Presented by Chean Lee ( Balee ) General Engineering Research Institute

1. Numerical validation of acoustic field simulation of electronic package Presented by Chean Lee (Balee) General Engineering Research Institute Electronic and Ultrasonic Engineering Supervisors Prof. Dave Harvey Dr. Guangming Zhang 25 March 2011

2. Presentation Objective • Project Objectives • Introduction : Acoustic Microscopy • Introduction : Simulation • Introduction : Validation • Simulation Setup • Harmonic Response Analysis • Governing Equations • Conclusion • Further work

3. Project Objective • Clarify defect detection mechanism • Limited published literature regarding subject • Primary focus on new generation 3D IC packages • Understand acoustic performance within 3D IC packages • Balance optimum resolution vs. penetration • Analyze defect detection mechanism of engineered faults

4. Introduction : Definition of Acoustic • Longitudinal wave which consists of compression and rarefaction Audible Ultrasound Infrasound 20Hz 20kHz 100kHz • Destructive Ultrasound • (>10 W/cm2) • Sonochemistry • Welding • Cleaning • Cell Disruption • Kidney Stone Removal • Non-Destructive Ultrasound • (0.1 – 0.5 W/cm2) • Flaw detection • Medical Diagnosis • Sonar • Chemical Analysis Seismology Human Hearing Animal Navigation & Communication Medical Diagnostics. Destructive & Non Destructive tools.

5. Introduction : Acoustic Microscopy Imaging (AMI) • Non-Destructive technique • Sensitive to voids, delaminations and cracks • Detects flaws down to sub-micron • Image non-transparent solids or biological materials • Study microstructures of specimen X-Ray AMI Unreflowed Solder Bump, AMI presents better contrast of defect

6. Introduction : AMI Resolution Characteristics • Increasing frequency largely lowers depth penetration • Dispersion and attenuation • Lower frequency reduces resolution • Exacerbated by frequency downshift 50MHz 230MHz

7. Introduction : AMI Operational Characteristics • Couplantor medium is required • Usually deionized water • Reflection occurs at the interface between two mediums • Air has low acoustic Impedance (Z) • Z = ρV = density * sound velocity of medium • Water to Steel ratio ~ 20:1 • Air to Steel ratio ~ 100,000:1 (near 100% energy reflected) Pulse Echo Change in Impedance (Interface)

8. Introduction : Current Issues facing AMI • Electronic packages are shrinking and/or stacking • Technique is approaching resolution limits • Image processing techniques not broadly reliable • Transducers have fixed operational frequencies • Optimal frequency difficult to determine

9. Introduction : Application of Simulation • Provide practical feedback when designing real world systems • Diminish cost of system building • Rapid Prototyping • Simulate design decisions before construction phase • Permit the system study of various level of abstraction • Allow for Hierarchical Decomposition (top-down building technique) of complex systems

10. Introduction : AnsysMultiphysics APDL • ANSYS Parametric Design Language • Scripting and automate task in ANSYS • Automate complex and repeated task • Virtually all ANSYS commands can be used in APDL • No compilation. Modifications are immediately realized • Resultant macro files are small and easy to share • ANSYS Workbench • Significantly better Graphic User Interface • bi-directional association with CAD • Advance contact pre-processing capabilities • Advance meshing and defeaturing tools • HOWEVER, • Ansys Workbench does NOT support Acoustic Simulation

11. Introduction : Importance of numerical validation • Simulation provides an expectation to aid work • Experimental and simulated results cannot usually be directly compared • Simplifying assumptions or heuristics are applied to reduce computational resources • May significantly affect simulation accuracy • High abstraction has a tendency to have over simplified or omitted lower level details • AND MOST IMPORTANTLY • Large number of parameters involved • Rubbish in, rubbish out

12. Introduction : Importance of numerical validation Two examples of experimental vs simulated results Example 1 : Wide spectrum comparison between simulated and actual frequency response or a microwave cavity

13. Introduction : Importance of numerical validation Example 2 : Comparison of prediction and monitoring result of flip chip solder joint failure Source: Ryan Yang, Solder Joint Reliability Conclusion: Experimental results alone is inadequate to validate a simulation

14. Simulation Setup: 1. Choice of Elements Ansys contains a large library of elements. Each with it’s unique abilities and method of use.

15. Simulation Setup : 1. Choice of Elements Not all elements are suitable for a specific job PLANE Elements SOLID Elements FLUID Elements

16. Simulation Setup : 2. Element Shape • Models usually tested with multiple mesh resolution/configuration • Ensure circular areas are adequately smooth/circular • Mesh resolution and type fits geometry size • Generally “look right”, results largely determined by mesh quality Tetrahedral (triangular) Hexahedral (square) Coarse Mesh Fine Mesh Coarse Mesh Fine Mesh

17. Simulation Setup : 2. Element Shape Triangular vs. Quadrilateral (square) mesh Uniform, organized mesh Chaotic, Complex Mesh (inaccurate and/or extra computational resource) Noise and unpredictable propagation patterns were observed

