Juergen Hausselt

Injection molding of LIGA and LIGA-similar microstructures using filled and unfilled thermoplastics

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 invented and developed at Forschungszentrum Karlsruhe. 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 microParts Company, Dormund, Germany, cooperating within 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 production of ceramic LIGA or LIGA-similar microstructures at Forschungszentrum 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.

Innovations in molding technologies for microfabrication

Micromolding is a key technology for the economic production of components for microsystems. It is applied in several manufacturing techniques including the LIGA process. Especially MicroInjection Molding allows cost-effective large-scale production of components for many applications to be used in microsystems technology. Using special molding machines, lateral dimensions in the micrometer range, structural details down to 200nm and maximum aspect ratios of more than 20 are achieved. Examples for applications are PSU-made housings for microfluidic systems or microcomponents made of PMMA for cardiac catheters. PC or LCP are appropriate materials for interconnection devices in microoptics and electronics. Other examples are injection molded lost plastic molds for electroforming or electroless plating of metal microstructures. An important economic factor is the optimization of the molding process and tool using different simulation techniques. Recently, novel techniques for manufacturing metal or ceramic microstructures were developed by adapting Powder Injection Molding to microtechnologies. Using commercially available feedstocks, microstructures were made of metals or ceramics. Rapid manufacturing of microcomponents is achieved by the so-called Photomolding process using reactive polymer resins as photocurable material and e.g. mold inserts fabricated by laser ablation. The addition of micro- or nanosized ceramics to the resin allows the molding of filled composite with enhanced mechanical properties. Subsequent debindering and sintering steps yield the pure ceramic microcomponents.

Innovative molding technologies for the fabrication of components for microsystems

Economic success of microsystems technology requires a wide range of materials as well as the related manufacturing processes. A suitable technology for medium/large scale production is micro injection molding which actually allows the manufacturing of plastic microstructures with 20 microns minimum thickness, structural details of approximately 0.2 microns or maximum aspect ratios of more than 20. These microstructures are, for example, applied as components in micro optics, micro fluidics or minimally invasive surgery. This is demonstrated by microparts that are currently available or will be available soon. For higher economic efficiency and cost reduction, fully electrical injection modeling machines of higher accuracy have been applied. Also, micro insert injection molding reduces mounting costs. Manufacturing of metal or ceramic microparts by powder injection modeling allows large-scale production of complex shaped microstructures with a wide range of materials. Typical examples are sintered structured like stepped LIGA- gear wheels with minimal dimensions of 50 microns in different metal and ceramic materials. Micro Precision Casting originating from conventional investment casting is a suitable process for small/medium-scale production. Examples are microturbine housings made of precious metal alloys. An approach similar to rapid prototyping applies photocurable reactive resins. Photoinduced molding of low viscous resins under ambient conditions leads to significantly reduced cycle times. Additionally, rapid testing of new composite materials can be performed easily. Microcomponents molded from polymers and different composites like dyes with nonlinear optical properties and nanosized ceramic powders will be presented.

Micromolding of polymer waveguides

In microsystem technology the fabrication of either passive or active micro optical components made from polymers becomes more and more evident with respect to the intense expanding application possibilities e.g. in telecommunication. Actually, the LIGA process developed at the FZK, Germany allows the direct fabrication of microcomponents with lateral dimensions in the micrometer range, structural details in the submicrometer range, high aspect ratios of up to several hundreds and a final average surface roughness of less than 50 nm in small up to large scales. The molding of polymer components for microoptical applications, especially in the singlemode range, is determined by the achievable maximum accuracy of the molding technique itself and of the acceptable tolerances for low damping and coupling losses. Following the LIGA and related technique e.g. mechanical microengineering we want to present in this work the fabrication of polymer singlemode waveguides using a combination of micromolding and light- curing steps.

Micro PIM moves into the zone of industrial possibility

Increasing demand for ever-smaller devices presents challenges for materials science. German researchers are looking at the possibilities of micro powder injection moulding, and how to match the process to the needs of large-scale industrial production…

Particle size dependent viscosity of polymer-silica-composites

In this paper the influence of micro- and nanosized particles on the flow behaviour of unsaturated polyester resinsilica-composites will be compared. Commercially available micro-sized quartz filler and different hydrophilic or hydrophobic nanosized Aerosils were investigated with respect to the change of the viscosity as well as the flow activation energy with filler load. Apart from particle size and specific surface area the polarity of the filler’s surface has a strong impact on the resulting flow behaviour and the accessible maximum filler load. The dependence of the relative viscosity upon the filler load was described using different empirical approaches as established in thermoplastic or wax based feedstock systems containing porcelain, alumina or PZT.

New developments of process technologies for microfabrication

Economic success of microsystems technology requires cost- effective fabrication in large series as well as a great diversity of materials processing technologies. The different techniques of micro molding meet all these requirements. An important economic factor is the reduction of cycle time by process and tool optimization with simulation techniques. Actually, minimal cycle times are about two minutes in certain cases. Evolution of thermoplastics processing technologies is demonstrated by application of technical or even high- performance polymers like PEEK, PMMA or PSU. For manufacturing of metal microstructures, we develop three possibilities: microstructures like stepped LIGA gear wheels are obtained from galvanization on lost molds, which have been injection molded using conductively filled polymers. Additionally, electroless plating is used to replicate nonconducting plastic microstructures and the metal injection molding (MIM) process is under development. A quite different approach uses polymer precursors containing monomer/polymer mixtures in reaction injection molding. We chose photoinduced polymerization without any preheating step using photopolymerizable resins. Avoiding the time consuming thermal cycle, molding takes place at ambient temperature. Due to the low viscosity, the microcavities should be filled completely. The process is characterized by the integration of a powerful UV-source and a partially glass made molding tool.

Manufacturing of High-Grade Micro Components by Powder Injection Molding

Powder injection molding (MicroPIM) has a considerable potential for the production of high-value metal and ceramic micro components. This does not only apply to technical aspects but, due to the deployability of mass production, also to economic ones. The current status can be summed up by the following key data: latest trials revealed smallest struc-tural details in the 10µm range or lower. Theoretical densities of up to 99% were achieved depend-ing on the particular powder applied. Typical materials processed are metals (Fe, Cu, 316L, 17-4PH, W and W-alloys etc.) or ceramics (aluminum/zirconium oxide etc.). Best surface qualities were obtained with ultrafine or even nano-doped ceramic powders. Another major line of development is multi-component or assembly injection molding. These proc-esses do not only reduce assembly expenditure, but also allow for the use of new functional material combinations. Interesting examples are ceramic micro heating elements or gear wheel/shaft samples which can be performed as fixed or movable combinations. Micro inmold-labelling using PIM feed-stocks offers further promising opportunities.

Micro systems need a boost in manufacturing methodologies

While macroscopic powder injection moulding is drawing the attention of mass manufacturing and winning plaudits for its high process and economic efficiency, its micro variant still faces challenges…