Thermal Comparison of Polycrystalline Diamond and AlN in Power Semiconductor Device Packages

At a Glance

Metadata	Details
Publication Date	2018-01-01
Journal	Lincoln (University of Nebraska)
Authors	Brandon M. Guenther
Analysis	Full AI Review Included

Technical Documentation & Analysis: Polycrystalline Diamond for High-Performance Power Electronics

Executive Summary

This analysis reviews research demonstrating the superior thermal performance of Polycrystalline Diamond (PCD) films compared to conventional Aluminum Nitride (AlN) Direct Bond Copper (DBC) substrates for Wide Bandgap (WBG) power semiconductor packaging.

Thermal Performance Breakthrough: PCD substrates exhibited a thermal transient response time 50 to 150 times faster than standard AlN DBC substrates, confirming PCD’s role as a critical thermal management solution for high-power SiC and GaN devices.
Material Superiority: PCD offers thermal conductivity up to 1540 W/mK and dielectric strength up to 100,000 kV/mm, significantly surpassing AlN (180 W/mK, 17 kV/mm).
Interface Optimization: The Cobalt-coated PCD (Co-PCD) film showed a 3x faster thermal transient response time than Copper-coated PCD (Cu-PCD), suggesting superior adhesion and lower thermal resistance at the metal-diamond interface.
Addressing Reliability Challenges: The research highlights the necessity of managing Coefficient of Thermal Expansion (CTE) mismatch and surface roughness, critical areas where 6CCVD offers specialized material engineering and polishing solutions.
Application Focus: PCD is validated as the optimal electrical isolation layer for next-generation WBG devices operating at high junction temperatures (250-300 °C) and high power densities.

Technical Specifications

Parameter	Value	Unit	Context
PCD Thermal Conductivity	1540	W/mK	Measured value for PCD films tested
AlN Thermal Conductivity	180	W/mK	Standard DBC substrate reference material
PCD Dielectric Strength	10 - 100,000	kV/mm	Potential range, significantly higher than AlN
AlN Dielectric Strength	17	kV/mm	Standard DBC substrate reference material
PCD CTE	1.0	ppm/K	Low CTE, critical for thermal stress management
AlN CTE	4.5	ppm/K	Standard DBC ceramic CTE
PCD Film Thickness	300	µm	Thickness of PCD layer tested
PCD Lateral Dimensions	1.5 x 3.5	mm	L_PCD x W_PCD of test samples
Metal Coating Thickness	50	nm	Co or Cu coating thickness on PCD surface
Transient Response Improvement	50 to 150	times faster	PCD vs. AlN DBC (normalized steady state)
Co-PCD vs. Cu-PCD Speed	3	times faster	Co-PCD transient response vs. Cu-PCD
WBG Operating Temperature	250 - 300	°C	Target junction temperature for SiC/GaN devices

Key Methodologies

The thermal comparison relied on precise fabrication and advanced thermal modeling techniques:

PCD Film Fabrication: Polycrystalline diamond films were deposited onto bulk copper/carbon-fiber (Cu/CF) composite substrates using a combustion flame Chemical Vapor Deposition (CVD) process.
Substrate Tuning: The Cu/CF substrate composition was tuned (via densification) to control the CTE, aiming for a better match with the deposited diamond film.
Metalization: Two types of PCD films were prepared: Co-PCD (Cobalt coated on one surface) and Cu-PCD (Copper coated on both surfaces). These coatings were applied to smooth the rough PCD surface for interconnection.
Sample Preparation: A commercial Powerex IGBT module (AlN DBC) was deconstructed, and the DBC section was isolated for comparison.
Thermal Measurement: Transient temperature profiles were measured using an emissivity-calibrated FLIR E60 thermal (IR) imaging camera and Type K thermocouples while samples were heated on a hot plate (up to 200 °C).
Thermal Modeling: A Cauer-equivalent Thermal Resistor-Capacitor (RC) circuit model was developed and modified (including constriction and edge effects) to de-convolve the thermal effects of the baseplate and solder layers, isolating the performance of the DBC/PCD substrate only.

6CCVD Solutions & Capabilities

This research confirms that high-quality PCD is essential for maximizing the potential of WBG semiconductors. 6CCVD is uniquely positioned to supply the required materials and engineering services to transition this research into reliable commercial products.

