Dissimilar material processing means processing multiple materials with different properties into a single functional component through lamination, stacking, die-cutting, partial placement, and so on.

In the field of thermal management, there are combinations such as the following.

● Graphite and insulating film

● Copper foil and thermally conductive adhesive

● Aluminum foil and resin film

● Heat dissipation sheet and foam

● Ceramic sheet and metal foil

● EMI material and insulating material

● TIM and carrier film

● Waterproofing material and heat dissipation material

By combining different materials, a single component can be given multiple roles.

In thermal management, it is not enough simply to release heat.

In actual products, multiple requirements exist at the same time, such as

● Conducting heat

● Spreading heat

● Insulating electricity

● Suppressing noise

● Fixing components

● Conforming to steps

● Preventing water and dust

● Absorbing vibration

For example, copper foil is well suited to spreading heat.

However, it also conducts electricity.

That is why, to use it around circuits, a combination with insulating materials may be necessary.

In other words, dissimilar material processing is a technology that compensates for the weaknesses of one material with another material.

In dissimilar material components, not all materials conduct heat in the same way.

One material receives heat from the heat source.

One material spreads heat in the in-plane direction.

One material passes heat to the cooling component.

One material blocks heat.

In other words, even within a single laminated component, each material has a different thermal role.

For example, a heat path such as

Receive heat with TIM

↓

Spread heat with graphite

↓

Pass heat to the metal enclosure

can be created.

What matters is not gathering high thermal conductivity materials.

It is giving each material a clear role.

The reason dissimilar material processing is difficult is that each material behaves differently during processing.

For example, there are differences such as

● Metal foil deforms plastically easily

● Films stretch easily

● Adhesive materials stick to blades easily

● Graphite chips easily

● Ceramics crack easily

● Foams crush easily

● Gels deform and flow easily

It is difficult to cut all materials cleanly under a single set of conditions.

In other words, in dissimilar material processing, not only the hardest material,

but also the softest material

the stretchiest material

the most fragile material must be considered.

In thermal management, hard heat spreading materials are sometimes combined with soft TIM or adhesive materials.

For example,

● Metal foil and gel

● Graphite and foam

● Ceramics and adhesive material, and so on.

Hard materials easily maintain their shape.

Soft materials, on the other hand, easily conform to steps.

This combination is functionally effective.

During processing, however, only the soft material may be crushed or squeezed outward.

As a result,

● Variation in total thickness

● Uneven edges

● Adhesive squeeze-out

● Shape deformation

● Interlayer misalignment

occur.

In other words, while using different hardnesses as a function,

it is necessary to manage differences in deformation during processing.

Resin films and adhesive materials can stretch under tension.

Metal foil and ceramics, on the other hand, do not stretch the same way.

When a stretchy material is laminated in a stretched state onto a material that does not stretch easily, a force arises after processing that tries to return it to its original state.

As a result,

● Curl

● Warping

● Wrinkles

● Interlayer stress

● Positional misalignment

can occur.

Even if it is flat immediately after processing, it may warp over time.

In other words, in dissimilar material processing, not only the moment of lamination,

but also how the materials move after lamination must be considered.

Materials expand when temperature rises and contract when temperature falls.

However, the amount of expansion differs from material to material.

Metals.

Resins.

Ceramics.

Adhesive materials.

Each has a different coefficient of thermal expansion.

When different materials are laminated together, temperature changes cause each material to try to move by a different amount.

However, because they are bonded to each other, they cannot move freely.

As a result, stress arises at the interface.

This leads to

● Warping

● Peeling

● Cracks

● Edge lifting

● Changes in contact pressure

In other words, in dissimilar material components, not only initial performance but also the state after temperature changes is important.

In dissimilar material components, layers that conduct heat well and layers that do not conduct heat very well are mixed.

For example, a resin adhesive is laminated onto high thermal conductivity copper foil.

Copper foil on its own conducts heat well.

