Parametric analysis and design of ultra fine assembly of micro dies

Feature size reduction of silicon IC has led to denser circuitries. An example of die size reduction is the emergence of ´dust-like´ silicon dies used in radio frequency identification (RFID) tags, which is well beyond the ability of commercial assembly machines to pick and place onto substrates for mounting. Self-assembly approaches based on liquid surface tension driven processes are used in place of individual pick and place for these micro dies. The process is capable of aligning and interconnecting large number of micro dies simultaneously. However, die tilting had been observed if the alignment design is not controlled. Self-alignment of micro dies on planar surfaces driven by liquid surface tension is analyzed using thermodynamics in this study. Numerical models developed in this study revealed that the tilting is not thermodynamically favored in alignment of regular dies because the system is dominated by body force. Micro dies have smaller body forces, and thermodynamics revealed that tilting is favored. Based on the model, the parameters that control tilting criteria are presented. Alignment with high accuracy can be achieved by adjusting the liquid volume and the binding site geometry.