Tim Pawlak——电子产品的机械可靠性分析

2020-02-27 55浏览

2.PCB Assembly Reliability Analysis • PCB Assembly Failure Modes • Challenges of modeling PCB Assemblies • ANSYS Mechanical Workflow − Trace Mapping − Thermal Analysis – Joule Heating Hot Spot Detection − Solder Reflow – Board-Level Warpage Analysis − Vibration – Modal and Random Vibration Analyses − Automated Post-Processing − Thermal Cycling - Solder Joint Fatigue • Conclusion 2 © 2016 ANSYS, Inc. July 26, 2017 ANSYS Confidential
3.PCB Assembly Failures Modes • Mechanical failure of PCB assemblies are primarily due to thermal and vibration issues. • As packages become thinner and boards become thicker, the risk of failure increases and becomes harder to predict using traditional design rules. • ANSYS provides a full set of tools to model the entire PCB assembly efficiently. This allows engineers to foresee issues during the design process. 3 © 2016 ANSYS, Inc. July 26, 2017 ANSYS Confidential Electronics failure modes US Air force Avionics Integrity Program Thermal Vibration Humidity Dust
4.Challenges of Modeling PCB Assemblies • Geometry complexity − PCB − Electronics Components − Complex material models for solder PCB • 11 layers • 21,000 bodies (including trace and via) Anand’s Viscoplasticity model R. Darveaux, “Effect of Simulation Methodology on Solder Joint Crack Growth Correlation”, ECTC 2000 4 © 2016 ANSYS, Inc. July 26, 2017 Board designfrom:https://kosagi.com/w/index.php?title=Kovan_Main_PageElectronics components open hardware robotics platform • 585 bodies • 324 solder bodies on one chip ANSYS Confidential
5.ANSYS Mechanical Workflow PCB assembly CAD • PCB sliced so that each layer is a separate body (for trace mapping) ODB++ layout file for trace mapping 5 © 2016 ANSYS, Inc. July 26, 2017 Submodel of chip with solder balls Solder reflow warpage simulation • With submodeling of crucial components Operating condition thermal stress simulation with joule heating Model and random vibration analysis Joule heating results from DCIR Simulation ANSYS Confidential
6.Trace Mapping • The first step in accurate simulation of modern PCB assemblies is to capture the distribution of copper in each layer of the board. • Trace mapping calculates an equivalent material property for each element in the PCB mesh based on the proportion of trace and substrate covered by the element. • This leads to more accurate thermal, warpage and vibration simulation results. ECAD Data ODB++/BRD/MCM/SIP/ANF etc. Mesh High resolution Cartesian metal map calculation Metal map on actual mesh, layer by layer. 6 © 2016 ANSYS, Inc. July 26, 2017 ANSYS Confidential
7.Thermal Analysis – Joule Heating Hot Spot Detection • In high powered PCBs, joule heating inside the PCB can result in localized high temperature regions. • High temperatures can cause PCB and nearby components to degrade over time, leading to failure. • ANSYS SIWave provide an easy to use wizard that guides users in the setup of DCIR simulations. 7 © 2016 ANSYS, Inc. July 26, 2017 Load ECAD layout file ANSYS Confidential Electrical Schematic Assign voltage and current to high powered pins
8.Thermal Analysis – Joule Heating Hot Spot Detection • Current, resistance and losses are calculated on the PCB for every electrical net. • The electrical resistance losses are exported to ANSYS Mechanical and mapped on to the steady state thermal simulation 8 © 2016 ANSYS, Inc. July 26, 2017 ANSYS Confidential
9.Thermal Analysis – Joule Heating Hot Spot Detection • In this thermal analysis wehave:− 5 packages with high energy dissipation. − Convection boundary condition to simulate the effect of stagnant air. − Joule heating in the traces of the PCB Hot Chips 9 © 2016 ANSYS, Inc. Joule heating locations July 26, 2017 ANSYS Confidential Temperature Deformation
10.Solder Reflow – Board Level Warpage Analysis • In modern lead-free PCB assemblies, the solder reflow process can cause failure. • The melting temperature of lead-free solder can be over 170° C. This can cause significant deformations due to mismatch of thermal expansion coefficients (CTE) between different materials. Solder reflowprofile:p68 Handbook for Robustness Validation of Automotive Electrical/ Electronic Modules. ZVEI Die Electroindustrie 10 © 2016 ANSYS, Inc. July 26, 2017 ANSYS Confidential Warpage 170°C -> 22°C
