Printed Circuit Design & Fab - February 2009 - (Page 37)

SiMulation FiGurE 6. Board design flow incorporating DC analysis. thickness. What-if DC simulations of current density for various configurations were used to confirm the potential to reduce layer count. Analysis of a design variation with two layers removed showed that most layers remained under defined current thresholds, with one layer showing excess current density. Design changes were considered to address the problem, and in the end, two changes improved the design. An additional ounce of copper was added to the layer that exceeded current density limits, and a power island was added to the design’s 10 signal layers at the VRM pin locations. Simulations of the new design confirmed that the three power plane layers could safely be reduced to one layer with maximum densities staying below the specified 20 mA/mil2 threshold. Beyond that, the resulting design was significantly less expensive to manufacture. DC simulation and high-impact design improvements. Accurately simulating DC behavior to predict and prevent issues is far superior to waiting to find and fix problems late in the game. Left unresolved, excess current density and IR drop lead to product instability and field failure. Focus on a quality DC implementation avoids these problems and provides additional cushion to deal with AC noise. Further, an understanding of robust DC performance provides insight into overall AC / DC power delivery system behavior. DC simulation can be added to design flows without disrupting existing methodologies. The combination of easy implementation and the clear ability to improve every design make effective DC simulation an essential part of the PCB and IC package design process. pCd&f rEFErEncES 1. International Technology Roadmap for Semiconductors (ITRS), 2007 edition, System Drivers. 2. Sam Chitwood, Sigrity, Inc., “IR Drop in high-Speed IC Packages and PCBs, Printed Circuit Design and Manufacture, April 2005, Pgs. ” 16-18. Design Flow Considerations DC analysis throughout the design process enables design teams to predict and prevent problems to avoid costly late stage rework. The flow in FiGurE 6 has been demonstrated to improve design reliability and to prevent field failures. From a flow standpoint, communication between the DC simulation environment and the layout software used for the project is valuable. This can enable DRC style information to be seen while layout progresses to give cues for design improvement. Simulations lead to design improvements that minimize the DC portion of the total AC / DC budget while assuring robust performance. A DC first approach is generally recommended with AC analysis quickly following to enable further adjustments for low-, mid- and high frequency noise. In some flows, DC analysis results are exported as SPICE sub-circuits that can be used for further analysis for detailed thermal studies. For some designs, it is valuable to create compact DC-equivalent resistor models of multiple structures to facilitate system-level analysis, which can include PCB, IC package and on-chip models. As noise margins compress, it is no longer practical to rely on spreadsheet approaches for DC assessment. When used for early planning and as layout progresses, DC simulation enables designers to manage risks and improve their designs. Selection of the best possible VRM and remote sense locations improves DC performance. IR drop and current density risks are often more difficult to identify than to resolve. The best DC analysis tools provide fast runtimes with the accuracy needed to isolate these obscure but significant threats. Actionable feedback in the form of color mapped visualization and pass / fail checks builds a clear connection between the FEBRUARY 2009 lESliE landErS is vice president of marketing at Sigrity, Inc; leslie@sigrity.com and tanit virutchaPunt is a power integrity specialist at Sigrity, Inc; tanit@sigrity.com ADVERTISER INDEX To learn more about the advertisers in this issue, go to pcdandf.com and select Advertiser Index in the home page menu. This will provide you with a direct link to the Web site of each advertiser. ADVERTISER Altium Bare Board Group Compufab DownStream Technologies eFabPCB EzPCB Fine Circuits Front Panel Express Imagineering Imagineering – full page IPC Expo JetPCB Inc. Mentor Graphics PAGE # Cover 3 45 46 5, 11 46 44 45 44 45 3 47 45 Cover 4 ADVERTISER One Stop Assembly Online Electronics PCB Artist PCB East 2009 PCB FAB Express PCB Phoenix 2009 PCB UPdate PCB-Pool Saturn PCB Design SEP Simberian Inc. Sunstone Circuits Superior Processing Virtual PCB Virtual PCB Chats Wise Software PAGE # 44 44 46 17 45 29 33 25 44 46 21 1 45 9 27 23 National Instruments/ Cover 2 Electronics Workbench Group NEC Informatec Systems NPI Award 7 13 The advertising index is published as an additional service. The publisher does not assume any liability for errors or omissions. printEd CirCuit dESign & fAB 37 http://www.pcdandf.com http://www.digikey.com/Suppliers/us/Altium.page http://www.onestopassembly.com http://www.pcborder.com http://www.bareboard.com http://www.pcbartist.com http://www.compufab.com http://www.pcbeast.com http://www.downstreamtech.com http://www.pcbfabexpress.com http://www.efabpcb.com http://www.pcbshows.com/phoenix http://www.ezpcb.com http://www.finecircuits.com http://www.pcbupdate.com http://www.frontpanelexpress.com http://www.pcb-pool.com http://www.saturnpcb.com http://www.pcbnet.com http://www.sep.co.kr http://www.simberian.com http://www.ipcapexexpo.org http://www.jetpcb.com http://www.sunstone.com http://www.superior-processing.com http://www.mentor.com/rd/padspaper4 http://www.virtual-pcb.com http://www.ni.com/multisim http://www.virtual-pcb.com/attendees/#chats http://www.emistream.com http://www.wssi.com/pcdm http://www.pcdandf.com/npiaward

Table of Contents Feed for the Digital Edition of Printed Circuit Design & Fab - February 2009

Printed Circuit Design & Fab - February 2009 Contents Our Line Market Watch Around the World Happenings ROI Tip Jar BGA Bulletin Interconnect Strategies Final Finsh Forum Defects Database Embedded Active Components In Multilayer LCP Packages Simulation: The Need for Speed Advanced Registration Systems The DC Design Squeeze Ad Index Do You Really Want a Better Autorouter? Designing With Conductive Materials, Part 1 Off th eShelf Marketplace On the Forefront

Printed Circuit Design & Fab - February 2009

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