Thermal Pyrolytic Graphite Research Articles

Rigorous Reliability Testing of an Encapsulated Thermal Pyrolytic Graphite (TPG) Heat Spreader for Passive Thermal Management Applications

Continued microelectronic miniaturization has resulted in higher power density, increasing the need for high performance thermal management. One possible solution for board-level thermal management is to fully encapsulate a high thermal conductivity material, such as Thermal Pyrolytic Graphite (TPG; ~1700 W/mK) in a metal (such as 6061 aluminum), producing an efficient passive heat spreader for thermal dissipation. The metal shell provides sufficient mechanical strength at a small detriment to the overall thermal conductivity. Reliability and consistent performance over time are critical for thermal management systems, especially in Defense and Aerospace applications. MIL-STD-883H provides test parameters for reliability involving exposure to mechanical shock (Method 2002.5), mechanical vibration (Method 2005.2), and thermal shock (Method 1011.9), with traditional evaluation criteria involving microelectronic device performance and/or a visual examination. For this work, the reliability of aluminum encapsulated TPG test coupons was evaluated with more demanding criteria: a visual examination, X-ray inspection, acoustic microscopy, and thermal conductivity performance testing, both before and after the previously discussed MIL-STD-883H exposures. The encapsulated coupons showed excellent robustness; the thermal conductivity properties remained constant with an average value around 965 W/mK, and the non-destructive imaging revealed excellent bond quality for the metal encapsulation, with no evidence of delamination. This more stringent evaluation criteria after MIL-STD-883H testing provides a better way to evaluate the reliability of passive thermal management systems. The study results also demonstrate the metal encapsulated TPG heat spreader as a superior thermal management solution with high performance and high reliability for demanding applications.

Thermal Management in High-Density High-Power Electronics Modules Using Thermal Pyrolytic Graphite

Abstract Tremendous effort is going on towards the packaging of power electronics modules to reduce the parasitic impedances and in turn, the voltage spikes during switching transients of power devices. The heat dissipated in terms of switching losses for high frequency applications need to be eliminated further to have some flexibility regarding the layout and, for the safe functioning of a power module by reducing junction temperature. Thermal pyrolytic graphite (TPG), with its high basal-plane thermal conductivity along the vertical direction helps direct heat towards the module bottom (cooling system), whereas its extremely low through-plane thermal conductivity along the horizontal direction guarantees minimum heat coupling among devices placed on the substrate surface. FEA simulations to verify thermal benefits of TPG and experimental results have been shown in this work which validates the junction temperature drop of up to 17 °C when using TPG as substrate and heat spreader compared with traditional materials.

Improving Heat Conduction of Insulated Metal Substrate with Thermal Pyrolytic Graphite Core for SiC Power Module Packaging

TPG-core IMS concept was jointly explored in this study. Integrating high thermally conductive TPG graphite core into IMS is expected to simultaneously achieve high thermal conductivity from TPG and electrical functionalities from IMS. Nearly 2x thermal conductivity and 30% weight saving was demonstrated on TPG-core IMS compared to conventional Cu-core IMS. Significant junction temperature reduction (11°C) in steady state and power cycling was revealed by the thermal analysis as the result of improved thermal spreading in plane and through the thickness. The study also proved the manufacturability and compatibility of this TPG-core IMS structure to the existing IMS production and power module assembling. The integration of TPG and IMS paves a new packaging route to increase heat load, improve reliability, simplify module design and reduce assembling cost and number of steps.

Thermal Decoupling in Power Electronics Modules Using Thermal Pyrolytic Graphite

Abstract The device within a power electronics module package will fail if the maximum junction temperature is not within the device's permissible maximum temperature rating specified by the manufacturer. Modern electronic miniaturization demands multi-chip module (MCM) packaging providing different semiconductor technology integration, reduced number of component interconnects, and lower power supply. But the huge amount of heat generated by each chip produces thermal coupling among devices, leading to an increase in the junction temperature. The power device specifications in the datasheet assume the devices being mounted on a suitable heatsink. Wide bandgap (WBG) devices like silicon carbide (SiC) devices can generally sustain a maximum junction temperature of about 175 °C – 200 °C. The junction temperature of the WBG devices becomes severe in a high-density high-power module. This highlights the need for a thermal management system to limit the maximum junction temperature within the device's permissible range. As a result, the power module needs to be connected to a heatsink to effectively increase the surface area of the heat dissipation junctions. A high conductivity material based heatsink extracts heat effectively from the module as the thermal resistance value remains low. In this paper, preliminary thermal analysis is done for a high density high-power module where the high in-plane thermal conductivity of thermal pyrolytic graphite (TPG) is exploited in substrate as well as heatsink designs. TPG brings down the junction temperature to a considerably lower level, leading to a safer power module functioning. This paper focuses on the design and proper alignment of the substrate and heatsink with respect to the module layout so that maximum junction temperature is reduced by proper heat extraction far below the operating temperature of the devices and also extent of reduction of the thermal coupling among the power devices placed next to each other on the same plane within the power module.

