What do these thermal terms mean?

[BehindEnemyLines]

I was looking thru Berquist catalog, and they've these thermal terms I don't understand.

Thermal Conductivity (W/m-K)
Thermal Conductivity (W/m?¹-K?¹)
TO-220 Thermal Performance (°C-in²/W) @ various psi
Thermal Impedance (°C/W) @ various psi

Heat Capacity (J/g-K)
Young's Modulus (psi/kPa)

Of course, whether the bigger number is better or lower number is better for each of them. It seems that the thermal performance and thermal impedance decrease as pressure (psi) increases.

Explanation in layman terms is appreciated.

 

[Mday]

Originally posted by: BehindEnemyLines
I was looking thru Berquist catalog, and they've these thermal terms I don't understand.

Thermal Conductivity (W/m-K)
Thermal Conductivity (W/m?¹-K?¹)

http://en.wikipedia.org/wiki/Thermal_conductivity

TO-220 Thermal Performance (°C-in²/W) @ various psi
Thermal Impedance (°C/W) @ various psi

Watt here is used as a measure of heat. TO-220 refers to a package design of MOSFET package. Um, the actual transistor you would buy. now at various PSI just refers to the atmospheric pressure for the most part (which is related to how high you are relative to sea lvl). Heat dissipation in air varies with the atmospheric pressure. Thermal impedance refers to how much temperature change is going to occur per Watt of heat dissipated. Thermal performance refers to how large the area of contact has to be with respect to the thermal impedance.

Since you wanted some "good bad" stuff... There isnt any. It's application specific.

Heat Capacity (J/g-K)

This refers to how much heat is needed in order to raise its temperature per mass. With respect to the units you gave, its how many JOULES does it take to raise ONE GRAM of a substance by one degree KELVIN.

Young's Modulus (psi/kPa)

This is a characteristic of a material based on a ratio between stress and strain. This is typically used to describe elasticity. It is used to predict the elongation when a material is under stress. This is before the material fails (yield strength).

 

[BehindEnemyLines]

If the material is used mainly for CPU and chipset applications, then how would the values of thermal conductivity and thermal impedance impact heat dissapation capability? I'm considering using the Gap Pad VO Ultra Soft for a laptop's chipset, and the Hi-Flow 225FT for the mobile Athon 4 1.2GHz (also considering Arctic Silver 5 since I've it now). Would the gap pad be surfficient for the chipset? And which is better for the CPU?

I've the following thermal pads & compound:

Gap Pad VO Ultra Soft
Thermal conductivity: 1.0 W/m-K
Thermal impedance vs. Pressure: not mentioned
Heat Capacity: 1.0 J/g-K
Hardness, bulk rubber, (Shore 00): 15

Typical applilcations include:
Telecommunications, computer and peripherals, power conversion, between heat generating semiconductors and a heat sink, area where heat needs to be transferred to a frame, chassis, or other type of heat spreader

Gap Pad 2500S80
Thermal conductivity: 2.7 W/m-K
Thermal impedance vs. Pressure (°C-in²/W@psi): 2.10@10; 2.05@25; 1.89@50; 1.74@100; 1.61@200
Heat Capacity: 1 J/g-K
Hardness, bulk rubber, (Shore 00): 80

Typical applilcations include:
Multiple heat generating components to a common heat sink, graphics chips to heat sinks, processors to heat sinks, mass storage drives, wireline/wireless communicatiion hardware

Hi-Flow 225FT
Thermal conductivity: 0.7 W/m-K
Thermal impedance vs Pressure (°C-in²/W@psi): 0.13@10; 0.10@25; 0.09@50; 0.07@100; 0.06@200
Heat capacity: not mentioned
Phase Change Temperature: 55°C

Typical Applications Include:
Computer and peripherals, high performance computer processors, burn in testing, heat pipes, mobile processors

Arctic Silver 5
Thermal Conductance:
>350,000W/m2 °C (0.001 inch layer) --> In Celsius not Kelvin temp scale

Thermal Resistance:
<0.0045°C-in2/Watt (0.001 inch layer)

 

[Mday]

since you're talking about a thermal transfer material (referred to as thermal compound if its a slurry, or a thermal pad if a pad), you want HIGH THERMAL CONDUCTIVITY. As for the temperature scale, a change in one degree Kelvin is equivalent to a change in one degree celsius.

 

[BehindEnemyLines]

I understand it better now. I'm wondering whether 1.0 W/m-K OR 3.0 W/m-K of thermal conductivity is sufficient for a VIA VT8362 chipset used for laptops.