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	Baise University, University of Science and Technology Beijing
Citations	18
Analysis	Full AI Review Included

Executive Summary

This research investigates the interface behavior and fabrication of high-thermal-conductivity (TC) diamond/Cu composites for heat sink applications, focusing on nanosized surface coatings to mitigate interfacial thermal resistance (ITR).

Core Achievement: The use of a nanosized Titanium (Ti) coating on diamond particles significantly enhanced interfacial bonding, resulting in a peak TC of 475.01 W m^-1 K^-1 for a 40 vol.% composite.
Failure Mechanism (Cu Coating): Nanosized Copper (Cu) coatings failed due to the “nano effect.” At elevated sintering temperatures (1243-1313 K), the Cu segregated and spheroidized, transforming the uniform coating into localized micron-sized contacts, thereby increasing ITR.
Success Mechanism (Ti Coating): The nanosized Ti layer remained stable, forming a strong interfacial “bridge” via the reaction products: Titanium Carbide (TiC) with the diamond and Cu-Ti intermetallic compounds/solid solutions with the copper matrix.
Density and Defects: Ti-coated composites achieved high relative densities (up to 98.5%), minimizing defects (cavities, pores) that typically form around uncoated diamond particles and severely degrade TC.
Optimal Conditions: The highest TC was achieved at 40 vol.% diamond content, sintered at 1313 K, demonstrating that process control and interface design are critical for maximizing thermal performance.

Technical Specifications

Parameter	Value	Unit	Context
Peak Thermal Conductivity (TC)	475.01	W m^-1 K^-1	40 vol.% Ti-coated diamond/Cu composite (1313 K)
Coefficient of Thermal Expansion (CTE)	10.93 x 10^-6	K^-1	40 vol.% Ti-coated diamond/Cu composite (1313 K)
Relative Density (Peak)	98.5	%	40 vol.% Ti-coated diamond/Cu composite (1313 K)
Thermal Diffusivity (a) (Peak)	172.75	mm² s^-1	40 vol.% Ti-coated diamond/Cu composite (1313 K)
TC of Pure Copper (Bulk)	~400	W m^-1 K^-1	Reference material
TC of Raw Diamond (MBD-4)	~1450	W m^-1 K^-1	Reinforcement material
TC of Uncoated Composite (Baseline)	262.82	W m^-1 K^-1	40 vol.% uncoated diamond/Cu composite (1243 K)
TC of Cu-Coated Composite	339.53	W m^-1 K^-1	40 vol.% Cu-coated diamond/Cu composite (1243 K)
Diamond Particle Size	98-106	µm	Synthetic single-crystal MBD-4 type
Copper Powder Size	~75	µm	Purity 99.85 wt.%
Coating Layer Thickness (Nominal)	~100	nm	Nanosized Cu or Ti layer
Sintering Temperature Range Tested	1193 to 1363	K	Powder metallurgy fabrication

Key Methodologies

The diamond/Cu composites were fabricated using a standard powder metallurgy (PM) process combined with vacuum ion plating for surface modification.

1. Raw Material Preparation and Modification

Diamond Source: Synthetic single-crystal diamond particles (MBD-4 type, 98-106 µm).
Coating Method: Vacuum ion plating was used to deposit a nanosized layer (~100 nm) of either Cu or Ti onto the diamond surfaces.
Coating Morphology (Ti): Ti coatings exhibited two distinct morphologies: nanosized particles with {111} preferred orientation and columnar structures with {100} preferred orientation.

2. Composite Fabrication (Powder Metallurgy)

Mixing: Diamond particles (30-60 vol.%) were mechanically mixed with pure copper powder for 2 hours.
Cold Pressing: Samples were compacted under a pressure of 500 MPa for 5 minutes.
Hot Pressing/Sintering:
- The cold-pressed slurry was extruded in a graphite mold.
- Pressure applied: 50 MPa.
- Hold Time: 10 minutes (until cooled down).
- Cooling Rate: 10 K min^-1 (using circulating cooling water).
- Sintering Temperatures Tested: 1193 K, 1243 K, 1313 K, and 1363 K.

3. Characterization Techniques

Microstructure and Fracture: Field Emission Scanning Electron Microscopy (SEM, SUPRA 55, ZEISS) combined with Energy Dispersive Spectroscopy (EDS) mapping.
Thermal Properties (TC, a, C_p): Laser scattering TC instrument (LFA 427, NETZSCH) used cylindrical specimens (12.7 mm diameter, 3 mm thickness). TC was calculated as the product of density (ρ), specific heat capacity (C_p), and thermal diffusivity (a).
Coefficient of Thermal Expansion (CTE): Measured using a thermomechanical analyzer (NETZSCH DIL 402C) on cuboid specimens (25 mm length, 4 mm width, 3 mm height).
Density: Measured by the Archimedes method.
Airtightness: Tested using a helium mass spectrometer (ZQJ 530) at 5 MPa for 3 hours.

Commercial Applications

The development of diamond/Cu composites with high TC and low CTE is crucial for advanced thermal management in high-power electronics, addressing thermal stress and heat accumulation issues.

High-Power Microelectronics: Essential for packaging materials in devices following Moore’s Law, where miniaturization and integration increase heat flux.
Semiconductor Substrates: Used as heat sink materials for next-generation semiconductors, including:
- Silicon Carbide (SiC) devices (3^rd generation).
- Gallium Nitride (GaN) devices (3^rd generation).
- Gallium Arsenide (GaAs) and Indium Phosphide (InP) devices (2^nd generation).
Thermal Spreading Devices: Fabrication of high-stability, high-quality heat spreaders and heat sinks for CPUs, GPUs, and power modules where thermal stress mismatch with the chip must be minimized.
Aerospace and Defense Electronics: Applications requiring robust thermal management under extreme operating conditions and high reliability.

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

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