thermal management
Advances in Thermal Management Materials
and Adhesives for Electronics
The demand for thermal management materials and adhesives is
driven by the unwanted and potentially harmful heat generated by
ever-shrinking electronic components and systems in all areas of the
electronics market, including aerospace, automotive, consumer,
communications, industrial, medical, and military. In recent years more
functionality has been included in a single device and the size of each
new device has gotten smaller. Miniaturized components in tight
packages with high power output create the challenges that design
engineers are now facing.
Cooling Device
Thermal Interface
Material (TIM)
Heat-Sensitive
Component
Thermal management needs are also expanding in ”hot” niche markets
like batteries and LEDs, where increased complexity, density, and
intensity are causing manufacturers to look for new materials and
designs for better thermal conductivity, dissipation, and insulation.
Thermal Interface Material
Thermal interface material eliminates voids so that no trapped air
remains between the interface material, power device surface,
and heat sink surface.
Factors in Thermal Management
There are important basic factors that need to be considered in any
approach to thermal management. These include:
• Good heat sink or heat pipe design and proper airflow
• A high, thermally conductive interface material that is as
thin as possible
• Elimination of voids along the interface material so that no trapped
air remains between the interface material, power device surface,
and heat sink surface
Supporting high-power ICs on today’s PCBs require working within the
limitations of thermal conductivity, coefficient of thermal expansion (CTE),
weight, and rigidity. Balancing these different considerations is tricky.
For example, where copper can be very useful in thermal management,
it is not able to manage a board’s CTE, and it substantially increases
board weight.
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Thermal Interface Materials (TIMs)
As the miniaturization trend continues across a wide range of
industries, the importance of good thermal interface design has
led to development of new thermal interface materials (TIMs).
Choosing a TIM that will work in an application, an engineer
might consider power density, heat dissipation, bond line
thickness,Cleavage
processing
requirements, and reworkability.
Load
TIMs can be broadly categorized as:
• Polymer matrix composites (PMCs) – different types of
carbon fibers combined with a variety of thermosetting
and thermoplastic resins, including epoxy, cyanate ester,
liquid crystal, nylon, polycarbonate, ABS, PBT, and
polyphenylene sulfide
• Metal matrix composites (MMCs) – silicon carbide particlereinforced aluminum, beryilia particle-reinforced beryilium,
carbon fiber-reinforced aluminum, copper-tungsten, copper
molybdenum, aluminum silicon, and Invar silver
• Carbon/carbon composites (CCCs) – carbon nanofibers,
vapor grown carbon fibers, nano-graphene platelets,
pyrolitic graphite, and other carbon/carbon mixes
Advanced TIMs can provide better thermal management
characteristics as well as improvements in weight and strength
and are being integrated into a range of thermal management
solutions, including:
• Insulating, hybrid, and nonwoven papers
• Insulating solders
• Grease
• Phase change materials
• Conductive adhesives
Insulating hybrid and nonwoven papers
Light weight carbon composite laminates, aramid papers, and
nonwovens can all be used for heat insulation/dissipation.
Easily die-cut to complex shapes, they provide:
• Excellent high temperature, abrasion, and chemical resistance
• Smooth surfaces
• High torsional rigidity and stability
• High or low conductivity for absorbing, reflecting,
or conducting heat
Advanced TIMs can provide better thermal management characteristics as well as
improvements in weight and strength for advanced electronics assemblies.
Solder
New formulations in solder are delivering added thermal
control to today’s high performance, high energy, and high heat
applications. Advances in solder thermal management include:
• Lead-free die attach solder alloys
• Active solder – lead-free solder with titanium or rare-earth
elements added
• Eutectic bonding/soldering where silicone is alloyed
with metals such as gold or aluminum to offer better
heat dissipation/management
Thermal Grease
The traditional interface material in electronics is thermal
grease. Available in silicone or non-silicone varieties,
thermal grease provides:
• Low thermal resistance through excellent gap filling
• Extremely thin bond line
• Re-workable
• Easy application, including automated dispensing
• Low cost with good reliability
Thermal grease also can be applied as a thermal interface pad,
where the grease is impregnated in the pad. The thermal pad
offers the same “wetting” capability as thermal grease, but can
be die-cut to custom shapes for “drop-in-place” assembly.
Issues with grease can include contamination (for silicone
grease), pump-out during thermal cycles, and imprecise or
inconsistent application.
Phase Change Materials
Phase change materials (PCMs) are often used to supplement
some of the issues related to grease. PCMs are solids at room
temperature but change to liquid once the excess heat of a
device pushes the material past its melting point. Typically
composed of a coating of phase change compound on an
aluminum or polyimide substrate, new PCMs can be coated
directly onto a release liner without using a substrate.
This improves performance by creating a better flow when
the PCM is in the liquid stage, and better gap and void filling.
The interface is thinner without the substrate, resulting in more
efficient heat transfer.
