As AI accelerators, high-performance computing processors, chiplets, HBM stacks and high-power semiconductor devices continue to increase computing density, thermal management is becoming one of the main limitations of advanced electronic packaging.
Increasing transistor density improves computing performance, but it also concentrates more heat into a limited package area.
Traditional thermal management materials such as copper, aluminum, AlN ceramics and Cu-Mo alloys remain important, but some high-heat-flux applications require a combination that is increasingly difficult to achieve:
- very high thermal conductivity
- rapid lateral heat spreading
- controlled coefficient of thermal expansion
- dimensional stability
- mechanical strength
- compatibility with semiconductor packaging processes
Diamond-copper composites, commonly written as Diamond/Cu or Cu-Diamond, are attracting interest because they combine the extremely high intrinsic thermal conductivity of diamond with the manufacturability and high thermal conductivity of copper.
The objective is not simply to add diamond particles to copper.
The real engineering challenge is to create an efficient thermal pathway across thousands or millions of diamond-copper interfaces while controlling thermal expansion, density, machinability and packaging reliability.
This article explains how diamond-copper heat spreaders work, what controls their thermal conductivity and CTE, and where they may fit into AI, HPC, HBM and advanced semiconductor packaging.
What Is a Diamond-Copper Composite?
A diamond-copper composite is a metal-matrix composite in which diamond particles are distributed within a copper matrix.
Copper provides:
- elevata conducibilità termica
- good metal-processing capability
- mechanical support
- compatibility with many packaging processes
Diamond provides:
- extremely high thermal conductivity
- low coefficient of thermal expansion
- high stiffness
- excellent thermal stability
Diamond itself can exhibit thermal conductivity well above that of copper, while conventional copper is typically around 400 W/(m·K) near room temperature.
High-quality synthetic diamond can reach approximately 1,000–2,000 W/(m·K) or higher depending on diamond type, purity and measurement conditions.
Recent research reviews report optimized diamond-copper composites approaching approximately 900 W/(m·K), showing why the material system is receiving increased attention for high-performance thermal management.
However, the thermal conductivity of a composite is not simply the average of copper and diamond.
The interface between them is critical.
Why Copper Alone Is Not Always Enough
Copper is already one of the most widely used heat-spreading materials in electronics.
It provides:
- elevata conducibilità termica
- low material cost compared with many advanced thermal materials
- excellent machinability
- mature plating and joining technologies
For many semiconductor packages, copper remains entirely sufficient.
The challenge appears when heat flux becomes highly concentrated.
An AI accelerator, high-end CPU or advanced power device may contain localized regions that generate significantly more heat than neighboring areas.
These thermal hotspots create two different problems:
- removing heat vertically from the chip
- spreading heat laterally before transferring it into the cooling system
If lateral heat spreading is insufficient, the center or hotspot region of a device can operate at a significantly higher temperature than the surrounding package.
That temperature gradient can affect:
- device performance
- frequency stability
- leakage current
- reliability
- package stress
- cooling-system requirements
A higher-conductivity heat spreader can reduce local temperature gradients by distributing thermal energy over a larger area.
Why Not Use Pure Diamond?
If diamond has such high thermal conductivity, it may seem logical to use a solid diamond heat spreader.
In selected high-performance applications, CVD diamond can indeed be used for thermal management.
However, pure diamond introduces several practical considerations:
- high material cost
- difficult machining
- difficult metallization and joining
- low coefficient of thermal expansion
- limited large-area manufacturing economics
- package-integration complexity
Diamond-copper composites attempt to combine the best characteristics of both materials.
Instead of relying on an entire solid diamond plate, the composite creates high-conductivity diamond pathways inside a metallic copper matrix.
This can potentially provide a more practical balance between thermal performance, CTE and manufacturability.
Thermal Conductivity of Diamond-Copper Composites
The thermal conductivity of a Diamond/Cu composite depends on several interacting factors.
The most important include:
- diamond thermal conductivity
- diamond particle size
- diamond volume fraction
- diamond distribution
- copper purity
- porosity
- interfacial bonding
- interface-layer composition
- interface-layer thickness
- manufacturing process
This explains why two Diamond/Cu materials containing the same percentage of diamond can still show significantly different thermal performance.
