버블의 항력을 이용한 유체-자가조립 연구

Abstract

Pick-and-place robots are generally used to do system packaging. However, pick-and-place robots have some defects for which they can’t catch hold of chips below 200um or flexible material blocks. Thus, fluidic self-assembly is proposed here. Fluidic self-assembly is a method which uses flow of fluid to attach a chip to a required position. In this study, we used a new method to perform an experiment with some bubbles which aims at supplementing the attaching method of solder and chip and also the defect of which the chip can’t be attached to the required position of the substrate. We fabricated a Si wafer with Cu micro pattern of 650um x 650um using photo lithography. After that, solder balls were attached onto the Cu micro pattern. In this experiment, we used the solder ball with size of 400um, 500um 600um. Solder ball was made by Sn96.5/Ag3/Cu0.5. The experiment was carried out in the liquid GALDEN D40 at 230℃which is higher than solder ball melting point. Capillary forces from molten solder ball can be used to bond micro-scale block (950umx 950um) in a self-assembly process. Air injection velocity to the bubble is calculated from the relational expression between capillary force and drag force. As a result, it is affirmed that this study proposed a more stable attaching method than the previous studies which focused on adjusting the drag force of bubbles. We plan to apply the equipment to adjust the bubble velocity and position.