Surface-Tension-Driven Self-Assembly of 3-D Microcomponents by Using Laser Reflow Soldering and Wire Limiting Mechanisms

This paper proposes a surface-tension-driven self-assembly method for manufacturing highly 3-D microstructures in microelectromechanical systems (MEMS). By using laser reflow soldering, various MEMS microstructures, even including the thermal-sensitive components, are able to be effectively assembled. Moreover, an energy-based numerical model is established for predicting the equilibrium geometry of a self-assembled structure. Based on the calculated results of energy and torque, an analysis is carried out on the factors affecting the self-assembled equilibrium position. In addition, the self-assembly process is also investigated experimentally by fabricating a popped-up microstructure with two light-emitting diodes die. Experimental studies, combined with the modeling results, have demonstrated that the self-assembly angle can be controlled within ±2.5^°. Furthermore, in order to enhance the precision of self-assembly, a novel low-cost wire limiter structure fabricated by the wire bonding process is presented, which reduces the assembly angle variation down to ±0.5^°.