Development of optical fiber laser array method for assessing quality of chip packages

Abstract

This research focuses on the development of an improved laser ultrasonic inspection system for quality evaluation of microelectronic packages of all sizes. This new system uses an optical fiber array consisting of two optical fiber probes, instead of the single fiber probe used in the original inspection system. This array is used to generate ultrasonic vibrations in chip packages while laser interferometry measures the induced vibrations at discrete points on the chip surface. In addition, hardware and software modifications were implemented to improve the safety and reliability of the system. The new system was evaluated by using it to detect the presence of defects (cracks, open solder bumps, etc.) in ball grid array (BGA) packages supplied by CISCO. Various types of defects were induced in these packages by bend, shock, and cycle shock tests. The results obtained with this new system were validated with results obtained through cross sectioning and polishing of the BGA packages by CISCO. Additionally, tests comparing the behavior of different incident beam configurations were conducted to investigate the impact of multiple beam configurations on the measurement results.