SUBJECT: Ph.D. Dissertation Defense
BY: Vishnu Vardhan Reddy Busi Reddy
TIME: Thursday, May 7, 2020, 1:00 p.m.
PLACE:, Virtual
TITLE: Development of Dual-Fiber Array Laser Ultrasonic System for Inspecting and Assessing Area-Array Microelectronic Packages
COMMITTEE: Dr. Suresh Sitaraman, Chair (ME)
Dr. Karim Sabra (ME)
Dr. Tequila Harris (ME)
Dr. Madhavan Swaminathan (ECE)
Dr. C. P. Wong (MSE)


Failures in solder ball interconnects makes a microelectronic packaging system inoperable. These failures often result from defects during assembly and/or due to damage accrued from thermo-mechanical and other loads during operation after the assembly. Currently, both destructive testing as well as non-destructive testing such as X-ray and acoustic microscopy are being used to detect solder interconnection failures. However, both destructive and non-destructive testing have significant limitations. Therefore, there is an increased demand for a reliable and robust inspection technique for the evaluation of solder ball interconnections, especially in area-array microelectronic packages. The objective of this research is to develop a non-contact, non-destructive, accurate, and high sensitive, Dual-Fiber Array Laser Ultrasonic System (DALUS) for inspecting and assessing area-array microelectronic packages. DALUS is a significant forward of the previous Single Laser Ultrasonic System (SLUS) in the sense that this new developed system has dual laser beams to excite at two spatially distinct locations and thus allowing higher total energy to be delivered on to the package under inspection. Higher laser energy produces higher strength ultrasound waves in the test sample, which improved the sensitivity of the system as well as facilitated the inspection of large and multi-leveled packages. This developed system is employed to detect failures in industrial packages subjected to drop testing, thermal cycling test, and mechanical bend testing. The utility of the developed system is demonstrated in a holistic manner through these tests which produced different sizes and nature of cracks at various locations. In parallel to the experiments, finite-element simulations are carried out to correlate the damage predictions from the simulations and the experimental results.