Fanless Thermal Solution Design Guide for IoT Applications
The internet of things (IoT) network of interconnected devices is driving an explosion of integrated-electronic components (IC) for embedded applications. Transceivers and computers in this segment are adapting a module based approach, where the memory, logic or RF, and power regulating components are placed on a single board. These module based systems and sensors will be deployed at the IoT edge, where environmental considerations have challenging implications for thermal and mechanical design.
In order to function reliably in harsh environments with extended operating ambient temperature ranges, electronics housings for IoT solutions that support low-power components with fan-less designs in sealed enclosures will be desirable. This paper is intended to be a practical guide for the thermal designer to quickly size and implement an optimized fanless thermal solution. We review the boundary conditions applicable to various segments relevant to IoT applications. We then present a guide for fanless thermal solution design, with an overview of analytical free-convection plate-fin heatsink optimization, radiation considerations, TIM selection, as well other relevant fanless boundary condition concerns.
We begin with simplified equations for back-of-the envelope sizing calculations and then dive into analytical expressions for optimizing the heatsink fin spacing. We then compare the simplified computations with extensive simulation results and provide heatsink size dimensions based on segment ambient specifications for a typical IoT compute module with varying thermal design power, fin height aspect ratio, and heatsink material. Finally, we present a simplified example of an automotive software defined cockpit (SDC) design to demonstrate the application of these design considerations.
Mike Schroeder, Thermal Mechanical Systems Engineer - Intel Corp.
High Efficient Heat Dissipation on Printed Circuit Boards
This paper describes the various techniques for effectively dissipating heat from heat generating electrical components on printed circuit boards. Small copper coins that are matching the shape of the electrical components are located underneath the component and are integrated in the PCB construction. The heat from the component will be dissipated by the copper coin to a heat sink. The thermal conductivity of such kind of copper coin is about 10 times higher than usually achieved with so called thermal via arrays. Several different methods of integrating copper coins into the construction of PCB’s have been developed and will be presented.
New developments such as the “Chip-on-Coin” technique are providing solutions for highly miniaturised electronic circuits and micropackaging. The integration of copper coins into PCB’s is suitable for all common substrates including RF and microwave substrates as well as for conventional PCB substrates. Just recently also rigid-flexible circuit boards can be equipped with copper coins.
Markus Wille ∙ R&D Manager – Schoeller Electronics Systems GmbH
Ultrathin Thermal Ground Planes for High Heat Flux
As electronic systems continue shrinking, the waste heat is generated at ever increasing power densities. Vapor chambers and thermal ground planes (TGPs) are passive thermal management systems which employ the evaporation of an encapsulated liquid to lift heat from a hot spot, convection of the hot vapor to spread the heat, condensation of the vapor to reject heat at a condenser, and capillary pumping of the liquid to return it to the hot spot; they offer an excellent solution to reduce the heat flux from a high-heat flux electronic system. However, TGPs suffer from two issues in high heat flux applications: first, the wick has a limited capillary pressure, and therefore there is a limit to the maximum power they can sustain; second, the liquid and wick introduce an evaporative thermal resistance.
We have developed TGPs with a thickness of <0.5 mm for high heat flux applications off of a 3 mm x 3 mm heat source. With a thin copper wick, we demonstrate a transition from thick-film evaporation to enhanced evaporation/boiling above 100 W/cm2 which reduces the evaporation resistance by a factor of 2. With low-area applications for electronic modules of 4 cm x 2.5 cm or 3.5 x 3.5 cm, the TGP cools a hot-source by >10°C compared to an equivalently sized copper heat-spreader, which corresponds to an effective thermal conductivity of >3,000W/m-K. We will cover models to show improvement of the TGP in terms of reducing thickness, increased power, and increased effective thermal conductivity.
