How do I find Contact Resistance values?

[srkangas]

I am looking for contact resistances for various values. I was wondering, does anyone know of a place or a document which has recorded data or experimental findings for different materials?
I think I am right in saying that contact resistance is only found through analytic testing...?

 

[MintJulep]

I just got this from my librarian. I haven't actually seen a copy yet, but it sounds like it might have what you are looking for.

...........................

Purdue Research Foundation recently licensed CINDAS LLC to disseminate materials properties technical data that was generated through research and testing over the past 20 years. This data has been published in two new electronic databases that are significant additions to any technical library.

THERMOPHYSICAL PROPERTIES OF MATERIALS DATABASE (TPMD):
The TPMD covers thermophysical properties such as thermal expansion, thermal conductivity, specific heat, thermal diffusivity, and thermal radiative properties like total emittance, spectral reflectance, spectral transmittance, and spectral and solar absorbance. This is the most comprehensive database of its type available. There are over 5,000 materials and over 50,000 data curves in the TPMD. The materials covered include: elemental metals, ferrous and non-ferrous alloys, single, binary, ternary oxides and mixtures of oxides; non-oxide compounds, minerals, polymers, composites, and animal and vegetable natural substances.

MICROELECTRONIC PACKAGING MATERIALS DATABASE (MPMD):
The MPMD contains data and information on thermal, mechanical, electrical, and physical properties of electronics packaging materials. The MPMD was initially developed through both basic and applied research, using both experimental techniques and literature searches by the Center for Information and Numerical Data Analysis and Synthesis
(CINDAS) at Purdue University in conjunction with the Semiconductor Research Corporation (SRC). There are over 600 materials and over 11000 data curves in the MPMD; and, it is constantly being updated and expanded with the latest materials developments.

Both the MPMD and the TPMD incorporate a newly developed data management and analysis system that allows the user to not only readily search for and access the data, but also
to compare a property of several materials on the same
graph. All datasets contain the composition of the material, the experimental conditions, the raw and smoothed data, references and dynamic graphic display. A unit conversion feature is incorporated in the system and the data can be easily exported into modeling programs. The features and capabilities of the system are too lengthy to describe in a letter. Please try the demo for each of the databases and get additional information by going to our website:

http://cindasdata.com

The MPMD and TPMD are available in electronic format in a web-based version or on a CD-ROM that can be either networked or used on an individual PC. Downloadable order forms and pricing information are available on our website. You can also contact us directly by E-mail or by phone:

CINDAS LLC
PO Box 3814
West Lafayette, Ind. 47996-3814

Phone/Fax: +1 765-746-2039
Toll Free: +1 800-696-7549 (US and Canada only)

Please feel free to contact us with any questions or comments.

The staff of CINDAS LLC

 

[iainuts]

I've generally considered contact resistance to be negligable. Looking back in my heat transfer book, it also mentions contact resistance, and states it's generally negligable. Nevertheless, it does have some information on it, about 2 pages, including a table of thermal resistances given various interfaces in a vacuum, and various interfaces given a few fluids (air, helium, hydrogen, silicone oil, glycerine).

I'd assume contact resistance could be estimated, assuming there's a fluid, by using the estimated fluid thickness and thermal conductivity of the fluid, but I'd also assume there's some contact between the two solids which increases the overall thermal conductivity of the joint. Therefore, estimating a film thickness and conductivity will result in slightly less heat transfer/higher dT than actual.

Let me know if you'd like the pages I have, I can email. Leave a note here.

 

[ko99]

Interfaces may be neglible when the heat is well spread before reaching the interface and other losses in the thermal path are high.

However when the power density is high, interface losses can be THE thermal bottleneck.

It's also very difficult to predict. Surface finishes, part alignment, clamping forces, and heat distribution effect results more than the material selection.

More data exists for interfaces that use a filler material. Try these sites:

http://www.chomerics.com

http://www.bergquistcompany.com

http://www.thermagon.com

ko (

http://www.ecooling.biz)

 

[IRstuff]

A somewhat relevant article:

http://www.coolingzone.com/Content/Library/Papers/May 1997/Article 03/May 1997_03.html

TTFN

 

[ruth44]

There was an article in "Machine Design" of Sept. 15 1960 by W.J. Graff titled:
"Thermal Conductance across metal joints".
It shows graphs of conductance vs pressure for several combinations.
I have a PDF file with the article, the readability is poor in some parts.
I'd be happy to email a copy to those interested. just post your email address here.

 

[kyong]

Reverse of contact resistence for a symplified model will be

hc = 1/Lg * (Ac/A * 2*ka*kb/(ka+kb) + Av/A*kf)

Lg=thickness of void thickness
Ac=contact area
Av=void area
A=Ac+Av, total area
ka, kb=conductivity of material of each side
kf=conductivity of fluid(air or something else) filled in void
Radiation is not included.

The main problem is that it's extremely difficult to know Ac. That's why we need experiments.
However, form the above equation, we can know a few things.
1) Increasing kf by increasing fluid pressure or filling liquid will decrease contact resistence.
2) Increasing Ac by increasing contact pressure or smoothing surface will decrease contact resistence.

Depending on various conditions, contact resistence will vary widely. Even with the same two contacting materials, 100 times difference will not be surprizing. The order of the value is around the order of fouling factors in heat exchanger design.

Here are two example values :
304 stainless steel, ground to 1.14 micron, temperature=20 deg C, contact pressure = 40~70 bar, void fluid=air ==> 0.003 h ft2 deg F/ Btu

Copper, ground to 1.27 micron, temperature=20 deg C, contact pressure = 12~200 bar, void fluid=air ==> 0.00004 h ft2 deg F/Btu

kyong