Finite Element Modeling of System Design and Testing Conditions for Component Solder Ball Reliability Under Impact

In this paper, the effects of system design and testing conditions on the dynamic behavior of solder balls of components are studied through finite element analysis. The current JEDEC drop test board (JESD22-B111) is used as a baseline model. The model is then extended to several new configurations, which consider the effects of major component placement, secondary component attachment, and drop orientations at system level. Some findings are summarized as follows. There exists a region near the mounting support, where the board bends in the opposite direction as the board in the center. This localized bend mode causes excessive stresses in solder balls for the components close to the mounting support areas. The attachment of a secondary component on the opposite side of a major component has different effects: symmetric placement can reduce the stresses in the major component. However, the off-centered placement gives rise to the additional stresses in solder balls on the far edge of the major component, and therefore can lead to a higher failure rate. Components respond differently under 0
^°
(face-down) and 180
^°
(face-up) horizontal drops, respectively, as the magnitude of tensile and compressive stresses in one vibrational period is not symmetric. In addition, horizontal drop may be the worst drop orientation for solder ball damages, compared to the other drop orientations. The vertical (90
^°
) drop has very limited damages to solder balls. The above findings and predictions have been verified experimentally. The results provide insight to the system- and board-level designs in product development.