Lamination is the process of laminating multiple materials together.

In thermal management components,

・Heat dissipation sheets and adhesive materials

・Graphite and insulating films

・Metal foil and adhesive materials

・TIM and protective films

・EMI materials and insulating materials

・Sealing materials and heat dissipation materials, and so on

are laminated.

However, stacking materials does not simply add up their functions.

Every time a layer is added, interfaces also increase.

As interfaces increase, so do the effects of

・Contact thermal resistance

・Air bubbles

・Foreign matter

・Interlayer delamination

・Thickness variation

・Differences in thermal expansion

That is why high-precision lamination requires not only

the technology to laminate materials together,

but also the technology to stabilize interfaces.

Lamination methods include the roll-to-roll method, which laminates continuous reel materials, and the sheet-by-sheet method, which applies sheet materials one at a time.

The roll-to-roll method is suited to mass production and continuous supply.

Management of

・Tension differences

・Meandering

・Winding pressure

・Material stretching

・Roll parallelism

is necessary.

With the sheet-by-sheet method, it can be easier to handle individual positioning and complex shapes.

However,

・Positional variation from operation to operation

・Air bubble entrapment

・Takt time

・Material handling

can be challenges.

It is not a question of which is better.

It must be chosen according to

・Material configuration

・Component size

・Production quantity

・Required accuracy

・The customer’s supply format

When laminating roll materials together, tension is applied to each material.

If materials are laminated while only one of them is pulled strongly, when the tension is released after processing, the material tries to return to its original length.

As a result,

・Warping

・Curl

・Waviness

・Dimensional change

・Interlayer stress

occur.

Especially with combinations of

・Metal foil and resin film

・Thick materials and thin materials

・Hard materials and soft materials

the effects of tension differences tend to appear.

Even if it looks flat after lamination, it may warp the moment the release film is peeled off.

In other words, what should be evaluated is not only the appearance immediately after processing.

It is flatness in the state in which the customer actually uses it.

In lamination, materials are compression-bonded between rollers.

This pressure is generally called nip pressure.

If pressure is insufficient,

・Air bubbles remain

・The adhesive surface does not make sufficient contact

・Interlayer adhesion becomes weak

may result.

On the other hand, if pressure is too high,

・Soft materials are crushed

・Adhesive squeezes out

・Materials stretch

・Graphite cracks

・Thickness changes locally

may result.

What matters is not maximum pressure.

That pressure is applied uniformly across the material width.

That the pressure suits the material configuration.

That the combination of speed and pressure is appropriate.

In other words, lamination conditions must be considered as

a combination of pressure, speed, temperature, and tension.

If the compression bonding rollers are not perfectly parallel, pressure differs between the left and right sides of the material.

Only one side is compression-bonded strongly, and pressure is insufficient on the other side.

As a result,

・Air bubbles remain on one side

・The amount of adhesive squeeze-out differs between left and right

・Thickness becomes slanted

・Material flows diagonally

・It meanders during winding

may result.

With large-area components and wide materials, slight roller differences affect the entire product.

Equipment accuracy is necessary not only for dimensional accuracy, but

for creating uniformity across the entire contact surface.

If lamination speed is too fast, materials come into contact before air is pushed out.

The time for adhesive material to conform to the irregularities of the mating surface also becomes shorter.

Conversely, if it is too slow, not only does productivity drop, but the adhesive material stays in contact with the roller longer, and deformation and adhesion may increase.

The appropriate speed differs depending on

・Softness of the adhesive material

・Roughness of the material surface

・Component width

・Compression bonding pressure

・Processing temperature

In other words, lamination speed is not merely a production capacity setting.

It is a condition for interface formation.

The adhesive layer is necessary for fixing materials.

It also has the role of filling surface irregularities and increasing actual contact area.

However, adhesive material can conduct heat less well than metals or heat dissipation materials containing high thermal conductivity fillers.

If the adhesive layer is too thick, thermal resistance increases.

If it is too thin, it cannot conform to surface irregularities and steps, and air layers remain.

In other words, for adhesive thickness, there is no simple answer that the thinner, the better.

