STM32F746IGT7 working at Extreme Temperature

[Athiravinod]

Dear Team,

I am using the STM32F746IGT7 microcontroller in our design. As per the datasheet, the specified maximum junction temperature is 125°C.

We would like to understand the implications of operating the IC at approximately 145°C, which is above the specified maximum junction temperature. Specifically:

• Will the IC sustain permanent damage if operated at 145°C?
• Could its functionality or performance be affected at this temperature?
• What kind of degradation or long-term effects can be expected?
• Is there any possibility of immediate failure, or could the IC continue to operate with reduced reliability?

The requirement for operation at this elevated temperature was identified after the board had already been populated with this IC. Therefore, we would like to assess the practicality and reliability of operating the existing design at approximately 145°C.

Kindly provide your recommendations and any relevant application notes or reliability data for operation beyond the specified junction temperature.

Best Regards,
Athira

[mƎALLEm]

Hello ​@Athiravinod and welcome to the ST community,

TJmax is 125°C and 145°C TJ is out of specification and we cannot guarantee the reliability of the product.

If it works: it will reduce the life time of the product and increase considerably the power consumption that, most probably, it will damage the device.

[mfgkw]

… and even worse: if “operated at 145°C” means the ambient temperature, then the junction temp will be even higher (because of power consumption).

This is why DS 10916 states for your F746IGT7 “Industrial temperature range, –40 to 105 °C” (in “8. Ordering information”).

In this case you are ~40°C too high...

[mƎALLEm]

Indeed ..

[Andrew Neil]

We would like to understand the implications of operating the IC at approximately 145°C

The implications are that you will be using it outside its specified operating conditions - so its behaviour is undefined.

ST have designed, qualified, and tested it to operate up to the specified 125°C - there are no guarantees beyond that.

 

The same would apply to any other manufacturer’s product - this is why they publish specifications!

[Andrew Neil]

This is what ST’s Sidekick AI had to say in response to, “operating beyond maximum specified temperature”:

Summary

Operating an STM32 beyond its specified temperature range is not guaranteed: once the device is outside the product operating temperature range, its electrical parameters are no longer guaranteed to remain within specification, and beyond the maximum operating temperature range there is a high probability of permanent damage. If temperature exceeds the absolute maximum ratings, those limits are only stress ratings; functional operation is not implied, and prolonged exposure can reduce reliability or lead to failure.

Detailed Explanation

1) What “beyond maximum specified temperature” means

STM32 documentation distinguishes between:

• the product operating temperature range, beyond which the device’s electrical parameters are not guaranteed to stay within specification, and
• the maximum operating temperature range, beyond which there is a high probability of permanent damage to the device.

The “maximum specified operating range” refers to the junction temperature, while the “operating temperature range” in a datasheet may refer to either ambient temperature or junction temperature, depending on the specific STM32 device.

2) Consequences of operating above the limit

If an STM32 operates above the specified operating temperature range:

• correct functionality is no longer guaranteed because the electrical characteristics are outside their guaranteed range,
• reliability can be affected with prolonged exposure,
• and if the temperature exceeds the maximum operating or absolute maximum limits, there is a risk of permanent damage or device failure.

3) Absolute maximum ratings are not operating conditions

Several STM32 datasheets state that absolute maximum ratings are stress limits only; they do not imply that the device will function correctly at those values.

So, operating above the maximum specified temperature should be treated as a stress event, not as a valid operating mode.

4) The exact limit depends on the STM32 part

The allowed maximum temperature is device-specific and is defined in the datasheet Operating conditions section. Example datasheets show that the limits can be expressed as maximum ambient temperature and/or maximum junction temperature, and may vary with power mode.

One cited example states maximum ambient temperature of 85°C for maximum power dissipation and up to 105°C for low-power dissipation, with a junction temperature range up to 105°C for VOS0 and up to 130°C for VOS3, VOS2, and VOS1.

5) Junction temperature must remain below the datasheet limit

STM32 documentation also states that the maximum operating junction temperature TJT​J​​ must never exceed the value given in the device’s general operating conditions table.

