Effect of physical vapor deposition metallic thin films on micro injection molded weld line mechanical properties

Micro injection molded polymeric parts coated with functional thin films/layers show off the promising applications in microsystems area. But the unfavorable and unavoidable defect of weld line in micro injection molding part leads to detrimental mechanical and surface properties. The possibility of the functional thin film for enhancing micro injection molded weld lines was investigated. Two typical coating materials (aluminum and titanium) with various film thicknesses (400, 600, 800 nm) were deposited on one side of the micro injection molded weld line tensile sample via physical vapor deposition (PVD) method. The coated micro weld line samples were characterized by tensile tests. The results show that PVD films of aluminum and titanium can reinforce the strength and stiffness of micro injection molded weld line, even at thin thickness levels. But when the film thickness is increasing, the weaker adhesion between metallic films and polymers decreased the PVD films’ enhancing performance for micro weld line mechanical properties due to the degradation of polymers related to longer time exposure under high temperature.     

Metal-ceramic-composite casting of complex micro components

Metal-ceramic-composite casting has a huge potential as a new manufacturing method for the production of complex-shaped micro sized parts or microsystems consisting of different metals and ceramics. The fundamental advantage of this method is the capability of multi-component part fabrication in one step avoiding first time consuming joining or assembling techniques; second the used material combinations can fulfill complex functionalities and enhanced mechanical properties. One of the most challenging factors in micro composite casting is a stable mechanical bonding between the used individual materials. But under consideration of the different physical properties like thermal expansion coefficient as well as of the wettability of the ceramic inserts and of the applied metal casting material it is possible to manufacture form and force fitting microsystems. Within the framework of this feasibility study complex metal-ceramic micro composites have been realized successfully using the lost-wax casting process. Casting experiments were performed at different muffle preheating temperatures with Al-bronze of the type CuAl10Ni5Fe4 as casting material. The ceramic parts, respectively inserts cast around by metal are micro gear wheels (2.5 mm diameter) consisting of ZrO₂ and Al₂O₃.     

Replication and bonding techniques for integrated microfluidic systems

From the technical and economic points of view, systems integration, and packaging represent a crucial step in the production of microsystems. Compared to purely silicon- or glass-based systems, the variety of materials and geometries available for purely polymer microfluidic systems is much larger, due to the outstanding material properties. Moreover, polymers may be shaped and joined by comparably simple methods. Examples are polymer microreplication as well as various bonding methods. With them, complete polymer microsystems can be integrated. In addition, a number of established, compatible processes are available for the integration of functional elements that may also be made of other materials.     

Replication and bonding techniques for integrated microfluidic systems

From the technical and economic points of view, systems integration, and packaging represent a crucial step in the production of microsystems. Compared to purely silicon- or glass-based systems, the variety of materials and geometries available for purely polymer microfluidic systems is much larger, due to the outstanding material properties. Moreover, polymers may be shaped and joined by comparably simple methods. Examples are polymer microreplication as well as various bonding methods. With them, complete polymer microsystems can be integrated. In addition, a number of established, compatible processes are available for the integration of functional elements that may also be made of other materials.

     

An intermediate-layer lithography method for generating multiple microstructures made of different conducting polymers

An intermediate-layer lithography (ILL) method has been developed in this work to generate multiple microstructures of different conducting polymers on the same substrate. Previous and current efforts in developing conducting polymer microsystems mainly focus on generating a device of a single function. When multiple micropatterns of different conducting polymers are produced on the same substrate, many microsystems of multiple functions can be envisioned. However, existing techniques present significant technical challenges of degradation, low throughput, low resolution, depth of field, and/or residual layer in producing conducting polymer microstructures. To circumvent these challenges, the ILL method has been explored to generate multiple micropatterns of different conducting polymers in a parallel manner. In this method, conducting polymer materials and a non-conducting polymer intermediate layer are first coated on a substrate, and are then patterned through a mold insertion at a raised temperature. In this work, the ILL has been used to successfully pattern three types of commonly used conducting polymers on the same substrate under a single mold insertion, and simulation has been conducted to gain a good understanding of the molding process. Due to distinctive advantages of simplicity, low cost and high throughput, the ILL has promising applications in fabricating micropatterns for polymer-based microsystems.     

Replication quality of micro structures in injection moulded thin wall parts using rapid tooling moulds

Injection moulding of micro structured polymer parts is often limited due to the replication quality of the structured surfaces. To enhance the replication quality process parameters, e.g., pressure, temperature or injection velocity, are adapted. Here, the mould temperature is the most important factor. This paper investigates the influence of the mould temperature on the replication of micro structured surfaces using amorphous and semi-crystalline polymers. Using rapid tooling moulds and a dynamic tempering system allows mould temperatures about the solidification temperatures during injection and a sufficient cooling for save ejection of the part. The results reveal that for amorphous polymers the mould temperature should be above the glass transition temperature for high replication quality. For semi-crystalline polymers the high cooling velocity seems to inhibit the crystallization process and this leads to a sufficiently low viscosity to achieve high replication quality.     

