■ What Are Burrs?
Burrs are protrusions or excess portions left on edges when materials are die-cut or cut.
They can occur when processing metal foil, films, adhesive materials, graphite, ceramic-based materials, and so on.
Burrs are small.
In thermal management components, however, these small burrs become a major problem.
■ Burrs Cause Lifting
When there are burrs on the edges of a component, part of it may lift when laminated.
Air layers form in the lifted parts.
Air conducts heat poorly.
As a result, heat has difficulty flowing.
In other words, burrs become a cause of air layers.
■ Burrs Also Cause Insulation Defects
Burrs on metal foil and conductive materials are also electrically dangerous.
Burrs pierce insulating layers.
They contact surrounding components.
They become conductive foreign matter.
As a result, it may lead to
● Short circuits
● Electrical leakage
● Dielectric breakdown
● Noise paths
In other words, burrs on thermal management components become not only a heat problem,
but also an electrical safety problem.
■ What Is Foreign Matter?
Foreign matter is something that should not be there getting mixed in.
For example,
● Die-cut scrap
● Metal particles
● Graphite particles
● Film fragments
● Adhesive residue
● Dust
● Ceramic particles
● Release liner fragments, and so on.
Even small foreign matter has a large impact on thermal management components.
■ Foreign Matter Destroys Contact
When foreign matter gets onto a contact surface, that part is raised.
Then the component lifts.
Air layers form in the lifted parts.
When air layers form, heat has difficulty flowing.
In other words, foreign matter becomes a cause of increased contact thermal resistance.
This is a separate problem from the thermal conductivity of the material.
■ Foreign Matter Creates Localized Hot Spots
When foreign matter worsens contact in one part, heat has difficulty escaping only in that part.
Then a localized temperature rise occurs.
This is a hot spot.
In AI servers, EVs, smartphones, and wearable devices, localized heat concentration affects performance and safety.
In other words, foreign matter can create heat problems from a small point.
■ Conductive Foreign Matter Is Especially Dangerous
Conductive foreign matter such as metal particles and graphite particles requires particular care.
Conductive materials such as copper foil, aluminum foil, and graphite are sometimes used in thermal management materials.
If their particles or scraps remain around circuits, they may lead to short circuits and noise defects.
In other words, conductive foreign matter is an electrical risk generated from thermal management components.
■ What Are Steps?
Steps are states in which there are differences in the height of components or materials.
For example,
● Differences in component height
● Differences between mounted components on a board
● Differences in adhesive layer thickness
● Edge differences in laminated components
● Overlaps of processed edges
● Thickness differences between base materials and adhesive materials, and so on.
Thermal management components must conform to these steps.
If they cannot conform, lifting and air layers occur.
■ If It Cannot Conform to Steps, Heat Stops
When a heat dissipation sheet or TIM cannot conform to a step, part of it lifts.
Air gets into the lifted part.
Then heat has difficulty flowing.
In other words, steps become a cause of air layers. Because component heights become complex, countermeasures for steps are important.
■ Soft Materials Are Strong Against Steps, but Have Other Challenges
Gels and flexible heat dissipation sheets are suited to absorbing steps.
However, soft materials also have challenges such as
● Deforming easily
● Squeezing out easily
● Unstable thickness
● Being hard to handle in automated processes
In other words, for step countermeasures, it is not good enough just to be soft.
A balance between step absorption and volume production stability is necessary.
■ Hard Materials Are Weak Against Steps
On the other hand, ceramics, metal plates, hard heat dissipation materials, and so on have difficulty conforming to steps.
Even if their thermal conductivity is high, heat will not flow if they lift at steps.
In other words, with hard materials, contact design is more important
than material performance.
As necessary, combinations with flexible TIM or adhesive materials are required.
■ Burrs, Foreign Matter, and Steps in AI Servers
In AI servers, GPUs, HBM, power supply components, and high-speed communication components are arranged at high density.
Thermal management components around them also become complex.
If there are burrs or foreign matter here, it may lead to
● TIM lifting
● Worse contact with the cooling plate
● Conductive foreign matter remaining
● Insulation defects
● EMI defects
In other words, in AI servers, minute processing defects can lead to major performance degradation.
■ Burrs, Foreign Matter, and Steps in EVs and ESS
In EVs and ESS, battery cells, cooling plates, busbars, insulating materials, and thermal insulation materials are combined.
If there are burrs or foreign matter here, it may lead to
● Heat dissipation defects
● Insulation defects
● Cell temperature differences
● Waterproofing defects
● Wear due to vibration
● Reduced long-term reliability
Around batteries in particular, safety is important.
That is why burrs, foreign matter, and steps are not just process defects, but risks related to safety.
■ Effects in Smartphones and Wearables
In smartphones and wearable devices, components are small and thin.
That is why the effects of minute foreign matter and steps tend to be large.
