Initial Work on Acoustic Simulation using Ansys APDL Presented by Lee Chean Shen General Engineering Research Institute Electronic and Ultrasonic Engineering Group Supervisors Prof. Dave Harvey Dr. Guangming Zhang 22 January 2010

Destructive & Non Destructive tools. Introduction – Acoustic Microscopy What is Acoustic? Longitudinal wave which consists of compression and dilation Infrasound Audible Ultrasound Human Hearing 20Hz 20kHz 100kHz Animal Navigation & Communication Seismology Medical Diagnostics. Destructive & Non Destructive tools. 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

Introduction – Acoustic Microscopy What is Acoustic Microscopy Imaging (AMI)? Non-Destructive technique Sensitive to voids, delaminations and cracks Detects flaws down to sub-micron Image nontransparent solids or biological materials Study microstructures of specimen X-Ray AMI Unreflowed Solder Bump, AMI presents better contrast of defect

Introduction – Acoustic Microscopy Resolution characteristics of AMI technique. Increasing frequency largely lowers depth penetration Attenuation usually increase with frequency Lower frequency reduces resolution More information captured 230MHz 50MHz

Introduction – Acoustic Microscopy AMI Operational Characteristics - Transducer Transducer is cut/tuned to specific frequency, typically three types; Piezoelectric High frequency, low power (MHz region) Voltage applied to crystal, medium required Transducer is cut to frequency Magnetostriction (EMAT) Metal core responds to magnetic field Material dependant, no coupling required Photoacoustic Pulsed laser applied to specimen Thermal wave phenomena Very high frequency Measures material properties

Introduction – Acoustic Microscopy AMI Operational Characteristics - Medium Tranducer lensed to modify beam focus Ansys Model Construction (results in Review section)

Introduction – Acoustic Microscopy AMI Operational Characteristics - Medium EMAT only applicable to specific materials Photoacoustic may require protective layer Piezoelectric - Couplant 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)

Introduction – Acoustic Microscopy AMI Operational Characteristics - Configuration Two typical methods Pulse Echo – Image derived from reflections (Popular) Through Transmission – Image derived from received signal Through Transmission Pulse Echo Gate

Issues Current issues facing AMI Electronic packages are shrinking and/or stacking Technique is approaching resolution limits Image processing techniques not broadly reliable Transducers have relatively narrow operational frequencies Optimal frequency difficult to determine

Objectives Nonlinear acoustic Imaging 2nd order harmonic provides higher resolution Common in medical acoustics Require single frequency transducer Penetration depth proportional to fundamental wave Not all material generate harmonic waves Generated waves needs to reach receiver Explore implementation on stacked (3D) die

Objectives 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

Methodology - Ansys What is Ansys? Finite Element Multiphysics Simulation Software Accurate simulation of complex coupled-physics behaviour Broadly defined into two interface Structural Mechanics Explicit Dynamics Electromagnetics Fluid Dynamics Acoustics ETC Ansys Mechanical APDL Ansys Workbench

Methodology - Ansys What is Finite Element Method? Complete system is distributed into a large number of discreet elements Complex system of nodes which form mesh grids Mesh grid contain material and structural properties Area anticipating stress/load tend to have higher density of node Mesh resolution increases computational time

Tetrahedral (triangular) Methodology - Ansys Comparison of Mesh Resolution 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) Fine Mesh Coarse Mesh Coarse Mesh Fine Mesh

Methodology - Ansys What is Ansys Mechanical APDL ? Also known as; Ansys Classic “Old” Ansys Reliant mostly on command lines and scripts Primitive GUI

Methodology - Ansys What is Ansys Workbench? Ansys with user friendly GUI “Idiot-proof” Ansys Powerful module based project assembly/management

Review Transducer Simulation – Pressure Magnitude 30,000Hz @ 1500m/s (water medium) Ansys APDL Mirror Result Mirror Result Main Lobes Side Lobes

Review Transducer Simulation – Acoustic Lens 30,000Hz @ 1500m/s (water medium) Triangular mesh @ 15 elements per wave Expected shift of focus point Node reaction to applied load PCIRC,0,1,0,90 RECTNG,0,0.025,0,0.1 CYL4,0,0.25,0.2 (double radius) pcirc,0,1,0,90 RECTNG,0,0.025,0,0.1 CYL4,0,0.15,0.1

Further Work Scale up transducer simulations to MHz region Validate simulation with measured results Implement Non-Linear simulation General simulation cleanup Introduce materials into focused region Study acoustic defect detection mechanism

Thank You

Source & Citations Eindhoven University of Technology http://w3.chem.tue.nl/en/the_department/research_groups/process_development/research/ultrasound/ The Principles of Medical Ultrasound http://www.mrcophth.com/commonultrasoundcases/principlesofultrasound.html HyperPhysics Utrasound Guide – Georgia State University http://hyperphysics.phy-astr.gsu.edu/Hbase/sound/usound.html CALCE – University of Maryland http://www.calce.umd.edu/general/Facilities/sam.htm Acoustic Microscopy Guide – University of Hawaii http://www.soest.hawaii.edu/~zinin/Zi-SAM.html Resolution improvement of acoustic microimaging by continuous wavelet transform for semiconductor inspection – LJMU GERI Guang-Ming Zhang, David M. Harvey, Derek R. Braden. The NDE Analysis of Tension Behaviour in Nicalon/SiC Ceramic Matrix Composites Jeongguk Kim, Peter K. Liaw, Hsin Wang http://www.tms.org/pubs/journals/JOM/0301/Kim/Kim-0301.html Fundamentals of Ultrasonic Imaging and Flaw Detection – National Instruments http://zone.ni.com/devzone/cda/tut/p/id/3368 Phased Array Tutorial - Olympus http://www.olympus-ims.com/en/ndt-tutorials/transducers/construction/ About HIFU – Maple Leaf HIFU http://www.hifu.ca/physician/about_hifu.php Finite-element method – McGill University http://audilab.bmed.mcgill.ca/AudiLab/teach/fem/fem.html Introduction to Finite Element Analysis – Virginia Tech http://www.sv.vt.edu/classes/MSE2094_NoteBook/97ClassProj/num/widas/history.html Modeling and Meshing Guide, Chapter 7 – Ansys http://www.kxcad.net/ansys/ANSYS/ansyshelp/Hlp_G_MOD7_3.html