HTOL test introduction

High Temperature Operating Life (HTOL) is a core test method for evaluating the long-term reliability of chips. This test accelerates the exposure of potential defects by simulating the continuous working state of the chip in extreme environments such as high temperature and high pressure, thereby predicting the lifespan and stability of the chip under normal use conditions in a short period of time. HTOL is regarded as the "ultimate test" in chip reliability verification, which is directly related to the long-term quality and service life of products.

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Test conditions and time requirements

At its core, HTOL testing lies in the application of stresses and thermal stresses that are much higher than those under normal operating conditions. The temperature is usually set between 125°C and 150°C, and high temperatures are the main factors that accelerate the chemical reaction and diffusion process. In terms of voltage, a voltage higher than the rated operating voltage is generally 1.1 times the rated voltage, but it shall not exceed the absolute maximum rated voltage. During the test process, the chip needs to be powered on and run typical loads or specific test programs to ensure that most of the internal circuits are switched and switched to simulate real-world working scenarios. The standard test period is 1000 hours, during which functional backtesting needs to be carried out at nodes such as 168 hours and 500 hours. According to the AEC-Q100 standard, Grade 0 devices can be tested for 1000 hours at 150°C for about 10 years of actual life, Grade 1 at 125°C for about 10 years, and Grade 2 at 105°C for about 5 years.

 

Sample selection and testing process

Samples must be randomly drawn from production batches and have passed all routine tests. According to the zero-failure sampling theory, the common sample size is 77 or 231, and high-standard fields such as automotive electronics require stricter failure rate targets and require larger sample sizes. The AEC-Q100 standard requires a minimum of 77 chips from each of the three non-continuous production batches, for a total of 231 chips. For chips with flash memory, a flash erase experiment is performed before testing, and checkerboard format data is written in flash memory. During the test, it is necessary to continuously read the flash memory, and at the same time run the digital part scan test, the built-in memory self-test, and each analog module. The test hardware can choose the submother structure or socket solution, and the peripheral components should be selected with high-temperature and high-voltage components and equipped with fuses to prevent short circuits.

Failure mechanism and result judgment

Common failure mechanisms in HTOL testing include electromigration, gate oxygen degradation, solder joint bond failure, and parameter drift. Electromigration refers to the migration of metal interconnect atoms to form cavities or whiskers caused by high currents, triggering open circuits or short circuits. Gate oxygen degradation includes time-lapse dielectric breakdown, which leads to gate oxygen layer defect accumulation and eventual breakdown, and gate oxygen layer defect accumulation, and threshold voltage drift. Solder creep and bond wire shedding at high temperatures are also common failure modes, while parameter drift such as increased leakage current and frequency drop will reflect a decrease in transistor driving capability. The most commonly used criteria adopted by HTOL are "zero failure", i.e. no failure is allowed at the planned sample size and test time. If failure occurs, failure analysis is required to locate the root cause, and re-verify after optimizing the design or process. After passing the test, the acceleration factor can be calculated by using acceleration models such as the Arrhenius model to calculate the expected failure rate under normal use conditions.

Industry application and practice

HTOL is the core project of group B accelerated lifecycle simulation testing in the AEC-Q100 standard, and is especially critical for automotive-grade chips. Many semiconductor companies have adopted HTOL as an indispensable quality gateway in the commercialization process. For example, a semiconductor company performs 1,000 hours of HTOL testing at 125°C for all mass-produced products, and uses sub-motherboard or socket solutions to seamlessly connect aging with backtesting of automated test equipment. During the testing process, the electrical parameters and temperature data of the chip are monitored in real time, and the cause of the abnormal chip is located through various analysis methods and fed back to the design team. Through rigorous HTOL verification, chipmakers can effectively screen for early failures, evaluate product life, and optimize design, providing high-reliability product support for key fields such as photovoltaic energy storage and electric vehicles.