Heterogeneous Integration of Diamond Heat Spreaders for Power Electronics Application

At a Glance

Metadata	Details
Publication Date	2023-05-01
Authors	Henry A. Martin, Marcia Reintjes, Dave Reijs, Sander Dorrestein, Martien Kengen
Institutions	Delft University of Technology
Citations	7
Analysis	Full AI Review Included

Technical Documentation & Analysis: Diamond Heat Spreaders for Power Electronics

Executive Summary

This research successfully validates the use of MPCVD diamond heat spreaders for advanced thermal management in high-power electronic packages, directly addressing the critical need for superior heat dissipation in miniaturized systems.

Performance Achievement: The thermally enhanced Power Quad-Flat No-Lead (PQFN) package demonstrated a ~9.6% reduction in maximum device junction temperature at 6.6W input power compared to standard packages.
Thermal Gradient Improvement: The diamond heat spreader effectively redistributed heat, resulting in a significantly lower thermal gradient across the active device surface, mitigating localized hot spots.
Integration Method: A robust heterogeneous integration approach was employed, utilizing a double pressureless sintering process with nano-silver (Nano-Ag) paste to bond thinned silicon dies (50 µm) to 110 µm CVD diamond slabs.
Material Optimization: Parametric simulations identified optimal layer thicknesses: 50 µm for the Silicon Thermal Test Chip (TTC) and 100-110 µm for the diamond heat spreader.
Reliability Confirmed: The enhanced packages exhibited high thermo-mechanical stability, showing less than 2% thermal degradation after 200 thermal cycles ranging from -55°C to 150°C.
Scaling Efficiency: The efficiency (percentage reduction in junction temperature) of the diamond heat spreader was proven to scale positively with increasing power input, confirming its benefit for high-power density applications.

Technical Specifications

The following hard data points were extracted from the experimental results and material optimization sections of the research paper.

Parameter	Value	Unit	Context
Diamond Thermal Conductivity (Grade 1)	1800	W/mK	CVD Diamond material property
Diamond Thermal Conductivity (Grade 2)	1000	W/mK	CVD Diamond material property
Input Power (Test Condition)	6.6	W	Applied to Resistor 1 for 1 second
Input Heat Flux (Test Condition)	~10.5	W/mm²	Equivalent flux density
Junction Temperature Reduction (Max)	~9.6	%	Enhanced PQFN vs. Standard PQFN (at 6.6W)
Silicon TTC Thickness (Optimized)	50	µm	Thinned substrate thickness (parameter a)
Diamond Heat Spreader Thickness (Experimental)	110	µm	CVD Diamond slab thickness (parameter b)
Thermal Cycling Range	-55 to 150	°C	Thermo-mechanical reliability test range
Thermal Degradation (200 cycles)	< 2	%	Package reliability metric
Backside Metalization Stack (TTC/Diamond)	Ti/Pt/Au (100/200/600)	nm	Sputter coating for adhesion promotion
Sintered Interface Thickness	~35	µm	Nano-Ag sinter layer thickness
Resistor Resistance Sensitivity (Spiral)	72	Ω/°C	Used for temperature sensing (TCR)

Key Methodologies

The heterogeneous integration process involved precise material preparation, metalization, and a double-sintering assembly sequence:

Substrate Thinning: Commercial Thermal Test Chips (TTCs) were mechanically polished on the backside to reduce the Silicon substrate thickness from 400 µm down to the optimized 50 µm.
Adhesion Metalization: Both the thinned TTC backside and the CVD diamond heat spreader slabs (110 µm thick, 4mm x 4mm) were sputter coated with a Ti/Pt/Au stack (100/200/600 nm) to promote adhesion for subsequent sintering.
Die-Diamond Sintering: Nano-Silver (Nano-Ag) sinter paste was dispensed onto the metalized diamond. The thinned, metalized TTC was wet mounted and subjected to a pressureless sintering process under a Nitrogen atmosphere.
Leadframe Assembly: Nano-Ag paste was screen printed onto the copper lead frame die pad. The pre-sintered die-diamond stack was wet mounted onto the lead frame.
Stack-Leadframe Sintering: The complete assembly was sintered again using a similar pressureless process under Nitrogen, resulting in a final sintered interface thickness of approximately 35 µm.
Final Packaging: Electrical connections were established using 99.99% pure gold wire bonds (25 µm wire, 50 µm bump), followed by transfer molding with an epoxy compound and singulation into PQFN packages.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-quality MPCVD diamond materials and precision processing services required to replicate, optimize, and scale this advanced thermal management research.

