Thermally conductive liquid materials for electronics packaging
directly addressed by
equipment manu-
facturers and now
have technically and
Equation 8
economically viable
solution on the
Where Δρ is the density difference, g
market.
is gravitational acceleration, η is the
viscosity of the dispersion (which de-
References
pends upon local particle concentration
1. Bar-Cohen, A.,
according to Equation 2) and r is particle
“Computer-related
radius.
thermal packaging
at the millennial
divide”. Electronics
liquid. Settling velocity of particles, which
Cooling, 2000, Vol6,
is inversely proportional to shelf life, can
No
be approximated as in Equation 8.
2. Azar, K., “The
Typically over time there is some
history of power dis-
stratification if the dispersion is left un-
sipation”. Electronics
disturbed. Shelf life is typically defined as
Cooling, 2000, Vol 6,
time during which there is no appreciable
No 1.
settling and final properties of the material
3. Harper, C.H.,
in the application are unchanged. There
“Electronic Packaging
are also procedures for remixing if the
and Interconnection
material is otherwise chemically stable.
Handbook”, Mc
Volumes: For high volume usage (5-10
Graw Hill 2000
cc per application and 106-107 applica-
4. Sergent, J. E.;
tions per year) it is economical to package
Krum, A., “Ther-
the material in pails or drums and use
mal Management
some pumping equipment to deliver the
Handbook: For
material on an assembly line. This option
Electronic Assem-
requires higher fixed costs in capital and
blies”, Mc Graw Hill
lower operating expenses. For moderate us-
2000.Biggs, D. M.
age (
~
1 cc, 104-106 applications per year)
“Thermally Conductive Polymer Composi-
16. Bird, R. B.; Stewart, W.E.; Lightfoot,
the liquids can be pre-packaged in 1-k or
tions”. Polymer Composites, 1986, Vol 7, No
E.N., “Transport Phenomena”, 2006, 2nd
2-k cartridges, which can be used in simple
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3, p.125.
Ed, Wiley. (and references there in)
11/5/2008 1:51:14 PM
automated machines that essentially push
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the material out of the cartridge using a
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piston. In this case the operating expenses
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may be slightly higher due to extra packag-
etsch, R. R., “Methods of Predicting Ther-
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ing but the fixed costs are lower. Finally,
mal Conductivity of Composite Systems:
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for smaller volume still, packaging in small
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Sanja Misra is director of R&D with The
Conclusions
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Berquist Company in Chanhassen, Minnesota,
In this paper the main thrust has been
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to focus on the physics, which underlies
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thermally conducting materials mainly
13. Thomas, D.G., J. Colloid Sci., 1965, Vol
due to lower modulus during assembly
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and better wet out. For greater success,
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15. Kitano, T.;Kataoka, T.; Shirota, T.,
particulate filler. These issues are being
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www.globalsmt.net Global SMT & Packaging – December 2008 – 25
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