Flip chip self-alignment mechanism and modeling

The self-alignment motion of the chip bond pads to the corresponding substrate bond pads is critical to the yield and reliability of next generation flip chip technology. Modeling the self-alignment mechanism has been the subject of numerous research programs focusing primarily on the quasistatic equilibrium deformation of molten solder joins. In this paper, a mathematical model of the self-alignment mechanism for low cost, next generation flip chip processes is proposed. The model is structured to handle two cases of misalignment. For small misalignments (e.g., <0.25% of the pitch), the mathematical model is analytically solved based on a linear regressive restoring force model. For large misalignments (e.g., >0.25% of the pitch), the impact of solder wetting on the self-alignment mechanism is analyzed. Following the investigation a new relationship between molten solder restoring force and misalignment was discovered.