First demonstration of drop-test reliability of ultra-thin glass BGA packages directly assembled on boards for smartphone applications

This paper reports the first demonstration of the drop-test reliability performance of large, ultra-thin glass BGA packages that are directly mounted onto the system board, unlike the current approach of flip-chip assembly of interposers, involving additional organic packages which are then SMT assembled onto boards. The packages, 18.4mm × 18.4mm in size made of 100μm-thick glass, were also successfully assembled, for the first time, in a SMT line. The effect on drop reliability of the glass BGAs with circumferential polymer collars was studied extensively. While the glass BGA packages met the reliability requirements, both with and without polymer collars, the polymer collars were found to further enhance the drop performance, as well as the fatigue life of solders. Finite element modeling was used to understand strain-relief mechanisms and provide design guidelines for reliability. The glass substrates fabrication process along with the formation of polymer collars by spin coating is detailed. The glass package-to-PCB assemblies were formed using SMT-compatible processes with standard equipment, followed by reliability testing through thermal cycling and drop tests. The compiled failure data from drop testing was fitted into a Weibull distribution plot. Comprehensive failure analysis was performed to assess the structural integrity of the glass substrates and identify the predominant failure mechanisms in drop test.