■ Why Are Adhesive Materials Needed?
Adhesive materials do not exist simply “to stick things together.”
In reality, they play many roles, such as
● Fixing components
● Vibration damping
● Waterproofing
● Dustproofing
● Insulation
● Shortening processes
● Supporting automation
In other words, an adhesive material is not a mechanical component,
but a functional component.
■ However, Adhesive Materials Tend to Stop Heat
Ordinary adhesive materials do not conduct heat as well as metals or graphite.
For example,
thermal resistance can increase when an adhesive material is placed between copper plates compared with when the copper plates are in direct contact.
In other words, the adhesive material itself can become a wall against heat.
■ What Is a Thermally Conductive Adhesive?
That is why thermally conductive adhesives were developed.
These are materials in which thermally conductive fillers are dispersed in the adhesive.
For example,
● Alumina
● Boron nitride
● Ceramic fillers, and so on may be used.
This makes it possible to release heat to a certain extent while retaining the function of applying.
■ Thermal Conductivity Alone Cannot Be the Basis for Judgment
What is important here as well is
that judgment cannot be made from catalog specifications alone.
For example,
even with an adhesive material with high thermal conductivity, if
● It is too thick
● There are air bubbles
● Compression bonding is insufficient
● The contact area is small
heat will not actually flow.
In other words, adhesive materials are also strongly affected by contact thermal resistance.
■ Thickness Determines Thermal Performance
With adhesive materials, thermal performance changes with even a slight change in thickness.
For example, thermal resistance can differ greatly between 0.05 mm and 0.20 mm.
In other words, even with the same material, thickness control is extremely important.
■ It Also Changes with Compression Bonding Conditions
The performance of adhesive materials also changes with the compression bonding method.
For example, with insufficient pressure, air bubbles remain.
Then air layers form.
Air conducts heat poorly.
In other words, even if it looks applied, heat may not be getting through.
■ Adhesive Materials Are Increasing in AI Servers
In AI servers,
heat dissipation sheets
graphite
insulating materials
EMI materials, and so on are applied in large numbers.
In other words, the number of adhesive materials is also increasing.
The more components there are, the more adhesive layers there are.
Then thermal resistance accumulates.
That is why, in AI servers, not only the performance of the adhesive material itself, but even how many layers are applied becomes important.
■ In EVs and ESS, Long-Term Durability Is Important
It is not uncommon for EVs and ESS to be used for more than 10 years.
During that time, they repeatedly experience
● High temperatures
● Low temperatures
● Vibration
● Humidity
● Temperature cycles
Adhesive materials can, due to these effects,
● Peel
● Harden
● Flow
● Degrade
In other words, initial performance alone is meaningless.
Long-term reliability is important.
■ Adhesive Materials Can Also Absorb Stress
Adhesive materials do not only stop heat.
Soft adhesive materials can also absorb stress caused by differences in thermal expansion.
For example,
copper
resin
ceramics differ in their coefficients of thermal expansion.
If they are fixed as is, stress concentrates.
However, the presence of a soft adhesive material can relieve the stress in some cases.
In other words, adhesive materials can contribute not only to thermal management,
but also to improved reliability.
■ Stronger Adhesion Is Not Always Better
When choosing adhesive materials, looking only at adhesive strength is dangerous.
If it is too strong, rework is impossible.
Component replacement becomes difficult.
Conversely, if it is too weak, it will peel off during long-term use.
In other words, adhesive materials require design suited to the application.
■ Where to Apply It Also Matters
For both thermally conductive sheets and adhesive materials, performance changes depending on where they are applied.
For example, a 1 mm positional shift alone
can move it off the heat source.
Then performance drops significantly.
In other words, with adhesive materials, application accuracy is also important.
■ In the AI Era, Adhesive Materials Will Also Evolve
In AI servers,
wearables,
robots,
and EVs, heat density will rise further in the future.
Then there will be more situations that conventional adhesive materials cannot handle.
For example, adhesive materials that simultaneously have
● High thermal conductivity
● High insulation
● High heat resistance
● Flame retardancy
● Flexibility
● Long life
will be required.
