FEM thermal analysis of Cu/diamond/Cu and diamond/SiC heat spreaders
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2017-03-01 |
| Journal | AIP Advances |
| Authors | Garuma Abdisa Denu, Jibran Hussain Mirani, Jiao Fu, Zongchen Liu, Hongxing Wang |
| Institutions | Ethiopian Civil Service University, Xiâan Jiaotong University |
| Citations | 11 |
| Analysis | Full AI Review Included |
Thermal Management Design Optimization for High-Power Electronics using 6CCVD Diamond
Section titled âThermal Management Design Optimization for High-Power Electronics using 6CCVD DiamondâExecutive Summary
Section titled âExecutive SummaryâThe attached research performs a critical Finite Element Method (FEM) analysis on diamond-based heat spreaders, identifying key challenges related to thermal stress and proposing optimized material stack designs. This summary outlines the core findings and the resultant design requirements directly supported by 6CCVDâs advanced Material Processing Capabilities.
- CTE Mismatch Stress Identified: The primary challenge in copper/diamond/copper (Cu/D/Cu) devices is the large coefficient of thermal expansion (CTE) mismatch (Diamond: 1.2x10-6/K vs. Copper: 17x10-6/K), generating high interfacial thermal stress (up to 2.14 GPa).
- Carbide Interlayer Solution: Introducing a thin, 1”m Chromium Carbide (Cr7C3) interlayer significantly mitigated thermal stress in the Cu/D/Cu stack, demonstrating up to a 28% reduction in maximum stress at 250°C operating temperature.
- Optimal Diamond Thickness: Effective thermal conductivity (Keff) and heat flux increase linearly with diamond layer thickness, necessitating high-quality CVD diamond films in the range of 50”m to 250”m to maximize thermal performance.
- Stress-Free Alternative (Diamond/SiC): The diamond/Silicon Carbide (D/SiC) system demonstrated inherently superior thermal stability and lower stress due to the closely matched CTEs (SiC: 4.3x10-6/K), eliminating the necessity for complex adhesion interlayers.
- High-Temperature Reliability: The D/SiC system exhibited stable performance and low stress across temperatures up to 235°C, confirming its capability for reliable heat spreading at large temperatures without destructive thermal failure.
- Validation of CVD Diamond Need: The results confirm that high-purity, thick CVD diamond films are essential for increasing Keff, validating the continued engineering need for specialized MPCVD materials in high-power thermal management.
Technical Specifications
Section titled âTechnical SpecificationsâThe following table extracts critical material parameters and performance metrics used or derived from the FEM thermal analysis.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Required Diamond Thickness Range | 0.1 - 250 | ”m | Optimal range for high Keff and heat flux |
| Simulated Device Area (3D) | 10 x 10 | mm | Standard high-power device footprint |
| Diamond Thermal Conductivity (Îș) | 2500 | W/mK | High-grade CVD Diamond required for simulation |
| Diamond CTE (α) | 1.2 x 10-6 | 1/K | Very low coefficient, source of mismatch |
| Copper CTE (α) | 17 x 10-6 | 1/K | High coefficient, primary stress generator |
| Silicon Carbide CTE (α) | 4.3 x 10-6 | 1/K | Closely matched to diamond for low-stress interfaces |
| Carbide Interlayer Thickness | 1 | ”m | Cr7C3 thickness required for stress relief |
| Maximum Operating Temperature (T) | 235 | °C | Highest thermal stress test point (maximum stress increases with T) |
| Maximum Calculated Stress (Without Interlayer) | 2.14 | GPa | Cu/D/Cu device stress at 250°C |
| Maximum Calculated Stress (With Interlayer) | 1.53 | GPa | Cu/D/Cu device stress at 250°C (28% reduction) |
| Bottom Forced Convection (h) | 1500 | W/m2K | Simulating connection to a large, actively cooled heat sink |
Key Methodologies
Section titled âKey MethodologiesâThe study relied on Finite Element Method (FEM) simulation to model the thermo-mechanical response of composite heat spreader structures.
- Simulation Software and Technique: FEM analysis performed using COMSOL Multiphysics to calculate effective thermal conductivity (Keff), thermal stress (Ï), and heat flux.
