Automated EMC Rule Checking for PCB Designs in the Real-World

Transcription

1 Automated EMC Rule Checking for PCB Designs in the Real-World Bruce Archambeault, PhD IEEE Fellow Archambeault EMI/EMC Enterprises Missouri University of Science & Technology Adjunct Professor IBM Distinguished Engineer Emeritus May 2016

2 Overview Typical EMC design process Tools to help during different phases in the design process EMC Design Rules Examples May 2016 Bruce Archambeault, PhD 2

3 Common EMC Design Process (Unfortunately) EMC engineer will provide EMC rules and recommendations to product design team Product design engineers will largely ignore EMC rules Too costly Too hard Often unrealistic Product is built, tested, and fails EMC May 2016 Bruce Archambeault, PhD 3

4 Common EMC Design Process (2) (Unfortunately) EMC engineers works in lab to debug/fix EMC problem Once fix is found, redesign cycle to build fixed product Product is tested in EMC lab If fail (again), repeat as necessary May 2016 Bruce Archambeault, PhD 4

5 The old way OLD vs.. NEW Never time to do it right but always time to do it over The new way Design up-front to pass the first time Should be accountable if not pass the first time We (EMC technical community) know how to pass the first time May 2016 Bruce Archambeault, PhD 5

6 Issues Time-to-Market Never make up for lost market share for delayed first customer ship dates Cost Everything is cost sensitive EMC band-aids more costly than doing it right the first time Reasonableness EMC can not make unreasonable demands If the product does not work or cost too much, passing EMC does not matter Customers rarely care if product passes EMC May 2016 Bruce Archambeault, PhD 6

7 Different Levels of EMC Design Process Before the product design process Design Rule Development Training During the product design process Apply design rules Use automated design rule checker May 2016 Bruce Archambeault, PhD 7

8 Before the product design process -- Design Rule Development Evaluate rules from classes, books Some will NOT work for your product family Use fullwave simulation tools to evaluate and understand gray areas Different techniques for different types of problems Need to Validate results Develop set of design rules May 2016 Bruce Archambeault, PhD 8

9 Before the product design process -- Training Engineers need to know what to do during design before they begin the design Be careful about many so-called EMC experts A simple presentation of do s and don'ts is a WASTE OF TIME Need to understand why and how to make design trade-offs May 2016 Bruce Archambeault, PhD 9

10 During The Product Design Process Apply rules already validated PCBs have too much stuff for an effective manual review Use automated design rule checker Must fit smoothly into existing design process Help designers prioritize rule violations Never expect all rules to have no violations Some post layout analysis helps confirm the prelayout design rules/approach May 2016 Bruce Archambeault, PhD 10

11 After The Product Design Process EMC testing Validate design rules Modify design rules if necessary Use as training for design engineers May 2016 Bruce Archambeault, PhD 11

12 Design Process Before Develop design rules Training During Apply rule checking tools After Validate and modify design rules as appropriate May 2016 Bruce Archambeault, PhD 12

13 EMC Design Rules Reference Critical net crossing split in reference plane Critical net changing reference plane Critical net too close to edge of reference Wiring/Crosstalk Length of exposed critical net Critical net isolation Single ended and Differential May 2016 Bruce Archambeault, PhD 13

14 EMC Design Rules Decoupling Decoupling capacitor density Distance to IC power pin Length of trace between capacitor and via Length of trace between IC power pin and via Placement Filter distance from I/O connector May 2016 Bruce Archambeault, PhD 14

15 Examples of Rule Importance Trace crossing split in nearest reference plane with stitching capacitor across split Trace changing reference layer with return via too far away Trace close to edge of reference plane Simulations courtesy of CST May 2016 Bruce Archambeault, PhD 15

16 Microstrip with split in reference plane May 2016 Bruce Archambeault, PhD 16

17 Animation of split plane return current Split plane current no stitch Stitch positioned center of Stitch positioned to side of capacitor trace trace May 2016 Bruce Archambeault, PhD 17

18 Near Field Above PCB due to stitching capacitor in different positions across split plane May 2016 Bruce Archambeault, PhD 18

19 Critical Net Changing Reference Layer With ground vias at different distances Cut view May 2016 Bruce Archambeault, PhD 19

20 Animation of ground via return current With GND vias at 0.65mm distance No GND vias in proximity to signal via Ground-reference via May 2016 Bruce Archambeault, PhD 20

21 Electric Field Variation with Ground-reference Vias at Different Distances May 2016 Bruce Archambeault, PhD 21

22 Example of Critical Trace Close to Edge of Ground Reference plane May 2016 Bruce Archambeault, PhD 22

23 Near Electric Field Results May 2016 Bruce Archambeault, PhD 23

24 DURING DESIGN PHASE Straightforward EMC Automated Rule checking Humans can t pay attention to all details in PCB CAD file Establish rule limits before design phase Decide which PCB traces are important Visual examination of violations to determine importance May 2016 Bruce Archambeault, PhD 24

25 Establish Rule Limits Use variety of tools and techniques described earlier Rule limits for different data rates, etc Automated tools have some default limits to help get started May 2016 Bruce Archambeault, PhD 25

26 Automated Design Rule Set Up Example May 2016 Bruce Archambeault, PhD 26

27 Decide Which PCB Traces/Components are Important Traces High speed clock, strobe, data/address busses Sensitive inputs to ICs? I/O lines High speed vs low speed I/O Components Decoupling capacitors Filters May 2016 Bruce Archambeault, PhD 27

28 Tagging Example May 2016 Bruce Archambeault, PhD 28

29 Violation Viewing Violation viewing Nets highlighted Only layers involved are visible Boxes around violation for faster viewing Allows fast determination of violation importance! Allows designer to immediately correct violation if desired May 2016 Bruce Archambeault, PhD 29

30 Violation Viewing Example Trace Crossing Split in Reference Plane May 2016 Bruce Archambeault, PhD 30

31 Violation Viewing Example #2 Critical Net Close to Edge of Reference Plane May 2016 Bruce Archambeault, PhD 31

32 EMC Automated Rule Checking Summary Allow users to select rules and options to fit board constraints and technology Reads PCB CAD file directly Allows users to manually or automatically tag nets and components View violations for fast decision making May 2016 Bruce Archambeault, PhD 32

33 EMC Design Process and Tools EMC is NOT a black art, nor is it magic! Do it right the FIRST TIME Tools exist today to help engineers Tools do NOT replace the need to understand the effects Can you afford to not use these tools? May 2016 Bruce Archambeault, PhD 33