The Interface and Fabrication Process of Diamond/Cu Composites with Nanocoated Diamond for Heat Sink Applications

At a Glance

Metadata	Details
Publication Date	2021-01-22
Journal	Metals
Authors	Yaqiang Li, Hongyu Zhou, Chunjing Wu, Zheng Yin, Chang Liu
Institutions	University of Science and Technology Beijing, Baise University
Citations	18
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Performance Diamond/Cu Composites for Heat Sinks

Executive Summary

This research validates the critical role of interface engineering in maximizing the thermal conductivity (TC) of diamond/copper (Cu) composites for high-power heat sink applications.

Core Achievement: Achieved a high TC of 475.01 W m⁻¹ K⁻¹ in 40 vol.% diamond/Cu composites by utilizing a nanosized Titanium (Ti) coating on the diamond particles.
Interface Solution: The Ti coating acts as an effective “bridge,” forming stable TiC and Cu-Ti intermetallic compounds during sintering, which drastically reduces interfacial thermal resistance.
Failure Analysis: Nanosized Cu coatings failed due to the “nano effect”—segregation and spheroidization at elevated sintering temperatures (1193 K to 1313 K)—resulting in low relative density and poor TC.
Material Requirement: The success hinges on using high-quality synthetic diamond particles (Ib-type MBD-4) combined with precise, reactive metal coatings.
Scalability: The fabrication method (powder metallurgy) is suitable for large-scale production, providing an immediate pathway for manufacturing high-performance thermal management substrates.
6CCVD Value Proposition: 6CCVD provides the necessary high-quality MPCVD diamond materials (PCD/SCD) and specialized Ti metalization services required to replicate and scale this high-TC composite technology.

Technical Specifications

The following table summarizes the key performance metrics and material parameters achieved in the study, focusing on the optimal Ti-coated composite.

Parameter	Value	Unit	Context
Peak Thermal Conductivity (TC)	475.01	W m⁻¹ K⁻¹	40 vol.% Ti-coated diamond composite
Optimal Sintering Temperature	1313	K	For Ti-coated diamond/Cu composite
Optimal Diamond Volume Fraction	40	vol.%	For maximum TC (Ti-coated)
Relative Density (at Peak TC)	98.5	%	Ti-coated composite at 1313 K
Coefficient of Thermal Expansion (CTE)	10.93	10⁻⁶ K⁻¹	40 vol.% Ti-coated composite at 1313 K
Raw Diamond TC (Reference)	1450	W m⁻¹ K⁻¹	Synthetic Ib-type MBD-4 (250 ppm N)
Raw Diamond Particle Size	98-106	µm	Used for composite reinforcement
Nanosized Coating Thickness	~100	nm	Initial Cu or Ti layer thickness
Uncoated Composite TC (Reference)	262.82	W m⁻¹ K⁻¹	40 vol.% at 1243 K
Sintering Pressure (Hot Press)	50	MPa	Applied during 10-minute hold time

Key Methodologies

The diamond/Cu composites were fabricated using a conventional powder metallurgy route combined with advanced surface modification.

Raw Material Selection: Synthetic Ib-type MBD-4 diamond particles (98-106 µm) were chosen for their high intrinsic TC (1450 W m⁻¹ K⁻¹). Copper powder purity was 99.85 wt.%.
Surface Modification: Nanosized Cu or Ti layers (approximately 100 nm thick) were deposited onto the diamond particle surfaces using a vacuum ion plating process.
Mixing and Compaction: Diamond particles (30-60 vol.%) were mechanically mixed with copper powder for 2 hours, followed by cold pressing at 500 MPa for 5 minutes.
Sintering Process: Samples were hot-pressed in a graphite mold at 50 MPa pressure. Sintering temperatures were varied between 1193 K and 1363 K to determine the optimal process window.
Cooling: A controlled cooling rate of 10 K min⁻¹ was maintained using circulating cooling water.
Interface Mechanism: The Ti coating successfully reacted with the diamond (forming TiC) and diffused with the copper matrix (forming Cu-Ti intermetallics), creating a strong, low-resistance thermal pathway.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the foundational materials and specialized services required to replicate and advance this high-performance thermal management research.

Applicable Materials

The research confirms that high-quality synthetic diamond is essential. 6CCVD offers materials tailored for thermal composite applications:

Polycrystalline Diamond (PCD) Substrates: Ideal for large-area heat sink applications. 6CCVD provides PCD wafers up to 125 mm in diameter and thicknesses from 0.1 µm to 500 µm, offering excellent thermal spreading capabilities and customizable CTE matching.
Single Crystal Diamond (SCD) Plates: For ultra-high-end applications requiring maximum intrinsic TC and purity. 6CCVD supplies SCD plates up to 500 µm thick, suitable for use as high-performance thermal inserts or reinforcement particles.
Diamond Substrates: Available up to 10 mm thick for robust, high-load thermal applications.