However, when heat flows in the thickness direction, it must pass through the adhesive layer.

That is why the adhesive layer can determine the overall thermal resistance.

In other words, the performance of a dissimilar material component can be limited not by the highest-performance material,

but by the part on the heat path that conducts heat least well.

In thermal management, only materials that conduct heat seem important.

However, there are cases where materials that conduct heat poorly are necessary.

For example, thermal insulation materials are sometimes used for purposes such as

● Blocking heat to surfaces that people touch

● Slowing heat propagation between battery cells

● Protecting surrounding sensors from heat

● Preventing only part of the enclosure from becoming hot

● Guiding heat in another direction

In other words, in thermal design, it is important not to release heat in every direction,

but to create directions in which heat is released and directions in which it is stopped.

By placing heat dissipation materials and thermal insulation materials where needed through dissimilar material processing, it may be possible to control the flow of heat.

In electronic devices and EVs, electricity must be insulated while releasing heat.

However, metals and graphite, which conduct heat well, are electrically conductive.

So

● Metal foil

● Graphite

● Insulating film

● Thermally conductive adhesive

are combined.

What matters here is the position and range of the insulating layer.

If the insulating material is too small, the conductive material is exposed.

If the lamination shifts, insulation distance becomes insufficient.

If there are burrs, they may penetrate the insulating layer.

In other words, in dissimilar material components that achieve both heat dissipation and insulation,

not only material performance, but also positional accuracy and edge quality determine safety.

In high-performance electronic devices, EMI/EMC countermeasures are needed at the same time as heat.

Conductive metal foil and graphite can sometimes be used for electromagnetic countermeasures.

However, if the grounding method or insulation state is wrong, the expected noise countermeasure will not be achieved.

In addition, adding EMI material can change the heat path.

That is why

● Where to release heat

● Where to send noise

● Where to insulate

● Where to ground

must be considered at the same time.

In other words, in combined heat and noise components, the path of heat and

the path of electricity must be designed separately.

In outdoor equipment, automotive components, and wearable devices, both thermal management and waterproofing are necessary.

Heat dissipation materials alone cannot stop water.

Waterproofing materials alone can trap heat.

So heat dissipation materials are combined with sealing materials and adhesive materials.

However, if there are steps or foreign matter in the waterproof line, gaps occur.

The edges of the heat dissipation material can also lift the sealing material.

In other words, to achieve both heat dissipation and waterproofing, it is not enough just to combine materials;

a continuous sealing structure that water cannot enter must be created.

In dissimilar material processing, it is not necessary to stack materials over the entire surface.

Different materials can be placed only where needed.

For example, methods such as

● Placing TIM only at the heat-generating part

● Placing graphite only at the hot part

● Placing insulating material only around conductive parts

● Placing waterproofing material only around the perimeter

● Placing EMI material only in specific parts

Partial placement may lead to

● Reduced thickness

● Reduced material usage

● Reduced thermal resistance

● Weight reduction

● Cost reduction

However, partial placement creates steps at the boundaries.

That is why the height and position of the steps must be managed.

Steps are generally treated as a problem.

However, steps are sometimes created intentionally by partially placing dissimilar materials.

For example, designs that

● Apply contact pressure only to specific components

● Make contact with components of multiple heights at the same time

● Fill gaps between components

● Conform to the enclosure shape

In this case, the step is not a defect but a function.

However, unless it is made at the intended height and position, poor contact or overcompression occurs.

In other words, in dissimilar material processing, not only the technology to eliminate steps, but also the technology to accurately create necessary steps is important.

After laminating multiple materials, outer shapes or holes are sometimes die-cut.

However, the appropriate processing conditions differ for each material.

Conditions for cutting metal foil.

Conditions for cutting resin film.

Conditions for cutting adhesive material.

Conditions for cutting foam.

These must all work in a single processing operation.

If the conditions do not match,

● Metal burrs

● Film stretching

● Adhesive stringing

● Foam crushing

● Graphite chipping

● Interlayer delamination

occur.

