can be designed with card cages, card-slots, and access doors to simplify connecting DUT boards and driver boards with ATE stations.
Chamber Air Flow
In most cases a forced convection oven with recirculating airflow will provide the best distribution of heat and significantly speeds the time-to-temperature and heat transfer to parts. Temperature uniformity and performance depends on a fan design that directs air to all areas of the chamber.
The chamber can be design with a horizontal or vertical airflow. It is important to know the direction of inserting the DUT based on the airflow of the chamber.
Custom ATE Wiring
When it comes to measuring over hundreds of devices, inserting wires through an aperture or test hole may not be practical. Custom wiring connectors can be mounted directly to the oven to facilitate the electrical monitoring of the device with an ATE.
How A Burn-in Oven Controls Temperature
The burn-in oven uses a temperature controller executing a standard PID (proportional, integral, derivative) algorithm. The controller senses the actual temperature value versus the desired setpoint value, and issues corrective signals to the heater calling for application ranging anywhere from no heat to full heat. A fan is also used to equalize the temperature through the chamber.
The most common sensor used for accurate temperature control of the environmental oven is a Resistance Temperature Detector (RTD) which a platinum-based unit typically referred to as a PT100.
Sizing The Chamber
If you are using an existing oven, basic thermal modelling based on factors such as the oven’s thermal capacity and losses, heat-source output, and DUT mass will allow you to verify that the oven and heat source are sufficient to reach desired temperature with a thermal time constant short enough for tight loop response under the controller’s direction.
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