Electronics Protection - July/August 2013 - (Page 6)

Feature Formable Phase Change Materials as Latent Heat Sinks for Portable Electronic Devices Jackson Sutherland, Chemist Outlast Technologies LLC Powerful Devices and Overheated Consumers Advances in computing technology have led to electronic devices that can achieve extraordinary processing feats in the smallest and slimmest of devices. While most consumers have grown accustomed to having such power in the palms of their hands, they have also unfortunately grown accustomed to the unpleasant heat produced from such compact and intensive electronic devices. In addition to increased touch and surface temperatures, elevated internal hardware temperature can lead to device performance degradation from heatrelated stress or firmware related decreases in CPU processing speed. To maintain the sleek designs of current devices, active cooling such as fans or liquid circulation cannot be implemented due to space restrictions. This device miniaturization inherently drives the required heat dissipation into even smaller volumes. This leaves a ready, and unfilled, market for passive thermal control heat-sinks and like products to deal with thermal relief in space-limited electronic devices. How Latent Heat Sink Phase-Change Materials Work One such method for passive cooling is realized through the incorporation of phase change materials (PCMs) into various matrices. A PCM is any material that has a high enthalpy of fusion (usually reported in Joules/gram, J/g), also known as the latent heat of the material. The latent heat of a material is the amount of energy required for a unit mass of material to undergo a phase change. Note that during a phase change, the temperature of the material remains constant. An explanation of this phenomenon can be given through basic kinetic theory. According to kinetic theory, the average kinetic energy is equal to the absolute temperature. So, by adding heat energy to the system, we are able to increase the kinetic energy and thus the temperature. However, a substance in a given phase can only reach a certain kinetic energy because it is bound by intermolecular forces of neighboring molecules. With enough energy, these intermolecular forces are overcome and a phase change occurs. After each phase change, additional degrees of freedom are added to the molecule, allowing for increased kinetic energy, and thus allowing the temperature to once again rise. As an example, consider the most familiar PCM, H2O. In its solid form, ice, the strong intermolecular interactions of the crystal lattice limit the molecules to vibrational motion only. As energy is added to the system, the molecules within the lattice will vibrate with more and more intensity, relating to an increase in temperature, but they will reach a maximum vibrational energy at 0°C. At this temperature, energy that is introduced to the system is used to overcome the intermolecular forces of the crystal lattice, releasing molecules into their liquid state. Once in the liquid state, the H2O molecules are then able to not only vibrate, but also rotate. The temperature can once again increase with an input of energy. This process will occur again for the vaporization process at 100°C when the molecules gain translational motion. Phase Change Material Formulation for Electronics The Outlast LHS-89, the PCM used in this study, contains a proprietary blend of PCM that melts and absorbs energy between the ranges of 36°C and 42°C. These temperature ranges are significant to control both touch/surface temperatures, and internal processing temperatures. Physiologically, buffering this temperature range is of significance because in the average person, heat-associated pain is 6 signaled to the central nervous system at 43°C. Some heat related discomfort does still occur at lower temperatures, giving reason to begin buffering temperatures at those lower than 43°C. In an attempt to control extreme temperatures at the device surface, the firmware of most current devices will step down the processing speed of the CPU to limit heat generation once a given internal temperature is reached. Consequentially, this gives need for the material to be able to buffer temperature within the device as well. Through differential scanning calorimetry, the Outlast LHS-89 PCM composite was measured to have 160 J/g of latent heat. This translates to over 1.1 kilojoule of energy buffering capacity with the use of just over 7 grams of product. There are certain considerations intrinsic to the application, which had to be accounted for in the formulation of LHS-89. Chemical compatibility is of utmost importance when adding material to any electronic device. For this reason, the Outlast LHS-89 contains no inorganic components, is pH neutral, inert and incorporates no readilyreactive moieties. The thermal stability of the product was rigorously tested through thousands of heating and cooling cycles to assure no loss of energy absorption or temperature buffering performance of the LHS-89 over time. The LHS-89 does not run, leak or outgas, and adheres to UL-94 flame retardant requirements for electronic devices. Application Testing A Samsung Galaxy S3 with 1.5 GHz dual core Qualcomm Krait CPUs, Qualcomm Adreno 225 GPU and a Qualcomm Snapdragon S4 MSM8960 SoC was tested as purchased and with the LHS-89 placed beneath the EMI shield of the device (Figure 1). Before all tests were performed, the device was allowed to equilibrate at 28°C for one hour. To test the efficacy of the LHS-89 at internally cooling the device and delaying a temperature-related decrease in process- Figure 1. Outlast LHS-89 in place underneath the EMI ing speed due to firmware throttling, the internal CPU temperatures were recorded shield of the test device. while a Dhrystone test was continuously run on both processors. During this test both processor units clocked at 1.5 GHz until the firmware throttled down the CPU speed due to overheating at a CPU temperature of 57°C. A continuous Dhrystone benchmark was selected since it is an extremely CPU-intensive task and has good repeatability throughout tests (Figure 2). The LHS89 was able to absorb enough heat to allow both CPUs to run at maximum processing speed for 4.73 minutes, compared to the 1.99 minutes without Outlast LHS-89. This corresponds to a 137 percent increase in time at maximum processing speed. In a second test, the ability of Outlast LHS-89 to decrease exterior touch temperature was assessed. A benchmark test (Open GL 2.5.1 Egypt) was continuously run while the external hot spot temperature of the device with and without Outlast LHS-89 was recorded through IR thermography at regular time intervals (Figure 3). A reduction in hot spot temperature of at least 4°C was achieved from the time interval of two to 20 minutes. This reduction in hot spot temperature resulted in the device with Outlast LHS-89 remaining below the 43°C threshold associated with temperature related pain for 2.5 times as long as the device without Outlast LHS-89 (six minutes compared to 15 minutes). Figure 3 gives thermal images of the device with and without Outlast LHS-89 at selected time intervals while running the Open GL 2.5.1 Egypt looped gaming benchmark. July/August 2013 www.ElectronicsProtectionMagazine.com http://www.ElectronicsProtectionMagazine.com

Table of Contents for the Digital Edition of Electronics Protection - July/August 2013

Electronics Protection - July/August 2013
Newer Technology Releases Next-Generation Power2U AC/USB In Wall Charging Solution
Subzero Engineering Introduces PolarXpress DCiM SaaS Monitoring Solution
Specifiers of Enclosures for Components in Outdoor Applications: Be Aware of Material Selection Issues
Formable Phase Change Materials as Latent Heat Sinks for Portable Electronic Devices
How to Protect Electronic Circuits from Power Surges
Diamond Heat-Spreaders: Growth Methods and Applications
Standards-Based Design & Electronic Packaging Solutions
Reducing Room-Level Bypass Airflow Creates Opportunities to Improve Cooling Capacity and Operating Costs
Harnessing Laboratory Wind Tunnels
New DVR Enclosure with Prepackaged Thermoelectric Cooler
New Silver Conductive Aqueous Based Sodium Silicate System for EMI/RFI Shielding
Citizen and MechaTronix LED Cooling Cooperate On New Generation CitiLED COB’s
Eaton Expands 5P UPS Product Line to Provide Efficient Protection for Any IT Environment
Flex-Block System Puts Free-Standing Enclosures on New Footing
Gore Introduces Acoustic Vent for Protecting Electronic Devices
Industry News
Calendar of Events

Electronics Protection - July/August 2013