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Publications

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Conference / Venue

July 2016 Breaking Down the Thermal Management Challenges in Forced Convection Tablets” – William Maltz, Electronics Cooling Solutions, and John Parry, Mentor Graphics
Accommodating higher performance computing in small form-factors such as a tablet is a thermal management challenge. Touch temperature is as important as processor temperature. Cooling by natural convection alone isn’t enough for the higher power density of a high-performance tablet, instead forced convection has to be used. This article examines the thermal management challenges of forced convection in a tablet form factor.
Desktop Engineering Magazine
June 2016 “Application of Phase Change Materials in Handheld Computing Devices” – William Maltz, Darryl Moore and Arun Raghupathy
Consumer handheld devices, such as smart phones and tablets, are excellent candidates for the use of phase change materials (PCMs). The design of handheld products with PCMs can extend product working operating range, minimize throttling, and reduce reliance on fans for transient load use cases to reduce acoustic noise and extend battery life. This study looks at opportunities and challenges for applying PCMs to handheld and computing devices using a forced convection tablet as an example.
Electronics Cooling Magazine
June 2016 Influence of Temperature Gradient on Electromigration – Failures in 3D Packaging – Ramdev Kanapady, Darryl Moore, Arun Raghupathy  
In this paper, influence of temperature gradient in interconnects due to Joule heating in 3D packaging on electromigration failure is presented. Black’s Mean Time to Failure (MTF) model relates exponentially to the temperature of interconnects which is assumed to be constant hence does not take into account temperature gradient. The developed electromigration model incorporates the driving force due to temperature gradient in addition to the effects of current density, vacancy concentration gradients and stress gradients in the interconnects and due to coefficient of thermal expansion mismatch with surrounding materials. Effectiveness of the developed finite element model is illustrated complex C4 solder bumps of flip-chip packages using COMSOL Mutliphysics® software. It is shown that for same current density in the complex C4 solder bumps of flipchip packages it is possible that failure times could be lower for lower solder average temperature with higher temperature gradient than for higher solder temperature with low temperature gradient.
ITHERM 2016
Las Vegas, NV USA
June 2016 Experimental and Computational Evaluation of Phase Change Materials for Handheld Computing – Ramdev Kanapady, Darryl Moore, Arun Raghupathy
In the current work, numerical evaluation of phase change material along with experimental validation of the same in a handheld device is presented. The value addition and driving force towards the use of phase change material (PCM) is not only due to limited heat dissipation capability and computational sprinting power load patterns in processors but also to have better user experiences of these hand held devices such as low touch temperatures, no fan noise and possibility of extended battery life by reducing the discharge cycles without fan loads. Direct placement of PCMs on the die or encapsulating the heat pipe, that has the quickest response to temperatures as a passive thermal management strategy is explored in this study. This paper proposes an accurate phase change model for transient thermal management using COMSOL Multiphysics® software. Impact of geometry of PCM material and its properties on the transient behavior of the CPU’s temperature is provided. The model validations are carried out by comparing the results with controlled experimental results. The PCM material and their material properties are being provided by Outlast Technologies.
ITHERM 2016
Las Vegas, NV USA
March 2016 Thermal Management Challenges in Forced Convection Tablets – Darryl Moore and Arun Raghupathy
This short webinar presented by Electronic Cooling Solutions will discuss thermal management challenges in forced convection tablets. For high performance tablets, forced convection is required to provide sufficient thermal management for the device. Forced convection introduces a number of additional user experience concerns such as battery life and acoustics. This webinar explores these challenges and details their work regarding FloTHERM XT thermal model calibration with T3Ster measurement data, thermal design with FloTHERM XT, and acoustic testing.
Mentor Graphics – Webinar
Mechanical Analysis Multimedia
March 2016 “Application of Phase Change Materials in Handheld Computing Devices” – Darryl Moore
With peak loads in the order of minutes and ergonomic considerations limiting surface temperatures and acoustical noise, handheld devices, such as smart phones or tablets, are excellent candidates for use of phase change materials (PCMs). The experimental and numerical evaluation of such materials used to enhance the performance of a forced convection cooled tablet is presented in this study. The PCM design parameters, including specific heat capacity, operating points (i.e., melt temperatures), thermal conductivity, and volume of phase change required for a specific time delay, are examined in the context of a tablet application.
SEMI-THERM 32
San Jose, CA USA
September 2015 Thermal Design Parameters and Significance of Spreading – Bharath Nagendran, Arun Raghupathy, William Maltz
Tablet computers, due to their advantages in size, weight, touch-interactive features, and the availability of mobile broadband data, are increasingly replacing laptop computers. As the performance of these tablets comes closer to matching that of laptops, applications that require high performance computing have become accessible from these devices. The increase of computational performance in such small form factors is mainly limited by the available thermal management technologies. The skin temperature of the tablet and the acoustic noise of these hand-held devices are of greater importance than for a conventional laptop due to closer human interactions. Due to these constraints there has been increasing demands made on the thermal engineers working on tablet devices. Therefore, the current thermal management strategies need to be improved to meet the growing performance demand. This work focuses on non-conventional heat rejection techniques such as thermal ground plane (TGP) and graphite spreaders are introduced in the tablet to enhance the spreading.
IMAPS ATW – Thermal Management
Los Gatos, CA USA
August 2015 “Best engineering practice for thermal characterization of stacked dice FPGA devices” – Arun Raghupathy (ECS), Gamal Refei-Ahmed, Hoa Do, Brian Philofsky (Xilinx)