Dr. Ryan Lewis, Director of R&D - Kelvin Thermal Technologies
Performance Investigation of Fans Placed in Series
When designing equipment that use fans for forced convection cooling, the situation frequently arises when the airflow impedance through the system is high enough that one fan will not provide the pressure and consequently the airflow needed to cool the unit. When this situation occurs and there is no acceptable solution available that will provide adequate airflow with a single fan, two fans in series may be able to provide the needed airflow. Two fans in series should, in theory, be able to double the available static pressure of just one fan. However, if the second fan is simply placed downstream of the first fan, there will be a degradation in the theoretical static pressure developed by the fan pair.
This presentation will show the results of an investigation to determine how close a series fan arrangement can come to doubling the static pressure while minimizing the amount of space required for the two-fan combination. The presentation will consist of using CFD simulations with a rotating frame of reference around the impellers to predict the series fan performance and will also show how well the simulations agree with actual test data taken using an airflow test chamber to measure the pressure and airflow of the series arrangements.
Guy Wagner, Director - Electronic Cooling Solutions
Thermal Conductivity Measurement by Steady-State and Flash Diffusivity Methods and Instruments
The thermal managements of any systems require reliable thermal conductivity data of the components that are employed. Understanding both the advantage and limitation of various measurement methods and instruments associated with the thermal conductivity range of materials, geometries and sizes of the samples available for testing, sample status (solid, powder, liquid) is essential to choose the proper methods in accordance with ASTM, ISO standards to obtain reliable thermal conductivity data.
The presentation will cover the measuring principles and instrumentations of heat flow thermal conductivity meters, and flash diffusivity analyzers, and their applications on various materials such as polymers, metal/alloys, carbon/graphite, ceramics, liquids/pastes/powders in different shapes, sizes, and status in the temperature range -150°C to 1600°C. The comparisons between different methods and the cautions that must be taken for the correct measurement are discussed.
Kadine Mohomed, Ph.D, Applications Manager – TA Instruments
Piero Scotto, Manager, ThermoPhysical Properties Product line – TA Instruments
Heng Wang, Ph.D., Sr. Product Marketing Specialist, Thermophysical Properties - TA Instruments
Natural-Graphite-Sheet Heat Sinks
The attractive thermal properties and low price of natural graphite sheets (also known as flexible graphite sheets) make them suitable for thermal management applications. They have already penetrated the electronics cooling market in some areas, such as thermal interface materials (TIM). At Laboratory for Alternative Energy Conversion we compared heat sinks manufactured from natural graphite and aluminum. Two cases were studied: with and without an electrically insulating TIM. In cases without an insulating TIM, a 31% reduction in the total thermal resistance was seen, which led to a 19% lower heat source temperature.
When an insulating TIM was added between the heat source and the heat sinks no significant difference in performance was observed. This behavior is explained by the difference in hardness of the heat sink material, which significantly affects the thermal contact resistance (TCR). To reduce the TCR between components and metal heat sinks in applications where electrical insulation is not needed thermal grease, gap fillers or other forms of interface agents are typically used, but these often suffer from pump out or dry out. Our results show that with graphite heat sinks it is possible to have the same TCR reduction without any pump out or dry out. The weight of the graphite heat sink was 20 g, only 44% of weight of the aluminum one (45.6 g). The stiffness of the heat sink reflects the lower weight; i.e., graphite heat sinks are more sensitive to breaking if they are dropped or impacted by other objects.
At the beginning of my presentation I will give an overview of graphite in the thermal management context. In particular, I will highlight the differences between natural flake graphite and synthetic graphite (Panasonic PGS sheet is the most popular form of synthetic graphite).
Martin Cermak, Laboratory for Alternative Energy Conversion - Simon Fraser University
Comparison of Advanced Flexible Heater Technologies
The flexible heater market is a $3.1B industry worldwide, 1/3 of which is polyimide-based flexible heaters and the market is expected to reach $1.4B in 2021 . There are distinct advantages of polyimide heaters when compared with other heating element technologies. For example, they have a high temperature range (>200C), quick response times and are very lightweight. Due to the advantages of polyimide heaters, they are used in a number of different industries including medical, aerospace, automotive and industrial applications as well as a variety of applications such as comfort heating, freeze protection, process heating and composite curing.
