Progress in the Copper-Based Diamond Composites for Thermal Conductivity Applications

At a Glance

Metadata	Details
Publication Date	2023-06-01
Journal	Crystals
Authors	Kang Chen, Xuesong Leng, Rui Zhao, Yiyao Kang, Hongsheng Chen
Institutions	Harbin Institute of Technology
Citations	27
Analysis	Full AI Review Included

Executive Summary

Core Challenge: The increasing miniaturization and integration of microelectronics require thermal management materials with thermal conductivity (TC) significantly exceeding traditional substrates (120-150 W/(mK)).
Solution Focus: Copper-based diamond composites (Cu/Diamond) are targeted, leveraging diamond’s ultra-high TC (1200-2500 W/(mK)) and copper’s high electrical conductivity.
Limiting Factor: Poor natural wettability between Cu and diamond creates high interfacial thermal resistance (ITR), severely limiting composite TC.
Key Strategy: ITR is minimized by interfacial modification, primarily through coating diamond particles or alloying the Cu matrix with strong carbide-forming elements (e.g., Zr, B, Cr, Ti). These elements form stable carbide layers (e.g., TiC, WC, ZrC) that enhance bonding.
Performance Achievement: Optimized composites have achieved thermal conductivities exceeding 900 W/(mK), with peak reported values up to 930 W/(mK) (using Cu-Zr matrix) and 913 W/(mK) (using Cu-B matrix).
Process Optimization: The optimal diamond volume fraction for cost-effective, high-TC composites is typically 50-60 vol%. Forming techniques like Pressure Infiltration (PI) and Spark Plasma Sintering (SPS) are critical for achieving high density and controlled interface thickness.

Technical Specifications

Parameter	Value	Unit	Context
Diamond Intrinsic TC	1200 - 2500	W/(mK)	Pure diamond material
Copper Matrix Intrinsic TC	398 - 400	W/(mK)	Pure copper material
Target Composite TC	>900	W/(mK)	Required for advanced thermal management
Highest Achieved TC (Zr Alloy)	930	W/(mK)	Cu-0.5 wt% Zr matrix, Pressure Infiltration
Highest Achieved TC (B Alloy)	913	W/(mK)	Cu-0.3 wt% B matrix, Pneumatic Infiltration
Interfacial Thermal Resistance (h_c)	2.9 x 10⁷	W/(m²K)	Experimental value used in modeling
Optimal Diamond Volume Fraction	50 - 60	vol%	Recommended range for high TC and cost-effectiveness
Typical Diamond Particle Size	100 - 300	µm	Size range used in recent high-performance studies
Ti Coating Thickness for Max TC	220	nm	Achieved 811 W/(mK) via Pressure Infiltration
SPS Sintering Temperature Range	800 - 970	°C	Used for Spark Plasma Sintering
HTHP Sintering Pressure	6.0 - 6.5	GPa	Used for High-Temperature and High-Pressure sintering

Key Methodologies

The primary engineering focus is on reducing interfacial thermal resistance (ITR) through two main strategies, followed by high-density forming techniques:

1. Interfacial Modification Strategies

Diamond Surface Metallization (Pre-Coating): Coating diamond particles with strong carbide-forming elements (Ti, Cr, W, Zr) prior to composite fabrication.
- Electroplating (EP): Depositing metal (often Cu) onto a pre-coated diamond surface (e.g., W or TiC) to improve adhesion and density.
- Magnetron Sputtering (MS): Depositing uniform, controllable carbide layers (e.g., WC) with thicknesses typically ranging from 45 nm to 400 nm.
- Salt Bath Coating (SBC): Heating diamond and metal powder in molten salt (e.g., NaCl-KCl) to form thin carbide coatings (e.g., TiC, WC, Cr₇C₃).
Matrix Alloying (In Situ Carbides): Adding reactive elements (Ti, B, Cr, Zr) directly to the copper matrix powder. Carbides form in situ at the diamond interface during the high-temperature forming process, enhancing wettability.

2. Forming Techniques

Pressure Infiltration (PI): Molten copper is infiltrated into a densely packed diamond preform under external gas pressure (e.g., 1.5 MPa). This method is highly effective for filling gaps and achieving high density, leading to some of the highest reported TC values.
Spark Plasma Sintering (SPS): Uses pulsed current and pressure to rapidly sinter mixed powders at relatively low temperatures (800-970 °C). Offers fast preparation but is limited by mold size and pressure constraints.
Vacuum Hot-Press Sintering (VHPS): Sintering mixed powders in a vacuum furnace under pressure. Provides uniform, slow heating, which helps reduce thermal stress but lowers preparation efficiency.
High-Temperature and High-Pressure (HTHP) Sintering: Uses extreme conditions (high GPa pressure) to achieve high density, even with diamond volume fractions exceeding 70 vol%. High cost and limited sample size are drawbacks.

Commercial Applications

The exceptional thermal conductivity of optimized copper-based diamond composites makes them ideal for high-performance thermal management in demanding engineering sectors:

Electronic Packaging: Used as substrates and heat spreaders for high-power density components (e.g., CPUs, GPUs, FPGAs) where heat flux is critical.
Aerospace and Military: Applications requiring materials with high thermal stability, low coefficient of thermal expansion (CTE), and high TC, such as radar systems and avionics.
Power Electronics: Thermal management for high-voltage and high-current devices, including IGBT modules and power converters.
Optoelectronics: Heat dissipation for high-power laser diodes and LED arrays, ensuring stable operating temperatures and long-term reliability.
Miniaturized Systems: Essential for maintaining performance and reliability in highly integrated microelectronic devices where conventional materials fail to dissipate heat effectively.

View Original Abstract

Copper-based diamond composites have been the focus of many investigations for higher thermal conductivity applications. However, the natural non-wetting behavior between diamond particles and copper matrix makes it difficult to fabricate copper-based diamond composites with high thermal conductivity. Thus, to promote wettability between copper and diamond particles, the copper/diamond interface must be modified by coating alloying elements on the diamond surface or by adding active alloying elements with carbon in the copper matrix. In this paper, we review the research progress on copper-based diamond composites, including theoretical models for calculating the thermal conductivity and the effect of process parameters on the thermal conductivity of copper-based diamond composites. The factors that affect interfacial thermal conductivity are emphatically analyzed in this review. Finally, the current problems of copper-based diamond composites and future research trends are recommended.

Tech Support

Original Source

DOI: https://doi.org/10.3390/cryst13060906

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