The Diamond-Copper Interface Is the Critical Challenge
Diamond and copper do not naturally form an ideal thermal interface.
Copper has poor chemical affinity and limited wettability with diamond.
If diamond particles are simply surrounded by copper without effective interfacial bonding, microscopic gaps or weak contact can create significant thermal resistance.
Heat must move:
Copper → Interface → Diamond → Interface → Copper
every time it crosses a reinforcement particle.
If the interface is poor, the theoretical benefit of the diamond can be lost.
Research reviews consistently identify diamond-copper interfacial thermal resistance as one of the major limitations on composite thermal conductivity.
The problem is particularly important because heat transport occurs differently in the two materials:
- copper transfers heat largely through electrons
- diamond transfers heat mainly through phonons
The interface therefore represents a transition between different thermal-transport mechanisms.
Interface Metallization and Carbide-Forming Elements
One widely studied solution is to modify the diamond surface before incorporating it into copper.
Potential interface-modification elements include:
- Ti
- Cr
- W
- Mo
- Zr
These elements can form carbide-containing interfacial layers that improve bonding between diamond and copper.
For example, a thin carbide-forming layer may improve:
- wettability
- interfacial adhesion
- contact quality
- thermal transfer across the interface
However, more interface material is not automatically better.
Many carbide layers have lower thermal conductivity than either copper or diamond.
If the interface layer becomes too thick, it can itself become a thermal barrier.
Therefore, interface engineering is a balancing problem:
the layer must be thick enough to create strong and continuous bonding, but thin enough to avoid adding excessive thermal resistance.
Research on Diamond/Cu composites repeatedly identifies interface-layer composition and thickness as major factors determining final thermal conductivity.
Diamond Volume Fraction
Increasing the proportion of diamond can potentially increase composite thermal conductivity and reduce CTE.
But the relationship is not linear.
At relatively low diamond content, copper remains the dominant continuous phase.
As diamond content increases, more highly conductive diamond participates in heat transport.
However, excessively high diamond loading can create problems with:
- densification
- copper infiltration
- particle contact
- porosity
- machining
- mechanical integrity
- interface area
Manufacturers therefore optimize the diamond volume fraction according to the required combination of:
- thermal conductivity
- CTE
- mechanical properties
- thickness
- processing method
The best composition for one heat spreader is not necessarily the best for another.
Why Diamond Particle Size Matters
Diamond particle size also affects thermal performance.
Smaller particles create much more total interface area for the same diamond volume fraction.
That can improve microstructural uniformity, but it also means heat must interact with more diamond-copper interfaces.
If interfacial thermal resistance is significant, excessive interface area can reduce effective thermal conductivity.
Larger diamond particles may reduce the number of interfaces that heat must cross.
However, very large particles can introduce other challenges such as:
- poor surface finish
- non-uniform microstructure
- difficult thin-section machining
- local stress concentration
Particle-size distribution therefore needs to be engineered rather than simply maximized.
Porosity and Density
Porosity is especially undesirable in a thermal-management material.
Air-filled or poorly bonded pores have extremely low thermal conductivity compared with copper or diamond.
Even relatively small amounts of porosity can therefore reduce effective thermal performance.
High-quality Diamond/Cu heat spreaders require strong densification and good copper filling around the diamond reinforcement.
Manufacturing methods may include:
- pressure infiltration
- vacuum infiltration
- hot pressing
- high-pressure processing
- powder metallurgy
- spark plasma sintering
- other specialized consolidation processes
The preferred process depends on composition, geometry, cost and required thermal properties.
What Is CTE and Why Does It Matter?
CTE means Coefficiente di espansione termica.
It describes how much a material expands when temperature increases.
This is critically important in semiconductor packaging because a package contains many different materials.
Examples may include:
- silicon
- copper
- ceramic substrates
- solder
- underfill
- organic substrates
- molding compounds
- thermal interface materials
- heat spreaders
If two bonded materials expand at very different rates, temperature changes create mechanical stress.
Repeated thermal cycling can eventually contribute to:
- solder fatigue
- interface delamination
- die cracking
- deformazione
- TIM degradation
- package reliability problems
Copper Has a Relatively High CTE
Copper provides excellent thermal conductivity, but its CTE is substantially higher than that of semiconductor materials such as silicon and many wide-bandgap materials.
