<title>Injection molding of LIGA and LIGA-similar microstructures using filled and unfilled thermoplastics</title>

Abstract

Micromolding is a key technology for the economic production of micro-components for microsystems. It is applied in several microstructuring techniques including the LIGA process which was i nvented a nd developed at Forsch ungszentrum Ka risruhe.Injection molding of multiple-use LIGA tool inserts produced by deep-etch X-ray lithography and electroforming allows the economic production of components for most applications using microsystems technology. Such microstructures are produced in small and large series and commercialized by Forschungszentrum Karlsruhe and the m icroParts corn pany, Dortmu , Germa ny, cooperati ng with i n the framework of a license agreement.Special molding machines are applied for the production of single-or multi-stepped microstructures of a few micrometers in lateral dimension and structural details in the submicrometer range. Maximum aspect ratios of several ten up to 600 are achieved. In contrast to compact disc production, the machines are equipped with a special control unit, by means of which tool temperature is often kept above the melting temperatures of the plastics processed during injection. Evacuation of the tool cavity is required for the complete filling of the microstructurized nest area of the mold. Cycle time is mainly determined by the heating and cooling of the whole molding tool. Recently, novel techniques were developed for the prodiiction of ceramic LIGA or LIGA-sim ilar microstructures at Forsch ungszentrum Karlsruhe, where further development of the LIGA technique has been performed for more than a decade. Using lost plastic microstructures and sometimes even metal tools, microstructures are made of structural (e.g., aluminum oxide, zirconium oxide) and functional ceramics (e.g., PZT). Current development activities are aimed at producing lost plastic molds for metal microstructures by injection molding. Molding tests with conductively filled thermoplastics have been carried out to manufacture lost molds for e.g. spin nozzles.

Injection molding of polymer micro- and sub-micron structures with high-aspect ratios

“…The injection molding process is anticipated to hold great potential in the mass production of uniform, good quality polymer micro-and sub-micron structures [5]. However, satisfactory molding results of polymer micro-and sub-micron structures whose aspect ratios exceed two are hard to obtain with the existing injection molding equipment and techniques for polymers [6,7] for various reasons [8].…”

The Micro Injection Moulding Process for Polymeric Components Manufacturing

“…If the cavities contain micro features that are so small that they cannot be vented in the standard way through the parting plane or special bore holes, it is necessary to develop a system dedicated to the evacuation of the air from the cavity. Some applications are reported in literature of creating the vacuum in the mould [11,12,13].…”

Micro injection molding for mass production using LIGA mold inserts

“…By means of deep-etch X-ray lithography and electroforming, tools with minute structural details in micron range, largest tool heights of up to several mm, and lateral wall roughness in the nm range (Ra = 70 nm typically) can be produced (Guckel 1996). Plastic molding of high aspect ratio micro structures (HARMs) using LIGA made mold inserts has been investigated for past decade (Ruprecht 1995;Despa 1999;Piotter 2002;Yorita 2004). Some work lead to the commercial application of certain…”