■ Why Vapor Chambers Are Used in Smartphones
In smartphones, heat generation is increasing due to
● High-performance SoCs
● High-speed communication
● High-performance cameras
● Fast charging
However, it is difficult to make the body thicker.
Large fans cannot be installed either.
That is why technology for dispersing heat over a wide range inside a thin enclosure becomes important.
With a vapor chamber,
Heat near the SoC
↓
Spread over a wide area of the enclosure
this keeps any one part from becoming extremely hot.
In other words, in smartphones, the purpose is not only to cool components,
but also to equalize the surface temperature that users touch.
■ In AI Servers, Handling High Heat Flux Becomes Important
In AI semiconductors, a large amount of heat is generated from a small area.
Simply handing this heat as is to a large heat sink may not make full use of the entire heat sink.
So vapor chambers and the like are used to spread heat over a wide area.
Especially in air cooling, the role of converting
the small heat source area of the chip
into
the large area of the heat sink
becomes important.
In the future, structures combining vapor chambers and liquid cooling are also conceivable.
In other words, a vapor chamber is
neither a technology exclusively for air cooling,
nor a technology exclusively for liquid cooling.
It is a heat-spreading technology that sits between the heat source and the final cooling device.
■ In 3D Semiconductors, Spreading Heat Alone May Not Be Enough
In 3D semiconductors, heat sources exist inside.
That is why simply placing a vapor chamber on the surface may not solve the thermal resistance from the inside to the surface.
In other words, the first half of the heat path,
Internal heat source
↓
Package surface
↓
TIM
↓
Vapor chamber
becomes important.
If heat stops here, the performance of the vapor chamber cannot be fully used.
In 3D integration, not only technology for spreading heat,
but technology for extracting heat from the inside becomes important.
This is covered in detail in 7-6.
■ The Vapor Chamber Concept Can Also Be Applied to Robots
In high-performance robots, heat generation is increasing from
● AI computing units
● Motor drivers
● Batteries
● Communication components
However, it is difficult to place large fans or large heat sinks.
So the concept of using thin heat-spreading components to
spread local heat into the enclosure and frame
becomes important.
Depending on the application, combinations of graphite, heat pipes, vapor chambers and the like become candidates.
■ The Direction in Which Heat Is Spread Is Also Important
It is not necessarily good to spread heat uniformly in all directions.
For example, on one side of a product there may be
● Batteries
● Temperature-sensitive sensors
● Parts that people touch
On the opposite side there may be
● A metal enclosure
● A heat sink
● Cooling components
In this case,
spreading heat in a direction you do not want to heat is not desirable.
So heat is guided in the desired direction by combining
● The shape of the vapor chamber
● The placement of graphite
● Thermal insulation materials
● The position of the TIM
● Contact areas
In next-generation thermal design, what matters more than spreading heat as much as possible is where to spread heat.
■ There Are Limits to Shape Freedom
A vapor chamber has a vapor space and wick structure inside.
That is why it cannot necessarily be freely drilled or processed into complex shapes like a general metal plate.
There are constraints from the internal structure on the outer shape, bending, holes, notches and so on.
In other words,
the vapor chamber itself is a specialized technology separate from ordinary metal foil processing.
On the other hand, the components placed around it,
● TIM
● Insulating films
● Adhesives
● EMI materials
● Protective materials
may need to be processed into complex shapes.
This is where the point of contact with precision processing manufacturers lies.
■ Multifunctionality Is Advancing Around Vapor Chambers
In actual products, a vapor chamber is not placed alone.
Around it there are
● TIM to transfer heat
● Insulating materials to stop electricity
● Adhesives to fix
● EMI materials to suppress noise
● Protective films
● Cushioning materials
In other words, it is necessary to achieve not only heat spreading, but also insulation, fixing, noise suppression and protection at the same time.
If each sheet is applied in a separate process, opportunities for misalignment increase.
Where possible, supplying multiple materials laminated in advance may reduce customer processes.
■ The Concept of Integrating Surrounding Components
For example,
Vapor chamber
＋
Insulating film
＋
Adhesive
are integrated in the required positional relationship.
Or they are supplied as
TIM
＋
Carrier film
＋
Positioning shapes
This may lead to
● Fewer applications
● Improved positional accuracy
● Reduced parts management
● Easier automation
On the other hand, as the number of layers increases,
● Thermal resistance
● Warping
● Thickness
● Interfaces
also increase.
In other words, integration is not a case of the more, the better.
It is important to combine the necessary functions in the necessary number of layers.
■ The Researcher's Perspective: Vapor Chambers Cannot Be Evaluated by Thermal Conductivity Alone
A vapor chamber is not a simple metal plate.
Inside,
● Evaporation
● Vapor movement
● Condensation
● Liquid return by capillary action
occur simultaneously.
That is why performance changes with
● Working fluid
● Wick structure
● Vapor space
● Thickness
● Orientation
● Heat input
● Cooling position
It is difficult to express all performance with just a single number for simple “thermal conductivity.”
Furthermore, in actual products,
● TIM
● Contact area
● Contact pressure
● Surrounding components
are also added.
Therefore, evaluation must be done not on the vapor chamber alone,
but on the entire actual heat path.
■ The Shop-Floor Perspective: It Is Not That Adding a High-Performance Component Makes It Cool
A vapor chamber was adopted.
But the temperature does not drop.
In this case,
one should not suspect only insufficient performance of the vapor chamber itself.