A cited calculation method is:

text

T_J(max) = T_A(max) + P_D(max) × Θ_JA

where:

• TA(max)T​A​​(max) is the maximum ambient temperature,
• PD(max)P​D​​(max) is the total power dissipation,
• Θ_JA is the junction-to-ambient thermal resistance of the package.

Because Θ_JA depends on the package, the same STM32 family can have different thermal margins depending on its package option.

[Ozone]

> I am using the STM32F746IGT7 microcontroller in our design. As per the datasheet, the specified maximum junction temperature is 125°C.

> We would like to understand the implications of operating the IC at approximately 145°C, which is above the specified maximum junction temperature.

Simple.
This is NEVER going to work.

“Junction temperature” is the result of ambient temperature plus heat internally generated by the IC itself.
The maximal ambient temperature for this device might be somewhere at 80...100°C, depending on the device design
Beyond the maximal junction temperature (and +125°C are already selected devices) it will fail totally. 
Definitely operationally, but most probably doing permanent damage.

[LCE]

semiconductor at high temperature → conductor

There’ll probably be some domino effect destroying the device.

But as you have the boards anyway: try it!

Please track the temperature and behavior - and show us some pictures afterwards! :D

[mƎALLEm]

and show us some pictures afterwards! :D

“and show us some pictures of grilled chips” 😁 

[Andrew Neil]

 

[rich.g.williams]

 

STM32F746IGT7 - LQFP 176 pins  - Industrial temp range 

The package is probably an advantage - pins not balls and lots of them.

The datasheet charts many things that are temperature dependent including HSI (internal osc)

You can adjust core voltage VOS and run SYS CLOCK at reduced frequency 

You can turn off any unused peripheral clocks 

Running your main code in SRAM means no wait states so lower SYS CLOCK will be equivalent. Expect Flash to deprogram over time so write code to check Flash, running your entire app in SRAM may have advantages. Booting it from Flash at startup when the Flash is still cool (or at ambient)

Optimise some aspects of code 

Turn off all unused GPIO

Any GPIO’s used, set them for lowest drive and slowest transition

Raise SYS CLOCK for milliseconds when needed

Consider using a Peltier 

You have two things working for you see the info encircled in red

The second table is for another device but shows VOS is important and SYS CLOCK is important and that this device will work at 130 deg C in VOS1 at 200MHz and the core can go as low as VOS3 - for this device

The main thing working for you is storage temperature at 150 deg C

The next thing is current consumption - if you can get your current consumption down, your core voltage down then look at the sums  35mA over 3.0 volts is 105 mWatt and over an LQFP176 that’s peanuts will raise package temp a few degrees maybe

You can run the whole IC on as low as VCC of 1.8V if that’s not possible you could use 3.0V 

The aim would be to keep power consumption to the sub 100mW level. Then the device begins to look like its being stored not used.  

Acid test as ​@LCE suggested and if this is important to you, put a few in an oven and test at 145 150 155 160 degrees for days

[Ozone]

> Acid test as ​@LCE suggested and if this is important to you, put a few in an oven and test at 145 150 155 160 degrees for days

The memory and bus timing falls apart, and the test board will crash and fail within one of reaching the temperature limit.
Probably reversable, but I wouldn’t push it.

 

[Ejack1979]

Plan A: Reselect a chip that works at/above this temperature.
Plan B: Make an air-conditioning/cooling box for the board/system.

[Ozone]

Plan C: Move the controlling unit to a place with acceptable ambient temperatures.

[Andrew Neil]

STM32V8 is promising operation at 140°C junction temperature.

 

Unfortunately delayed:

https://community.st.com/stm32%2Dmcus%2Dproducts%2D25/stm32v8%2Dseries%2Ddatasheet%2Dand%2Dnucleo%2Davailability%2D162750?postid=751852#post751852

 

[unsigned_char_array]

Almost frying temperature!

[MM..1]

• ​@Athiravinod simply basic physics laws… MCU live stored under 150 then exactly you can use it in low power mode =no high speed , no high current complete power into chip not exceed 10mW ambient 145 max. maybe 147,5 C
  BUT no recommend flash write at this temp, forget MHz clocks etc.
  all clocks will be shifted by temp, crystals too if used (LSE) 
• test it and will see