■ Why Heat Dissipation Sheets Are Needed
In electronic devices and batteries, heat must be released from heat-generating components.
For example,
● GPUs
● CPUs
● Power supply components
● Battery cells
● Communication modules
● LEDs
● Motor control boards, and so on.
When these components generate heat, it leads to reduced performance, degradation, malfunction, and shorter lifespan.
That is why it is necessary to create a path to release the generated heat somewhere.
One of the materials used to create this heat path is the heat dissipation sheet.
■ The Difference Between Heat Dissipation Sheets and TIM
Heat dissipation sheets and TIM are sometimes treated as similar terms.
In fact, there are areas where they overlap.
However, the way of thinking about them is slightly different.
TIM is mainly a material placed between heat-generating components and heat-dissipating components to lower contact thermal resistance.
In other words, the central role of TIM is to make the interface work.
Heat dissipation sheets, on the other hand, are used in a broader sense.
Heat dissipation sheets are used for purposes such as
● Conducting heat to other components
● Spreading heat in the in-plane direction
● Connecting components and enclosures
● Releasing heat while insulating
● Filling gaps
● Putting things into a form that is easy to mount
In other words, it is easier to understand if you think of TIM as an interface material,
and a heat dissipation sheet as a sheet material that creates heat paths.
■ The Basic Roles of Heat Dissipation Sheets
The main roles of heat dissipation sheets can be broadly divided into three.
1. Conducting Heat
First is the role of conducting heat from heat-generating components to heat-dissipating components.
For example,
Electronic component
↓
Heat dissipation sheet
↓
Enclosure: it creates a path for heat like this.
In this case, the heat dissipation sheet requires thermal conductivity in the thickness direction.
In other words, this is the role of releasing heat from heat-generating components to the outside.
2. Spreading Heat
Next is the role of spreading localized heat in the in-plane direction.
When only the area around a heat-generating component gets hot, a hot spot occurs.
So the heat dissipation sheet diffuses heat in the in-plane direction.
This makes it easier to suppress localized temperature rises.
In this application, in-plane thermal conductivity is important.
Graphite sheets in particular are used to spread heat in the in-plane direction.
3. Making Heat Paths Work in Volume Production
The third is the role of making heat paths work in volume production processes.
Even if heat should flow according to the design, in reality there are
● Gaps between components
● Tolerances
● Steps
● Positional misalignment
● Surface roughness
● Assembly variation
Heat dissipation sheets have the role of creating a path for heat while absorbing these real-world variations.
In other words, a heat dissipation sheet is also a material that turns theoretical thermal design into a form that can be used on the shop floor.
■ Performance Required of Heat Dissipation Sheets
The performance required of heat dissipation sheets differs depending on the application.
Typical examples include the following.
● Thermal conductivity
● Electrical insulation
● Flexibility
● Compressibility
● Heat resistance
● Flame retardancy
● Thickness accuracy
● Adhesiveness
● Processability
● Long-term reliability
● Low outgassing
In other words, a heat dissipation sheet is not a material chosen simply by thermal conductivity.
■ Choosing by Thermal Conductivity Alone Leads to Failure
There is a common misconception about heat dissipation sheets.
That is the idea that the higher the thermal conductivity, the better.
Of course, thermal conductivity is important.
In reality, however, performance is not determined by thermal conductivity alone.
For example, even with high thermal conductivity, if
● It is too hard to adhere closely
● It is too thick
● Air bubbles get in
● It does not match the pressure conditions
● The lamination is misaligned
● Insulation is insufficient
● It cracks during processing
sufficient performance may not be achieved.
In other words, with heat dissipation sheets, material specifications and
mounting state must be considered separately.
■ Thickness Greatly Affects Thermal Performance
With heat dissipation sheets, thickness is extremely important.
In general, heat passes through more easily when the material is thinner.
However, if it is too thin, it cannot absorb steps and tolerances between components.
Conversely, if it is too thick, thermal resistance tends to increase.
In other words, with heat dissipation sheets, it cannot be said that thinner is better,
nor that thicker is safer.
The necessary thickness must be designed to suit the application.
■ Softness Is Also Important
Heat dissipation sheets must conform to the irregularities and steps on component surfaces.
That is why softness and compressibility are important.
If too hard, the sheet does not adhere closely and air layers remain.
If too soft, it may lose its shape, shift position, or have problems with long-term reliability.
In other words, with heat dissipation sheets, the balance between thermal conductivity and flexibility is important.
■ Electrical Insulation Is Often Required
In electronic devices and EVs, insulation is often required at the same time as heat dissipation.
For example, this is the case when you want to release heat from a heat-generating component but do not want it to be electrically conductive.
In this case, a heat dissipation sheet is required to conduct heat and, at the same time,
not conduct electricity.
This is extremely difficult.
This is because materials that conduct heat well can, in general, also conduct electricity easily.
That is why, for insulating heat dissipation sheets, both material design and mounting design are important.
■ Heat Dissipation Sheets with Adhesive
Some heat dissipation sheets come with an adhesive layer.
Adding adhesive makes them easier to apply and easier to handle in volume production processes.
However, the adhesive layer can act as thermal resistance.
In addition, heat and aging can cause
● Reduced adhesive strength
● Peeling
● Positional misalignment
● Adhesive residue
● Changes in thickness
In other words, with adhesive-backed heat dissipation sheets,
the balance between ease of application and thermal performance is important.