For example, problems arise such as
● Heat dissipation sheets lifting
● Gaps forming in waterproof tape
● Graphite particles coming off
● Adhesive material squeezing out
● Contact with the enclosure worsening
In wearable devices, slight lifting or steps can also affect wearing comfort.
■ The Researcher's Perspective: Minute Defects Dominate Mounted Performance
In research and development, material properties are emphasized.
In actual products, however, minute defects such as burrs, foreign matter, and steps can dominate performance.
In thermal management in particular,
● Contact area
● Air layers
● Pressure distribution
● Interface condition
● Insulation distance
are important.
In other words, to achieve performance as per research values, mounting design that suppresses minute defects is necessary.
■ The Shop-Floor Perspective: Burrs, Foreign Matter, and Steps Are "Visible Defects," and Also Invisible Performance Defects
On the shop floor, burrs and foreign matter are often treated as cosmetic defects.
In thermal management components, however, that is not all.
Small cosmetic anomalies lead to
● Increased thermal resistance
● Poor contact
● Insulation defects
● Waterproofing defects
● Noise defects
● Reduced long-term reliability
In other words, burrs, foreign matter, and steps, while being visible defects,
create invisible performance defects.
■ Problems That Tend to Occur with Burrs, Foreign Matter, and Steps
In volume production processes, the following kinds of problems can occur.
● Die-cutting burrs
● Metal particles
● Graphite particles
● Ceramic particles
● Adhesive residue
● Film fragments
● Remaining die-cut scrap
● Lamination steps
● Edge lifting
● Uneven compression bonding
● Short circuits due to conductive foreign matter
● Waterproof line defects due to foreign matter
These affect not only thermal performance but the combined functions as a whole.
■ What to Check to Reduce Burrs, Foreign Matter, and Steps
To stabilize in volume production, the following must be checked.
● Whether die-cutting conditions are appropriate
● Whether the blade condition is stable
● Whether burrs are appearing on material edges
● Whether the material sheds particles
● Whether the structure tends to retain foreign matter
● Whether the material configuration can absorb steps
● Whether compression bonding conditions are appropriate
● Whether they can be detected in inspection
● Whether automated processes entrain foreign matter
● Whether particles or scraps come off during packaging and transport
In other words, countermeasures for burrs, foreign matter, and steps include not only processing conditions, but also material selection, process design, and inspection design.
■ OTIS's Perspective
OTIS is not a company that develops thermal materials themselves.
However, we may be able to contribute in the area of mass-processing thermal management components while suppressing burrs, foreign matter, and steps.
What matters from OTIS’s perspective is
● High-precision die-cutting
● Microfabrication
● Edge quality
● Particle shedding countermeasures
● Foreign matter management
● High-precision lamination
● Lamination design that takes steps into account
● Reel supply
● Supply formats for automated processes
Thermal management materials are not finished just by choosing good materials.
Not creating unnecessary burrs, not leaving foreign matter, and controlling steps is important.
■ What OTIS Can Do
At OTIS, in cleanroom manufacturing, through
● Heat dissipation sheet processing
● Graphite processing
● Metal foil processing
● Insulating material processing
● Adhesive material processing
● EMI material processing
● High-precision die-cutting
● Microfabrication
● High-precision lamination
● Lamination of dissimilar materials
● Reel supply
● Designing supply formats for automated processes
and more, we may be able to contribute to making thermal management components with minimal burrs, foreign matter, and steps.
■ Outside OTIS's Expertise
On the other hand, OTIS is not a company that specializes in
● Development of materials themselves
● Thermal design of entire finished products
● Equipment design for customers’ entire lines
● Dedicated thermal simulation analysis
● Dedicated EMI analysis
However, in the area of supplying thermal management components to volume production processes with burrs, foreign matter, and steps suppressed,
we may be able to play an important role.
■ Industries Where This Technology Will Be Important
★★★★★ AI servers
★★★★★ EVs and batteries
★★★★★ ESS and energy storage systems
★★★★★ Smartphones
★★★★☆ Wearable devices
★★★★☆ Robots
★★★★☆ Communication equipment
■ Summary
Small burrs, foreign matter, and steps destroy thermal performance
In thermal management, the thermal conductivity and thickness of materials tend to attract attention.
On the volume production floor, however, burrs, foreign matter, and steps can destroy performance.
Burrs create lifting.
Foreign matter destroys contact.
Steps create air layers.
As a result, it may happen that
● Thermal resistance increases
● Hot spots occur
● Insulation defects occur
● Waterproofing declines
● Noise defects result
In other words, burrs, foreign matter, and steps are not small cosmetic defects.
They are important management items for making thermal management work in volume production.
Thermal management materials deliver their true performance only when they are cleanly processed, free of foreign matter, and applied with steps taken into account.
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.
