■ What Is Thinning?
Thinning means reducing the thickness of films, sheets, foils, adhesive layers, and so on.
Thin-film components used in thermal management include, for example, the following.
● Thin TIM
● Graphite sheets
● Copper foil
● Aluminum foil
● Insulating films
● Thermally conductive adhesives
● EMI countermeasure films
● Waterproof and sealing films
In smartphones, wearable devices, 3D semiconductors, AI servers, and EV electrical components, multiple functions must be incorporated into limited spaces.
That is why thinning is also required of thermal management materials.
■ Why Is Thinner Advantageous for Heat?
Thermal resistance inside a material is generally affected by thickness.
For the same material and the same area, the greater the thickness, the longer the distance heat travels.
As a result, thermal resistance in the thickness direction tends to become larger.
In other words, for TIM and heat dissipation sheets placed between heat-generating components and cooling components,
thinner often makes it easier for heat to pass through.
That is why, in AI semiconductors and power semiconductors that generate more and more heat, demand for thin TIM and thin insulating heat dissipation materials becomes strong.
■ However, Thinner Is Not Always Better
If you consider only thermal resistance, you want to make things as thin as possible.
However, actual component surfaces have
● Irregularities
● Warping
● Steps
● Dimensional tolerances
● Surface roughness
If the material is too thin, it cannot absorb these.
As a result,
● Air layers remain
● Parts do not make contact
● Pressure becomes uneven
● Edges lift
In other words, even if you think you have lowered thermal resistance by making the material thinner, poor contact can increase overall thermal resistance.
■ With Thinning, Interfaces Become More Dominant Than the Material Interior
In thick materials, the thermal resistance inside the material can account for a large proportion.
When thinned, however, the thermal resistance inside the material becomes smaller.
Then, relatively,
contact thermal resistance
interfacial thermal resistance have a larger influence.
In other words, the further thinning advances, the more performance tends to be determined not by the thermal conductivity of the material itself but by
● Adhesion state
● Surface roughness
● Air bubbles
● Compression bonding
● Adhesive layers
● Foreign matter
The thinner things get, the more it changes from a material problem to an interface problem.
■ You Also Want to Make Adhesive Layers Thinner
Adhesive layers are sometimes used to apply heat dissipation components.
However, adhesive materials often do not conduct heat as well as metals or graphite.
That is why adhesive layers also become thermal resistance in the heat path.
So the demand arises to make the adhesive layer thinner.
However, if the adhesive layer is made too thin,
● Insufficient adhesive strength
● Insufficient conformity to surface irregularities
● Peeling
● Lifting
● Reduced waterproofing
can occur.
In other words, with adhesive layers too, a balance between thinness and bonding reliability is necessary.
■ Thinner Insulating Films Are Better for Heat, but Reduce Safety Margin
When you want to stop electricity while releasing heat, insulating films are used.
Insulating films also make it easier to lower thermal resistance when they are thinner.
However, making them thinner causes problems such as
● Reduced margin against dielectric breakdown
● Greater susceptibility to burrs and foreign matter
● Greater impact of pinholes
● Metal edges coming closer
● Tearing easily during processing
In other words, in insulated heat dissipation, wanting to make it thin to cool it and
wanting to give it thickness to ensure safety collide.
■ The Thinner Metal Foil Gets, the Harder It Is to Handle
Copper foil and aluminum foil are used as materials for spreading heat.
Making them thinner is advantageous for weight reduction and space saving.
However, thin metal foil has challenges such as
● Wrinkling easily
● Folding easily
● Warping easily
● Being greatly affected by burrs
● Deforming easily during transport
● Meandering easily during winding
In addition, with thin foil, minute scratches or cracks can affect performance and reliability.
In other words, metal foil becomes higher-performance when made thinner,
while on the other hand the thinner it is made, the more difficult process design becomes.
■ Graphite Also Suits Thinning, but Becomes More Fragile
Graphite sheets are thin and light and easily spread heat in the in-plane direction.
That is why they are important in smartphones and wearable devices.
However, thin graphite is prone to
● Cracking
● Chipping
● Particle shedding
● Interlayer delamination
● Breakage when folded
● Scratches during transport
Furthermore, lamination with insulating films and adhesive materials is often necessary.
In other words, with graphite, even if the material itself is made thinner, layers increase for protection and insulation, and the overall thickness can increase.
■ With Thinning, Wrinkles Destroy Performance
A typical problem that tends to occur with thin-film materials is
wrinkles.
When there are wrinkles, the material does not adhere closely to the flat surface.
As a result,
● Air layers
● Insufficient contact area
● Uneven pressure
● Application misalignment
● Cosmetic defects
occur.
Especially in thermal management components, heat has difficulty flowing where there are wrinkles, which may create hot spots.
