Thermally conductive liquid materials for electronics packaging
Thermally conductive
liquid materials for
electronics packaging
by Sanjay Misra, Ph.D., The Bergquist Company, Chanhassen, MN, USA
introduction
manufacturing contrasting the differences
One-part and 2-part liquid In any electronics assembly the thermal
between pre-formed gaskets as well as ‘non-
adhesives and sealants have
pathway between die and component,
conducting’ liquids. We will end with a
long been part of the materials
component and board, board and heat
summary of the most important aspects of
portfolio used in electronics
sink/chassis, inevitably contains interfaces
thermally conductive liquid materials.
packaging. More recently
or even gaps. These interfaces are a potential
we have seen the advent of
barrier for heat flow - which can affect both
Thermal interface materials
thermally conductive liquids
performance as well as reliability of the
Thermally conductive polymeric materials
electronics. Thermally conductive polymeric
as gap fillers and adhesives
or thermal interface materials (TIMs) typi-
materials have been used in electronics
for providing a conductive
cally comprise of a polymer matrix within
assemblies since the late 80s when ther-
which thermally conductive particles have
pathway for heat. Thermally
mal management started to become more
been dispersed. The term thermally conduc-
conductive liquids, while
visible due to increasing power density in
tive is of course relative. Table 1 lists some
similar to their predecessors electronics
1,2
. Initially elastomeric gaskets
typical thermal conductivity values for some
in many respects, differ in
with relatively higher modulus ((O)
~
10
materials.
their rheology, handling and
MPa) and lower thermal conductivity (< 1
The objective of thermally conductive
dispensing characteristics of
W-m
-1
-K
-1
) appeared in the market for limited
materials is to eliminate air gaps. As the
these materials. The sig-
applications that replaced the mica/grease
table shows, the thermal conductivity of air
nificant advantages of using
combination. As power density and variety
is 2-3 orders of magnitude lower than that
thermally conductive liquids
in electronics packaging exploded in the
of typical thermal interface materials. Heat
90s, so did the development of thermally
can best be realized when
transfer can be improved significantly by
conductive materials in general. Increas-
understanding some funda-
ingly thermal management of electronics
Material Thermal Conduc-
mental characteristics of these
has become an important aspect of design
tivity (W-m
-1
-K
-1
)
materials.
activity rather than an afterthought
3,4
. As
Argon 0.018
This article presents the a result the design and usage of thermally
performance, manufacturing
conductive materials has also grown in
Air 0.026
and reliability issues related
sophistication. Typical Elastomers 0.1-0.2
to thermally enhanced liquids
Thermally conductive polymeric materi-
Alumina 20
(adhesives and gap fillers) and
als are now available in a variety of delivery
contrasts significant differences
formats and a wide range of properties. In
Aluminum Nitride 180
vis-à-vis solid pad-like materials
the recent years, the use of dispense-in-place
Boron Nitride 360 (in-plane); 1
and/or cure-in-place liquids has become
and unfilled liquids. Insights
(thru-plane)
more popular as manufacturing volumes
into storage, handling,
have grown. This is because significant ef-
Aluminum 220
dispensing and reliability of
ficiencies in material usage, manufacturing
Copper 380
such materials will be provided.
concerns regarding assembly stress, thermal
performance improvement, and structural
Pyrolytic Graphite 1500 (in-plane);
adhesion can be addressed with the use of
50 (thru-plane)
Keywords: Fillers, Dispersions,
thermally conductive liquids. Diamond 2000
Rheology, Thermal Conductivity,
In this paper we will start with a general
Single Walled 6000 (along length)
Dispensing, Manufacturing
description of thermal interfaces. In two
Carbon Nanotubes
subsequent sections will then address the
basic structure and properties of thermally
Thermal Interface 1-10
conductive materials—thermal conductiv-
Materials
This paper was originally presented at
ity and rheology. Next, we will detail issues
Table 1. Typical thermal conductivity values for some
SMTAI 2008.
relating to application performance and
materials.
18 – Global SMT & Packaging – December 2008
www.globalsmt.net
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