If a large copper heat spreader is rigidly coupled to a semiconductor structure, the difference in expansion during thermal cycling must be managed by the package architecture.
This is one reason engineers consider composites rather than evaluating thermal conductivity alone.
Diamond Can Lower the Effective CTE
Diamond has a very low coefficient of thermal expansion.
When diamond particles are incorporated into copper, they restrict the thermal expansion of the copper matrix.
The effective CTE of the composite can therefore be substantially lower than that of pure copper.
By adjusting:
- diamond volume fraction
- particle size
- particle distribution
- interface condition
engineers can tune the thermal and mechanical behavior of the composite.
This creates one of the key advantages of Diamond/Cu:
high thermal conductivity and lower CTE can potentially be achieved within the same material system.
This is particularly valuable because many conventional material choices involve a tradeoff.
High-conductivity metals tend to have relatively high CTE, while many low-CTE materials provide lower thermal conductivity.
CTE Matching Does Not Mean Making Every Material Identical
A common misunderstanding is that the heat spreader should have exactly the same CTE as silicon.
That is not necessarily the engineering objective.
A semiconductor package contains multiple interfaces, compliant materials and bonding layers.
The correct target CTE depends on the complete stack.
Engineers need to consider:
- die size
- heat-spreader thickness
- attachment method
- solder or TIM properties
- substrate material
- operating temperature
- thermal cycling range
- package stiffness
Therefore, CTE should be optimized at the package level rather than selected from a single numerical comparison.
Diamond-Copper vs Copper
The most direct comparison is with conventional copper heat spreaders.
Copper Advantages
Copper offers:
- mature supply chain
- excellent machinability
- elevata conducibilità termica
- established plating processes
- relatively low cost
Diamond-Copper Advantages
Diamond/Cu can potentially offer:
- substantially higher effective thermal conductivity
- lower CTE
- improved lateral heat spreading
- improved dimensional stability
Diamond-Copper Limitations
Potential disadvantages include:
- higher cost
- more difficult machining
- more complex manufacturing
- interface-control requirements
- less mature supply chain
- greater variation between material grades
Therefore, Diamond/Cu is unlikely to replace ordinary copper everywhere.
Its strongest value proposition is in applications where thermal performance is sufficiently important to justify the additional material complexity.
Diamond-Copper vs Cu-Mo and Cu-W
Copper-molybdenum and copper-tungsten composites are established electronic packaging materials.
They are often selected because Mo and W lower the thermal expansion of copper.
These materials can provide excellent:
- dimensional stability
- mechanical reliability
- CTE control
However, adding Mo or W generally reduces thermal conductivity compared with pure copper.
Diamond reinforcement offers a different possibility.
Because diamond itself has extremely high thermal conductivity, adding diamond can potentially:
- reduce CTE
- increase thermal conductivity
at the same time.
That combination is the central reason Diamond/Cu is interesting for future high-heat-flux packaging.
Diamond-Copper vs AlN
Aluminum nitride is widely used when both electrical insulation and heat conduction are required.
AlN offers an important advantage that Diamond/Cu generally does not:
electrical insulation.
Diamond/Cu contains a continuous metallic copper phase and is electrically conductive.
Therefore, the materials serve different roles.
AlN may be preferable for:
- electrically insulating substrates
- power module substrates
- ceramic packages
Diamond/Cu may be preferable where:
- electrical conductivity is acceptable
- extremely high lateral heat spreading is required
- the component functions primarily as a heat spreader or lid
The two materials may even appear within the same thermal stack.
What Is a Heat Spreader?
A heat spreader is different from a conventional heat sink.
A heat sink transfers heat to air, liquid or another cooling medium.
A heat spreader is typically positioned much closer to the semiconductor die.
Its job is to redistribute concentrated heat from a relatively small hotspot across a larger surface area.
A typical thermal path may look like:
Semiconductor Die
↓
Thermal Interface
↓
Heat Spreader
↓
Cold Plate / Heat Sink
↓
Air or Liquid Cooling
The higher the heat spreader’s lateral thermal conductivity, the more effectively it can reduce local hotspot temperature.
