■ What Is Lamination?
Lamination means stacking different or similar materials as multiple layers to make a single component.
In the field of thermal management, laminated configurations such as the following can be considered.
● Graphite + insulating film + adhesive material
● Copper foil + thermally conductive adhesive
● Aluminum foil + insulating material + protective film
● TIM + carrier film + release film
● EMI material + insulating material + adhesive material
● Heat dissipation material + waterproof sealing material
● Ceramic sheet + adhesive + metal foil
Each layer has a different role.
In other words, a laminated component is not multiple materials stacked together, but multiple functions combined into one.
■ Why Is a Single Material Not Enough?
Many materials that conduct heat well also conduct electricity easily.
Copper.
Aluminum.
Graphite.
These are effective for heat spreading, but may not be usable as is in places that require electrical insulation.
So an insulating film is added.
However, the insulating film alone cannot fix the component, so adhesive material is added.
Furthermore, a protective film may be added to prevent breakage and particle shedding of the component.
As a result, it becomes a laminated configuration of
heat spreading layer
insulating layer
adhesive layer
protective layer
The more complex product requirements become, the harder lamination is to avoid.
■ Lamination Makes It Possible to Integrate Functions
When multiple components are assembled separately, the number of processes increases.
Positioning also increases.
The number of parts also increases.
On the other hand, if multiple materials can be laminated in advance and supplied as a single component, it may lead to
● Fewer parts
● Fewer assembly processes
● Fewer application operations
● Fewer positioning operations
● Fewer work errors
● Easier automation
In other words, lamination leads not only to making materials multifunctional, but also to simplifying the customer’s process.
■ However, the More Layers There Are, the More Thermal Resistance Tends to Increase
When heat passes through a laminated component in the thickness direction, it passes through every layer in turn.
Thermally conductive layer.
Adhesive layer.
Insulating layer.
Protective layer.
Each has thermal resistance.
Adhesive materials and resin films in particular can conduct heat less well than metals or graphite.
That is why, even if a high thermal conductivity material is used, if there are layers that conduct heat poorly above and below it, the thermal performance of the laminate as a whole drops.
In other words, looking only at the highest-performance layer does not tell you the performance of the laminate as a whole.
■ The Thermal Resistance of a Laminate Is Additive
In laminated structures where heat flows in the thickness direction, the thermal resistance of each layer accumulates.
For example, when heat flows through
● A heat dissipation sheet
● Adhesive material
● Insulating film
● Another adhesive material
the thermal resistance of each is added to the whole.
Even if the thermal resistance of each layer is small, it can become impossible to ignore as the number of layers increases.
Furthermore, in reality, there is not only thermal resistance inside the materials, but also interfacial thermal resistance between layers.
That is why, for the laminate as a whole, in addition to the thermal resistance of each material,
the thermal resistance of each interface must also be considered.
■ The More Interfaces There Are, the More Easily Heat Stops
When two materials are laminated together, an interface forms between them.
Even if they look closely bonded, at a microscopic level there may be
● Surface irregularities
● Air
● Foreign matter
● Uneven adhesive
● Uneven pressure
As a result, heat has difficulty flowing at the interface.
As the number of layers increases, these interfaces also increase.
In other words, in lamination, adding one layer of material
also means adding one interface that may stop heat.
■ Laminating High Thermal Conductivity Materials Does Not Guarantee High Performance
For example, suppose high thermal conductivity graphite is used as the center layer.
Even if graphite alone has high heat spreading performance, if
● A thick adhesive layer
● An insulating film that conducts heat poorly
● An interface containing air bubbles
are added, the thermal performance as a laminate drops.
In other words, using a high thermal conductivity material and heat actually flowing well are not the same.
In a laminate, the layer or interface that conducts heat least well can dominate the overall performance.
■ Match the Lamination Direction to the Direction You Want to Release Heat
When designing laminated components, it is necessary to clarify in which direction you want heat to move.
Do you want to conduct it in the thickness direction to a cooling component?