In other words, wrinkles in thin-film materials are not a cosmetic problem, but a heat path problem.
■ With Thinning, Stretching Becomes a Problem
Resin films, adhesive materials, and flexible sheets can stretch during transport and lamination.
When materials stretch, problems arise such as
● Dimensions change
● Hole positions shift
● Outer shapes deform
● Lamination positions shift
● Application positions become unstable
Especially in fine components, even slight stretching becomes a relatively large error.
In other words, with thinning, material stretching leads to misalignment of functional positions.
■ With Thinning, the Effect of Static Electricity Becomes Larger
Thin films are light.
That is why they are easily affected by static electricity.
Materials stick to equipment.
Two sheets overlap.
Suction positions become unstable.
They attract foreign matter.
Problems like these occur.
Because thermal management materials include conductive materials such as graphite and metal foil, managing static electricity and conductive foreign matter is important.
In other words, with thinning, not only thermal design but also static electricity and foreign matter countermeasures are necessary.
■ With Thinning, Transport Becomes More Difficult
In volume production, thin-film materials must be transported stably within equipment.
However, thin materials may
● Sag
● Meander
● Lift
● Get caught
● Stick to rollers
● Stretch under tension
That is why tension management is important in reel supply.
If tension is too weak, it meanders.
If it is too strong, it stretches.
In other words, in thin-film processing, not only the technology to cut materials,
but also the technology to transport materials stably is important.
■ With Thinning, Die-Cutting Conditions Become Stricter
When die-cutting thin-film materials, the effects of blades and processing conditions become larger.
For example, depending on
● Blade wear
● Blade edge shape
● Clearance
● Processing speed
● Material support method
● Pull from the adhesive material
problems such as
● Burrs
● Deformation
● Stringing
● Remaining die-cut scrap
● Distorted outer shapes
occur.
In other words, in thin-film processing, what matters is not only whether it is cut,
but whether it is cut without distorting the intended shape.
■ With Thinning, the Impact of Lamination Misalignment Becomes Larger
Thermal management components are sometimes made by laminating multiple thin-film materials.
For example, laminations of
● Graphite
● Insulating films
● Adhesive materials
● EMI materials
● Protective films
The thinner each layer, the larger the impact on functional areas of what is individually a small misalignment.
Insulating layers shift.
Conductive materials are exposed.
It comes off the heat source.
Waterproof lines break down.
In other words, with thinning, lamination accuracy determines product performance.
■ With Thinning, the Proportion of Thickness Variation Becomes Larger
For example, if a material 1 mm thick has a variation of 10 μm, that is 1% as a proportion.
However, if a material 50 μm thick has a variation of 10 μm, that is 20%.
In other words, even with the same absolute variation, the relative impact becomes larger the thinner the film.
This thickness variation changes
● Thermal resistance
● Compression ratio
● Contact pressure
● Insulation performance
● Lamination state
In other words, with thinning, thickness differences of a few μm can no longer be ignored either.
■ With Thinning, Evaluation Also Becomes More Difficult
Thin materials are also difficult to measure.
The material is crushed by the pressure during thickness measurement.
The values of soft materials change depending on where they are measured.
The thickness of adhesive materials changes with temperature and time.
In laminated materials, it is hard to measure the thickness of each layer separately.
In other words, with thinning, not only making things,
but also measuring them correctly becomes difficult.
■ Thinning in AI Semiconductors and 3D Semiconductors
In AI semiconductors and 3D semiconductors, many layers are stacked in limited spaces.
That is why thinning of TIM, insulating materials, adhesives, redistribution layers, and so on is important.
However, the thinner the layers become, the larger the effects of
● Interfacial thermal resistance
● Warping
● Differences in thermal expansion
● Minute air layers
● Interlayer delamination
In other words, in 3D semiconductors, both the technology to make things thinner
and the technology to bring thin layers into correct contact are necessary.
■ Thinning in Smartphones and Wearables
In smartphones and wearable devices, product thickness and weight are important.
That is why heat spreading sheets, insulating films, and adhesive materials must also be made thinner.
However, making them thinner makes it more likely that
● Uneven surface temperature
● Application misalignment
● Air bubbles
● Edge lifting
● Graphite breakage
● Reduced waterproofing
occur.
In wearable devices close to the human body, slight thermal unevenness leads to discomfort.
In other words, thinning is also directly linked to the user experience.
■ Thinning in EVs and Batteries
In EVs, thinning of insulating materials, heat dissipation materials, and adhesive materials is required for weight reduction and space saving.
However, around batteries,
● High-voltage insulation
● Flame retardancy
● Vibration durability
● Safety during thermal runaway
● Long-term reliability
are also necessary.
In other words, in EVs, wanting to make it thin and
wanting to keep a safety margin collide.
