China
Africa
Explore chapters and articles related to this topic
ThermoMechanical Design
Published in Fred D. Barlow, Aicha Elshabini, Ceramic Interconnect Technology Handbook, 2018
According to the second law of thermodynamics, conductive heat flows from a relatively small dissipating element to the ambient in a complex manner. As described in Fourier’s law in Subsection 3.2.2.1, the heat flow is three-dimensional. When a high thermal conductivity material is placed in the heat path as shown in Figure 3.4 [11], the heat flow in the x and y horizontal directions is greater than in the vertical direction z. The heat will spread with a resulting increase of the effective thermal cross–sectional area A (in Equation 3.22) of a relatively poor thermal conductivity material. This provides a lower thermal resistance than the configuration without the heat spreader. The heat spreader is typically a high-thermal-conductivity material and is placed between the dissipating element and the heat sink.
White Light-Emitting Diode: Fundamentals, Current Status, and Future Trends
Published in Wengang (Wayne) Bi, Hao-chung (Henry) Kuo, Pei-Cheng Ku, Bo Shen, Handbook of GaN Semiconductor Materials and Devices, 2017
Bingfeng Fan, Yi Zhuo, Gang Wang
Thermal management is based on the use of thermal resistance networks. A thermal resistance network is analogous to an electrical resistor network using parallel and series resistances to represent heat transfer paths. In place of a voltage potential across a resistor, a temperature potential exists, and instead of current flowing through the electrical circuit, heat flows through the thermal network. Figure 14.10 shows the thermal resistance network for a complete Luxeon LED package mounted on a chip carrier (heat spreader) by solder or bonding adhesive. The heat spreader consists of a high-conductivity material such as copper. Such a network is generally utilized to evaluate the heat transport performances of this system. From Figure 14.10 it can be inferred that these thermal resistances are in a series configuration: Rsystem=Rcihp+Rchip−sub+Rsubmount+…+Rheatsink-envir
Metals
Published in Andrea Chen, Randy Hsiao-Yu Lo, Semiconductor Packaging, 2016
Andrea Chen, Randy Hsiao-Yu Lo
Generally, aluminum or copper metals are used as heat spreader or heat sink materials. These two metals are good at moving heat isotropically, but due to high contact resistance, they tend to be inefficient in transferring heat away from components. More exotic materials like graphite can work as heat spreader material. Graphite has anisotropic heat transfer properties—excellent in the x-y plane but a poor conductor in the z-axis. Graphite is very lightweight but tends to be much more brittle than either aluminum or copper.
Diamond as the heat spreader for the thermal dissipation of GaN-based electronic devices
Published in Functional Diamond, 2022
Benefitted from the high breakdown voltages (10 times higher than Si), high switching speed (over GHz), compact size, and tunable electronic architecture [1–7], III-V nitride semiconductor is becoming one of the best candidates for high-power electronics to enable the increasing power density and high conversion efficiency. The commercialized AlGaN/GaN high electron mobility transistors (HEMTs) have led to the entry into the medium-power market, and play a central role for the RF and millimeter-wave applications [8–11]. In the applications of 5 G communications, radar, and electronic warfare, the HEMTs devices can offer more than 10 times higher power density than the existing Si technologies [12]. This giant power induces a huge amount of heat in the chip area, creating localized hot spots with fluxes above 10 kW/cm2 and package-level volumetric heat generation that can exceed 100 W/cm−3. The high-level power dissipation results in the challenges using conventional approaches for the thermal management. With the increased power density, self-heating inside the devices becomes an essential issue that accelerates the failure and poor reliability in the real application. Thermal dissipation through conventionally used approaches is no longer adequate. To achieve the effective thermal dissipation, the heat spreader with a much higher thermal conductivity is required.
Fabrication and Thermal Characterization of Composite Cu-CNT Micropillars for Capillary-driven Phase-Change Cooling Devices
Published in Nanoscale and Microscale Thermophysical Engineering, 2019
G. Rojo, S. Ghanbari, J. Darabi
In this work, composite Cu-CNT micropillars were fabricated on a copper substrate as a wick structure for potential use in capillary-driven heat pipes and vapor chambers. Copper has excellent thermal and electrical conductivities and is commonly used as a heat spreader in electronic cooling applications. However, copper has a high coefficient of thermal expansion (CTE) and its corrosion resistance is relatively poor. On the other hand, CNTs possess a low coefficient of thermal expansion, a very high thermal conductivity, and a high corrosion resistance [22]. Thus, the reliability of electronic devices can be improved if materials with low coefficient of thermal expansion, high thermal conductivity, and better corrosion resistance such as composite Cu-CNT structures are used. Figure 2 illustrates a simplified process flow to fabricate composite Cu-CNT mushroom-like micropillars. One of the crucial steps in the fabrication of a micropillar array is making a template. The photolithography process is the standard technique for pattern transfer in microfabrication. However, this method is very expensive and requires cleanroom environment and sophisticated equipment. In this study, a polystyrene mesh net with an opening size of 50 µm and a thickness of 112 µm was used as a micropillar array template. While these dimensions may not be the optimum geometry, this was the smallest mesh net that was commercially available. This method was found to be a very rapid and inexpensive way to make the micropillar pattern and was suitable to demonstrate the proof of concept. First, a copper substrate was polished using waterproof sandpapers with grit sizes of 600, 800 and 1000. Next, the polyester mesh template was bonded to the polished copper plate by applying heat and pressure. The template was sandwiched between the polished substrate and a backing plate of a similar size, and a uniform pressure was then applied on the template using a clamp. To prevent bonding of the template to the backing plate, a plastic sheet was placed between them. The entire fixture was placed in an oven for 1 hour at 140°C. After heat treatment, the specimen was removed from the oven and allowed to cool at room temperature. The clamp and the backing copper plate were then removed.