Diamond/Cu is especially interesting in this heat-spreading function.
Why AI Accelerators Need Better Heat Spreading
AI processors contain enormous numbers of transistors operating simultaneously.
Modern accelerator packages may also combine:
- GPU or accelerator dies
- chiplets
- HBM stacks
- silicon interposers
- advanced substrates
- high-speed I/O
The thermal challenge is therefore not simply total package power.
Power distribution across the package is often non-uniform.
Some regions generate much higher heat flux than others.
A high-performance heat spreader can help redistribute this heat before it reaches the external cooling solution.
This can potentially help:
- reduce hotspot temperature
- lower temperature gradients
- improve cooling utilization
- maintain performance under sustained workloads
As device power density continues increasing, recent research has placed growing emphasis on diamond-containing composites as next-generation heat-spreader materials.
Diamond-Copper for HPC Packages
High-performance computing systems have similar thermal challenges.
Modern CPUs and accelerators increasingly use:
- large dies
- multiple compute tiles
- 2.5D integration
- Impilamento 3D
- heterogeneous integration
Each architecture changes the heat-flow path.
Traditional thermal design assumes heat moves primarily vertically from the chip toward the package lid.
In chiplet and 3D architectures, lateral heat spreading becomes increasingly important because different dies may generate different heat loads.
Diamond-copper materials can potentially be used as:
- package heat spreaders
- thermal lids
- thermal inserts
- local heat-spreading plates
- submounts
However, the actual architecture must account for electrical isolation, joining, surface finish and package stress.
HBM and 3D Packaging Thermal Challenges
HBM achieves high bandwidth by vertically stacking multiple memory dies.
This provides significant electrical-performance advantages, but stacking creates a more difficult thermal path.
Heat generated within the stack must travel through multiple materials before reaching the cooling solution.
When HBM is integrated beside a high-power accelerator on an advanced package, thermal interaction between the processor and memory also becomes important.
Diamond/Cu may therefore be evaluated as part of the heat-spreader architecture surrounding advanced AI/HPC packages.
However, it should not be described as a universal solution for HBM.
The complete thermal path includes:
- silicon dies
- bonding interfaces
- underfill
- interposer
- thermal interface materials
- package lid
- cold plate
Improving only one layer cannot eliminate every thermal bottleneck.
Thermal Conductivity Is Not Enough
A material with extremely high measured thermal conductivity can still perform poorly in an actual package.
The full thermal resistance includes:
**Die
- Die-to-TIM Interface
- TIM
- TIM-to-Heat-Spreader Interface
- Heat Spreader
- Spreader-to-Cooler Interface
- Cooling System**
If interface resistance dominates, increasing heat-spreader conductivity may provide diminishing returns.
This means Diamond/Cu should be evaluated using package-level thermal simulation rather than material conductivity alone.
Through-Plane vs In-Plane Thermal Performance
Heat spreaders often need strong thermal conductivity in two directions.
Through-Plane
Heat must move vertically away from the semiconductor die.
In-Plane
Heat must spread laterally across the heat spreader.
A material with excellent through-thickness conductivity but poor lateral spreading may still allow hotspots.
Diamond particle:
- orientation
- distribution
- morphology
- connectivity
can influence effective thermal transport.
For high-performance packaging, thermal conductivity should therefore be considered directionally when the composite microstructure creates significant anisotropy.
Surface Flatness Matters
Diamond/Cu heat spreaders may be attached close to semiconductor dies or thermal interface materials.
Poor flatness can create:
- non-uniform TIM thickness
- local air gaps
- higher contact resistance
- uneven mechanical loading
For high-power devices, small variations in interface thickness can affect thermal performance.
Heat-spreader specifications may therefore include:
- flatness
- parallelism
- thickness tolerance
- surface roughness
These parameters can be as important as bulk thermal conductivity.
Surface Roughness and TIM Performance
The mating surface between a heat spreader and TIM must also be controlled.
An extremely rough surface creates microscopic voids.
An unnecessarily polished surface may increase processing cost without producing a proportional thermal advantage.