Applicable Materials

To replicate and extend this high-performance thermal management research, 6CCVD recommends the following materials:

Polycrystalline Diamond (PCD) Substrates: High-purity, thermal-grade PCD is required to achieve the 1540 W/mK conductivity demonstrated. 6CCVD offers PCD wafers up to 125mm in diameter, suitable for large-scale power module manufacturing.
Custom Thickness PCD: The tested PCD thickness (300 µm) falls well within our standard PCD thickness range (0.1 µm to 500 µm). We can provide custom thicknesses to optimize the PCD-to-Copper thickness ratio (e.g., 2:1 ratio suggested for reduced thermal stress).
Boron-Doped Diamond (BDD): For applications requiring specific electrical properties or enhanced adhesion layers, 6CCVD can supply BDD films, which maintain high thermal stability while offering tunable conductivity.

Customization Potential

The research highlights two critical engineering challenges: metal adhesion/interface quality and CTE mismatch. 6CCVD directly addresses both:

Research Requirement/Challenge	6CCVD Capability & Solution
Metal Adhesion/Interface Quality (Co-PCD outperformed Cu-PCD)	Custom Metalization: We offer in-house deposition of Au, Pt, Pd, Ti, W, and Cu. This allows engineers to test various adhesion layers (like Cobalt or proprietary alloys) to optimize the thermal interface resistance (R_th) and mechanical reliability.
Surface Roughness (PCD rough surface complicates soldering)	Precision Polishing: 6CCVD guarantees ultra-smooth surfaces. We achieve roughness values of R_a < 5 nm on inch-size PCD wafers, eliminating the need for thick, thermally resistive intermediate smoothing layers mentioned in the research.
Custom Dimensions & Geometry (Small test pieces used)	Large Area & Custom Cutting: We supply PCD plates up to 125mm. Our advanced laser cutting services ensure precise, complex geometries required for modern IGBTMOD and power module layouts.
Thermomechanical Stress Management (CTE mismatch failure risk)	Material Stacks: We work with clients to design multi-layer diamond stacks or composite structures to manage the overall package CTE, ensuring long-term reliability under thermal cycling.

Engineering Support

6CCVD’s in-house PhD team specializes in MPCVD diamond growth and characterization. We can assist with material selection and optimization for similar High-Power WBG Device Packaging projects, focusing on:

Thermal Modeling Validation: Providing precise material parameters (thermal conductivity, specific heat, density) for accurate Cauer RC circuit modeling.
Dielectric Testing: Assisting researchers in performing the recommended dielectric breakdown strength tests on custom-fabricated PCD films.
Reliability Testing: Consulting on optimal metalization schemes (e.g., Ti/Pt/Au stacks) to ensure the metal-PCD interface can withstand the rigors of thermal cycling (as noted in the outlook section of the thesis).

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. Global shipping (DDU default, DDP available) ensures rapid delivery of critical materials worldwide.

View Original Abstract

The desire for improved thermal management in power semiconductor device packaging is becoming increasingly important due to the progression towards implementing wide-bandgap semiconductor (WBG) materials, such as silicon carbide (SiC) and gallium nitride (GaN). These semiconductor materials have the capability of operating at much higher voltages, temperatures, and frequencies compared to standard silicon-based devices. However, utilizing this enhanced operating region will induce larger thermomechanical stress within the package structure as a consequence of operating at higher junction temperatures around 250-300 °C. To handle the higher and improved operating characteristics from the WBG semiconductors, the current package technology is modified by increasing heat flow through its layers. This modification will improve reliability and operating lifetime of device packages in high power applications.\nThe focus of this research was on enhancing the thermal performance of the direct bond copper (DBC) substrate in a standard package design by considering the implementation of polycrystalline diamond (PCD) films as a replacement for the commonly used DBC (AlN) substrates. The use of these PCD films in a standard device package has been examined in detail using an emissivity-calibrated thermal (IR) imaging camera experiment that measures and compares the top surface temperature profiles of a commercial module package and two PCD films (Co-PCD and Cu-PCD).\nThe results from this thermal experiment showed that both of the PCD films reached steady state considerably faster than the AlN substrate. The accelerated top surface temperature profiles of the PCD films demonstrated a faster thermal transient response time, an increased heat flow, and lower thermal resistance that can potentially handle the high operating characteristics of WBG semiconductors. In addition, the Co-PCD film displayed a faster thermal transient response time compared to the Cu-PCD film. The resulting thermal analysis on PCD films can be used to aid future research pertaining to dielectric breakdown strength tests, studying lateral heat flow, ways of interconnection into a device package, and mechanical behavior under thermomechanical stress within a package.\nAdviser: Jerry L. Hudgins

Tech Support

Original Source

DOI: None