Through-Life Non-Destructive Monitoring of Solder joints using Ultrasound

1. Through-Life Non-Destructive Monitoring of Solder joints using Ultrasound • Ryan S.H. Yang • 04/11/2011 • Supervisors: • David M. Harvey • Guang-Ming Zhang

2. Presentation Outline • Introduction • Reliability Assessment • Acoustic Micro-Imaging • Experimental Procedure • Feature Extraction • Results and Discussion • Conclusion

3. Introduction 1910 Ford Model T

4. Introduction 2011 Ferrari Enzo

5. Introduction

6. Introduction Required Operation Temperature • “How long will this component last?” • The reliability of the electronic that operate in harsh environment become a major concern. • Among the reliability concern, solder joint reliability is the most critical issue, in many cases they are the weakest link in terms of product reliability.

7. Introduction • Thermo-mechanical stresses in the solder joints caused by Coefficient of Thermal Expansion (CTE) mismatch. Imposes shear stress and Cyclic Strain Crack Initiation and Growth Figure 2: Thermal mechanical expansion a b cooling heating CTE a < CTE b a a b b

8. Reliability Assessment • Solder joint fatigue failure could occur after thousands of cycles, which could mean 10 or 20 years of usage. • Accelerated Thermal Cycling (ATC) is a test that mimic the field service condition, and accelerated it with larger temperature range to reduce the test time. • ATC test is commonly used to generate rapid ageing of the solder joint. • Acceleration Factor (Coffin Manson equation):

9. Reliability Assessment Thermal cycling test chamber and test profile

10. Reliability Assessment Common Solder joint failure monitoring • Electrical Testing. • The electrical continuity is monitored during the thermal cycling test. • Whenever a fracture occurs in a solder joint, the resistance reading will increased dramatically, thus indicating a failure. • Spikes higher than 300 ohms (IPC-SM-785 standards, IPC, 1992) • Electrical indication of failure can be intermittent as the fractured solder joint is still in contact to the substrate. • We need some robust technique!!

11. Acoustic Micro Imaging • Acoustic Micro Imaging (AMI) • Able to solder joint cracked during the thermal cycling test • Non-destructive inspection • Reflected, refracted or absorbed with respect to the differences between acoustic impedances Reaction of ultrasound wave in an object

12. Input Output (A-scan & Image) Scan motion Ultrasound wave Flip chip De-ionised water A-scan Front surface Chip to Bump Interface Bump to Board Interface Acoustic Micro Imaging

13. Acoustic Micro Imaging Face down Chip Metalized Pads Underfilled Solder balls Connectors Test Board Figure 4: C-scan image of chip-to-bump interface

14. Acoustic Micro Imaging • Typical resolution: • 250 microns for 10MHz • 75 microns for 30MHz • 25 microns for 100MHz • 10 microns for 230MHz • Factors affect the resolution in the acoustic image: • Frequency • Focal Length • Fluid Path • Signal Strength

15. Test Board • Organic FR4 test board of 0.8mm thickness • 14 flip chips on both sides of the board • Die Thickness = 725μm • die size = 3948μm × 8898μm • 109 solder bumps • Ball height = 125μm

16. Accelerated Thermal Cycling • Accelerated Thermal cycling (ATC) test was carried out for 96 cycles. Test boards were investigated every 8 cycles by performing AMI imaging. Accelerated Thermal Cycling Test Profile

17. Acoustic Micro Imaging Figure 5: C-scan image of bump before and after test

18. Acoustic Micro Imaging Histogram of bump before and after ATC test

19. Input image, Io(x,y) Find image gradient field Thresholding Circular Hough transform Radial gradient measurement Multiply with Constraint function Region growing Gradient based Circular Hough Transform Tagging and Labelling Radial Gradient based Region Growing ROIs Defined Feature Extraction INTENSITY, AREA AND HISTOGRAM extracted for each solder joint Feature Extraction

20. Feature Extraction Gradient based Circular Hough transform

21. Feature Extraction Radial Gradient based Region Growing Let H be the set of all unallocated pixels Let N be the set of 8-connected neighbours pixels Grow the seed pixels by the following rules Repeat the growing until the all the neighbour pixels have been grown, i.e.

22. Feature Extraction Radial Gradient based Region Growing

23. Result and Discussion Performance Analysis:- Error Ratio & Area Similarity

24. Result and Discussion Mean Intensity VS Area Plot

25. Result and Discussion Similar Characteristic Plot

26. Result and Discussion Fails at 24 cycles Histogram Distance VS Thermal Cycles • A sharp jump in histogram distance value after certain cycles indicates a severe failure of a solder joint.

27. Result and Discussion Fails at 24 cycles Mean intensity VS Thermal Cycles • A sharp jump in mean intensity value after certain cycles indicates a severe failure of a solder joint.

28. Result and Discussion Fails at 24 cycles Area VS Thermal Cycles • A sharp jump in area value after certain cycles indicates a severe failure of a solder joint.

29. Result and Discussion Figure 11: AMI Monitoring plot for Bottom Row

30. Result and Discussion Figure 12: 3D Plot for AMI Monitoring

31. Result and Discussion • The creep energy dissipation for individual bumps of specific solder volume over a single thermal cycle were solved using ABACUS FE simulation software.

32. Prediction and Monitoring Comparison of Prediction and Monitoring Result

33. Conclusion • The failure distribution pattern over a short number of cycles was able to be tracked and monitored by an AMI inspection technique. • The reliability distribution pattern measured from AMI provides evidence of strong correlation between FE prediction and accelerated test results. • A robust monitoring technique in solder joint through lifetime performance is one of the key factors to ensure high quality electronics products.

34. 1910 – 2011 – 2110?! Thank You for your Attention !! AutobotBumbleBee