Designing Your PCB for High Reliability. John Isaac Director of Market Development Systems Design Division

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1 Designing Your PCB for High Reliability John Isaac Director of Market Development Systems Design Division

2 Reliability What Makes Electronic Systems Fail? Heat Vibration Electromagnetic interference PCB assembly faults PCB fabrication High Temperatures EMI PCB Assembly Faults Vibration & Shock

3 The Issues with Testing for Reliability Reliability problems do not manifest themselves as quality issues in manufacturing A system could pass final test after manufacturing This system could fail in the field due to prolonged stress Creating prototypes and testing does not always work The test could pass on the prototype given a small but unacceptable failure rate Very difficult to simulate years of stress in test chambers Multiple prototypes & testing increase time-to-market and cost

4 The Answer Virtual Prototyping During Design Software can predict reliability issues Avoid design practices that may lead to failures Can simulate months in a test chamber Predict product failures in hours that can take years to fail in the field

5 Mentor s Virtual Prototyping Products for Increased Reliability X Re-spins Reduces Prototypes & Re-spins Systems Design Prototypes NPI Manufacturing Virtual Prototyping Here Results in Higher Reliability Products, Faster Competitive Product Low Cost Reliable High Performance Small form factor Functionality

6 AVOIDING PCB ASSEMBLY RELIABILITY ISSUES

7 DFM (with reliability checks) Can Avoid Design Issue that may Cause Field Failures Number of DFM Categories Available Fabrication 277 Assembly 270 Packaging Substrate 105 Microvia 45 Panel 38

8 Understanding the Reliability Risks Reliability issues are those that may not manifest themselves as being issues until they have undergone some level of field testing or usage 10 Manufacturing violations Reliability issues

9 Design Issues which Affect Reliability Fabrication Examples Acute angles create acid traps. While these may not cause failure at test, the acid continues to etch even after lamination, weakening the circuit. Silkscreen on pads will create problems with solder quality which may not manifest as a problem until it is put into use. Non-plated thru holes too close to copper puts stress on the prepreg, causing a possible fracture in the circuit. Starved thermal vias prevent proper heat containment and may effect quality of hole plating, resulting in a potential cracked barrel.

Design Issues which Affect Reliability Assembly Examples Traces under lowlying components can cause the component to rock, creating a weak solder joint.

Tall components too close to adjacent components can cause shadowing at wave solder. A poor solder joint cannot easily be checked.

10 Design Issues which Affect Reliability Assembly Examples Traces under lowlying components can cause the component to rock, creating a weak solder joint. It can be sufficient to pass ICT, but no robust enough to withstand vibration. Tall components too close to adjacent components can cause shadowing at wave solder. A poor solder joint cannot easily be checked. Different trace widths connecting pads can cause tombstoning. Partial tombstoning makes the connection susceptible to field failure. Vias drilled through SMD pads need to be plugged. Otherwise they can have voids in the vias which can show up as intermittent opens.

11 THERMAL ANALYSIS FOR INCREASED RELIABILITY

12 Reliability Issue Excessive Heat Increasing IC power dissipation driven by speed and density Boards exceeding 300W Systems exceeding 1000sW Smaller form factors driving heat density Alcatel-Lucent, >300W per blade

13 Systems Performance Degrades and Components Fail with too Much Heat Examples of the importance of heat sinks Above critical junction temperature More powerful ICs in a smaller space increases heat density Reliability decreases exponentially Performance degrades

14 Mechanical Analysis Thermal Simulation Capabilities - IC Package, PCB, & System Package PCB System Facility Design Flow Heat Flow Ambient 14

15 Mentor Graphics Unique Technologies Across the Complete Thermal Design Flow IC Package Design PCB Design Expedition Enterprise Mechanical Design Design Thermal Simulation Thermal Testing 15

16 FloTHERM - Thermal Management of Electronic Systems MCAD Designer for Systems Level/ Complete Enclosure Enclosure Thermal PCB Thermal PCB Design Enclosure Design PCB Designer for PCB-Level Thermal Management Electrical Designer Mechanical Designer

17 Identifying Thermal Improvement Opportunities: Shortcut Classic Temperature Plot You have a problem Thermal Shortcut Displayed Guidance to Solution GAP PAD Thermal Design Change: Introduce a Gap Pad?

18 Thermal Opportunities: Shortcut Original Temperature New Temperatures 74% Reduction in Junction Temperature

19 Identifying Thermal Improvement Opportunities: Bottlenecks Temperatures with Gap Pad installed You still have a problem Thermal Bottlenecks Displayed Guidance to Solution EXTRUSION GAP PAD Thermal Design Change: Replace Gap Pad with Chassis extrusion?