This paper will outline property comparison among polyimide heater technologies including etched-foil heaters using a polyimide substrate and the dual layer all-polyimide film. Heaters with similar power densities will be selected and evaluated based on various criteria including voltage and current inputs as well as temperature outputs, time to thermal stability, temperature uniformity and heat up / cool down time. Other criteria that will be reported in this paper will include weight, thickness, resistance and flexibility. And conclusions will be drawn regarding the best use-cases for each type of polyimide-based heater technology.
Matthew Manelis, Application Engineer – DuPont Electronics & Communications
Nashay Naeve, Business Development Leader - DuPont Electronics & Communications
Thermal Runaway Prevention of Li-ion Batteries by Novel Thermal Management System
Due to their energy density, higher voltage, and negligible memory effects, lithium-ion batteries are the popular choice for a wide range of applications. Larger power demands and increasing cell density of lithium-ion battery packs result in high operating temperatures, especially under peak loads. Because of the susceptibility of most commercial lithium-ion cell chemistries to degrade or age at or above 60°C, this leads to rapid loss of capacity over subsequent charge/discharge cycles as well as reduced overall power output. Reducing detrimental thermal effects through the use of latent heat system (LHS) materials that absorb and store thermal energy, has proven highly effective.
Another impressive feature of LHS Battery Materials is their ability to eliminate the potential for Thermal Runaway or Propagation in battery packs. Thermal Runaway and Propagation potential is a growing safety concern in many applications due to the possibility of serious fire in the event the cells are physically damaged or short circuited.
A novel thermal management system will be demonstrated which offers a solution to both these safety and performance concerns through the use of latent heat storage (LHS) material that are able to absorb and store significant thermal energy, substantially increasing the overall safety and thermal stability of a battery system. The ability of these LHS- based systems to maintain optimal cycling performance and inhibit thermal runaway will be explored and the benefits of these materials into a variety of application-specific design configurations will be detailed.
Mark Hartmann, CTO/R&D – Outlast Technologies LLC
Heat Pipes as Thermal Solution for PCBs
Rapidly ongoing miniaturization in combination with increasing electronic functionality -particularly in high end applications- leads to the need of progresses in the PCB cooling technology. Improved thermal performance of PCBs should allow -with lowest possible additional cost- to remove the power loss from components in such a way that their maximum temperature during operation does not exceed allowed levels. Heat decentralization, i.e., heat spreading and heat guiding in the PCB is one opportunity to achieve high cooling effectiveness from passive systems. In order to provide an effective heat transport from the chip into the lateral direction of the PCB, embedded miniaturized heat pipes are a promising solution for the heat spreading problem.
Jonathan Silvano de Sousa, PhD, Project Leader R&D – AT&S Austria
Power Density and Thermal Management Roadmap of Next Generation Telecom Equipment
The network traffic in telecommunication industry has grown rapidly every year since its inception. With the extrapolation from current equipment, future nodes would consume and dissipate up to 100’s of kilowatts of power. In response to the projected growth, new design and architecture are needed in order to face the power-density challenges in the next generation telecommunication networks. There are two aspects of these issues. One is the network architecture and another is telecommunication equipment design. The thermal management of latter case is the focus of this paper
This paper first describes the trends and the critical thermal issues in the current telecommunication industry, and then follows with the possible solutions to the issues. The thermal technology map is developed as a general guideline to select the proper cooling schemes for the system under consideration. The discussion is then extended to the development of liquid cooled telecommunication equipment which is a must to meet power density challenge in the future systems. General design guidelines of liquid cooling are discussed in details. Because of the rapid growth in energy consumption and its related cost, the energy efficiency of the data center becomes a major issue to be considered in the industry. This paper also presents the critical steps needed to achieve the energy efficiency at the equipment and in data center by integrating thermal management into system design.
Lian-Tuu Yeh, Ph D & PE, ASME Fellow – Thermal Consultant