Temperature Controlled Capillary Driven Sequential Stacking Self-Assembly using Two Different Adhesives

In this paper, a new temperature controlled sequential stacking self-assembly technique is proposed. This method utilizes capillary force generated by two different liquid of TEGDMA (triethyleneglycol dimethacrylate) and 42Sn-58Bi solder as adhesives. TEGDMA with an additional thermal initiator is liquid at room temperature and hardens by heat. 42Sn-58Bi solder is solid at room temperature and melts at 138 degC. Since TEGDMA and 42Sn-58Bi solder are selectively utilized as adhesives by setting the process temperature at room temperature for TEGDMA and 150 degC for 42Sn-58Bi solder, the sequential self-assembly of different components can be realized. The feasibility of the proposed process and alignment accuracy are experimentally and theoretically examined using 1 mm square silicon chips as test components. The first component assembly on a substrate is carried out at room temperature using TEGDMA, and the second component assembly on the assembled component is carried out at 150 degC using 42Sn-58Bi solder. Both assembly steps are carried out in EG (Ethylene Glycol) solvent with an additional sulfuric acid. It was confirmed that the first and the second assembly were successfully done at room temperature and at 150 degC, and alignment accuracy of the first and the second assembly were 33 mum and a few mum, respectively.