Printed Circuit Design & Fab - May 2008 - (Page 21) FIGURE 3. Equivalent circuit model of a via with top and bottom stubs. This is a differential pair transmission line model. Not shown are the various reference planes the via passes through. FIGURE 2. Measured insertion loss of a backplane trace with and without a long via stub. At the resonance, the entire backplane performance is dominated by the tiny via stub. Data is courtesy of Molex Corp. with a signal layer transitioning from the top layer to layer second from the top, with a resulting residual stub of about 200 mils long. Of course, changing any of the geometry features, such as clearance holes, location of return vias, plane-to-plane spac- ing and even barrel diameter, will change the performance. In the absence of a measurement or a full wave 3D simulation for every via, we can get a very good estimate of the electrical impact of a via, and identify the main features that affect its performance, by modeling it. The modeling should combine simple, uniform, single ended or differential transmission lines that are evaluated for performance using a SPICE simulation tool. An example of the circuit topology of a differential via is shown in FIGURE 3. There are only two parameters that define a single ended transmission line; its characteristic impedance and its time delay. For a differential via, you must include both its odd and even mode impedances as well as the time delay. What is the characteristic impedance of a via barrel, with its return path being a combination of adjacent return via and coupling to the planes it passes through? The answer is BOARD SIMPLE Simplify PCB design with PADS libraries for every interconnect in our catalog. www.samtec.com/pads http://www.samtec.com/pads
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 Printed Circuit Design & Fab - May 2008 - Printed Circuit Design & Fab - May 2008 (Page Cover1) Printed Circuit Design & Fab - May 2008 - Printed Circuit Design & Fab - May 2008 (Page Cover2) Printed Circuit Design & Fab - May 2008 - Printed Circuit Design & Fab - May 2008 (Page 1) Printed Circuit Design & Fab - May 2008 - Contents (Page 2) Printed Circuit Design & Fab - May 2008 - Contents (Page 3) Printed Circuit Design & Fab - May 2008 - Our Line (Page 4) Printed Circuit Design & Fab - May 2008 - Our Line (Page 5) Printed Circuit Design & Fab - May 2008 - Market Watch (Page 6) Printed Circuit Design & Fab - May 2008 - Market Watch (Page 7) Printed Circuit Design & Fab - May 2008 - Around the World (Page 8) Printed Circuit Design & Fab - May 2008 - Around the World (Page 9) Printed Circuit Design & Fab - May 2008 - Around the World (Page 10) Printed Circuit Design & Fab - May 2008 - Around the World (Page 11) Printed Circuit Design & Fab - May 2008 - Happenings (Page 12) Printed Circuit Design & Fab - May 2008 - Happenings (Page 13) Printed Circuit Design & Fab - May 2008 - ROI (Page 14) Printed Circuit Design & Fab - May 2008 - ROI (Page 15) Printed Circuit Design & Fab - May 2008 - EMC For the Real World (Page 16) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page PCB-1) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page PCB-2) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page PCB-3) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page PCB-4) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page PCB-5) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page PCB-6) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page PCB-7) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page PCB-8) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page PCB-9) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page PCB-10) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page PCB-11) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page PCB-12) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page PCB-13) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page PCB-14) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page PCB-15) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page PCB-16) Printed Circuit Design & Fab - May 2008 - PCB East Conference Brochure (Page 17) Printed Circuit Design & Fab - May 2008 - Positive Plating (Page 18) Printed Circuit Design & Fab - May 2008 - Positive Plating (Page 19) Printed Circuit Design & Fab - May 2008 - Don't Let your Signals Stub Their Toes (Page 20) Printed Circuit Design & Fab - May 2008 - Don't Let your Signals Stub Their Toes (Page 21) Printed Circuit Design & Fab - May 2008 - Don't Let your Signals Stub Their Toes (Page 22) Printed Circuit Design & Fab - May 2008 - Don't Let your Signals Stub Their Toes (Page 23) Printed Circuit Design & Fab - May 2008 - Improve PCB Layout With Skill Utility Programs (Page 24) Printed Circuit Design & Fab - May 2008 - Improve PCB Layout With Skill Utility Programs (Page 25) Printed Circuit Design & Fab - May 2008 - The Next Generation Design Tool Challenge (Page 26) Printed Circuit Design & Fab - May 2008 - The Next Generation Design Tool Challenge (Page 27) Printed Circuit Design & Fab - May 2008 - The Next Generation Design Tool Challenge (Page 28) Printed Circuit Design & Fab - May 2008 - Thermally Conductive Microwave Materials (Page 29) Printed Circuit Design & Fab - May 2008 - Thermally Conductive Microwave Materials (Page 30) Printed Circuit Design & Fab - May 2008 - Thermally Conductive Microwave Materials (Page 31) Printed Circuit Design & Fab - May 2008 - PCB Dielectric Degradation in Lead-Free Assembly Applications (Page 32) Printed Circuit Design & Fab - May 2008 - PCB Dielectric Degradation in Lead-Free Assembly Applications (Page 33) Printed Circuit Design & Fab - May 2008 - PCB Dielectric Degradation in Lead-Free Assembly Applications (Page 34) Printed Circuit Design & Fab - May 2008 - PCB Dielectric Degradation in Lead-Free Assembly Applications (Page 35) Printed Circuit Design & Fab - May 2008 - PCB Dielectric Degradation in Lead-Free Assembly Applications (Page 36) Printed Circuit Design & Fab - May 2008 - PCB Dielectric Degradation in Lead-Free Assembly Applications (Page 37) Printed Circuit Design & Fab - May 2008 - A Tale of Two Trade Shows (Page 38) Printed Circuit Design & Fab - May 2008 - A Tale of Two Trade Shows (Page 39) Printed Circuit Design & Fab - May 2008 - Eliminating Board Defects (Page 40) Printed Circuit Design & Fab - May 2008 - Eliminating Board Defects (Page 41) Printed Circuit Design & Fab - May 2008 - Eliminating Board Defects (Page 42) Printed Circuit Design & Fab - May 2008 - Off the Shelf (Page 43) Printed Circuit Design & Fab - May 2008 - Marketplace (Page 44) Printed Circuit Design & Fab - May 2008 - Marketplace (Page 45) Printed Circuit Design & Fab - May 2008 - Marketplace (Page 46) Printed Circuit Design & Fab - May 2008 - Ad Index (Page 47) Printed Circuit Design & Fab - May 2008 - BGA Bulletin (Page 48) Printed Circuit Design & Fab - May 2008 - BGA Bulletin (Page Cover3) Printed Circuit Design & Fab - May 2008 - BGA Bulletin (Page Cover4)
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