Optimization of a Capillary-Driven Self-Assembly Process

Fluidic self-assembly using capillary forces has shown great potential for the manufacture of heterogeneous and three-dimensional microsystems because of its self-aligning and parallel assembly nature. Alignment of the parts to their binding sites needs a high degree of accuracy especially in applications with high interconnect density. However, disturbance forces and part tilting threaten a correct assembly. The purpose of this work is to optimize the alignment accuracy of the part by varying the assembly parameters. Silicon parts are assembled onto a glass substrate in an aqueous environment. A hydrophobic heat-curable adhesive is used as a mechanical bond between the parts and the substrate. The capillary forces between the hydrophobic components act to align the parts. Vertical vibration is used for tilt correction, and a frequency of 30 Hz is shown to be most effective. In addition, part alignment has been measured as a function of adhesive volume. Lateral misalignment is shown to increase with larger adhesive volumes.