Simulation of forces acting on tiny chips during fluidic self-assembly

Fluidic self-assembly processes have been recently demonstrated to be a feasible method of assemblying tiny chips in a cost-effective manner. In order to successfully implement the fluidic self-assembly process, it is important to quantify the magnitudes of the restoring capillary force and torque between the chip and the binding site and to determine the fluid dynamic forces acting on the chip as fluid flows over the chip. This paper presents results of numerical simulations of these restoring capillary forces and torques, and discusses the effect of various parameters on them, such as lubricant volume, component orientation and contact angle. The results show that the restoring forces in both lift and shift directions decrease significantly with the volume of lubricant. Analysis of the sensitivity of the restoring torque to the contact angle between the lubricant and the self-assembled monolayer (SAM) in water is also carried out. It is observed that, at smaller contact angles, the maximum torque is insensitive to the contact angle between 0 to 40deg. It thus suggests that a lubricant with a contact angle less than 40 degrees can be used without loss of effectiveness. The equilibrium of the chip under the action of flow-induced and capillary forces has also been analysed