Do you want to spread it in the in-plane direction?
Do you want to guide heat to a specific place?
For example, while graphite excels at in-plane heat spreading, its heat conduction in the thickness direction may not be the same.
That is why, if the layer arrangement or material orientation is wrong, the expected heat path cannot be created.
In other words, in laminate design, not only what to stack but also in which orientation to stack it is important.
■ The Adhesive Layer Sits Between Fixing Function and Thermal Performance
In laminated components, adhesive material plays an important role.
Without adhesive material, the layers cannot be fixed.
However, adhesive material can become thermal resistance in the heat path.
Making the adhesive layer thicker
● Makes it easier to conform to surface irregularities
● Makes it easier to bond
● Makes it easier to absorb steps
On the other hand, thermal resistance in the thickness direction tends to increase.
Making it thinner is advantageous for heat, but
● Insufficient adhesive strength
● Lifting
● Peeling
● Insufficient conformity
may occur.
In other words, in the adhesive layer, thickness is needed for bonding and you want it thin for heat dissipation collide.
■ The Insulating Layer Also Becomes Thermal Resistance
To achieve both thermal management and electrical insulation, insulating films are sometimes used in laminated components.
Making the insulating layer thicker makes it easier to ensure insulation reliability.
However, the thicker it becomes, the harder it tends to be for heat to pass through.
Making it thinner is advantageous for heat, but the margin against
● Pinholes
● Burr penetration
● Dielectric breakdown
● Effects of foreign matter
● Breakage during processing
becomes smaller.
In other words, in the insulating layer too, a balance between thermal performance and electrical safety is necessary.
■ Protective Layers Are Necessary, but Can Also Interfere with Function
Films are sometimes laminated onto graphite and brittle materials for surface protection.
Protective layers can be expected to provide
● Prevention of particle shedding
● Prevention of breakage
● Added insulation
● Improved workability
On the other hand, adding a protective layer may
● Increase thickness
● Increase thermal resistance
● Change flexibility
● Cause warping
In other words, protection is necessary, but excessive protection can weaken the original thermal function.
■ Lamination Constrains Materials Against Each Other
When different materials are laminated together, each can no longer expand and contract freely.
For example, metal foil and resin film differ in how much they expand in response to temperature changes.
On their own, each can expand freely.
When laminated, however, they pull against each other.
As a result,
● Warping
● Curl
● Wrinkles
● Interlayer stress
● Peeling
● Cracks
can occur.
In other words, in a laminate, not only the properties of each material but also the combination of materials is important.
■ Differences in Coefficients of Thermal Expansion Cause Peeling
When a product warms up, each material expands.
When it cools, it contracts.
However, metals, resins, ceramics, and adhesive materials have different coefficients of thermal expansion.
When temperature changes are repeated, force is repeatedly applied to the interfaces.
As a result,
● Edge lifting
● Interlayer delamination
● Reduced adhesive strength
● Cracks
● Increased contact thermal resistance
can occur.
In other words, even if they are closely bonded in the initial state, they will not necessarily remain closely bonded after long-term use.
■ Asymmetric Laminates Warp Easily
When the laminated configuration differs between the front and back, warping tends to occur with changes in temperature and humidity.
For example, metal foil is applied to only one side.
A thick adhesive material is provided on only one side.
A different protective film is used on only one side.
In such asymmetric configurations, the contraction and expansion of each layer are not uniform.
As a result, the laminate as a whole bends.
When warping occurs, it leads to
● Transport defects
● Suction defects
● Application defects
● Reduced contact area
● Edge lifting
In other words, in laminate design, not only functional placement but also structural balance is important.
■ Foreign Matter Between Layers Destroys Performance
If foreign matter gets in during the lamination process, it is trapped inside the product.
When foreign matter gets into an interface, it may become
● Local lifting
● Air layers
● Pressure concentration
● Insulation defects
● Starting points for peeling
● Cosmetic defects
If it is conductive foreign matter, it can also cause short circuits and noise.