20 We Have Solved Our Thermal Problem 74% Drop 58% Drop

21 T3Ster Value to IC/Package Suppliers Accelerates package design process Enables better designs, more what-ifs Manufacturing quality checking, defect identification Fast, accurate thermal model creation In our lab the T3Ster is used to measure the thermal resistance of our packages in customer specific environments. Thanks to the T3Ster, our measurements are quick and easy to perform. NXP-Semiconductors We chose the T3Ster because of its compactness and ease of use, allowing us to improve data acquisition and processing of the transient thermal data. IBM Zurich Research Laboratory

22 VIBRATION AND STRESS VIRTUAL PROTOTYPING

23 Design for Reliability The Classic Highly Accelerate Life Testing (HALT) Process Physical Lifecycle (Chamber HALT) Testing Takes Weeks! Time testing can take months per pass Limited availability Very long term failure risks not exposed Re-design/prototype is expensive and time consuming

24 Physical HALT vs. Virtual HALT Reduce Re-spins, Faster Time-to-Results Physical Prototype & Testing Circuit Design & Schematic Layout Fabrication Assembly HALT Cycle Spin of Weeks/Months Mass Production Virtual Prototype & Testing Reduced Design Cycles Circuit Design & Schematic Layout HALT Fabrication Assembly Cycle Spin of Hours/Days Mass Production

25 xrobust Virtual HALT Results Analysis Patented Technology

26 Mentor s xrobust HALT Simulation Virtual prototyping of vibration Reduces prototypes Reduces design respins Increases product reliability More design scenarios Long term failures Reduces TTM and development costs or 3 Months 3 Hours We have used Mentor s HALT product now for five designs that will go into our new Infantry Combat Vehicle. Being able to analyze these PCBs using Mentor s HALT technology has significantly improved our design cycle times while identifying possible reliability issues. Israeli Ministry of Defense 26

27 AVOIDING FAILURES CAUSED BY ELECTROMAGNETIC INTERFERENCE

28 Subtle Layout Practices Can Cause EMI Reliability Issues Layout could be electrically correct but raise risk of EMI Examples of EMI causing layout practices: Nets crossing plane gap Reference plane changes Differential pair routing I/O nets with coupling Via to pin ratio on connectors ICs over splits Exposed critical trace routing I I Ic m

29 Expedition s EMI Checking During Layout PCB Expert System Rules-based verification tool User customizable to reflect your best practices Enables designers to avoid compromising EMI Reduces need for prototypes and test chamber testing

30 Same Analysis for Layout Designer Signal Ground Problem: Clock net crosses more than maximum allowable number of gaps (1) Advice: Look at gap crossing areas (markers) and reroute net to reduce number of crossings

31 AVOIDING FAILURES CAUSED BY POWER DISTRIBUTION NETWORKS

32 System-Level Power Optimization Trading-off Cost and Performance IC design for low power is driving need for complex Power Distribution Networks (PDNs) Multiple voltage rails to supply lower voltages and tolerances Increased current requirements Downstream impact on PCB/system design More power distribution networks (PDNs) CAD Designer must create complex area fills Voltage source (voltage regulator module) IC requiring power

33 High Current Densities in Power Distribution Networks Common problems: High current densities in plane neck-downs and vias Leads to dielectric or via breakdown, board failure, fires Causes increase in PCB and System heat dissipation Voltage source (voltage regulator module) ICs requiring power

34 Real World Customer Example Analysis of a power rail shows cut-outs that create a current density problem.

35 Design for Reliability Thermal Analysis Including Power Distribution Networks 3 problems exist: Excessive heat can cause PCB de-lamination and fusing Heat raises copper resistance and can reduce PDN voltages PDN heat contributes to PCB and system thermal management challenges The challenge: Analysis requires iterations to a convergent solution Current density through copper creates heat Heat dissipation changes the PCB/system temperature Temperature changes resistivity of copper Changing resistivity changes PDN current density

36 Integrating Co-Dependent Simulation & Analysis Products E.g. Power and Signal integrity are co-dependent with Thermal Analysis Current creates heat Heat changes resistivity Resistivity changes current - Current creates heat, HyperLynx Power and Signal Integrity Iterate to Convergence HyperLynx & FloTHERM Thermal Analysis Accurate PDN DC Drops & Current Densities Accurate Resistivity & Signal Integrity Accurate PCB/System Thermal Analysis Common Data Model

37 Integrating Power Integrity and Thermal Gives More Accurate Results Standalone Thermal Analysis Thermal with Current Density Max Temperature Hottest Spots

38 Hot Spots Created by Excess Current Density Hottest Spots

39 Designing for Product Reliability - Virtual Prototyping Software can predict reliability issues Avoid design practices that may lead to failures Predict product failures in hours to simulate months in a test chamber Predict product failures in hours that can take years to fail in the field

40 w w w. m e n t o r. c o m Your Initials, Presentation Title, Month Year

IIB. Complete PCB Design Using OrCAD Capture and PCB Editor. Kraig Mitzner. ~»* ' AMSTERDAM BOSTON HEIDELBERG LONDON ^ i H

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