Smart biomimetic structure applied to flexible substrate lift-off process

• Main Authors: Hung, Chih Yi, 洪志毅
• Other Authors: Sung, Cheng Kuo
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/7bkf8f

博士 === 國立清華大學 === 動力機械工程學系 === 104 === Flexible electronics manufacturing faces a bottleneck in lift-off process. This dissertation proposed a possible solution for the challenge by means of constructing a biomimetic structure as adhesive intermediate of carrier and substrate. Many insects possess evolved fibrillary structures on their feet to achieve extraordinary adhesion on vertical walls or ceilings. These fibrillary adhesive attachment systems consist of finely structured hairs with the size ranging from a few hundred nanometers to a few hundred micrometers, depending on the animal species. Learning from the fibrillary attachment systems of many insects, biomimetic structures were developed to achieve required adhesive characteristics herein. This research designed appropriate biomimetic structures to be used in lift-off process of flexible electronics manufacturing by finite element method and surface adhesive theorem. The geometries of biomimetic structures were pillar, pillar with rounded edge, mushroom and half-hourglass. Surface adhesive theorem was based on theory of elasticity and micro mechanics. The theorem of contact between a sphere and an elastic half-space were used to find contact area and adhesive force, and the shape effect was investigated by using JKR model and Lennard-Jones Potential. In lift-off process, tensile force and crack force between biomimetic structure and elastic substrate were calculated by Griffith condition. By varying relative peel angles, functional variables were built to estimate peeling process of adhesive structure in various conditions. The results show that the finer contact structures give rise to higher adhesion force. The mushroom-shaped tip enhances more adhesive force while the flat shape with rounded edge has the least adhesive force. The half-hourglass structure featuring a larger base can decrease the stress concentration at the bottom of the structure, so that the failure during the peeling process can be avoided. According to the results of simulation, the mold was made of nickel-cobalt alloy by three methods, including electrical discharge machining, electroforming and laser machining. The PEN was filled into the mold by nanoimprint and the adhesive forces of the structures were estimated by AFM.