The Impact of Substrate Vibrations on Self-Alignment Accuracy in BGA/Flip-Chip Assembly

Abstract

Solder self-alignment is a crucial manufacturing technology for the cost-effective assembly of optoelectronic devices that require precise positioning. However, concerns remain about the quality of self-alignment, especially due to dynamic factors like mechanical vibrations from conveyor belts during the manufacturing process. Additionally, there has been a lack of comprehensive experimental studies and models to fully address these issues. In this article, the dynamic behavior of a ball grid array (BGA) flip-chip assembly reflowed under forced environmental periodical vibration was investigated. Due to the low dissipative force of the molten solder joint, resonant oscillations between chip and substrate were observed at around 12 Hz driving frequency. The maximum chip’s oscillation amplitude can reach more than $100\mu$ m for only several microns’ driven amplitude on the substrate. This resonant motion can be “frozen in” during the solidification of the joint, resulting in large post-assembly misalignments. In order to reduce the adverse influence of environmental vibration on self-alignment accuracy, several feasible methods were proposed, including varying solder surface tension coefficient, adjusting solder joint aspect ratio, adjusting chip mass or the number of joint interconnections, in order to shift the resonant frequency of the to-be-assembled device to a range that is different from the frequency of environmental vibrations.