Material Based Structure Design: Numerical Analysis Thermodynamic Response of Thermal Pyrolytic Graphite /Al Sandwich Composites

Amine-grafted multiwalled carbon nanotubes (MWCNTs) based thermally conductive adhesive (TCA) was studied in the previous paper and applied here in thermal pyrolytic graphite (TPG)/Al radiator due to its high thermal conductivity, toughness and cohesiveness. In this paper, in an attempt to confirm the application of TCA to TPG/Al sandwich radiator, the thermodynamic response in TPG/Al sandwich composites associated with key material properties and structural design was investigated using finite element simulation with commercial available ANSYS software. The induced thermal stress in TCA layer is substantial due to the thermal expansion mismatch between Al plate and TPG. The maximum thermal stress is located near the edge of TCA layer with the von Mises stress value of 4.02 MPa and the shear stress value of 1.66 MPa. The reasonable adjustment of physical-mechanical properties including thermal conductivity, thermal expansion, Young,s modulus and the thickness of TCA layer, Al plate and TPG are beneficial for reducing the temperature of the top surface of the upper skin and their effects on the reduction of thermal structural response in some ways. These findings will highlight the structural optimization of TPG/Al radiator for future application.

Vacuum-compatible, ultra-low material budget Micro-Vertex Detector of the compressed baryonic matter experiment at FAIR

The Compressed Baryonic Matter (CBM) Experiment is one of the core experiments of the future FAIR facility near Darmstadt (Germany). The fixed-target experiment will explore the phase diagram of strongly interacting matter in the regime of high net baryon densities with numerous probes, among them open charm mesons. The Micro Vertex Detector (MVD) will provide the secondary vertex resolution of ∼50μm along the beam axis, contribute to the background rejection in dielectron spectroscopy, and to the reconstruction of weak decays. The detector comprises four stations placed at 5, 10, 15, and 20cm downstream the target and inside the target vacuum. The stations will be populated with highly granular CMOS Monolithic Active Pixel Sensors, which will feature a spatial resolution of <5μm, a non-ionizing radiation tolerance of >1013neq/cm2, an ionizing radiation tolerance of ∼3Mrad, and a readout speed of a few 10μs/frame. This work introduces the MVD-PRESTO project, which aims at integrating a precursor of the second station of the CBM-MVD meeting the following requirements: material budget of x/X0<0.5%, vacuum compatibility, double-sided sensor integration on a Thermal Pyrolytic Graphite (TPG) carrier, and heat evacuation of about 350mW/cm2/sensor with a temperature gradient of a few K/cm.

How Can Millions of Aligned Graphene Layers Cool High Power Microelectronics?

Thermal management is an increasingly critical problem in today's microelectronics industry. As power requirements increase and size requirements decrease, innovative materials with high thermal conductivity (TC), light weight, and many times low coefficient of thermal expansion (CTE) are desired to solve these thermal challenges. Thermal Pyrolytic Graphite (TPG*), a unique synthetic material produced by Momentive via chemical vapor deposition, contains millions of layers with highly-oriented stacked graphene planes and exhibits excellent in-plane thermal conductivity (&amp;gt;1500 W/m-K) and very low density (2.25g/cm3). In order to take advantage of its superior properties for thermal management, various forms of TPG-metal composite products were developed in the past few years. TPG composite with metal encapsulation simultaneously achieves high thermal conductivity from the TPG core and high mechanical strength from the metal shell. Momentive's proprietary bonding technology enables an intimate and strong joint between TPG and dissimilar metals, including Al, Cu, Sn, WCu, MoCu, AlSiC, and AlBe. In addition, the variety of compatible metals adds new functionalities to the TPG composite, such as platability and solderability for direct die attachment, CTE matching to semiconductor, and flexibility for off-plane connectivity. Also in this paper, three TPG composite categories, i.e.: TC1050* Heat Spreader, TPG Heat Sink and TPG Laminate, will be discussed in detail. Individually, their design guidance, performance, reliability, and application examples will be shared with the reader. With these three TPG composite products, Momentive has translated our extensive experience and success in thermal management at the system level, with TC1050 Heat Spreaders, to the device level, with TPG Heat Sinks and TPG Laminates.