Micromolding of Pb and Zn with Surface Engineered LiGA Mold Inserts
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J10.5.1
Micromolding of Pb and Zn with Surface Engineered LiGA Mold Inserts D. M. Cao1, D. J. Guidry2, W. J. Meng 1, K. W. Kelly 1, 2 1 Mechanical Engineering Department, Louisiana State University, Baton Rouge, LA, 70803, U.S.A. 2 Mezzo Systems Inc., LBTC, South Stadium Drive, Baton Rouge, LA, 70803, U.S.A. ABSTRACT Molding of Pb and Zn metal plates with LiGA (Lithographie, Galvanoformung, Abformung) fabricated Ni micro-scale mold inserts was carried out with as fabricated Ni inserts and Ni inserts conformally coated with Ti-containing hydrocarbon (Ti-C:H) coatings. The molding performance was characterized using scanning electron microscopy (SEM) and energydispersive spectroscopy (EDS), in terms of the generated features on the metal plates as well as the inserts condition after molding. The present results demonstrate that, in cases where significant metal/insert chemical interactions exist, surface modification of the mold insert is necessary to obtain satisfactory performance. Furthermore, conformal deposition of suitable engineered ceramic coatings onto Ni micro-scale mold inserts is effective for high temperature micromolding of reactive metals. INTRODUCTION Microfabrication techniques have been intensively investigated for applications in electrical, biochemical, and mechanical devices. Fabrication of high aspect ratio micro-scale structures (HARMs) with the LiGA technique, using X-ray lithography and electrodeposition [1], allows for novel mechanical devices with excellent performance. During the first step of the LiGA process, high-energy X-ray radiation is used to perform lithography on resists made of either polymethyl methacrylate (PMMA) or epoxy based SU-8. Development of the resist is followed by electrodeposition of metals and/or alloys into the resist structure. Chemical dissolution of the remaining resist results in either the final HARMs product or a metallic micro-scale mold insert. This mold insert may then be used to mass-produce secondary HARMs by compression molding [2]. X-ray lithography requires exposure of the resist through patterned masks to high-energy/high-intensity X-rays from a synchrotron source, making direct fabrication of HARMs with LiGA technique extremely expensive. Economic mass production of HARMs based microdevices is thus dependent upon the molding (Abformung) step of the LiGA process. Replication of metallic HARMs by compression molding using LiGA-fabricated inserts has not been successful to date, limiting the realization of many HARMs based micro-mechanical devices. Compression micromolding of metals is hindered mainly by the chemical/mechanical interactions between the hot metal and the insert, resulting in bonding that may lead to damage of the insert, the molded metallic part, or both. Although lubricants may be used in macro-scale molding [3], repeatable and uniform application of lubricants to micro-scale inserts is difficult, due to their small linear dimensions (~100 µm) and high aspect ratios (>4). An alternative approach is to modify the near-surface chemical/m
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