Conformity Magazine - November 2007 - (Page 52)

In the case of the 2U server example described here, refined heat sinks and a daughter card were added. The additional detail added to the model made it possible to accurately predict the junction operating temperatures of critical components. Engineers changed the physical layout of the board and system in order to minimize hot spots they had identified. Analyzing the Refined EMC Model A more detailed system-level model helps engineers quickly zero in on problem areas, such as a heat sink that acts as an antenna, and how the structure of the box contributes to electromagnetic interference. Just as with the thermal model, the more refined model helps identify problem areas that require Figure 5: Surface currents and electric-field distribution at 2 GHz. deeper investigation in subsequent This concurrent thermal and EMC design process employs a analysis steps. At the same time, top-down process that generates rough analysis results in the system-level analysis will typically clear the vast majority of early stages in order to identify areas of concern. Increasingly the design from an EMC standpoint in order to minimize the more detailed and accurate results are produced as the design additional time that is spent on it. process continues, providing the information needed to make design decisions with confidence prior to prototyping and As the design process continues, mechanical engineers testing. The result is that engineers can identify thermal and perform a detailed thermal analysis of components that have EMC issues in the early stages of the design process, long been identified as potential problems by the simulation with before prototypes are available, and perform design studies to the refined model. resolve them. In this case, the refined model simulation showed that a The step-by-step approach encourages engineers to consider custom heat sink was needed for a high-speed ASIC. The EMC requirements in parallel with the thermal/mechanical refined model simulation was used to generate boundary design process. This can significantly reduce the risk of costly conditions for a detailed model consisting only of the heat sink, component and thermal interface. Engineers adjusted the redesign that results from considering strongly coupled design fin size, thickness and spacing, heat sink material and interface requirements sequentially. material and re-ran the simulation in order to optimize the Dr. Andy Manning is the Director of Thermal Engineering at design from a thermal standpoint. Flomerics, Inc., and can be reached at andy@flomerics.com. Dr. David Johns is the Director of At the same time, the alternative heat sink designs were Electromagnetic Engineering at Flomerics, and can be simulated from an EMC standpoint, viewing the surface reached at david.johns@flomerics.com. currents and electric field distribution. Most of the board radiation was coming from the heat sinks, which were acting as non-intentional antennas. To minimize radiations from the heat sinks, different connections between the heat sink and PCB reference plane were evaluated, to provide return paths for the high frequency currents. The optimal number of FAST Link www.conformity.com/1160 connections and their locations were found by analyzing the surface current distribution. Engineers quickly corrected the problem by adding three additional connections. 52 Conformity noVEmBEr 2007 http://www.conformity.com/1160

Table of Contents Feed for the Digital Edition of Conformity Magazine - November 2007

Conformity - November 2007 Contents Editor’s Note Commission Sets Date, Terms for 700 MHz Auction FCC Reaffirms Roaming Obligations Commission Moves to Improve USF Management FCC Proposes Fines for Violations of E911 Handset Requirements Commission Levies $1 Million Plus Fines for Unsolicited Fax Advertisements GR-3150 - Lithium Battery Certification Levels Based on Criteria for General Product, Safety, and Performance, Part 2 ESD Open Forum Machinery Field Evaluation for the United States Validation, Verification, and Immunity Testing Techniques for EMC for Functional Safety Thermal/EMC Simulation Addresses New Mechanical Design Challenges Product Safety Equipment Buyer’s Guide FCC Releases Report on Telephone Numbering Resource Utilization Canada Still Has PCS Spectrum to Assign Updated Standards List for the EU’s Medical Devices Directive Updated Standards List for EU Directive on Active Implantable Medical Devices Call for Papers for the 2008 EOS/ESD Symposium Announced Mobile Phone Use in Hospitals May Be Dangerous CPSC Actions in the News IEC Standards Update UL Standards Update Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Product Reviews Looking Back: Items from Past Issues of Conformity Upcoming Events Advertisers

Conformity Magazine - November 2007

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