Applicable Materials

To achieve the thermal performance demonstrated (1000-1800 W/mK), the research requires high-purity, high-thermal conductivity CVD diamond.

Research Requirement	6CCVD Material Recommendation	Material Specification
High Thermal Conductivity (Passive Heat Spreader)	Thermal Grade PCD (Polycrystalline Diamond)	Wafers up to 125mm, thickness 0.1 µm - 500 µm. Cost-effective solution for large-area heat spreading.
Highest Purity/Performance (Grade 1 equivalent)	Optical Grade SCD (Single Crystal Diamond)	SCD plates up to 10x10mm, thickness 0.1 µm - 500 µm. Ideal for maximizing thermal transfer in critical hot spots.

Customization Potential

The success of this heterogeneous integration relies heavily on precise dimensional control and robust interface preparation, both of which are core 6CCVD capabilities.

Precision Thickness Control: The paper identified an optimal diamond thickness of 100-110 µm. 6CCVD offers SCD and PCD wafers with custom thicknesses from 0.1 µm up to 500 µm, ensuring researchers can precisely match their simulation-optimized dimensions.
Advanced Metalization Services: The experiment utilized a specific Ti/Pt/Au (100/200/600 nm) stack for adhesion promotion prior to Nano-Ag sintering. 6CCVD provides internal, high-quality metalization services, including Au, Pt, Pd, Ti, W, and Cu, allowing for the delivery of ready-to-bond, pre-metalized diamond heat spreaders.
Custom Dimensions and Dicing: The researchers used 4mm x 4mm diced slabs. 6CCVD provides custom laser cutting and dicing services for plates/wafers up to 125mm, ensuring application-specific geometries are delivered with high precision and clean edges suitable for high-density packaging.
Surface Finish Optimization: The paper noted that poor interface contacts (due to voids, Figure 7b) decrease efficiency. 6CCVD’s ultra-smooth polishing (Ra < 1 nm for SCD, Ra < 5 nm for PCD) minimizes surface roughness, which is critical for reducing contact thermal resistance (TCR) during the sintering process.

Engineering Support

6CCVD’s in-house PhD team specializes in the material science of MPCVD diamond and its integration into complex systems. We can assist engineers and scientists in optimizing material selection and processing parameters for similar Power Electronics Packaging and High-Density Heterogeneous Integration projects. Our expertise ensures the diamond material properties (purity, thermal conductivity, and surface finish) are perfectly matched to the required bonding methodology (e.g., Nano-Ag sintering, transient liquid phase bonding).

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

View Original Abstract

<p>Integrated Circuits and Electronic Modules experience concentrated thermal hot spots, which require advanced thermal solutions for effective distribution and dissipation of heat. The superior thermal properties of diamonds are long known, and it is an ideal material for heat-spreading applications. However, growing diamond films to the electronic substrate require complex processing at high temperatures. This research investigates a heterogeneous method of integrating diamond heat spreaders during the back-end packaging process. The semiconductor substrate and the heat spreader thicknesses were optimized based on simulations to realize a thermally enhanced Power Quad-Flat No-Lead package. The performance of the thermally enhanced PQFN was assessed by monitoring the temperature distribution across the active device surface and compared to a standard PQFN (without a heat spreader). Firstly, the thermally enhanced PQFN indicated a 9.6% reduction in junction temperature for an input power of 6.6W with a reduced thermal gradient on the active device surface. Furthermore, the diamond heat spreader’s efficiency was observed to increase with increasing power input. Besides, the reliability of the thermally enhanced PQFN was tested by thermal cycling from -55°C to 150°C, which resulted in less than 2% thermal degradation over two-hundred cycles. Such choreographed thermal solutions are proven to enhance the packaged device’s performance, and the superior thermal properties of the diamond are beneficial to suffice the increasing demand for high power. </p>

Tech Support

Original Source

DOI: https://doi.org/10.1109/ectc51909.2023.00029

References

2013 - Diamond-based heat spreaders for power electronic packaging applications