In other words, in integrated processing of dissimilar materials, it is not enough that all layers are cut;

all layers must be cut without losing their functions.

In dissimilar material components, half-cutting, in which only some layers are cut rather than all of them, is sometimes used.

For example, only the product component is cut, and the release film is left.

This makes it easier to supply the component in reel form and apply it automatically.

In half-cutting, however, managing the cutting depth is important.

If it is too shallow, the product remains connected when peeled off.

If it is too deep, it also damages the carrier or release film.

With dissimilar materials, the thickness of each layer also varies, so stable half-cutting becomes difficult.

In other words, blade management on the order of tens of μm determines the stability of the customer’s process.

In dissimilar material processing, adhesive material is often a problem.

Adhesive material is soft and moves with pressure and temperature.

When adhesive squeezes out from the edges during processing, it may

● Cause components to stick to each other

● Adhere to equipment

● Attract foreign matter

● Make outer dimensions unstable

● Stop automated supply

In addition, adhesive material can stretch into strings during die-cutting.

In other words, while adhesive material has the important function of fixing components,

it can also be a factor that makes the processing process unstable.

Graphite and ceramic-based materials have excellent thermal properties, but can be brittle.

If processed as is,

● Chipping

● Cracks

● Particle shedding

● Interlayer delamination

may occur.

So protective films or adhesive materials are sometimes laminated before processing.

Protective layers improve processability.

However, protective layers affect thermal resistance and thickness.

In other words, with brittle thermal materials, a balance between protecting the material and maintaining thermal performance is necessary.

Not all materials can be bonded easily.

Compatibility with adhesive materials differs depending on the nature of the material surface.

Materials with low surface energy.

Materials that shed particles easily.

Materials with rough surfaces.

Materials that are soft and deform.

These can have unstable adhesion.

Even if they are stuck in the initial state, they may peel off due to

● High temperature

● High humidity

● Vibration

● Chemicals

● Thermal cycling

In other words, in dissimilar material processing, what must be checked is not whether it can be applied,

but whether it can stay applied in the usage environment.

Surface treatment is sometimes used to improve adhesion between materials.

For example,

● Cleaning

● Plasma treatment

● Corona treatment

● Primer treatment

● Surface roughening, and so on.

Surface treatment may improve adhesion.

However, the effect of surface treatment can decline over time.

The time from treatment to lamination.

The storage environment.

Recontamination of the surface.

These must also be managed.

In other words, surface treatment is not something that is finished once it is done,

but a process that must be managed including subsequent processes.

When different materials are laminated together, warping and curl can occur.

Causes include

● Differences in coefficients of thermal expansion

● Tension differences

● Curing shrinkage of adhesive materials

● Differences in moisture absorption

● Asymmetry between front and back configurations

When warping is large, problems arise such as

● Automated machines cannot pick it up by suction

● Jamming during transport

● Application position shifts

● Edges lift

● Contact pressure becomes uneven

That is why material thickness, lamination order, tension, temperature, and so on must be adjusted.

The quality of dissimilar material components changes depending on the order in which they are processed.

Cutting the outer shape first and then laminating.

Laminating and then processing as one piece.

Processing part of it and then partially applying another material.

Each method has its own characteristics.

If each is processed individually first, each can be cut under suitable conditions.

However, lamination position accuracy is required.

If processed as one piece after lamination, outer shape positions are easy to align.

However, there is the difficulty of cutting all layers under the same conditions.

In other words, processing order must be decided not only from process convenience, but from the accuracy and function of the finished product.

If a customer is applying multiple materials one sheet at a time, supplying a dissimilar material component integrated in advance may reduce processes.

For example, if a customer is doing work such as

1.Applying insulating film

2.Applying graphite

3.Applying EMI material

4.Applying fixing tape

integrating these may make it possible to do it with a single application.