The optimum surface roughness depends on:
- TIM type
- bonding method
- contact pressure
- surface coating
Common interface systems can include:
- thermal grease
- phase-change material
- solder
- adhesive
- sintered metal
- direct metallurgical bonding
Therefore, surface finishing should be designed around the intended assembly process.
Can Diamond-Copper Be Machined?
Diamond/Cu is more difficult to machine than ordinary copper.
The copper matrix is relatively ductile, while diamond particles are extremely hard.
This creates a heterogeneous cutting environment.
Conventional machining may experience:
- rapid tool wear
- diamond particle pull-out
- edge defects
- poor surface finish
Manufacturing may therefore use combinations of:
- diamond grinding
- precision lapping
- lucidatura
- EDM where applicable to the conductive matrix
- laser processing
- specialized machining methods
Part geometry should be considered early in the design stage.
A simple rectangular heat spreader is much easier to manufacture than a highly complex thin-wall component.
Plating and Metallization
Diamond/Cu components may require surface metallization for:
- soldering
- brazing
- diffusion bonding
- corrosion protection
- package assembly
Possible metallization stacks depend on the application.
The copper-rich external surface may be plated or processed to provide suitable joining characteristics.
Important factors include:
- adhesion
- plating thickness
- solderability
- thermal resistance
- diffusion control
- thermal cycling reliability
Because a heat spreader is part of the thermal path, unnecessarily thick low-conductivity layers should be avoided.
Important Diamond-Copper Specifications
When purchasing Diamond/Cu heat spreaders, buyers should not request only:
“Diamond copper composite.”
A useful technical RFQ should include the following.
Dimensioni
Specify:
- length
- width
- thickness
- dimensional tolerances
Diamond Content
Specify required diamond volume fraction if already determined.
Otherwise, provide the thermal and CTE targets and allow the manufacturer to recommend a composition.
Conduttività termica
Specify:
- minimum thermal conductivity
- measurement direction
- test method
- test temperature
This is important because reported conductivity values may vary depending on measurement conditions.
Coefficiente di espansione termica
Specify:
- CTE requirement
- temperature range
CTE is temperature dependent, so a single value without a temperature range may be misleading.
Piattezza
Specify the maximum permissible flatness deviation.
Ruvidità della superficie
Provide required Ra or another defined surface specification.
Metallizzazione
Specify whether the component requires:
- Ni
- Au
- Ag
- Cu
- another plating system
depending on the intended joining process.
Applicazione
Indicate whether the component will be used for:
- AI accelerator
- HPC processor
- HBM package
- RF device
- laser device
- GaN amplifier
- SiC power module
- another high-power semiconductor system
Application information helps determine whether thermal conductivity, CTE or mechanical performance should receive the highest priority.
Diamond-Copper for Power Semiconductors
Diamond/Cu is not limited to AI processors.
Power semiconductor devices also generate high heat flux.
Potential application areas include:
- Dispositivi di potenza SiC
- GaN power devices
- RF power amplifiers
- microwave electronics
- high-power laser systems
In these applications, junction temperature strongly influences device efficiency and reliability.
A heat spreader with high thermal conductivity can help reduce thermal resistance between the device and the cooling system.
However, electrical isolation must be considered because Diamond/Cu is conductive.
Diamond-Copper for GaN and RF Applications
GaN RF and high-power devices can generate highly localized heat close to the active device region.
Diamond itself has attracted considerable interest for GaN thermal management.
Diamond/Cu composites may offer another approach when the design requires a larger structural heat-spreading component rather than a directly integrated diamond layer.
Potential functions include:
- carrier plates
- package bases
- thermal spreaders
- high-conductivity mounting structures
The best solution depends on the thermal path and package architecture.
Reliability Testing
Before Diamond/Cu can be adopted into a high-value semiconductor package, thermal conductivity alone is insufficient.
Reliability evaluation may include:
- thermal cycling
- high-temperature storage
- thermal shock
- mechanical testing
- metallization adhesion
- solder-joint evaluation
- warpage measurement
Recent reviews of diamond composite heat spreaders increasingly emphasize reliability alongside thermal conductivity because practical packaging applications require stable performance over repeated temperature cycles.
When Does Diamond-Copper Make Economic Sense?
Diamond/Cu is not intended to replace copper in every electronic product.