The appropriate thickness must be decided while looking at

・Required adhesive strength

・Surface roughness

・Assembly tolerances

・Compression bonding conditions

・Thermal resistance

Pressure during lamination and die-cutting can cause adhesive material to flow out from the edges.

Squeezed-out adhesive may

・Change outer dimensions

・Adhere to surrounding components

・Collect foreign matter

・Interfere with suction by automated machines

・Cause components to stick to each other

In addition, if adhesive flows out from one part, the adhesive layer thickness in that part becomes thinner, and the contact state can change.

Adhesive squeeze-out is not only a cosmetic problem, but also

a problem of thermal resistance and supply stability.

Thermal management components may have multiple functions beyond heat dissipation, such as

・Insulation

・EMI countermeasures

・Fixing

・Waterproofing

・Cushioning

・Light shielding

When the position of each layer shifts,

・The heat dissipation layer may not cover the heat source

・The conductive material may be exposed from the insulating layer

・The adhesive layer area may be insufficient

・The seal line may be interrupted

・The EMI layer may be off the place where it is needed

In other words, high-precision lamination is not the technology to stack materials neatly.

It is the technology to stack the necessary functions in the necessary positions.

In processing thermal management components, process order is also important.

The method of laminating materials first and then die-cutting the finished outer shape.

The method of die-cutting each material first and then positioning and laminating them.

Each has advantages and challenges.

Die-cutting after lamination makes it easy to align the outer shapes of each layer.

On the other hand, because materials with different hardnesses and thicknesses are cut at the same time,

・Burrs

・Interlayer delamination

・Adhesive stringing

・Deformation of soft layers by hard layers

may occur more easily.

Laminating after die-cutting allows optimal processing conditions to be set for each material.

On the other hand, lamination position accuracy and the number of processes become challenges.

What matters is not making one or the other the standard.

It is deciding the process order from the function of the finished product and volume production stability.

Even if a component is flat, free of air bubbles, and has correct outer dimensions immediately after processing, problems can arise after it is applied to the product.

For example, cases where

・There are steps on the component surface

・The mating surface is warped

・Application pressure is insufficient

・The component is hard and cannot conform

・It warps after temperature rise due to differences in thermal expansion

・There is oil or dirt on the application surface

In other words, thermal performance cannot be completed by the processing manufacturer alone.

It is necessary to understand

・Which surface the processed component will be applied to

・With what pressure it will be assembled

・In what temperature environment it will be used

・In which direction heat will flow

In prototyping, engineers sometimes apply items carefully one at a time.

They apply while avoiding air bubbles.

If misaligned, they reapply.

They press firmly.

They select good prototypes for evaluation.

As a result, good thermal performance is obtained.

In volume production, however, it is necessary to

・Transport at high speed

・Compression-bond for a fixed time

・Change material lots

・Deal with equipment wear

・Deal with changes in temperature and humidity

・Continuously produce tens of thousands or millions of pieces

Getting a good result once in prototyping and continuing to create the same contact state in volume production are different things.

That is why, in thermal evaluation, tests that reproduce volume production processing conditions, not just material performance, are important.

In AI servers, GPUs, HBM, power supply components, optical communication components, and so on are arranged at high density.

Because heat generation density is high, local contact defects tend to show up in temperature.

There are air bubbles in part of the TIM.

Graphite is slightly misaligned.

A component is lifting due to a burr on the insulating film.

Such small processing differences may affect

・GPU temperature

・Cooling fan load

・Computing performance

・Component life

・Power consumption

In thermal management components for AI servers,

rather than the highest performance of the material, processing technology that stabilizes the contact state across every unit is important.

In advanced semiconductors and 3D packaging, minute chips and thin packages are used.

If the thickness and burrs of thermal management components vary, not only cooling performance but also the stress applied to chips changes.

If there are locally thick parts, pressure concentrates there during fastening.

With thin chips and brittle joints, excessive pressure may lead to deformation or breakage.

In other words, in processing for advanced semiconductors,

contact pressure for cooling and pressure distribution that does not break things must be achieved together.

In EVs and next-generation batteries, large-area heat dissipation materials and insulating materials are used between cells, modules, and cooling plates.

With large components, multiple small wrinkles and air bubbles tend to occur.