■ Heat Dissipation Sheets Are Important in AI Servers
In AI servers, GPUs, memory, power supply components, and so on are generating more and more heat.
That is why heat dissipation sheets are important for
● Conducting heat to cooling components
● Mitigating hot spots
● Releasing heat while insulating
● Absorbing steps between components
In AI servers in particular, continuous operation and high reliability are required, so heat dissipation sheets need not only initial performance but also long-term stability.
■ Heat Dissipation Sheets Are Also Important in EVs and ESS
In EVs and ESS, heat must be controlled between battery cells, busbars, cooling plates, enclosures, and so on.
Here, not only heat dissipation but also
● Insulation
● Flame retardancy
● Vibration absorption
● Compression conformability
● Long-term durability
are important.
In other words, with heat dissipation sheets for EVs and ESS, thermal performance and
safety must be considered at the same time.
■ In Smartphones and Wearables, Thinness Is Important
In smartphones and wearable devices, the space for heat dissipation sheets is limited.
That is why it is important that they are
● Thin
● Light
● Bendable
● Processable into small shapes
● Easy to apply
In these applications, not only simple heat dissipation in the thickness direction, but also heat spreading in the in-plane direction is important.
■ The Researcher's Perspective: Heat Dissipation Sheets Are Multifunctional Composite Materials
In research and development, the following kinds of performance are required of heat dissipation sheets.
● High thermal conductivity
● Electrical insulation
● Flexibility
● Thinness
● Flame retardancy
● Low thermal resistance
● Long-term reliability
● Low outgassing
● Processability
In other words, a heat dissipation sheet is not just a thermally conductive material.
It is a multifunctional composite material combining thermal, electrical, mechanical, and process functions.
■ The Shop-Floor Perspective: The Performance of a Heat Dissipation Sheet Is Determined Once It Is Applied
The performance of a heat dissipation sheet is not determined by the material alone.
In reality, performance changes depending on
● What shape it is processed into
● What thickness it is made
● Where it is applied
● Whether air bubbles get in
● What pressure it is bonded with
● Whether it shifts in automated processes
● Whether contact is maintained after aging
In other words, with heat dissipation sheets, rather than the thermal conductivity in the catalog,
the thermal resistance after mounting is what matters.
■ Problems That Tend to Occur in Volume Production of Heat Dissipation Sheets
On the volume production floor, the following kinds of problems can occur with heat dissipation sheets.
● Burrs during die-cutting
● Particle shedding
● Cracking
● Deformation
● Lamination misalignment
● Thickness variation
● Air bubble entrapment
● Compatibility with release liners
● Stretching during transport
● Jamming during supply to automated machines
These affect not only thermal performance but also ease of assembly and yield.
In other words, with heat dissipation sheets, not only material selection,
but also processability and supply format are important.
■ OTIS's Perspective
OTIS is not a materials manufacturer that develops heat dissipation sheets themselves.
However, we may be able to contribute in the area of processing heat dissipation sheets into a form that can be used in volume production processes.
What matters from OTIS’s perspective is
● Processing into the intended shape
● Handling as close as possible to the intended thickness
● Supporting fine shapes
● Laminating with adhesive and insulating materials
● Laminating with dissimilar materials
● Supporting reel supply
● Making them into a form that is easy to handle in automated processes
● Suppressing variation in volume production
A heat dissipation sheet is a material and, at the same time, a process component.
That is why how to bring heat dissipation sheets into volume production processes is important.
■ What OTIS Can Do
At OTIS, through
● Heat dissipation sheet processing
● Graphite sheet processing
● Insulating heat dissipation sheet processing
● Processing of adhesive-backed heat dissipation materials
● High-precision die-cutting
● Microfabrication
● High-precision lamination
● Irregular-shape processing
● Lamination of dissimilar materials
● Reel supply
● Designing supply formats for automated processes
and more, we may be able to contribute to bringing heat dissipation sheets closer to a state in which they can be used in volume production.
Especially in AI servers, EVs, ESS, smartphones, and wearable devices, thinness, accuracy, lamination, and supply format are important.
■ Outside OTIS's Expertise
On the other hand, OTIS is not a company that specializes in
● Development of heat dissipation sheet materials themselves
● Filler formulation design
● Resin design
● Dedicated thermal simulation analysis
● Cooling equipment design
However, in the area of making heat dissipation sheets into a form that can be used in volume production processes,
we may be able to play an important role.
■ Industries Where This Technology Will Be Important
★★★★★ AI servers
★★★★★ GPUs and semiconductors
★★★★★ EVs and batteries
★★★★★ ESS and energy storage systems
★★★★☆ Smartphones
★★★★☆ Wearable devices
★★★★☆ Communication equipment
■ Summary
A heat dissipation sheet is a material that releases heat and a material that creates heat paths in volume production
A heat dissipation sheet is a sheet-type material used to release heat from heat-generating components, spread heat, and conduct heat to other components.
However, the essence of a heat dissipation sheet is not thermal conductivity alone.
Actual performance is determined by everything including
● Thickness
● Softness
● Electrical insulation
● Adhesiveness
● Processability
● Lamination accuracy
● Volume production stability
In other words, a heat dissipation sheet is something chosen by material specifications and, at the same time,
something whose performance is determined by its mounting state.
And the more heat density rises in AI servers, EVs, ESS, smartphones, wearable devices, and so on, the more important heat dissipation sheets will become.
A heat dissipation sheet is a material that releases heat.
At the same time, it is also a material for making thermal management work in volume production processes.
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.