For low- and moderate-power devices, ordinary copper may provide excellent performance at much lower cost.
Diamond/Cu becomes more attractive when:
- device value is high
- heat flux is extreme
- hotspot temperature limits performance
- package area is constrained
- cooling capacity is expensive
- CTE control is important
- conventional copper approaches its thermal limit
AI/HPC accelerators, high-power RF devices and advanced power semiconductor systems are therefore logical target applications.
The economic comparison should focus on:
cost per reliable device
rather than heat-spreader material cost alone.
If improved thermal spreading allows:
- higher sustained power
- lower junction temperature
- improved reliability
- reduced cooling demand
a more expensive heat-spreader material may become economically justified.
Diamond-Copper vs Conventional Heat-Spreader Materials
A simplified comparison is shown below.
| Materiale | Conduttività termica | CTE Behavior | Electrical Property | Main Strength |
|---|---|---|---|---|
| Copper | Alto | Relatively high CTE | Conductive | Cost and manufacturability |
| AlN | High for ceramic | Relatively low | Insulating | Thermal + electrical isolation |
| Cu-Mo | Moderate to high | Tunable/lower | Conductive | CTE control |
| Cu-W | Moderato | Low/tunable | Conductive | Dimensional stability |
| CVD Diamond | Extremely high | Very low | Usually insulating | Maximum thermal performance |
| Diamond-Copper | Very high potential | Tunable | Conductive | High conductivity + CTE control |
The table represents general material behavior.
Actual specifications vary substantially by material grade and manufacturing process.
Key Challenges for Diamond-Copper Heat Spreaders
Despite their potential, several technical challenges remain.
Interface Thermal Resistance
This remains one of the most important limitations.
Manufacturing Consistency
High conductivity requires repeatable:
- diamond distribution
- density
- interface chemistry
- processing conditions
Machining Cost
Diamond particles significantly increase machining difficulty.
Surface Metallization
Reliable semiconductor packaging requires well-controlled joining surfaces.
Material Cost
Diamond-containing composites remain more expensive than conventional copper.
Standardization
Unlike traditional copper, widely standardized Diamond/Cu commercial specifications are still developing.
For buyers, supplier-specific material qualification is therefore important.
Future Role in AI and HPC Packaging
As semiconductor architectures move toward:
- chiplets
- Imballaggio 2.5D
- 3D integration
- HBM
- heterogeneous integration
- higher accelerator power
the package is becoming part of the thermal-performance architecture rather than merely mechanical protection.
Cooling improvements such as liquid cold plates can remove large amounts of heat, but heat must first travel efficiently from the semiconductor hotspots to the cooling surface.
That is precisely where advanced heat spreaders become important.
Diamond/Cu is promising because it targets two important package requirements simultaneously:
very high thermal conductivity
e
controlled thermal expansion.
Whether it becomes widely adopted will depend not only on achieving record laboratory thermal conductivity, but also on:
- manufacturing cost
- consistency
- machinability
- plating
- joining
- package reliability
- high-volume production capability
Conclusione
Diamond-copper composites represent an important direction in advanced semiconductor thermal management.
The material combines the high thermal conductivity and low thermal expansion of diamond with the manufacturability and thermal performance of copper.
Its potential advantages include:
- substantially improved heat spreading compared with conventional copper
- lower effective CTE
- strong potential for high-heat-flux applications
- customizable thermal and mechanical properties
However, successful Diamond/Cu heat spreaders depend heavily on the microstructure.
Diamond volume fraction alone does not determine performance.
The most critical factors include:
- diamond quality
- particle size
- interface metallization
- interfacial thermal resistance
- composite density
- porosity
- manufacturing method
For AI accelerators, HPC processors, HBM-related advanced packaging, RF electronics and high-power semiconductor devices, Diamond/Cu may provide a useful thermal-management option when conventional heat spreaders approach their limits.
The correct question is therefore not simply:
“How high is the thermal conductivity?”
A more complete engineering question is:
“Can the heat spreader deliver high thermal conductivity, suitable CTE, low interface resistance, precise flatness and long-term package reliability at the same time?”
That combination will determine the practical value of diamond-copper composites in next-generation semiconductor packaging.