This paper presents a couple of new methodologies regarding package characterization. An important shortcoming of the JEDEC methodology for single-die packages is that it does not account for the real-world scenario of a package’s boundary condition. A new methodology is proposed to overcome this shortcoming by accounting for typical PCB conductivities and heatsink attachments to packages. The second methodology, presented in the paper, shows a better way to develop DELPHI-based boundary condition independent compact thermal models for 2.5D packages with multiple dies mounted on an interposer. This methodology, based on DELPHI-based techniques, accounts for the interaction between the multiple dies in a package. This is done by modifying the resistors generated from the optimization process. A number of verification cases show good fidelity of the compact thermal model to the detailed model.
2015 International 3D Systems Integration Conference
Sendai, Japan
March 2015 “Thermal Management Challenges in Forced Convection Tablets” – Arun Raghupathy
Handheld devices with computing capabilities that match laptops and desktops have recently emerged as market drivers in the consumer electronics industry. To accommodate such high performance in small form-factors like that of a tablet is a thermal management challenge. In touch-interactive electronics devices like tablets, skin temperature is as important as the processor temperature. Cooling by natural convection alone is insufficient to address the higher power density found in this class of high-performance tablet. Therefore, these devices require forced convection solutions. This study presents the thermal management challenges of a forced convection tablet using experimental and computational techniques. One such thermal challenge stems from the blower speed versus ergonomic requirements of acoustics. To understand more about this relation, the tablet is experimentally characterized for acoustics for several controlled blower speeds. The tablet is also characterized using airflow bench tests, infrared thermography and thermocouple measurements. The system-level thermal model of the tablet is constructed using FloTHERM XT®. The validated model serves as a test vehicle to study alternate thermal management strategies and understand their impact on the overall product design.
SEMI-THERM 31
San Jose, CA USA
September 2014 “A Study of the Maximum Theoretical Power Dissipation of Tablets Under Natural Convection Conditions” – Guy Wagner
This study determines the limits of natural convection cooling for ideal handheld devices of various sizes based on simulations. Four popular tables were tested to determine the surface temperature rise under heavy computational and graphics loads. The thermal performance of each tablet based on hot spot temperature is measured against the performance of an ideal tablet of the same size and a figure of merit for the efficiency of heat dissipation is calculated to see how well they perform against the ideal tablet. The factors affecting the maximum possible power dissipation are the available surface area and surface finishes, selection of the outer shell materials, thermal interface materials, heat spreaders and air gaps. In most cases, the limiting factor in the thermal design of these devices is not the temperatures of the internal components but the temperature of the external surfaces since these are in direct contact with the skin of the user. This study presents a method for analyzing the efficiency of the thermal design of these devices.
THERMINIC 2014
London, England UK
October 2014 “Experimental and Computational Characterization of Vapor Chamber Heatsinks” – Darryl Moore
This paper details an experimental procedure used to characterize the steady-state thermal performance of a vapor chamber heatsink assembly. The presentation will emphasize the methodology and process used in the design of the experiment including the use of computational modelling to validate the experimental setup and accuracy. A custom test fixture was designed and used to characterize the performance of a vapor chamber heatsink assembly for a number of power levels, air velocities, and orientations. A heatsink with a solid aluminum base was also evaluated to determine the improvement that could be obtained by using a heatsink with a vapor chamber base. A computational model of the heatsink and the vapor chamber was constructed and refined to match the experimental results.
IMAPS ATW – Thermal Management
Los Gatos, CA USA
November 2013 “Managing Temperature Difference Between Critical Components” – Guy Diemunsch, Guy Wagner
High performance electronic systems, using parallel circuits or components, require precise management of component temperatures. Therefore it is critical to have the components working at the same temperature. The standard solution is to have parallel cooling which means providing the same amount of cooling fluid at the same temperature to each identical component. However, this solution requires a high flow rate which often cannot be obtained. We propose a solution that will work with either air or liquid using serial cooling at a reduced pressure drop. The objective is to manage the thermal resistance between the fluid and the component to maintain, in all situations, the same junction temperature. We will do that within a single part to simplify the system assembly and guarantee performance. The design process implies 3 mains steps: – Define the worst case cooling parameters for the last component of the serial configuration. – Define the heat sink thermal resistance for each component placed upstream. – Define the flow management vs. the systems loads
IMAPS ATW – Thermal Management
Los Gatos, CA USA
November 2013 “Tablet Natural Convection Cooling Efficiency” – Guy Wagner, William Maltz
Handheld devices are increasingly capable of running applications that used to require laptop and desktop computers. The requirement that these devices provide better performance with a smaller form factor or size presents significant challenges, especially with the limitations of passive cooling. The current study presents a summary of the cooling solutions of several popular, commercially available tablets. The trends in power dissipation and thermal management techniques of handheld devices are presented. The factors affecting the maximum possible power dissipation are discussed. The effects of the selection of the outer shell materials, the thermal interface materials, heat spreaders and air gaps are presented. For all considered thermal management techniques of handheld devices, a figure of merit for the cooling solutions is defined as: Figure of Merit = Maximum Power Dissipation / Surface Temperature Rise, in (W/degC). This figure of merit allows for an objective comparison of the available cooling solutions.
Mentor Graphics – Engineering Edge
Vol 3, Issue 1
February 2010