If contact is poor in only one part, temperature differences may arise between cells.

In batteries, temperature differences affect

・Degradation rate

・Charge/discharge performance

・Safety

・Lifespan

That is why, in lamination for EVs, what matters is not

the highest performance at one point,

but finishing a wide area in a uniform state.

In smartphones, graphite, copper foil, insulating films, adhesive materials, and so on are used in extremely thin states.

Because the components are thin, even

・Small wrinkles

・Slight stretching

・Minute chipping

・Misalignment of tens of μm

affect interference with surrounding components and heat spreading performance.

Furthermore, because the gaps between components are narrow, adhesive squeeze-out and burrs are also hard to tolerate.

The more things are miniaturized, the more important processing accuracy and interface quality become.

In medical devices and biosensors, thermal management components are sometimes used close to the human body.

If there is local lifting or poor contact, it may lead to uneven surface temperature.

In addition, foreign matter, adhesive squeeze-out, and rough edges also affect safety and cleanliness.

In medical applications, reproducibility, including

・Processing environment

・Foreign matter management

・Material history

・Processing conditions

・Inspection records

is important.

In materials research, thermal conductivity and thermal resistance are important indicators.

In actual products, however, the actual thermal resistance changes due to

・Air bubbles

・Surface roughness

・Compression bonding pressure

・Adhesive layer thickness

・Burrs

・Positional misalignment

・Material deformation

In other words, the thermal conductivity of a material alone and thermal performance within a product are not the same.

In research and development, the performance of the material itself and

the effective performance after processing and mounting must be evaluated separately.

Developing high-performance materials and reproducing that performance in products are different technologies.

On the processing floor, the following are required:

・Reducing burrs

・Eliminating air bubbles

・Preventing wrinkles

・Aligning positions

・Not letting foreign matter in

However, these are not the goals.

The true goal is to repeatedly create

・The same contact area

・The same thickness

・The same position

・The same pressure

・The same heat path

In other words, processing quality lies not in creating the appearance on the drawing,

but in reproducing thermal performance in volume production.

When requesting processing of thermal management components, drawings alone may not sufficiently convey the design intent.

If possible, the following information should be shared with the processing manufacturer.

・Where the heat-generating part is

・Where heat is to be released

・Which part is the important contact surface

・Which layer is responsible for insulation

・Which positional misalignments affect function

・How much it will be compressed during assembly

・Whether application is automatic or manual

・Whether supply is in reels or sheets

・Operating temperature range

・Required inspection items

Critical dimensions and allowable defects cannot be judged by the processing manufacturer alone.

Thermal designers, materials manufacturers, processing manufacturers, and assembly manufacturers must share the functionally important points.

When mass-processing thermal management materials, at least the following items must be checked.

Die-cutting

・Whether the outer shape sufficiently covers the heat source

・Whether holes and cutouts narrow the heat path

・Whether die clearance suits the material

・Whether burr height can be managed

・Whether changes due to blade wear can be understood

・Whether there is adhesive stringing or incomplete cuts

・Whether there is graphite chipping or particle shedding

・Whether metal foil stretches or waves

・Whether flexible materials are crushed or deformed

・Whether force is applied to the product during scrap removal

・Whether half-cut depth is stable

Lamination

・Whether the lamination method makes it hard for air bubbles to get in

・Whether wrinkles or warping occur

・Whether tension differences are managed

・Whether nip pressure suits the material configuration

・Whether pressure is uniform across the roller width

・Whether lamination speed is appropriate

・Whether adhesive layer thickness is suitable for both heat and bonding

・Whether there is adhesive squeeze-out

・Whether the positional accuracy of each layer is sufficient

・Whether the environment prevents foreign matter contamination

・Whether flatness can be maintained even after peeling and application

Evaluation

・Whether thermal performance, not just appearance, is checked

・Whether it is checked not only immediately after processing but also after storage

・Whether evaluation is done under volume production conditions rather than manual application

・Whether warping and peeling after temperature cycling are checked

・Whether material lot differences are taken into account

・Whether blade wear during volume production is evaluated

This is OTIS’s main battlefield

Materials manufacturers develop high-performance thermal management materials.

Design companies think about where heat should flow from and to.