11.Solder Reflow – Board Level Warpage Analysis • Failure of packages on the board is related to the warpage of the package. (Stienberg:Designing Electronics for high vibration and shock) • Warpage of key packages are evaluated. Those with large warpage are selected for submodeling In a sub-model, the deformation results from the global model is mapped on to the cut boundaries of the submodel. Therefore the submodel behaves as if it is a part of the global model. 11 © 2016 ANSYS, Inc. July 26, 2017 ANSYS Confidential Plot of the z-direction warpage for package. Warpage
12.Solder Reflow – Board Level Warpage Analysis – Sub-Model Sub-model allows additional details to be included. • Solder balls automatically created based on ECAD Layout on selected packages. (324 bodies) Solderballs Boundary deformation from global model Max strain on the solder ball can point to failure location. Submodel deformation 12 © 2016 ANSYS, Inc. July 26, 2017 ANSYS Confidential
13.Vibration – Modal Analysis and Random Vibration Analysis • Vibration can be a cause for PCB assembly failure. • Simulation can be used to guide and evaluate the design to improve the chances for passing vibrations testing. • Typical simulationsare:− Modal – natural frequency − Random Vibration – vibration/fatigue during operations − Response Spectrum – Shock analysis (not shown in this presentation) 13 © 2016 ANSYS, Inc. July 26, 2017 ANSYS Confidential
14.Vibration – Modal Analysis • Modal analysis is the most basic of vibration analysis techniques. • Commonly used during design to avoid vibration issues Use the model with trace mapping and assign support locations 1st mode 2nd Mode 3rd mode 14 © 2016 ANSYS, Inc. July 26, 2017 ANSYS Confidential
15.Vibration – Random Vibration Analysis • Random vibrations analysis can be used to estimate fatigue life/failure due to vibrations. • As with all fatigue calculations, accurate random vibrations simulations requires correlations with various tests. • Steinberg through extensive testing, has formulated an equations to predict whether different electronics packages will pass certain random vibrations criteria. − Z = single amplitude dynamic displacement, in.; − L = length of component, in.; − B and t = board length and thickness − c = 1.0 for standard DIP; • 1.26 for a DIP with side-brazed leads; • 1.26 for a pin-grid array with two parallel rows of pins; • 1.0 for a pin-grid array with four rows of pins • 2.25 for leadless chip carrier 15 © 2016 ANSYS, Inc. July 26, 2017 ANSYS Confidential
16.Vibration – Random Vibration Analysis • In ANSYS, the appropriate Power Spectrum Density (PSD) load is applied to the supports of the PCB assembly. Support locations PSD 16 © 2016 ANSYS, Inc. July 26, 2017 ANSYS Confidential 3 Sigma deformation plot Calculate the deformation of each package.
17.Automation • ANSYS Mechanical can be automated using scripting or extensions. • A Python script is used here to automatically calculate the warpage of all bodies selected. • In addition, scripts can be turned into GUI extensions for easier reuse. GUI Extension 17 © 2016 ANSYS, Inc. July 26, 2017 ANSYS Confidential Python script Warpage results
18.Thermal Cycle - Solder Joint Fatigue • Solder joint fatigue due to thermal cycling can be predicted in ANSYS. Area of the crack separated from the rest of the solder ball. 18 © 2016 ANSYS, Inc. Anand viscoplasticity or the generalized Garofalo creep model used to model Solder July 26, 2017 ANSYS Confidential Simulate least 3 thermal cycles Calculate the accumulation of the volume-averaged nonlinear plastic work. Automated fatigue calculations using a script extension.
19.Conclusion • This presentation shows some of the key ways ANSYS Mechanical can be used to help predict failure in PCB assemblies. • Different workflows are available for designers and analysts. Everyone can gain additional insight into PCB reliability through the use of simulation. • This is a small selection PCB assembly simulations ANSYS has helped our customers perform. We are happy to discuss any additional issues you encounter. 19 © 2016 ANSYS, Inc. July 26, 2017 ANSYS Confidential