This leads to

● Shorter work time

● Less application misalignment

● Less parts management

● Less dependence on workers

● Easier automation

In other words, the value of dissimilar material processing is not only combining materials.

It is also replacing multiple customer processes with a single part.

Integrating multiple functions reduces customer processes.

However, integrating too much can cause other problems.

If even one layer is defective, the entire component becomes defective.

A change to one part of the specification requires redesigning everything.

It becomes difficult to replace individual materials.

The lamination process becomes complex and costs rise.

In other words, the more integrated, the better is not true.

It is necessary to judge how far to integrate and from where to leave things to the customer’s process.

In AI servers, multiple functions are needed around high-heat components.

● Heat transfer by TIM

● Heat spreading by graphite or metal foil

● Electrical insulation by insulating film

● Noise countermeasures by EMI material

● Fixing by adhesive material

If these can be integrated into a single multifunctional component, assembly processes may be reduced.

On the other hand, the paths of heat, electricity, and noise become complex.

That is why the role and placement of each layer must be clarified.

In 3D semiconductors and advanced packaging, materials with different properties, such as metals, insulating resins, adhesives, and ceramics, are combined at extremely close distances.

When differences in thermal expansion between materials are large, stress concentrates at minute interfaces.

As a result,

● Interlayer delamination

● Cracks

● Warping

● Bonding defects

● Increased thermal resistance

may occur.

In other words, in 3D semiconductors, not only being able to connect electrically,

but also different materials being able to coexist amid thermal changes is important.

Around batteries in EVs and ESS, heat, insulation, flame retardancy, adhesion, waterproofing, and vibration countermeasures are needed.

For example,

● Thermally conductive sheets

● Insulating films

● Flame-retardant materials

● Foams

● Adhesive materials

● Metal foil

may be combined.

Around batteries, long-term use and safety are important.

If peeling or misalignment occurs between dissimilar materials, not only thermal performance but also insulation, waterproofing, and safety functions may be lost.

In other words, in dissimilar material components for batteries, multiple functions must be maintained for the same period.

In smartphones and wearable devices, internal space is limited.

That is why there is strong demand to integrate into a single component

● Heat spreading

● Insulation

● Bonding

● Light shielding

● EMI countermeasures

● Waterproofing

Because components are small, even misalignment of tens of μm affects function.

In addition, thin metal foil, graphite, adhesive materials, and films must be handled at the same time.

In other words, in small devices, both the technology to laminate dissimilar materials thinly

and the technology to process them accurately into fine shapes are important.

In medical devices, in addition to thermal management,

● Biocompatibility

● Electrical insulation

● Waterproofing

● Flexibility

● Cleanliness, and so on are required.

In devices worn on the human body, hard heat spreading materials alone sometimes cannot be used.

They must be combined with soft resins, adhesive materials, and insulating materials.

That is why, in medical devices, thermal performance and safety and comfort in contact with the human body must be achieved together through dissimilar materials.

In robots, multiple challenges such as heat, vibration, noise, waterproofing, and insulation are concentrated in a single joint or unit.

Hard metal parts.

Soft foams.

Insulating films.

EMI materials.

Adhesive materials.

Combining these makes it possible to create multifunctional components.

However, robots keep moving.

That is why bending, vibration, impact, and thermal cycles are repeatedly applied to the interfaces between dissimilar materials.

Simply being stuck in a stationary state is not enough.

In dissimilar material components, evaluating only the properties of each material does not reveal the overall performance.

What matters is the boundary between one material and another.

At interfaces,

● Thermal resistance

● Stress concentration

● Adhesion

● Peeling

● Moisture ingress

● Electrical connection and insulation

occur.

In other words, the performance of a dissimilar material component is not simply the performance of material A plus

the performance of material B.

It is determined by the relationship between material A and material B.

When mass-producing dissimilar material components, all materials must be able to pass through the process.

If just one material

● Sticks to the blade

● Stretches

● Cracks

● Sheds particles

● Sticks due to static electricity

● Cannot withstand high temperatures

that material becomes a constraint on the entire process.

