Printed Circuit Design & Fab - May 2008 - (Page 47)

BGA Bulletin, continued from p. 48 Differential Pair Coupling and Pin Swapping When applying a shifted via pattern in order to increase route density, one of the results that will possibly need to be managed is that as the transition progresses through the layers with different patterns in the via span, the differential pair compliments may be moved away from each other. FIGURES 4 and 5 illustrate this problem. The ball pads for the differential pair compliments may be designed in the FPGA or ASIC to be placed closely to each other, but as fanout vias are added, the compliments may end up further apart than originally intended. A good solution, especially for FPGAs, is to pin swap, so that the ball pads are aligned in a manner that allows the fanout vias to remain close to each other. In Figures 4 and 5, swapping the differential pair compliments into the “A” and “A” locations will optimize the coupling. The ability to swap pins will be limited by bank locations, differential pair or single-ended pin assignments, and power and ground pin distribution. Finding the most effective swapping patterns (aligned vertically, horizontally, or on a diagonal) will depend on the fanout via pattern used in that area. of the BGA routed on the buried-via layers (FIGURE 6) will become 1024. With that number of pins, breakout and routing of the BGA is no longer the primary contributor to layer count, especially since the innermost pins in most BGAs are usually dedicated to power and ground. Principles Aligning blind via fanouts in well-organized patterns can significantly increase route density on those layers where it is incorporated. Increased route density means that more rows of ball pads around the perimeter can be routed on the blind via layers, which will result in effectively decreasing the size of the BGA routed on the buried via layers. Next month, we will start our look at the many types of effective HDI microvia fanout patterns. PCD&F Reducing the Effective Size of the BGA If the ball pads around the perimeter can be fanned-out and routed on the blind via layer (layer 2), then the effective size CHARLES PFEIL is an engineering director for Mentor Graphics, Systems Design Division; charles_pfeil@mentor.com; mentor.com/pcb. He has authored a book, BGA Breakouts and Routing, which explores in greater detail the content of this column. Please visit mentor.com/go/bga to order a copy, or meet Charles at the PCB East book signing event, Tuesday, May 13 at 5 pm and obtain a free autographed copy. Expand your global reach with electronic reprints! Your company took the time to write and submit a great article to Printed Circuit Design & Fab. Following publication, how can your company capitalize on the hard work you put into an article beyond the reach and lifespan of a single monthly issue? 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 in this index. ADVERTISER Accutrace Advanced Circuits Bare Board Group Cam Expert LLC Chemcut Circuitronix LLC Compufab PAGE # 45 44 44 45 33 45 46 9 35 47 3 44 45 35 19 45 7 5 Cover 4 ADVERTISER PAGE # Midwest Accurate Grinding 46 National Instruments/ Cover 2 Electronics Workbench Group Online Electronics OverflyPacific Corp. PCB Basics PCB East 2008 PCB Orlando 2008 PCB West 2008 PCB FAB Express PCB-Pool Precision Technologies Samtec Inc. Sierra Proto Express Simberian Inc. Sun Chemical Sunstone Circuits Superior Processing Uyemura Virtual PCB 44 44 15 13 41 31 46 22 46 21 Cover 3 27 23 1 46 11 37 DownStream Technologies eFabPCB Electronic Reprints EMA Design Automation EzPCB Fine Circuits Garrett Film Services Corp. Global Laminates Inc. Imagineering Intercept Technology MacDermid Mentor Graphics The answer: electronic reprints! An electronic reprint is in Adobe Acrobat (.PDF fomat) and features the following: • A cover page with your company’s marketing copy, PCD&F logo, and “as seen in the pages of PCD&F” text. • Your article in full color as it appeared in the print issue. • A back page containing marketing copy that you select or provide. • The right to post and distribute the article – for life! To purchase or inquire about electronic reprints today, send an e-mail to: pcdf_reprints@upmediagroup.com MAY 2008 The advertising index is published as an additional service. The publisher does not assume any liability for errors or omissions. PRINTED CIRCUIT DESIGN & FAB 47 http://mentor.com/pcb http://mentor.com/go/bga http://pcdandf.com

Table of Contents Feed for the Digital Edition of Printed Circuit Design & Fab - May 2008

Printed Circuit Design & Fab - May 2008 Contents Our Line Market Watch Around the World Happenings ROI EMC For the Real World PCB East Conference Brochure Positive Plating Don't Let your Signals Stub Their Toes Improve PCB Layout With Skill Utility Programs The Next Generation Design Tool Challenge Thermally Conductive Microwave Materials PCB Dielectric Degradation in Lead-Free Assembly Applications A Tale of Two Trade Shows Eliminating Board Defects Off the Shelf Marketplace Ad Index BGA Bulletin

Printed Circuit Design & Fab - May 2008

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