Self-assembly of three-dimensional microstructures in MEMS via fluxless laser reflow soldering

In order to overcome the three-dimensional (3-D) microstructures manufacturing difficulties, the special planar structures are fabricated first, and then the structures are assembled to construct the complex 3-D structures like origami, the art of paper folding. Using the surface tension of the molten solder, MEMS solder self-assembly technique offers a compatible solution for micro components assembly process. To predict the self-assembled structures, we developed a numerical 3-D model based on energy-minimization principle. Furthermore, MEMS solder ball self-assembly method via fluxless laser reflow soldering was proposed. The self-assembly experimental studies were conducted to verify the prediction model. It was shown that the final equilibrium angle and solder shapes matches well with the predicted results, and the error was less than 2°. The initial gap between the two pads was also analyzed to evaluate the effects of the hinge. It was found that for the LED dies used in the experiments, a hinge is unnecessary when the initial gap is less than 10μm.