SUBJECT: Ph.D. Proposal Presentation
BY: Vishnu Vardhan Reddy Busi Reddy
TIME: Wednesday, October 16, 2019, 12:00 p.m.
PLACE: MARC Building, 201
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 will make 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 such as cross-sectioning, dye and pry testing, as well as non-destructive testing such as daisy-chain electrical resistance measurement, X-ray, Scanning Acoustic Microscopy (SAM) are being used to detect solder interconnect failures. However, both destructive and non-destructive testing have significant limitations in detecting defects and failures. Thus, there is an increased demand for a new reliable and robust inspection method for the inspection 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 sensitivity Dual-Fiber-Array Laser Ultrasonic Inspection (DALUI) system for inspecting and assessing area-array microelectronic packages. The proposed system is a significant forward of the current Single Laser Ultrasonic Inspection (SLUI) system in the sense that the proposed system will have dual laser beams to excite at two spatially-distinct locations and thus, will allow higher total energy to be delivered on to the microelectronic package under inspection. Higher laser energy produces high-strength ultrasound waves in the sample, which will improve the sensitivity of the system as well as facilitate the inspection of large and multi-leveled packages. The developed system will be employed to detect cracks in microelectronic packages subjected to drop testing, thermal-cycling test, and mechanical bend testing. As these tests produce different size and nature of cracks at various locations within the solder interconnects, the utility of the developed system will be demonstrated. In parallel to the experiments, finite-element simulations that account for viscoplastic behavior of solder joints as well as the direction- and temperature-dependent properties of substrate and Printed Circuit Board (PCB) will be carried out. The damage prediction from the simulations and the experiments will be correlated.