After lamination, it is difficult to remove foreign matter.
That is why cleanliness before lamination and foreign matter management during the lamination process are important.
■ Lamination Misalignment Accumulates Layer by Layer
A small misalignment arises when two layers are laminated, and another layer is applied on top.
Then the misalignment from each process may accumulate.
For example, it happens that
● The heat dissipation layer is in the correct position
● The insulating layer shifts slightly to the right
● The adhesive layer shifts slightly upward
● Outer shape processing also shifts slightly
As a result,
● Conductive material may be exposed
● The heat source may not be sufficiently covered
● Adhesive area may be insufficient
● Insulation distance may be insufficient
● Assembly references may not match
In other words, with laminated components, not only the accuracy of each process,
but also the cumulative accuracy as a finished product must be looked at.
■ Thickness Variation Also Accumulates
Each layer has a thickness tolerance.
Base material.
Adhesive material.
Insulating film.
Protective material.
Even if each is within tolerance, the variation in overall thickness can become larger when laminated.
When overall thickness changes,
● Contact pressure
● Compression ratio
● Thermal resistance
● Assembly height
● Gaps between components
change.
In other words, in a laminate, it is necessary to manage not only that each layer is within specification,
but also whether the total thickness after lamination is stable.
■ Results Change with Press Conditions and Lamination Conditions
In the lamination process, pressure, temperature, speed, and time are important.
If pressure is insufficient,
● Air bubbles
● Insufficient adhesion
● Local lifting
remain.
If pressure is too high,
● Adhesive squeeze-out
● Material deformation
● Reduced thickness
● Breakage of brittle materials
may occur.
If the temperature is too high, materials may soften; if it is too low, they may not adhere sufficiently.
In other words, lamination quality is determined not only by the combination of materials but also by process conditions.
■ In Roll-to-Roll Lamination, Tension Is Also Important
When continuously laminating reel-form thin-film materials, tension is applied to each material.
Each material differs in
● Stretchability
● Stiffness
● Thickness
● Surface friction
● Curl from winding
When tension differences are large,
● Wrinkles
● Meandering
● Positional misalignment
● Winding misalignment
● Curl after lamination
occur.
That is why, in continuous lamination, not only the technology to apply,
but also the technology to transport each material in the same state is necessary.
■ Layer Misalignment Also Occurs in Processing After Lamination
When laminated material is die-cut, different forces are applied to each layer.
Hard metal foil.
Soft adhesive material.
Stretchy film.
Brittle graphite.
When these are processed all at once,
● Interlayer misalignment
● Adhesive stringing
● Edge delamination
● Burrs
● Particle shedding
● Material extrusion
may occur.
In other words, in processing laminated components, condition design may need to be matched not to the easiest material to process,
but to the hardest layer to process.
■ The More Layers There Are, the Harder Inspection Becomes
The internal state of laminated components is hard to see from the outside.
Even if there are no cosmetic problems,
● Internal air bubbles
● Interlayer foreign matter
● Partially insufficient adhesion
● Internal positional misalignment
● Interlayer delamination
may exist.
The more layers there are, the harder it is to identify which interface has a problem.
In other words, in lamination, at the same time as the process of making it, it is necessary to think about how to inspect it.
■ Clarify the Role of Each Material Before Laminating
When designing laminated components, it is necessary to check whether each layer is truly necessary.
What is this layer for?
Is it to conduct heat?
To insulate?
To bond?
To protect?
To transport in the process?
If layers with unclear roles are added, only thickness, thermal resistance, cost, and processes increase.
In other words, in laminate design, it is important not to stack as much as possible, but to stack only the necessary functions.
■ Think Separately About Process Layers and Product Function Layers
In laminated components, not only functional layers that remain in the finished product, but also auxiliary layers for processing and transport are sometimes used.
For example,
● Carrier films
● Protective films
● Release films
● Separators
● Temporary fixing tape, and so on.
These are sometimes peeled off in the customer’s process.