In other words, the process capability of dissimilar material processing can be determined not by

the easiest material to process,

but by the hardest material to handle.

When designing and processing thermal management components using dissimilar materials, the following must be checked.

● Whether the role of each material is clear

● In which direction heat is to flow

● In which direction heat is to be stopped

● Whether the thermal conductivity and thermal resistance of each material are appropriate

● Whether differences in coefficients of thermal expansion are not too large

● Whether differences in hardness or stretch cause warping

● Whether adhesion compatibility between materials is good

● Whether adhesion can be maintained after high temperature, high humidity, and vibration

● Whether all layers can be processed stably

● Whether burrs, chipping, particle shedding, or stringing occur

● Whether steps due to partial placement can be managed

● Whether the positional accuracy of each layer can be managed

● Whether it is easy to peel and apply in the customer’s process

● Whether integration has a process reduction effect

● Whether excessive integration has lost changeability

In other words, in dissimilar material processing, material selection, structural design, processing conditions, reliability, and the customer’s process must all be considered together.

Dissimilar material processing is an area where OTIS is highly likely to be able to provide value.

OTIS can combine materials with different properties, such as copper, aluminum, graphite, resin films, adhesive materials, and foams, and process them into functional components.

What matters from OTIS’s perspective is not only

● Processing thermal materials alone

● Cutting materials manufacturers’ sheets

It is integrating what customers need, such as

● Heat

● Insulation

● EMI

● Adhesion

● Waterproofing

● Cushioning

● Protection

into the necessary positions and shapes.

In other words, OTIS’s value lies not in selling materials,

but in turning different functional materials into a single part that customers can use.

At OTIS, through

● Lamination of dissimilar materials

● Partial lamination

● Multilayer structure processing

● High-precision die-cutting

● Half-cut processing

● Graphite processing

● Copper foil and aluminum foil processing

● Insulating film processing

● Adhesive material processing

● Foam processing

● EMI material processing

● Integrated processing of multifunctional components

● Reel-to-reel processing

● Reel supply

● Designing supply formats for automatic application

and more, we may be able to contribute to turning materials with different properties into a single functional component that can be used in volume production.

On the other hand, OTIS is not a company that specializes in

● Formulation development of thermal materials themselves

● Manufacturing of metal and resin raw materials themselves

● Semiconductor chip design

● Design of entire cooling systems

● Dedicated CFD analysis

● Safety design of customers’ entire products

However, in the area of combining functional materials with different properties and integrating challenges such as heat, insulation, noise, and bonding into a single component,

we may be able to play an important role.

★★★★★ AI servers

★★★★★ AI semiconductors and 3D semiconductors

★★★★★ EVs and batteries

★★★★★ Smartphones

★★★★★ Wearable devices

★★★★☆ Medical devices

★★★★☆ Robots

★★★★☆ Industrial equipment

Dissimilar material processing is not stacking materials, but making different functions coexist

In thermal management, it is difficult for a single material to meet every requirement.

That is why it is necessary to combine

● Materials that conduct heat

● Materials that spread heat

● Materials that insulate electricity

● Materials that fix components

● Materials that suppress noise

● Materials that stop water

● Materials that absorb vibration

However, different materials differ in

● Hardness

● Stretch

● Coefficient of thermal expansion

● Processability

● Adhesiveness

● Durability

That is why the more they are combined, the more difficult the design of processing and reliability becomes.

In other words, dissimilar material processing is not laminating multiple materials together.

It is preserving the strengths of different materials, compensating for their weaknesses, and making them coexist within the same part.

In future thermal management components, multifunctional components that integrate heat, insulation, noise, adhesion, waterproofing, and so on will increase more than single materials that handle only heat.

What will be needed then is not only gathering high-performance materials.

It is processing technology that can mass-produce materials with different properties without misalignment, without breaking them, without peeling, and with the same quality.

 

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.