New Approach to System Server Air Flow/Thermal Design Development, Validation & Advancement in Green Fan Performance Increasing thermal demands of high-end servers require increased performance of air-cooling systems in order to meet industry requirements. Increased air cooling performance will be attained through efficient distribution of the air flow to multiple electronic modules and improved aerodynamic power conversion efficiency of the server air movers and incorporating inter-stage air flow directional control structure between tandem fans that are arranged in series air flow. A new approach is used to measure and validate air flow rates for the server’s individual electronic modules.

 

SEMI-THERM 26
Hyatt Regency Hotel
Santa Clara, California USA
February 2010

Low Profile Heat Pipe Heat Sink & Green Performance Characterization for Next Generation CPU Module Thermal Designs Increasing thermal demands of high-end server CPUs require increased performance of air-cooling systems to meet industry needs. Improving the air-cooled heat sink thermal performance is one of the critical areas for increasing the overall air-cooling limit. One of the challenging aspects for improving the heat sink performance is the effective utilization of relatively large air-cooled fin surface areas when heat is being transferred from a relatively small heat source (CPU) with high heat flux.

 

SEMI-THERM 26
Hyatt Regency Hotel
Santa Clara, California USA
October 7, 2009

Validation Studies of DELPHI-type Boundary-Condition-Independent Compact Thermal Model for an Opto-Electronic Package  A Boundary-Condition-Independent (BCI) Compact Thermal Model (CTM) was generated for an opto-electronic transceiver package called SFP (Small Form-factor Pluggable device). The SFP has four internal power dissipating sources and the BCI CTM for the SFP was developed using the DELPHI methodology. This paper presents a detailed validation of the BCI CTM of the SFP in real-time applications using Flotherm, a Computational Fluid Dynamics (CFD)-based thermal analysis software package.

 

Therminic 2009
Leuven, Belgium
July 19, 2009

Development of Boundary Condition Independent Compact Thermal Models for Opto-Electronic Packages  An introduction to boundary condition independent reduced-order modeling of complex electronic components using the Proper Orthogonal Decomposition (POD)-Galerkin approach is presented in this extended abstract. Current work focuses on how the POD methodology can be used with the Finite Volume Method (FVM) to generate reduced-order models that are boundary condition independent.

 

Interpack 2009
San Francisco, California USA
July 15, 2009 Innovative Rack-Level Cooling Solutions

The presentation is limited to cooling solutions only at the rack level using a closed racks and commercially available products.

Huawei Symposium 2009
Palo Alto, California USA
March 15, 2009

Boundary-Condition-Independent Reduced-Order Modeling of Complex 2D Objects by POD-Galerkin Methodology  The objective of the current work is to introduce the concept of boundary-condition-independent (BCI) reduced order modeling (ROM) for complex electronic packages by the POD-Galerkin methodology. Detailed models of complex electronic packages are used within system-level models in Computational Fluid Dynamics (CFD)-based heat transfer analysis.

 

Semitherm 2009
San Jose, California USA
September 25, 2008

Development of Boundary Condition Independent Reduced-Order Models using POD  An introduction to boundary condition independent reduced-order modeling of complex electronic components using the Proper Orthogonal Decomposition (POD)-Galerkin approach is presented in this extended abstract. Current work focuses on how the POD methodology can be used with the Finite Volume Method (FVM) to generate reduced-order models that are boundary condition independent.

 

IMAPS Advance Technology Workshop on Thermal Management
Palo Alto, California USA

September 24, 2007

A Preliminary Study of Optimization Techniques for Compact Thermal Model Development of Multi-Heat Source Components  The difficulty in modeling the wide range of scales in Computational Fluid Dynamics (CFD) simulations of system level cooling solutions can be addressed by employing Compact Thermal Models (CTM) of electronic components. Compact thermal models, in their true sense, are boundary condition independent network of resistors that are developed primarily to predict junction temperature and heat flux through the boundaries of a processor.

 

IMAPS Advance Technology Workshop on Thermal Management
San Jose, California USA