- Geometry Modeling: Both 3D (10mm x 10mm) and 2D (100”m width) models were utilized to study dimensional effects.
- Material Setup:
- Layer Structure 1 (High Stress): Cu (top 2”m) / Diamond (up to 250”m) / Cu (bottom 100”m).
- Layer Structure 2 (Low Stress): Diamond (up to 200”m) / Silicon Carbide (SiC, 2”m).
- Adhesion Layer Study: The impact of a 1”m thick Chromium Carbide (Cr7C3) interlayer, deposited at the Cu-Diamond interface, was modeled to quantify thermal stress reduction.
- Thermal Boundary Conditions (TBCs):
- The electronic component was simulated as a heat source applying temperatures up to 235°C to the top surface.
- A high forced convection coefficient of 1500 W/m2K was applied to the bottom Cu layer to simulate connection to a high-capacity heat sink.
- Environmental/Ambient temperature and natural air convection (20 W/m2K) were applied to remaining outer surfaces.
- Performance Analysis: Thermal stress (Ï = αEÎT) was measured predominantly at the material interfaces where CTE mismatch strains were largest.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research highlights the critical need for ultra-high quality, dimensionally controlled CVD diamond materials and complex stacking capabilities (interlayers, hybrid substrates) to manage extreme heat flux and thermal stress. 6CCVD is uniquely positioned to supply the materials required to replicate, validate, and extend this critical thermal management research.
| Paper Requirement | 6CCVD MPCVD Capability | Value Proposition for Engineers |
|---|---|---|
| High Thermal Conductivity Diamond | Single Crystal Diamond (SCD) or High-Grade Polycrystalline Diamond (PCD). | Guaranteed high thermal conductivity (Îș > 2000 W/mK) necessary to achieve the calculated Keff and heat flux gains. |
| Thick Diamond Layers (0.1”m - 250”m) | SCD and PCD deposition available in thicknesses from 0.1”m up to 500”m. | Enables optimization studies for thickness dependence on Keff and interfacial stress, providing flexible material supply beyond the 250”m range studied. |
| Low-Stress Diamond/SiC Systems | Expert CVD growth processes optimized for various substrates, including Silicon Carbide (SiC). | Supplies diamond layers grown directly on CTE-matched SiC substrates, providing the low-stress heat spreader platform validated in the paper, ready for subsequent processing. |
| Custom Interlayers for Adhesion/Stress | Comprehensive in-house metalization services: Au, Pt, Pd, Ti, W, Cu. | Offers custom sputter deposition of metals (e.g., Ti/W used as carbide-forming/diffusion barriers) to replace or enhance the Cr7C3 interlayer function, improving bonding reliability to copper heat sinks. |
| Specific Small Dimensions (10mm x 10mm) | High-precision laser cutting and machining services for both SCD and PCD. | Delivers custom dimensions, micro-patterns, and optimized edge geometry required for critical thermal interfaces, ensuring exact fit for high-power semiconductor packages. |
| Surface Finish Requirements | Polishing capability to Ra < 1nm (SCD) and Ra < 5nm (PCD). | Guarantees extremely flat and smooth interfaces, minimizing thermal boundary resistance (TBR) which is not accounted for in the FEM stress analysis but is critical for real-world performance. |
Engineering Support
Section titled âEngineering SupportâThe analysis of Cu/diamond/Cu and diamond/SiC systems confirms that material selection and interface engineering are paramount in high-power thermal management. 6CCVDâs in-house PhD team provides comprehensive engineering support, assisting clients in selecting the optimal Optical Grade SCD or Thermal Grade PCD material systems, defining appropriate metalization stacks (e.g., Ti/Pt/Au for bonding), and achieving required thicknesses for replicating or extending near-junction heat spreader projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
The effects of thermal stress resulting from thermal cooling in copper/diamond/copper heat spreader is investigated using finite element method. A similar model of diamond/SiC heat spreader is compared without addition of interlayer. The effect of carbide interlayer in reduction of interfacial thermal stress is investigated. The results show that the carbide interlayer film thickness is critical in stress reduction for a copper/diamond/copper heat spreader device. Diamond/SiC device has lower interfacial stress without interlayer. The study of mechanical and thermal property of diamond heat spreader is useful for optimal designs of efficient heat spreader for electronic components.