Abstract
In this research, the improvements and design concepts of advanced wafer level package (WLP) are studied. Two major targets, the solder joint stress release and the integrated circuit (IC) signal fan-out, are especially focused. Due to the demands of the suitable analytic methods applied on the reliability assessment of advanced microelectronic packages, the related fundamental theories and testing approaches are proposed. In addition, the electromigration performance of the embedded IC related to the applied new packaging designs is examined by the presented experiment. Based on the objective design concepts, two types of novel packaging structures are fabricated to assist the investigation. One idea, the solder joint protection WLP (SJP-WLP), is developed by applying a delaminating layer interposed between the lowest insulation layer and the top surface of the silicon chip. Besides, the panel base package (PBP), which is fabricated on a selected panel material, is also designed to achieve both the capabilities of solder joint stress release and IC signal fan-out. Because of the applied new packaging materials and structures in advanced microelectronic packages, the thermal-mechanical behaviors are different from the conventional cases. By using the established analytic methods, the reliability assessment of solder joints, redistribution lines, and the back end of line (BEOL) of IC devices are studied. The fatigue parameters in prediction model are determined through the FE analysis and the related experiment. Therefore, the lifetime of metal traces under temperature cycling test can be predicted through the FE analysis together with the fatigue model. Besides, the four-point bending apparatus is used to directly impose mechanical loading on testing metal wires, and the influence from packaging designs on electromigration damage is studied. From the results, the applied mechanical stress has a small but finite effect on the MTTF of the Al/Si/Cu and Cu metal lines. However, this variation may lead to an error estimation when calculating the unknowns in the Black's equation. To improve the electromigration reliability and reduce the effects of the mechanical stress on the application of the Black's equation, the residual stress is suggested to be controlled to the mid-value between the compressive and the tensile yielding strength of the metal lines. In addition, metal lines with larger yielding strength are also favorable due to their better resistance of stress-induced voiding (SIV). The analytic procedures which are suitable for future microelectronic packages are proposed in this research. By means of the validation on the testing specimens, they can be applied well on the design, structural reliability assessment, and electromigration evaluation of the advanced WLP. To develop the advanced microelectronic packages, this research could be quoted as an important reference by the packaging engineers.