Customization Potential

The success of the Ti-coated composite relies on precise, high-quality metal deposition. 6CCVD’s in-house capabilities directly address the critical requirements identified in this paper:

Research Requirement	6CCVD Capability	Technical Advantage
Reactive Interface Layer (Ti)	In-House Metalization: We offer deposition of Ti, Pt, Au, Pd, W, and Cu.	Ensures optimal chemical bonding (e.g., TiC formation) necessary to minimize interfacial thermal resistance.
Large-Scale Heat Sinks	Custom Dimensions: PCD plates up to 125 mm diameter.	Facilitates direct scale-up from lab-scale (38 mm) to commercial inch-size wafers for power electronics packaging.
High Density/Low Defect Rate	Advanced Polishing: Ra < 1 nm (SCD) and Ra < 5 nm (PCD).	Provides ultra-smooth surfaces for subsequent composite processing or direct chip bonding, further reducing thermal boundary resistance.
Custom Volume Fractions	Material Supply: SCD/PCD materials available in various forms and thicknesses (0.1 µm - 500 µm) for composite reinforcement.	Supports precise material loading (e.g., 40 vol.%) and optimization studies for specific TC/CTE targets.

Engineering Support

The study highlights the complexity of interface design, particularly the failure mechanism of the Cu coating due to the “nano effect.”

Expert Consultation: 6CCVD’s in-house PhD team specializes in MPCVD diamond properties and interface chemistry. We offer consultation services to assist engineers and scientists in selecting the optimal diamond material and metalization scheme (e.g., Ti vs. Cr vs. Mo) to prevent thermal degradation and achieve target TC/CTE values for high-power microelectronics heat sink projects.
Global Logistics: We ensure reliable, global delivery of custom diamond materials (DDU default, DDP available), supporting international research and manufacturing supply chains.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

The coefficients of thermal expansion (CTE) and thermal conductivity (TC) are important for heat sink applications, as they can minimize stress between heat sink substrates and chips and prevent failure from thermal accumulation in electronics. We investigated the interface behavior and manufacturing of diamond/Cu composites and found that they have much lower TCs than copper due to their low densities. Most defects, such as cavities, form around diamond particles, substantially decreasing the high TC of diamond reinforcements. However, the measurement results for the Cu-coated diamond/Cu composites are unsatisfactory because the nanosized copper layer on the diamond surface grew and spheroidized at elevated sintering temperatures. Realizing ideal interfacial bonding between a copper matrix and diamond particles is difficult. The TC of the 40 vol.% Ti-coated diamond/Cu composite is 475.01 W m−1 K−1, much higher than that of diamond/Cu and Cu-coated diamond/Cu composites under equivalent manufacturing conditions. The minimally grown titanium layer retained its nanosized and was consistent with the sintering temperature. Depositing a nanosized titanium layer on a diamond surface will strengthen interfacial bonding through interface reactions among the copper matrix, nanosized titanium layer and diamond particles, reducing the interfacial thermal resistance and exploiting the high TC of diamond particles, even if defects from powder metallurgy remain. These results provide an important experimental and theoretical basis for manufacturing diamond/Cu composites for heat sink applications.

Tech Support

Original Source

DOI: https://doi.org/10.3390/met11020196

References

2015 - High thermal conductivity through interfacial layer optimization in diamond particles dispersed Zr-alloyed Cu matrix composites [Crossref]
2018 - Interface and mechanical/thermal properties of graphene/copper composite with Mo2C nanoparticles grown on graphene [Crossref]
2018 - The fabrication of functional gradient hypereutectic Al-Si composites by liquid-solid separation technology [Crossref]
2015 - The measurement of the adhesion force between ceramic particles and metal matrix in ceramic reinforced-metal matrix composites [Crossref]
2004 - Thermal properties of diamond/copper composite material [Crossref]
2008 - Thermal conductivity of diamond composites sintered under high pressures [Crossref]
2009 - Thermal stress and heat transfer characteristics of a Cu/diamond/Cu heat spreading device [Crossref]
2008 - Interfacial design of Cu-based composites prepared by powder metallurgy for heat sink applications [Crossref]
2012 - Interfacial characterization and thermal conductivity of diamond/Cu composites prepared by two HPHT techniques [Crossref]