Development of dual-fiber array laser ultrasonic system for inspecting and assessing area-array microelectronic packages
Busi Reddy, Vishnu Vardhan Reddy
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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 defects and 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 fast, robust, low cost, non-contact, non-destructive, accurate, and highly sensitive Dual-Fiber Array Laser Ultrasonic System (DALUS) for inspecting and assessing area-array microelectronic packages. DALUS is a significant path forward of the previous Single Laser Ultrasonic System (SLUS) in the sense that this newly developed system has dual laser beams to excite at two spatially-distinct locations and thus allowing higher total energy to be delivered onto the microelectronic package under inspection. The higher laser energy produces higher strength ultrasound waves in the test sample, which will improve the sensitivity of the system as well as facilitate 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, 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. Also, the measurement capability of DALUS is verified as per the industrial standards using gage repeatability and reproducibility analysis.