However, if the way they are peeled or the peeling force is not stable,
● The component may deform
● Foreign matter may get onto the adhesive surface
● The laminated component may be peeled off together
● Automated machines may stop
In other words, in lamination, it is necessary to design not only the functions of the finished product but also ease of handling during the process.
■ Lamination in AI Servers
In AI servers, multiple functional components are needed around GPUs, HBM, power supply components, and high-speed communication components.
For example,
● TIM to conduct heat
● Graphite or metal foil to spread heat
● Insulating materials to stop electricity
● EMI materials to suppress noise
● Adhesive materials to fix components
Assembling these separately increases processes and the number of parts.
If they can be made into an integrated laminated component, improved ease of assembly can be expected.
On the other hand, however, increasing interfaces also increases the risk of thermal resistance and poor contact.
In other words, in AI servers, multifunctionality and
simplification of the heat path must be achieved together.
■ Lamination in 3D Semiconductors
3D semiconductors stack chips, wiring layers, insulating layers, adhesive layers, and so on vertically.
Stacking shortens wiring distances and enables higher speed and higher density.
However, heat must escape to the outside through multiple layers and interfaces.
The deeper the heat source is inside, the more layers it passes through before reaching the exit for heat.
That is why
● Interlayer thermal resistance
● Material anisotropy
● Minute voids
● Interface delamination
● Differences in thermal expansion
are important.
In other words, in 3D semiconductors, there is the fundamental contradiction of improving performance by stacking
while making it harder to release heat by stacking.
■ Lamination in EVs and Batteries
In EVs and ESS, around battery cells,
● Heat dissipation materials
● Insulating materials
● Adhesive materials
● Flame-retardant materials
● Thermal insulation materials
● Waterproofing materials, and so on are used.
If these can be laminated as multifunctional components, assembly processes and the number of parts may be reduced.
However, around batteries, they must withstand high voltage, vibration, temperature changes, and long-term use.
If one layer peels, not only thermal performance but also insulation and safety may decline.
In other words, in EVs and batteries, the reliability of laminated components supports multiple safety functions at the same time.
■ Lamination in Smartphones and Wearables
In smartphones and wearable devices, internal space is limited.
That is why multiple functions such as
● Heat spreading
● Insulation
● Bonding
● Protection
● Light shielding
● EMI countermeasures
are required to be integrated into thin laminated components.
However, the thinner and more multilayered they become, the larger the effects of misalignment of tens of μm and small air bubbles.
In addition, in products close to the human body, even slight thermal unevenness leads to discomfort.
In other words, in small devices, lamination accuracy also affects surface temperature and user experience.
■ Lamination in Robots
In robots, multiple functions such as heat, insulation, noise, and waterproofing are needed inside limited joints and enclosures.
If laminated components save space, they can contribute to making robots smaller and lighter.
On the other hand, robots repeatedly undergo bending, vibration, impact, and thermal cycling.
That is why laminated components are required not only to adhere in a stationary state, but
not to peel off even while moving continuously.
■ The Researcher's Perspective: A Laminate Is Not a Collection of Materials but a Collection of Interfaces
When thinking about a laminate, attention tends to focus on the properties of each material.
The thermal conductivity of graphite.
The withstand voltage of insulating film.
The adhesive strength of adhesive material.
However, the performance of the laminate as a whole is not the simple sum of these.
The interfaces between materials determine
● The flow of heat
● The transmission of stress
● Peeling
● Moisture ingress
● Electrical insulation
In other words, a laminate is a collection of multiple materials and, at the same time, a collection of multiple interfaces.
■ The Shop-Floor Perspective: Lamination Is Not Finished Once Things Are Applied
On the shop floor, if materials are stuck together, it looks as if lamination has been done.