18. Simulation Setup : 3. Element Resolution (Mesh Density) Element per wave (EPW) defines the element resolution of the simulation according to the highest frequency present in the simulation. The number of elements WILL affect the quality of the result. Rule of thumb; 5 EPW = Draft 10 EPW = Low Resolution 20 EPW = High Resolution Anything above 20EPW (of the highest frequency) is deemed to be a waste of resources. However, any complex simulations above 10EPW is already difficult to manage without cluster computing. Following two slides are comparisons

19. Simulation Setup : 3. Compare Element Resolution 5 Element Per Wave Low Sampling Frequency (Illustrated by the triangle) Rough and blocky wave integration

20. Simulation Setup : 3. Compare Element Resolution 10 Element Per Wave Smooth wave integration

21. Simulation Setup : 4. Shape and Meshing defects Material layers Infinite Boundary (radius line) Fluid Medium (segmented to manage computational resource) Meshing application has a 32bit limitation Transducer Lens (Excited Directly)

22. Simulation Setup : 4. Meshing defects Discontinuous meshing. Two zones will not interact in the simulation. Therefore geometry has to be merged. This may cause problems with the meshing engine as geometry becomes larger.

23. Simulation Setup : 4. Meshing defects Mesh defect occurring at the interface between two materials. In this case, the segmented fluid medium (which has the same material properties) Will cause inconsequential discrepancies with low element resolution.

24. Harmonic Response Analysis Simulation uses a sustained cyclic load to produce a harmonic response. In other words, a continuous wave which is ideal for studying transducer design. Focus depth, spot size, axial pressure and beam shape are obtained from this method.

25. Harmonic Response Analysis : Transducer Shape Comparison Real Transducer : Model design based on existing transducer. Virtual Transducer : Design with reduced focal distance (half) for resource saving Note: In certain materials, the focal distance becomes shorter. 3.9 Gbytes 141 Gbytes

26. Harmonic Response Analysis : Transducer Shape Comparison Focus depth 1mm Focus depth 1.5mm Transducer axial pressure

27. Harmonic Response Analysis : Transducer Shape Comparison Real Transducer Virtual Transducer Axial cross section of transducer output

28. Governing Equations : Acoustic Wave Equation This equation neglects viscous dissipation. Therefore represents a lossless wave equation for sound in fluids. C = speed of sound = ρo= mean fluid density K = bulk modulus of fluid P = acoustic pressure t = time For Fluid-Structure Interactions , the transient dynamic equilibrium equation below is considered simultaneously with the above acoustic wave equation [M] = Structural Mass Matrix [C] = Structural Damping Matrix [K ] = Structural Stiffness matrix {ϋ} = nodal acceleration vector {ύ} = nodal velocity vector {U} = nodal displacement vector {Fa} = applied load vector The equation is employed using the generalized-α method. This method has been widely accepted to produce better results for Transient analysis (Chung, 1993)

29. Governing Equations : Validating Acoustic Wave Equation Longitudinal wave are normal incidence Therefore α = 0 Reflection Equation is can be simplified into Where Z = ρV = density * sound velocity of material

30. Governing Equations : Validating Acoustic Wave Equation Reflection Incident Pulse Fast Fourier Transform • Data is exported from Ansys and analyzed in Matlab • Easier • User Friendly

31. Governing Equations : Validating Acoustic Wave Equation First Interface 4 Interfaces First Reflection Result of Reflection calculation Calculated Result = 5.44 Ansys Result = 5.21

32. Conclusion The importance of validation is highlighted Broadband transient transducer successfully built into the simulation Most simulation defects and inconsistencies has been addressed Cost saving methods implemented with mixed success Basic calculated results correlate with simulated result

33. Further Work • Review calculations with comparisons between flat and focused transducers • Review accuracy of transducer lens (geometry) excitation method • Scale up simulation to higher frequencies • Find alternative resource saving methods • Conclude validation and Implement electronic packages in the simulation • Setup non-linear acoustic simulation with narrow band transducer

34. Sources and Citations J Chung, GM Hulbert. A time integration algorithm for structural dynamics with improved numerical dissipation: The generalized-α method. Journal of Applied Mechanics, June 1993, Vol 60, Pg 371. Sound Reflection. http://www.sal2000.com/ds/ds3/Acoustics/Wave%20Reflection.htm Computer Aided Engineering Associates Inc. Ansys-Customization and Automation with APDL. 2002. http://www.scribd.com/doc/25083369/ANSYS%C2%AE-Customization-and-Automation-With-APDL Alex Karpelson. Wide-band ultrasound piezotransducers with non-uniform electric field. NDT.net, Aug 2003, Vol 8, No 8. http://www.ndt.net/article/v08n08/karpels/karpels.htm Brian Lempriere. Ultrasound and Elastic Waves: FAQ. Academic Press, 2002. Ansys Reference Material. Theory Reference for the Mechanical APDL and Mechanical Applications. Mario Kupnik, Ira O. Wygant, and Butrus T. Khuri-Yakub. Finite element analysis of stress stiffening effects in CMUTs. IEEE International Ultrasonics Symposium Proceedings, pg 487, 2008. Goksen G. Yaralioglu, BarisBayram, AminNikoozadeh, B.T. Pierre Khuri-Yakub. Finite elemenetmodeling of capacitive micromachined ultrasonic transducers. Medical Imaging 2005: Ultrasonic imaging and signal processing, pg77, vol 5750 .

35. Thank You Questions Please?