The temperature distribution and the thermal behavior in ultra fine pitch micro SnAg solder bump under current stressing

The ultra fine pitch micro bump became the future trend due to the development of 3D IC. In this research, three-dimensional simulation was employed to examine the temperature distribution in micro SnAg solder bumps. According to the result, the temperature distribution in solder bump of micro bump is nearly uniform. In addition, the hot side is near the substrate side, whereas the cold side is near the chip size because of the longer lower trace. Under a tolerable current of 0.15 A, the temperature increment is only 0.3°C in solder. The thermal gradient approaches 1000°C/cm that is indicated from previous research as a critical thermal gradient. The thermomigration may happen in such gradient. Finally, the relationship between the applied current and the average temperature in upper Al trace was also measured in this study. The infrared microscope was used to confirm the credibility of the finite elements analysis. This study successfully demonstrates the temperature distribution in micro bump by finite elements analysis and infrared microscope.