Replication of metal-based high-aspect microscale structures by high temperature micromolding

Abstract

In microsystem technology a large range of materials will be available only after the necessary microfabrication technologies have been developed or adapted. More than a decade ago, the existing microfabrication technologies were restricted to structuring and shaping techniques producing three-dimensional microstructures out of silicon, mostly unfilled plastics or a few pure metals or binary alloys. However, the choice of materials for microcomponents is determined by the function and conditions of use of microsystems. Some microdevices can only work well when made of specific metal components. To meet this need, several microfabrication techniques have been developed, such as second electroforming of molded plastic mold, microcasting, microinjection molding, ultra precision micromilling, micro electrical discharge maching, and their modified techniques, each with a certain range of metal choices. In chapter 1, these techniques are reviewed briefly and compared with each other. More importantly, a new technique for fabricating microscale metal structures - high-temperature compression molding is proposed and the related issues are discussed, including surface engineering of the mold insert, molding behavior comparison between molding different metals and molding with surface modified inserts and unmodified inserts, and molding mechanics. Chapters 2, 3 and 4 focus on the first issue - surface engineering of the mold insert, including characterization of Ti containing hydrocarbon (Ti-C:H) coatings in terms of microstructure, mechanical properties, tribological characteristics and tribochemistry, and conformal coating of Ti-C:H over LiGA fabricated microscale structures. The second issue - molding behavior is discussed in chapters 5, 6 and 7, including preliminary experiments on micromolding of Pd and Zn, instrumented micromolding of Pb and high-temperature instrumented micromolding of Al with LiGA fabricated Ni inserts. Chapter 8 focuses on the third issue - the mechanics of molding. In this chapter, a simple mechanics model of the micromolding process was developed, which relates the stresses on the insert during micromolding primarily to the yield strength of the molded metal and frictional tractions on the sides of the insert. Finally, chapter 9 summarizes this whole dissertation research with main results and achievements highlighted and the future research discussed.