■ Thermal Resistance Is How Hard It Is for Heat to Flow
Simply put, thermal resistance is how hard it is for heat to flow.
As an image, it is close to a traffic jam on heat’s path.
■ It Is Easy to Understand with Water Pipes
For example, in a thick water pipe, water flows easily.
However, if a pipe is
● Thin
● Bent
● Clogged
water has difficulty flowing.
Heat is the same.
In other words, thermal resistance expresses how hard it is for heat to pass through.
■ Heat Flows Where It Can Flow Easily
Heat moves from high temperature to low temperature.
However, if there are places where it is hard to flow along the way, heat stagnates.
Then
● Temperature rise
● Hot spots
● Reduced performance
● Degradation
occur.
In other words, heat problems are also a battle against thermal resistance.
■ AI Semiconductors Are Heading Toward "Thermal Resistance Hell"
In the AI era,
● Higher density
● Stacking
● Miniaturization
are advancing rapidly.
As a result, escape routes for heat become narrower.
In other words, thermal resistance tends to increase.
This is becoming a problem in 3D semiconductors and elsewhere.
■ Heat Can Be Generated, but It Cannot Be Released
This is important.
For example, the computing performance of AI chips keeps rising.
At the same time, however, the problem of not being able to release heat is growing.
In other words, in the future, what will matter more than how much you can compute
is how much thermal resistance can be reduced.
■ Thermal Resistance Is Not Determined by Materials Alone
Here is an extremely important point.
Many people tend to think that you should just use a material with high thermal conductivity.
In reality, however, that alone is not enough.
This is because it gets clogged along the way.
■ The Whole System Stops at Its Weakest Point
For example, suppose there is a heat path like this:
CPU
↓
TIM
↓
Heat sink
↓
Air
In this case, if there is even one place with high thermal resistance somewhere, the performance of the whole system deteriorates.
In other words, thermal management is also a battle to reduce the worst spot.
■ In Fact, Contact Becomes a Huge Thermal Resistance
What matters here is contact.
For example,
● Lifting
● Steps
● Insufficient pressure
● Air layers
These alone can cause thermal resistance to rise sharply.
In other words, a phenomenon occurs in which the material is good but it does not cool.
■ Air Is a Huge Thermal Resistance
What is especially frightening is air layers.
Air conducts heat very poorly.
In other words, even a tiny gap can greatly worsen thermal performance.
In future industries, because
● Miniaturization
● Stacking
● Thinner films
are advancing, even gaps at the level of a few tens of μm become a problem.
■ Miniaturization Makes Thermal Resistance Rise Sharply
Here lies the difficulty of future industries.
For example, in
● Semiconductors
● Robots
● AR glasses
● EVs
miniaturization is advancing.
As a result,
● Heat paths become narrower
● Contact area decreases
● Heat density increases
In other words, the thermal resistance problem worsens rapidly.
■ Thermal Resistance Is Invisible
What makes it even more difficult is that thermal resistance is invisible.
For example, even just
● Slight lifting
● Tiny steps
● Uneven pressure
can change thermal performance.
But this often cannot be seen with the naked eye.
In other words, the thermal resistance problem is also an invisible traffic jam.
■ The AI Era Will Be a Battle Against Thermal Resistance
In the AI era,
● Increasing computing density
● Higher output
● Miniaturization
● Stacking
will advance.
As a result, thermal resistance becomes a major bottleneck.
In other words, in the future, what will matter is not only how high-performance something is,
but how much thermal resistance can be reduced.
■ The Researcher's Perspective: Designing Heat Paths Becomes Important
Current research includes
● High thermal conductivity materials
● TIM
● Heat dissipation structures
● Fine contact
● Heat spreading
● Liquid cooling
In other words, thermal design is also design for how to reduce thermal resistance.
■ The Shop-Floor Perspective: You Lose on Contact Rather Than on Theoretical Performance
On the shop floor, thermal resistance changes greatly due to
● Lifting
● Air layers
● Uneven pressure
● Tiny misalignment
● Material deformation
In other words, even if something is high-performance in theory, it may not actually cool.
■ Heat Problems Are Decided by the Process
For example, thermal resistance also changes with
● Lamination accuracy
● Pressure conditions
● Surface condition
● Processing accuracy
● Automation stability
In other words, thermal management is determined not only by material performance,
but by making the process work.
■ What Matters from OTIS's Perspective
From OTIS’s perspective, what matters in heat problems includes
● Microfabrication
● High-precision lamination
● Contact stability
● Thin-film processing
● Contact between dissimilar materials
● Tolerance control
● Volume production stability
In other words, OTIS is committed to processes that do not increase thermal resistance.
■ What OTIS Can Do
At OTIS, through
● Microfabrication
● High-precision die-cutting
● High-precision lamination
● Processing of thermal management materials
● Stacking of irregular shapes
● Support for automated supply
we may be able to contribute to making a state in which heat flows work in volume production.
■ Outside OTIS's Expertise
On the other hand, OTIS is not a company that specializes in
● Semiconductor design
● Dedicated CFD analysis
● GPU design
● Cooling equipment design
However, in the area of making heat solutions work in volume production processes, we may be able to play an important role.
■ Summary
The essence of heat problems is a battle against thermal resistance
Heat naturally tries to flow.
However, if there are places where heat has difficulty flowing along the way, heat stagnates.
This is thermal resistance.
And in future industries, due to
● Miniaturization
● Higher density
● Stacking
thermal resistance problems will become increasingly important.
In other words, in the future, what will become extremely important is not only how much heat is generated,
but how much thermal resistance can be reduced.
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.