What should be checked is
● Position relative to the heat-generating body
● TIM thickness
● Air bubbles
● Contact pressure
● Warping of the vapor chamber
● Contact state on the cooling side
● Where the heat is discharged
A vapor chamber spreads heat.
However,
heat that does not come in cannot be spread.
Heat with nowhere to go cannot be discarded either.
It only functions when everything is connected from the heat source to the heat discharge destination.
■ Things to Check at the Design Stage
When using a vapor chamber, at least the following points need to be checked.
Heat source
● How much heat is generated?
● How large is the heat generation area?
● Where are the hot spots?
● In which direction do you want to spread heat?
Contact interface
● Is the TIM appropriate?
● Is the TIM thickness appropriate?
● Will air bubbles occur?
● Is contact pressure sufficient?
● Is it correctly aligned with the heat source?
Vapor chamber
● Does it have the necessary heat transport capacity?
● Does its thickness fit in the product?
● Is there a possibility of dry-out?
● Is flatness sufficient?
● Will it deform under external force?
Surrounding components
● Is insulation needed?
● Where is adhesive needed?
● Are EMI countermeasures needed?
● Is step-absorbing material needed?
● Can materials be integrated?
Final heat discharge
● Where will the heat be discarded?
● A heat sink?
● The enclosure?
● Air cooling?
● Liquid cooling?
Choosing only a vapor chamber will not solve heat problems.
It is necessary to design it as a single path from the heat source to final heat discharge.
■ OTIS's Perspective: What OTIS Aims For Is Not the Vapor Chamber Itself, but "Above and Below It"
OTIS is not a company that develops or manufactures vapor chambers themselves.
Designing the internal
● Wick structure
● Working fluid
● Vacuum sealing
● Vapor flow paths
is outside our expertise.
However, for a vapor chamber to function in an actual product,
many thin-film functional components are needed above and below it.
For example, a configuration of
Heat-generating body
↓
TIM
↓
Vapor chamber
↓
Insulating material / adhesive
↓
Heat sink / enclosure
Here,
the TIM shifts by 0.2 mm.
The insulating film warps.
Adhesive gets in directly above the heat source.
Air bubbles occur.
There are burrs at the edges.
Such small processing differences may make it impossible to fully use the performance of the vapor chamber.
In other words, OTIS’s role is
not making vapor chambers.
It lies in making the surrounding components work so that heat correctly enters and correctly leaves the vapor chamber.
■ What OTIS Can Do
At OTIS, through
● High-precision die-cutting of TIM
● Thermally conductive sheet processing
● Graphite processing
● Copper foil and aluminum foil processing
● Insulating film processing
● Adhesive processing
● EMI material processing
● Foam and cushioning material processing
● High-precision lamination
● Lamination of dissimilar materials
● Partial lamination
● Half-cutting
● Reel-to-reel processing
● Supply formats for automated application
● Integration of multiple functional materials
we may be able to contribute to processing the functional components around vapor chambers into a state that can be used in volume production.
What is particularly important is placing
thermally conductive layers
insulating layers
adhesive layers accurately in the required positional relationships.
■ Outside OTIS's Expertise
OTIS is not a company that specializes in
● Design and manufacture of vapor chambers themselves
● Wick structure development
● Working fluid development
● Vacuum sealing technology
● Heat sink design
● Design of entire cooling systems
● Dedicated CFD analysis
However, by working with vapor chamber manufacturers, material manufacturers, cooling equipment manufacturers and customers, we may be able to contribute in the area of
turning the functional components that connect vapor chambers with heat-generating bodies and cooling components into forms that can be mass-produced.
■ Industries Where This Technology Will Be Important
★★★★★ AI servers and high-performance computing
★★★★★ Semiconductors and advanced packaging
★★★★★ Smartphones
★★★★★ Communication equipment
★★★★☆ Robots and automation equipment
★★★★☆ Wearable devices
★★★★☆ Automotive electronics
★★★★☆ High-performance industrial equipment
■ Summary
A vapor chamber is not a technology for cooling heat, but a technology for spreading heat
In high-performance electronic devices,
a large amount of heat is generated from a small place.
Trying to cool this heat as is raises local temperatures.
So a vapor chamber, using the cycle of
liquid evaporation,
vapor movement,
condensation,
and liquid return,
moves heat from a small heat source to a wide area.
However, vapor chambers also have limits.
Making them thinner makes the internal space smaller.
If the amount of heat is too large, dry-out occurs.
If they warp, the contact state worsens.
If the TIM lifts, heat does not get in.
If the final heat discharge destination is insufficient, heat cannot be discarded.
In other words,
a vapor chamber alone does not solve heat problems.
What matters is making everything from
Heat-generating body
↓
TIM
↓
Vapor chamber
↓
Heat sink / enclosure / liquid cooling
work as a single heat path.
And what is important for OTIS is not making the vapor chamber itself.
It is taking the thin functional materials around it,
TIM.
Insulating films.
Adhesives.
Graphite.
Metal foils.
EMI materials.
and processing them into the necessary shapes, thicknesses and positions so that the vapor chamber can deliver its original performance.
Even with a high-performance heat-spreading component, its performance cannot be used if the entrance and exit for heat are not correctly connected.
That is why what supports the performance of a vapor chamber is
not only the advanced phase-change technology inside.
It is the interfaces of just a few tens of μm to a few mm above and below it.
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.
