Thermal Test_Constant emperature vs. increase temperature

[neiltseng]

Hi all ,
i have a doubtful question
The products test thermal reliability @25deg at Thermal box , and the housing is 87deg approximately.
Will it be equivalent to the temperature +15 degree difference when I tested at 40 degrees?

or Any formula for it to explain how it is not the postive ratio ?


Thanks

 

[KlausST]

Hi,

I guess: yes.

But if you want a more reliable answer you should provide useful informations first.
Device datasheets, PCB photo, thermal conditions, like air flow....

Klaus

 

[neiltseng]

Hi Klaus,
many thanks for your reply
I understand that I can’t give enough information to get the answer what I want.
But, i can't provide too much . because some security about.

the fact, my customer need to know
Product test every components thermal value at 25deg+15deg and 40deg thermal value is equivale is or not.
but really condition , and the test result is not postive ratio between 25deg+15deg and 40deg.
i need provide some formula or fundamental to prove it.
but i have no idea and I don’t know what keywords to use to search google.

BR

 

[KlausST]

Hi,

For a raw estimation one can say 25°C + 15°C = 40°C.
This is true for a linear system.

Thermal conduction will be fairly linear.
Thermal airflow and thus convection will not be linear.
Thermal radiation will not be linear.

Klaus

 

[opampsmoker]

Well, FETs increase rdson with temperature, so you cant just do the "+15" thing.
Then again silicon diodes decrease Vf with temperature...but then SiC diodes increase Vf with temperature.

If youre product has lots of atmosphere (space) around it, then the increased convection currents at higher temp may well mean the "+15" thing will work.

But seriously, you need a thermal chamber to proove this out......the thermal chamber is king...........no calculation can gazzump a thermal chamber experiment.......none of that thermal software gets anywhere near a chamber.

Maybe you send your kit to China and they have test houses there which can thermal test your product for you.....they do it cheap and at loads of temperatures.
sorry i could not assist more.