Evaluation of FCBGA Package Subjected to Four-Point Bend Reliability Test Using Fiber Array Laser Ultrasonic Inspection System

Abstract

Unique two-beam laser ultrasonic inspection (LUI) probes were developed for the inspection of the quality of all types of chip packages. Microelectronic assembly houses demand reliable quality inspection tools that can identify all interconnect defects across the wide range of chip packages in order to allow for cost-effective rework (when applicable) and to prevent field failures. LUI is a noncontact, nondestructive, and cost-effective technique that can be used as both an online and offline tool for evaluating the quality of solder ball interconnections. In this paper, the authors present the development and validation of unique two-beam LUI probes. The developed probes were validated by using them to evaluate the quality of large flip-chip ball grid array (FCBGA) packages. These two-beam laser probes produce high-amplitude signal in multilayer packages. The high-amplitude signal, in turn, improves the signal-to-noise ratio, which facilitates the detection of very small defects as well as large defects. FCBGA packages that underwent four-point bending tests were successfully evaluated for defects such as laminate separations, pad cratering, and cracks. Finally, the packages were cross-sectioned for scanning electron microscopy (SEM) imaging to validate the LUI results. Finite-element (FE) simulation of the package with four-point bending loading conditions was also carried out to further validate the LUI results.