Especially with insulating materials and thermal insulation materials, the more thickness is reduced, the more difficult safety design can become.
■ Thinning in Robots
In robots, motors, sensors, wiring, and control boards are concentrated inside joints.
Using thin-film components can make joints smaller and lighter.
However, during operation,
● Bending
● Vibration
● Impact
● Thermal cycles
are applied.
Thin materials can also be prone to fatigue under repeated motion.
In other words, in robots, achieving both thinness and operational durability is important.
■ The Researcher's Perspective: With Thinning, Interface Properties Become More Important Than Material Properties
In research and development, the thermal conductivity, insulation, and heat resistance of thin-film materials are evaluated.
However, the further thinning advances, the greater the influence of interfaces compared with the material interior.
What becomes important is
● Surface roughness
● Contact pressure
● Interfacial thermal resistance
● Interlayer adhesion
● Differences in thermal expansion
● Residual stress
● Minute defects
In other words, thin-film thermal management is not only technology for making thin materials,
but also technology for making thin interfaces work.
■ The Shop-Floor Perspective: Thin Materials Move Even "When Nothing Is Being Done to Them"
Thin-film materials can change even after they are cut.
They warp.
They shrink.
Curl from winding comes back.
They stick due to static electricity.
Their dimensions change with temperature and humidity.
Adhesive material flows.
In other words, with thin-film materials, even if the dimensions are right immediately after processing, their state can change during transport, storage, and application.
In volume production, not only accuracy at the moment of processing, but also accuracy at the moment the customer uses it is important.
■ What to Check with Thinning
When designing and processing thin-film thermal management components, the following must be checked.
● How large the thermal resistance reduction effect of thinning is
● Whether surface irregularities and steps can be absorbed
● Whether there is sufficient margin in insulation performance
● Whether it stretches during transport
● Whether wrinkles or warping occur
● Whether it is affected by static electricity or foreign matter
● Whether deformation or burrs occur during die-cutting
● Whether lamination position can be maintained
● Whether thickness variation can be managed
● Whether it can be supplied stably in automated processes
● Whether peeling or lifting occurs even after thermal cycling
In other words, thinning is a challenge that includes not only material design but also processing, transport, application, and evaluation.
■ OTIS's Perspective
The intersection of thinning and heat problems is an area where OTIS is highly likely to be able to deliver value.
OTIS is not a company that develops thermal materials themselves.
However, in areas such as
● Transporting thin materials stably
● Processing into fine shapes
● Laminating dissimilar thin films with high precision
● Managing thickness and positional relationships
● Suppressing wrinkles, warping, and stretching
● Supporting reel supply
● Making them into forms that can be handled in automated processes
we may be able to contribute.
Thin-film materials cannot be used, however high-performance they are as materials, if they cannot be handled in the process.
Processing technology that turns thinness into function is important.
■ What OTIS Can Do
At OTIS, through
● Thin-film material processing
● Fine die-cutting
● Graphite sheet processing
● Copper foil and aluminum foil processing
● Insulating film processing
● Adhesive material processing
● EMI material processing
● High-precision lamination
● Lamination of dissimilar thin films
● Narrow-pitch shape processing
● Reel supply
● Designing supply formats for automated processes
and more, we may be able to contribute to bringing thin-film 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
● Semiconductor deposition processes
● Film formation of thin-film materials themselves
● GPU and semiconductor chip design
● Dedicated CFD analysis
● Design of entire cooling equipment
However, in the area of making thinned thermal management materials work in volume production in the intended shapes, positions, and supply formats,
we may be able to play an important role.
■ Industries Where This Technology Will Be Important
★★★★★ AI semiconductors and 3D semiconductors
★★★★★ Smartphones
★★★★★ Wearable devices
★★★★★ AI servers
★★★★☆ EVs and electrical components
★★★★☆ Medical devices
★★★★☆ Robots
■ Summary
Thinning lowers thermal resistance but raises process difficulty
Making thermal management materials thinner makes it easier to lower thermal resistance in the thickness direction.
It is also advantageous for space saving, weight reduction, and high-density mounting.
However, thinning causes problems such as
● Being unable to absorb steps
● Air layers remaining
● Wrinkles and warping
● Stretching
● Tearing
● Being affected by static electricity
● Greater effects of burrs and foreign matter
● A larger proportion of thickness variation
● Becoming harder to handle in automated processes
In other words, thinning is not simply making materials thinner.
It is making heat, insulation, adhesion, strength, and mass producibility work even when made thinner.
Future AI semiconductors, smartphones, wearable devices, and EVs will need even thinner thermal management components.
What will be important then is not only making the thinnest materials.
It is the technology to mass-produce thin materials without wrinkles, without misalignment, without breaking them, and in the same state.
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.
