(Dr. Jonathan Colton, advisor)

"Design and Manufacturing of Plastic Micro-Cantilevers by Injection Molding"

Abstract

Currently most Atomic Force Microscope cantilever tips are made with silicon processing techniques and materials. It would be desirable to have AFM tips made from plastics, such as Teflon and polystyrene. Plastics tend to be chemically inert and can be easily functionalized with biological agents. Plastic micro-cantilevers would also offer a wide range of stiffness, much lower than the ones produced out of silicon. This research uses the injection molding process to produce different polystyrene micro-cantilevers.

Several challenges in the manufacturing and design of these parts arise from the small scale (microns) of the parts. The first of these is the machining of the desired micro-molds. Micron-size parts require micron-size cavities, for this purpose micro-edm was successfully used to machine the cantilever molds in steel. The second challenge in micro-molding is the lack of understanding on how the processing parameters affect the filing of very small cavities. The many experiments carried out showed that the most influential parameter is the mold temperature. The experiments also showed that the current limitation on how small cantilevers can be injection molded is the tolerance between the different parts in the mold assembly. In this research cantilevers as small as 30µm x 15µm in cross-section were manufactured. The thinner cantilevers of 5µm and 10µm had a thin layer of flash around the edge of the cantilevers suggesting that a small gap exists in the parting plane of the mold. The last challenge in micro-molding is the small amount of work available in the theoretical models governing filling micro cavities. This research used a finite element model, to shine some understanding of how the micro-cantilevers are filled. The model agrees with the experiments that the main factor influencing the filling of the micro-cantilevers is the mold temperature.