The Application of Edge Effect in Solder Bump Defect Detection Presented by Chean Lee (Balee) General Engineering Research Institute Electronic and Ultrasonic Engineering Supervisors Prof. Dave Harvey Dr. Guangming Zhang 29 November 2013 1

Project Objective Clarify defect detection mechanism Primary focus on microelectronic packages Limited published literature regarding subject Analyze defect detection mechanism of engineered faults Realize possible exploitation or novel post processing Allow development of better algorithms By understanding the physical phenomena we can adapt this information to evaluate defects,

Introduction : Definition of Acoustic Longitudinal wave which consists of compression and rarefaction 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 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

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

Introduction : Pulse-Echo AMI Operational Characteristics Couplant or 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)

Introduction : Current Issues facing AMI Electronic packages are shrinking and/or stacking Technique is approaching resolution limits Image processing techniques not broadly reliable Features are not directly observable Transducers have fixed operational frequencies Optimal frequency difficult to determine Transducers are expensive to have a broad collection. So simulation has advantage.

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

Introduction : Ansys Multiphysics 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

Governing Equations : Acoustic Wave Equation C = speed of sound = ρo= mean fluid density K = bulk modulus of fluid P = acoustic pressure t = time This equation neglects viscous dissipation. Therefore represents a lossless wave equation for sound in fluids. 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 Approximate acosutic propagation mechanisn by solving acosutic wave equation The equation is employed using the generalized-α method. This method has been widely accepted to produce better results for Transient analysis (Chung, 1993)

The Problem : Edge Effect Phenomena

Validating Numerical Model First Interface 4 Interfaces How do we know we setup things correctly. By validating of course Result of Reflection calculation Calculated Result = 5.44 Ansys Result = 5.21 First Reflection

Post Processing in Matlab Reflection Incident Pulse Fast Fourier Transform Data is exported from Ansys and analyzed in Matlab Easier User Friendly

Solder Bump Assembly Model Virtual Transducer Water Silica Die Silica Die Silica Die Water Water Solder Bump Transient Solution 230 MHz Pulse-Echo B-Scan

Simulated AMI Data : B-Scan Raw Data

Simulated AMI Data : Processed Data Cross Section Transient View With further post processing we extract etc etc Shows us how the wave propagates and at what energy level Acoustic Propagation Map

C-Line Plot Methodology From Measured C-Scan Gate along one line of pixels From Simulated B-Scan Gate interface of interest

C-Line Plot : Comparison

Gap Type Defect Model Creating model with propagating crack. Air Gap (Crack) Solder Bump cross section post thermal cycling

Result: C-Line Plot of Defect (Simulated) Simulation C-Line Reduced data sets to clarify figure

Result: C-Line Plot of Defect (Measured) Measured C-Line C-Lines are aligned according to rise transition

Correlation Dip-XN/Dip-X0 Comparing features from edge effect minimum X-axis position No clear correlation observable

Correlation Dip-YN/Dip-Y0 Comparing features from edge effect minimum Y-axis position Possible fit up to 40µm air gap width

Conclusion Numerical simulations of microelectronic packages viable Presence of defect has affect on C-Line profile Edge Effect manifestation can be characterized and quantified Analysis of Edge Effect features informative for evaluation

Further Work Methodology requires more measured data Current data taken every 8 thermal cycles Better simulation resolution required Preliminary data took 1 month x 3 terminals Current data at “draft” resolution Apply wider variety of defects Voids, delaminations, etc Get more data in between shorter cycles

Thank You Questions Please?