Silicon Carbide Thermal Shock Parameter: 167C Explained

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Discussion Overview

The discussion revolves around the thermal shock parameter of Silicon Carbide, specifically the significance of the value 167°C in relation to thermal shock failure during rapid temperature changes. Participants explore its implications for a heat transfer project involving spray cooling of a simulated Intel chip, examining material properties and potential challenges.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant questions the meaning of the thermal shock parameter of 167°C, suggesting it might relate to a standard hardness value.
  • Another participant provides a reference to a lecture that discusses crack growth and thermal shock, indicating that thermal shock refers to stresses caused by temperature differences.
  • A participant mentions an equation for calculating the thermal shock parameter, relating it to fracture toughness but expresses uncertainty about its practical implications.
  • Concerns are raised about the potential for thermal shock when using spray cooling on Silicon Carbide, with one participant considering a gradual approach to avoid failure.
  • Discussion includes a temperature distribution scenario where one participant expresses concern that a 903°C bottom temperature could lead to shattering of the material.
  • Another participant confirms the 903°C temperature but clarifies that it pertains to the internal conditions of the chip, not the surface temperature.
  • One participant reports adjusting material selection to reduce the temperature difference to 40°C, alleviating thermal shock concerns.
  • Concerns are raised about the effects of high temperatures on electron mobility in silicon, suggesting performance issues at elevated temperatures.
  • Participants inquire about suitable insulating materials and thermal pastes for high-temperature applications.

Areas of Agreement / Disagreement

Participants express various viewpoints regarding the thermal shock parameter and its implications, with no consensus reached on its practical meaning or the best approach to mitigate thermal shock in the discussed application.

Contextual Notes

Participants mention various equations and references but do not fully resolve the implications of the thermal shock parameter or the specific material properties required for the project. The discussion reflects uncertainty regarding the effects of temperature gradients and material behavior under thermal stress.

Who May Find This Useful

This discussion may be of interest to materials scientists, engineers working on thermal management solutions, and researchers involved in high-temperature applications or ceramic materials.

Cyrus
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I am looking for a material to use, namely Silicon Carbide, and it gives a "Thermal Shock Paramter - 167C"

Obviously thermal shock is going to be failure when there is a rapid temperature change, but what does 167C mean? It's not a rate of cooling, just a temperature. I can't find anything on it in my book or in google. I am guessing it might be a value like a Hardness value set against a standard?

http://www.ceradyne.com/Uploads/Silicon_Carbide_data_sheet_10-03.pdf

I tried to call them but there closed for the rest of the week.
 
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I'm not familiar with the subject but I've found a lecture by Steve Roberts (Oxford) that might be helpful:

http://www-sgrgroup.materials.ox.ac.uk/lectures/ceramics.html

Take a look at "Handout 3: Crack growth and thermal shock", page 3.

Regards,

nazzard
 
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cyrusabdollahi said:
I am looking for a material to use, namely Silicon Carbide, and it gives a "Thermal Shock Paramter - 167C"

Obviously thermal shock is going to be failure when there is a rapid temperature change, but what does 167C mean? It's not a rate of cooling, just a temperature. I can't find anything on it in my book or in google. I am guessing it might be a value like a Hardness value set against a standard?

http://www.ceradyne.com/Uploads/Silicon_Carbide_data_sheet_10-03.pdf

I tried to call them but there closed for the rest of the week.
Are you looking for impact toughness? or fracture toughness? both of which change with temperature.

Thermal gradients induce localize stress fields, with the hotter portions normally under compression, while the cooler areas are under tension.
 
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I want to know what does this "thermal shock parameter" mean.

This is for my Heat Transfer Project, I am making a test rig to simulate an Intel Chip to test spray cooling.

If I suddenly turn on the spray cooling I might thermally shock the Silicon Carbide and destory it, so I want to know if I have to slowly turn on the spray cooling to replicate a qasi-equilirbium process to avoid thermal shock.
 
Thermal Shock Parameter = [Strength * (1-Poisson’s Ratio)] / (Elastic Modulus * Thermal Expansion Coeff.)
from - http://ceradyne.com/uploads/SiN%20Industrial%20Insert.pdf

Also see page 14 of http://www.ecm.auckland.ac.nz/course/phys130/ceramics.pdf

It is apparently related to fracture toughness, but I could only find an abstract that mentioned that fact. I think the parameter may be discussed in Callister's book on materials, but I'll have to dig it up.
 
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I saw that at the bottom, but it does not give me a 'feel' for what it really means.

As of now, its just some equation that does not tell me anything in terms of what will happen when I spray cool my simulated chip surface.

Hmm, I just saw this in your second link:

THERMAL SHOCK
Thermal shock refers to the thermal stresses that occur in a component as a result of
exposure to a temperature difference between the surface and interior or between
various regions of the component.
The peak stress typically occurs at the surface during cooling according to the
following equation:
sT = ( E a DT ) / (1-u)
When selecting a ceramic material for an application where thermal shock is expected
to be a problem, calculation of the appropriate thermal shock parameter (R) (or the
maximum allowable temperature difference, DTmax ) for various candidate materials
may be useful.

Crap, that's not what I wanted to hear. I have a temperature distribution of 70C to 903C over a span of 0.5cm. This thing will shatter. I'm going to have to find a new material.
 
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Is 903°C correct? In a chip? That's awfully hot.
 
It's correct. The surface temperature of the chip is at 70C, which is the correct operating temperature.

The temperature distribution results in the bottom surface of the chip to be 903C, but I don't care what the temperatures are at the bottom, that's not what's being simulated. But I do need to watch out for the bottom temperature because of (i) melting or (ii) thermal shock.

Because of (ii), I can't use this material anymore. I need a resistivity of 1-10 ohm-cm. I am looking at matweb for materials right now, but most don't have the right combination of properties.

This project is pushing the limits of current technology. We are putting 2000W through a 1cm^2 chip area. Very very difficult.

You have callisters book too. That book is a good paper weight. :smile:
 
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Ah yes, I played around with the numbers and material selection and I think I got a number that will work. The temp diff is only 40C, and so shock is no longer an issue. But now the material is very VERY thin, on the order of 0.8mm thick. (but still silicon carbide)

Fantabulous.
 
  • #10
This is crazy...903C!

If nothing else (melting the packaging, breaking stuff from differential thermal expansion, etc.) do you know how pathetically small electron mobilities in Si become at temperatures like that? Your chip will be at least several tens of times slower than it woulb be, close to room temperature.
 
  • #11
Cyrus..."fill in blank" is thy name!

You don't know all the details yet! :biggrin:

Don't worry, the chip is NOT at 903C. The Sillicon Carbide I was modeling the chip as, FOR THE SURFACE ONLY! Was at 70C. Due to internal heat generation and surface convection (h=400,000), the bottom temp would be at 903C. This is PERFECTLY FINE, because I AM NOT modeling the BOTTOM OF THE CHIP!

Anywho, don't sweat it. I will give you all a post with all the details once I am done with the project, as for now, I don't have the time to do all that, sorry.

Just trust me, it DOES Work. :wink:

breaking stuff from differential thermal expansion, etc.

Yes, based on that thermal shock parameter, it was a problem, but I have worked a way around it. (I think) I had to make the chip 0.8mm thick, but now the temperature differnce is only 40C. No more shock issues.
 
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  • #12
  • #13
Another question, anyone know of a material that I can use as an insulator? It has to be very thin, something I can spray on as a film on the order of nanmeters thick, if possible.
 
  • #14
Crap, anyone know of a thermal paste/grease that is good for temperatures in the range of 800C?
 

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