However, what truly must be checked is
● Whether it is applied in the intended position
● Whether there are no air bubbles
● Whether there is no foreign matter
● Whether thickness is stable
● Whether the edges are not lifting
● Whether it does not peel even after thermal cycling
● Whether it can be peeled and applied stably in the customer’s process
In other words, lamination quality must be judged not by whether it stuck,
but by whether it can be mass-produced while maintaining the necessary functions.
■ What to Check with Lamination
When designing and processing laminated thermal management components, the following must be checked.
● Whether the role of each layer is clear
● Whether unnecessary layers are included
● In which direction heat is to flow
● How large the thermal resistance of each layer is
● Whether interfacial thermal resistance is taken into account
● Whether the adhesive layer thickness is appropriate
● Whether there is sufficient margin in insulation
● Whether warping or peeling occurs due to differences in coefficients of thermal expansion
● Whether the accumulation of lamination misalignment can be managed
● Whether variation in total thickness can be managed
● Whether foreign matter or air bubbles get between layers
● Whether it can be die-cut stably even after lamination
● Whether wrinkles or meandering occur during reel transport
● Whether it can be handled in the customer’s automated process
● Whether each function can be maintained even after long-term use
In other words, in lamination, materials, interfaces, processing, supply, and reliability must be designed as a single component.
■ OTIS's Perspective
Lamination is an area where OTIS is highly likely to be able to provide value.
OTIS is not a company that develops thermal materials themselves.
However, in areas such as
● Combining different thin-film materials
● Laminating with the intended positional relationships
● Suppressing air bubbles and wrinkles
● Managing total thickness
● High-precision processing after lamination
● Applying only partially
● Providing adhesive only partially
● Creating supply formats suited to the customer’s process
we may be able to contribute.
The value of a laminated component does not lie in stacking materials.
It lies in integrating multiple functions, in the necessary places, at the necessary thicknesses, into a state that can be mass-produced.
■ What OTIS Can Do
At OTIS, through
● High-precision lamination
● Lamination of dissimilar materials
● Partial lamination
● Multilayer die-cutting
● Graphite sheet processing
● Copper foil and aluminum foil processing
● Insulating film processing
● Thermally conductive adhesive processing
● EMI material processing
● Protective film processing
● Fine-shape processing
● Reel-to-reel processing
● Reel supply
● Designing supply formats for automated processes
and more, we may be able to contribute to bringing multifunctional laminated thermal management components closer to a state in which they can be used in volume production.
■ Outside OTIS's Expertise
On the other hand, OTIS is not a company that specializes in
● Formulation development of thermal materials themselves
● Deposition in semiconductor front-end processes
● Semiconductor chip stacking technology
● Thermal simulation of entire finished products
● Design of entire cooling equipment
● Reliability assurance of customers’ entire products
However, in the area of laminating functional materials for heat, insulation, adhesion, noise, protection, and so on and turning them into a single component that can be mass-produced,
we may be able to play an important role.
■ Industries Where This Technology Will Be Important
★★★★★ AI semiconductors and 3D semiconductors
★★★★★ AI servers
★★★★★ Smartphones
★★★★★ Wearable devices
★★★★★ EVs and batteries
★★★★☆ Medical devices
★★★★☆ Robots
■ Summary
Lamination adds functions, but also adds interfaces
Lamination makes it possible to give a single component multiple functions, such as
● Heat conduction
● Heat spreading
● Insulation
● Adhesion
● EMI countermeasures
● Waterproofing
● Protection
It may also reduce the number of parts and the customer’s processes.
However, as the number of layers increases, so do the risks of
● Thermal resistance of each layer
● Interfacial thermal resistance
● Lamination misalignment
● Thickness variation
● Air bubbles
● Foreign matter
● Warping
● Peeling
In other words, lamination is not stacking materials.
It is stacking functions without stopping the flow of heat.
In future products, multifunctional components that integrate heat, insulation, noise, bonding, and so on will become more important than single-function components that only handle thermal management.
What will be needed then is not the technology simply to stack many layers.
It is the technology to choose only the necessary layers, manage the interfaces, and keep making the same quality in the intended positions and thicknesses.
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.