The PCM doesn’t pump-out of the interface like grease and
the PCM is more “manufacturing-friendly.” There’s no messy
application or cleanup necessary and in many cases, PCMs
provide greater reliable thermal management over the long
run than grease.
Thermal grease can be applied as a thermal interface pad, where the grease is
impregnated in the pad. The pad can then be die-cut to a specific application shape.
Using an adhesive for thermal management requires
considering potential tradeoffs in bond strength versus heat
dissipation where thick application increases the bond but
decreases heat dissipation. It is also important to consider how
much “filler” is in the adhesive. A lot of filler provides high shear
strength but lower flexibility. Finally, the coefficient of thermal
expansion (CTE) between the component, substrate,
and adhesive must be calculated.
Thermally Conductive Adhesive
Adhesives provide unique options for thermal management.
They are often the best choice where components are not
connected by mechanical attachment, or where the
micro-movement of substrates requires adhesion for a
component to maintain contact with the substrate. They are
often used with semiconductor packages as an interface
between a chip and a heat spreader. Thermally conductive
adhesives can be configured as:
• Interface pads – conformable adhesive pads that are easy
to handle and provide high conductivity
• Liquids – usually epoxies, ultra-thin bond line and
easy integration into manufacturing dispensing equipment
• Tapes – high mechanical strength plus good surface
wetting and excellent shock absorption
From identification and selection of the appropriate materials
and adhesives, to slitting, layering, laminating, precision
die-cutting, and packaging of the finished product, Fabrico
provides the design, prototyping, testing, and manufacturing
knowledge required for success.
In addition to semiconductor applications, thermally conductive
adhesives are popular in automotive electronics, where they
are used for attachment in addition to thermal management.
It is possible to use an adhesive that combines thermal and
electrical conductivity, for example, as an electrical ground to
a board. Or conversely, to use an adhesive that is thermally
conductive but electrically insulating.
When working with customers who are designing with thermal
management in mind, finding the right adhesives and materials
is often a process of elimination. The more knowledge of how
much heat the component generates, its place within the
overall product, and other thermal management details, the
shorter the process of selecting and matching appropriate
adhesives and materials.
All the possibilities will need to be assessed in regard
to suitability for the manufacturing process and cost.
Working with an Experienced
Converter/Materials Supplier
Working with an experienced thermal management materials
and adhesives converter and industrial assembly supplier, like
Fabrico, is essential to choosing the right thermal management
materials for a particular application.
Thermally conductive adhesive tapes provide high mechanical strength plus
good surface wetting and excellent shock absorption.
Electronics OEMs are looking for converters to provide:
• Precision die-cutting, multi-layer laminating, and slitting
to tight tolerances
• Access to a range of thermal management solutions
• Testing capabilities
Fabrico selects from servo driven rotary die-cutting, CNC
die-cutting, laser die-cutting, and water jet die-cutting to meet
the complex specifications of thermal management for electronic
components. For example, a servo driven rotary die-cutter can
maintain tight tolerances ranging from 0.015” to +/-0.005” at
speeds up to 500 fpm, and is ideal for the complex, multi-layer
die-cutting, and lamination that a thermal interface pad or tape
may require.
For complex foam tape die-cutting, water jet technology provides
clean edges with no distortion. Laser die-cutting, kiss-cutting,
slitting, and laminating can also be used in converting for
medical applications.
A converter with a fully equipped test laboratory can ensure that
customer materials meet designed-in specifications before they
move to the factory floor, often eliminating the need to test
materials at the customer’s facility. A complete test lab offers:
• Accurate and precise part dimension measurement
and verification;
• Adhesive/release liner to determine converting properties
and high speed application characteristics;
• Material strength measured to ensure that material meets
application requirements;
• Static shear testing to measure the cohesive strength of
the adhesive to withstand a fixed load over time;
• Material weight measurement to determine adhesive
coating weight;
• Microscopic imaging to determine differences between
adhesive and material over time;
• Dielectric testing to determine a material’s electrical
insulation properties;
• Thermal testing for materials and adhesives;
• Resistance and voltage testing to provide a complete profile
of the electrical properties of a material or adhesive.
Material Partners
Fabrico has strategic relationships with world-class materials
suppliers, such as 3M™, Loctite®, and Adhesives Research to
assist its customers in selecting the best material for the
intended use and to expedite materials sourcing. Whether
adhesive films or liquids, all critical material properties are
considered in every Fabrico project, including chemical,
thermal, and moisture resistance.
If a grease or liquid TIM is selected, the converter can provide
and plan for easy integration into the manufacturer’s process
with dispensing recommendations and solutions.
Fabrico Headquarters
4175 Royal Drive, Suite 800, Kennesaw, GA 30144
Phone: 678-202-2700 | Fax: 678-202-2702
Toll Free
: 800-351-8273 | E-mail: info@fabrico.com
www.fabrico.com
Fabrico is a trademark of EIS, Inc.; 3M is a trademark of the 3M Company.
Loctite is a Registered Trademark of Henkel AG & Co. KGaA.