In other words, adhesive materials are also evolving into thermal management materials.
■ The Researcher's Perspective: Adhesive Materials Are Interface Design Materials
In research and development, adhesive materials are not mere adhesives.
They are treated as materials that design the interface itself.
The required performance is wide-ranging, including
● Thermal conductivity
● Adhesive strength
● Electrical insulation
● Flexibility
● Heat resistance
● Flame retardancy
● Moisture resistance
● Long-term reliability
In other words, adhesive materials are materials that design mechanical, thermal, and electrical properties at the same time.
■ The Shop-Floor Perspective: Adhesive Performance Changes with How It Is Applied
On the volume production floor,
how it is applied
matters more than material performance.
For example, performance changes greatly depending on
● Air bubbles
● Wrinkles
● Foreign matter
● Insufficient compression bonding
● Release liner misalignment
● Application position
In other words, rather than a good adhesive material,
an adhesive material that is applied correctly is more important.
■ Problems That Tend to Occur in Volume Production for Heat × Adhesion
In volume production processes,
● Air bubble entrapment
● Application misalignment
● Peeling
● Uneven compression bonding
● Thickness variation
● Foreign matter contamination
● Deformation during reel supply
● Positional misalignment in automated application
● Adhesive squeeze-out, and so on can occur.
These affect not only thermal performance but also
waterproofing, insulation, and EMI performance.
In other words, adhesive materials are important components that also govern other performance.
■ OTIS's Perspective
OTIS is not an adhesive materials manufacturer.
However, in the area of combining adhesive materials with heat dissipation materials, insulating materials, metal foils,
graphite, EMI materials, and so on,
and processing them into a form that can be used in volume production, we may be able to contribute.
What matters from OTIS’s perspective is
● High-precision lamination
● Fine die-cutting
● Lamination of dissimilar materials
● Adhesive configuration design
● Release liner design
● Reel supply
● Support for automated application
● Dimensional stability
The value lies not so much in the adhesive material itself as in how the adhesive material is used.
■ What OTIS Can Do
At OTIS, through
● Thermally conductive adhesive processing
● Double-sided tape processing
● High-precision lamination
● Stacking with heat dissipation materials
● Stacking with insulating materials
● Fine die-cutting
● Irregular-shape processing
● Reel supply
● Support for automated application processes, and so on,
we may be able to contribute to making components that make heat × adhesion work in volume production.
■ Outside OTIS's Expertise
On the other hand, OTIS is not a company that specializes in
● Formulation development of adhesives themselves
● Resin design
● Adhesive chemistry
● Manufacturing of adhesive materials themselves
However, in processing technology that makes adhesive materials work as thermal management components, we may be able to play an important role.
■ Industries Where This Technology Will Be Important
★★★★★ AI servers
★★★★★ Data centers
★★★★★ EVs and batteries
★★★★★ ESS and energy storage systems
★★★★☆ Wearable devices
★★★★☆ Robots
★★★★☆ Smartphones
■ Summary
Applying and cooling are separate technologies
Many thermal management components are used by being applied.
However, applying and conducting heat are not the same.
Adhesive materials fix components, waterproof, insulate, and absorb stress.
On the other hand, they can also obstruct the flow of heat.
That is precisely why, with heat × adhesion, not only material performance but also
thickness,
compression bonding,
application position,
layered structure,
processing accuracy,
and mass producibility must be considered.
Future thermal management will not be determined only by what materials are used.
Its performance changes greatly depending on how they are applied and how they are mass-produced.
Column Supervisor: Koji Kakumoto (President, OTIS Co., Ltd.)
After studying abroad and working in planning and development at a trading company, he joined OTIS Co., Ltd. in 2011. While primarily working in the Corporate Planning Department, he has also served concurrently in manufacturing and technical divisions, and since 2018 has served as President, working to drive business growth and strengthen the organization.
This article is a general technical explanation intended for educational purposes and does not refer to any specific company, product, or technology.
