STM32 gotchas
57.'H7 lifetime may be surprisingly short (at elevated working temperatures)

Microcontrollers are generally considered to be industrial-grade equipment with decades of useful working life. Usually, FLASH retention time is seen as the major limiting factor, with normal retention times at usual working temperatures being usually quoted between 20 and 100 years for various microcontroller models and makers.

Enter the ultra-high performance 'H7 family, and this is no longer the case.

Contrary to most other microcontrollers, the 'H7 family with its blazingly fast multi-hundred-megahertz performance, and huge megabytes of memories, is built using an advanced 45nm silicon technology. However, small feature size not only increases the number of transistors which can be crammed onto a chip, and increases their speed, but also increases complexity of manufacturing and decreases all margins for potential errors. This also increases impact of fearsome effects like electromigration and unwanted diffusion, which change behaviour of both conductors and semiconductors on the chip.

These effects result in reduction of effective lifetime of the chip, depending on voltage of the digital power supply voltage (usually given by setting of the internal voltage regulator as VOS0..VOS3) - which in turn determines maximum operation frequency; and junction temperature. Note, that junction (chip) temperature may be significantly different from the ambient temperature.

This issue is discussed in AN5337. At the maximum digital power supply voltage - VOS0 - and 90°C junction temperature (which at the highest frequencies and many peripherals running can be realistically reached at ambient temperatures around 50°C, nothing unusual in less-than-well ventillated enclosures) the expected lifetime is around 5 years, rapidly decreasing to 2 years with a mere 15°C increase of junction temperature to the maximum allowed 105°C.

High performance comes at a cost. Welcome to the 21th century.