Equipment manufacturers design heat sinks, cooling plates, fans, and liquid cooling equipment.

However, to incorporate these technologies into actual products, processes are necessary that

・Cut to the necessary shape

・Laminate in the necessary positions

・Suppress air bubbles and foreign matter

・Manage burrs and chipping

・Put things into a state that can be handled in automated processes

・Reproduce the same quality even in volume production

This is OTIS’s main battlefield.

OTIS is not a company that develops thermal materials themselves.

Nor is it a company that designs cooling equipment.

Nor is it a company that designs semiconductor chips.

However, it can take excellent thermal management materials and

turn them into parts that actually function inside products.

No matter how excellent material performance is, if it lifts by 0.1 mm, heat has difficulty flowing.

If there are burrs of tens of μm, the contact surface becomes unstable.

If there are small air bubbles, hot spots remain.

If the stacking position shifts, heat dissipation, insulation, and fixing may all break down.

That is why what OTIS supports is

the last 1 mm of thermal performance.

At OTIS, we can contribute to turning thermal management materials into mass-produced parts through processing such as the following.

・High-precision die-cutting

・Fine outer shape processing

・Hole and cutout processing

・Half-cut processing

・Reel-to-reel processing

・High-precision lamination

・Lamination of dissimilar materials

・Partial lamination

・Graphite sheet processing

・Copper foil and aluminum foil processing

・Insulating film processing

・Thermally conductive adhesive processing

・Foam and flexible material processing

・Multilayer component processing

・Reel supply

・Examining supply formats suited to automatic application

・Process design that takes burrs, chipping, air bubbles, and positional misalignment into account

・Volume production inspection including image inspection

・Component integration that takes the customer’s assembly process into account

The value OTIS provides is not raising the numbers of materials.

It is creating a state in which those numbers are not lost in actual products.

OTIS is not a company that specializes in the following fields.

・Formulation development of thermally conductive materials themselves

・Semiconductor chip and GPU design

・Thermal design of entire products

・Dedicated CFD analysis

・Design of heat sinks and cooling plates

・Development of liquid cooling equipment and entire cooling systems

・Thermal performance assurance of customers’ entire finished products

However, by working with materials manufacturers, thermal designers, cooling equipment manufacturers, and customers,

we can contribute in the area of making the functions required by thermal design work in volume production as processed components.

Rather than doing everything in-house,

“This is what OTIS can do.”

“This is where we work with materials manufacturers.”

“This is where the knowledge of equipment manufacturers is needed.”

Clarifying roles in this way leads to good thermal management.

★★★★★ AI servers and data centers

★★★★★ AI semiconductors and advanced packaging

★★★★★ EVs and next-generation batteries

★★★★★ Smartphones and smart devices

★★★★★ Optical communications and high-speed communication equipment

★★★★☆ Medical devices

★★★★☆ Robots and automation equipment

★★★★☆ Aerospace

★★★★☆ Energy equipment

★★★★☆ Industrial equipment

Thermal performance begins with materials and is completed by processing

In thermal management, material selection is important.

However, just choosing materials does not solve heat problems.

Thermal management materials deliver their designed performance only when they are

・Die-cut into the correct shape

・Laminated in the correct position

・Laminated together without air bubbles or foreign matter

・Kept free of burrs and chipping

・Maintained at appropriate thickness and flatness

・Incorporated into the product with the correct pressure

0.1 mm of lifting.

Burrs of tens of μm.

Slight air bubbles.

Small positional misalignment.

These look like small differences on a drawing.

For heat, however, they are large differences that decide whether there is a path to flow through or not.

Die-cutting is not simply a process that creates the outer shape of materials.

It is a process that creates the shape through which heat flows.

Lamination is not simply a process that applies materials.

It is a process that creates the interfaces through which heat flows.

Materials manufacturers make excellent materials.

Thermal designers think up excellent heat paths.

Cooling equipment manufacturers make excellent cooling mechanisms.

However, whether these function in actual products depends on the final processed state.

That is precisely why OTIS wants to be not just a processing company, but a company that makes thermal management work in volume production processes.

Thermal performance begins with materials.

And it is completed by processing.

 

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.