■ Why Does Contact Become a Problem?
For example, even if you think you have brought
● A CPU
● A heat dissipation material
● A heat sink
into tight contact,
in reality, they are not in complete contact.
This is one of the essences of heat problems.
■ Metal Surfaces Are Uneven
Even metal that looks flat at first glance has, at the microscopic level,
tiny irregularities.
In other words, in reality, the surfaces are close to being in point contact.
■ Where There Is No Contact, There Is Air
What is problematic here is air layers.
As mentioned last time, air conducts heat very poorly.
In other words, even a tiny gap worsens the flow of heat.
This is contact thermal resistance.
■ Why "Good Materials but No Cooling" Happens
A phenomenon that often occurs on the shop floor is that you used a high-thermal-conductivity material but it does not cool.
In many cases, this is caused by contact thermal resistance.
In other words, there are cases in which how things are in contact matters more than material performance.
■ Contact Thermal Resistance Is the Final Enemy
This is extremely important.
For example, suppose there is a heat path like this:
CPU
↓
TIM
↓
Heat sink
Even if the materials themselves are high-performance, heat can stop at the contact areas due to
● Lifting
● Insufficient pressure
● Steps
● Surface roughness
In other words, the final contact ends up determining the performance of the whole system.
■ TIM Is a Gap-Filling Technology
What matters here is TIM (Thermal Interface Material).
Simply put, TIM is a material that fills gaps.
For example,
● Grease
● Sheets
● Gels
● Putty
These are used to reduce air layers.
In other words, TIM can also be described as a technology for reducing contact thermal resistance.
■ But Adding TIM Is Not the End of It
This is important on the shop floor.
Even with TIM, contact thermal resistance changes due to
● Insufficient pressure
● Uneven thickness
● Air bubbles
● Misalignment
● Changes over time
In other words, just using TIM is not enough.
■ In the AI Era, Contact Thermal Resistance Becomes Even More Important
In the AI era,
● Higher semiconductor density
● Stacking
● Miniaturization
will advance.
As a result, heat density rises sharply.
In other words, consider a small gap.
Even that can lead to a large rise in temperature.
■ A Few Tens of μm Can Stop the Future
In future industries, even just
● Lifting of a few tens of μm
● Tiny steps
● Uneven pressure
can change thermal performance.
In other words, in the future, a few tens of μm may determine
● AI performance
● EV lifetime
● Semiconductor performance
● Robot stability
■ Why Does It Become Difficult in Volume Production?
Even if there are no problems in prototyping, things can fall apart in volume production.
The reasons include
● Tolerances
● Assembly variation
● Pressure fluctuations
● Material deformation
● Automation errors
In other words, contact thermal resistance is also a problem that suddenly becomes difficult in volume production.
■ In EVs, Contact Is Directly Linked to Safety
EVs use components such as
● Batteries
● Heat dissipation plates
● TIM
● Insulating materials
If poor contact occurs here, it may lead to
● Heat concentration
● Degradation
● Thermal runaway
In other words, contact thermal resistance is not only a performance problem
but also a safety problem.
■ In Wearable Devices, Even Comfort Changes
In AR glasses and wearables, factors such as
● Contact with the face
● Curved surfaces
● Pressure
● Perspiration
are also involved.
In other words, for wearable devices, what matters is not only whether heat can be released,
but also whether it can make contact without discomfort.
■ The Researcher's Perspective: Interfaces Matter More Than Theoretical Performance
Current research includes
● Next-generation TIM
● Nanostructures
● Flexible heat dissipation materials
● Surface control
● Contact optimization
In other words, from now on, not only the material itself
but interfaces will become extremely important.
■ The Shop-Floor Perspective: Contact Thermal Resistance Is Invisible
On the actual shop floor, problems include
● Lifting
● Air bubbles
● Insufficient pressure
● Tiny misalignment
● Surface roughness
However, these often cannot be seen with the eye.
In other words, contact thermal resistance is also an invisible enemy.
In finished products, there may even be cases where air layers have gotten in without anyone noticing.
In such cases, the intended thermal management is likely to be cut in half or worse.
■ Contact Thermal Resistance Is Decided by the Process
From OTIS’s point of view, this is the most important part.
For example, contact thermal resistance also changes with
● Die-cutting accuracy
● Lamination accuracy
● Pressure conditions
● Material thickness
● Tolerances
● 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 contact thermal resistance problems includes
● Microfabrication
● High-precision die-cutting
● High-precision lamination
● Contact between dissimilar materials
● Pressure stability
● Tolerance control
● Automated supply
● Volume production stability
● Peel balance
In other words, OTIS is committed to making contact states in which heat flows work in volume production.
■ What OTIS Can Do
At OTIS, through
● Microfabrication
● High-precision die-cutting
● High-precision lamination
● Processing of thermal management materials
● Stacking of irregular shapes
● Thin-film processing
● Support for reel supply
we may be able to contribute to volume production processes that do not increase contact thermal resistance.
■ Outside OTIS's Expertise
On the other hand, OTIS is not a company that specializes in
● Semiconductor circuit design
● GPU design
● Dedicated CFD analysis
● Cooling equipment design
However, in the area of making contact thermal resistance work in volume production, we may be able to play an important role.
■ Summary: What Stops Future Industries May Be a Tiny Gap
In heat problems, material performance alone is not enough.
In reality, due to
● Lifting
● Air layers
● Pressure
● Contact conditions
contact thermal resistance arises.
And in future industries, due to
● Miniaturization
● Higher density
● Stacking
gaps of a few tens of μm become huge problems.
In other words, in the future, how well the final contact conditions for heat can be made to work will become increasingly important.
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.
