1. 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

2. 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,

3. 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

4. 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

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

6. 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: (near 100% energy reflected)
Pulse Echo
Change in
Impedance
(Interface)

7. 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.

8. 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

9. 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

10. 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)

11. The Problem : Edge Effect Phenomena

12. 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

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

14. 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

15. Simulated AMI Data : B-Scan Raw Data

16. 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

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

18. C-Line Plot : Comparison

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

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

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

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

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

24. 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

25. 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

26. Thank You
Questions Please?