Fabrication, metallographic and tribologic investigations of LIGA-microstructures made of nickelphosphorous alloys

 The performance and lifetime of micro electro mechanical systems (MEMS) is strongly affected by friction and wear. Because of the restrictions due to the fabrication process the variety of materials used for micro systems is not very manifold. This results often is very poor tribological properties, since the tribological pairings are disadvantageous with regard to friction and especially wear. We therefore investigated materials which can be fabricated by the process currently used for LIGA-microstructures, and have the potential of better properties concerning friction and wear. The results of our tribologic experiments showed, that nickel phosphorous alloys are a promising material for microsystems suffering wear, especially at high surface pressures (high loading). Their absolute values of the wear intensity, are at least one order of magnitude lower than those of nickel and copper, which are the materials mostly used today. Received: 27 June 1996/Accepted:12 July 1996     

Effect of vacuum venting and mold wettability on the replication of micro-structured surfaces

Micro injection molding enables the manufacture of micro-scale features with good accuracy at high production rates. However, the replication of complex micro and nano features is still challenging hindering the development of new functional surface topographies. The marked thermal gradient between injected polymer and mold surface and the reduced dimensions promote a rapid drop of melt temperature that causes the incomplete filling of the micro features. This study aims to investigate the combined effects of vacuum venting and mold wettability on the replication of micro-structured surfaces. A low-viscosity polystyrene and a cyclic olefin copolymer were selected and their wetting properties were evaluated. The results showed that a polymer with high wetting properties and an elevated viscosity dependence on temperature improves the replication of the micro features. Moreover, high interfacial effects can be exploited to significantly enhance the filling ratio when applying vacuum venting.

     

New approach for batch microfabrication of silicon-based micro fuel cells

This paper reports a novel and straightforward approach to the development of a compact micro direct methanol fuel cell. The device consists of a hybrid polymer membrane as a feasible microintegrable electrolyte to be used together with silicon current collectors. These current collectors consist in microfabricated silicon chips that incorporate a fine electrode grid. The membrane combines two polymers with different functionalities, Nafion^® as a proton conducting material and PDMS as a flexible mechanical support. The compatibility of this membrane with MEMS fabrication processes lies in the acknowledged bonding capabilities of the PDMS polymer to materials typically used in microsystems technologies—such as silicon, silicon dioxide and glass—as well as its ability to withstand variations of the Nafion^® volume. The compatibility of all the components with microfabrication processes will permit the application of batch fabrication techniques for the whole device, so contributing to a significant lowering of the fabrication costs.     

Tribology of microsystems

In this work the possibilities for the reduction of friction and wear in micro electro-mechanical systems (MEMS) are investigated. An improvement of the tribological behaviour of microsystems can be realized by optimizing the contact condition and by application of special coatings with low friction and low wear rates. For optimizing the contact condition a defined topography and surface profile is generated by photolithography. Furthermore tribological coatings with low friction and low wear rates are developed and investigated using nanoindentation and micro scratch experiments. Also novel results on micro structured surfaces coated with a-C:H and a-C films will be discussed. The results show the great potential of carbon-based coatings in combination with an optimized geometrical surface design.     

Technology of microthermoforming of complex three-dimensional parts with multiscale features

Thermoforming parts with micro-scale design features require use of thin polymer films. Low heat capacity and fragility of thin (<100 μm) polymer films requires new technical developments for precise heating and form pressure application. This paper will present results of an improved process based on a new replication machine. Temperature stability and pressure distribution is highly improved, even at reduced cycle times. With an upgraded temperature range microthermoforming of high temperature polymers is possible. This technology is well suited for the replication of three-dimensional micro parts with multiscale features. Replication of hollow parts with multiscale features is also possible. Outer dimension in macroscopic length scale and functional design features in microscopic length scale are combined with nanoscale surface structures in an affordable technology.     

Fabrication method of two-level polymeric microstructure with the help of deep X-ray lithography

Two- or multi-level microstructures are getting more important in several applications such as multi-component micro optical elements and various microfluidic systems. In the present study, a simple and efficient method is newly proposed for a fabrication of the two-level polymeric microstructures. Making a mother two-level microstructure consists of two processes: (1) the hot embossing process for a fabrication of microstructures on a PMMA substrate, and (2) the deep X-ray lithography using the hot embossed substrate for a high aspect ratio microstructure fabrication, resulting in a high aspect ratio microstructure containing smaller microstructures on its surface. Making use of so fabricated two-level microstructures as a mother structure, one could achieve a mass replication of the same microstructures via injection molding process with a metallic mold insert obtained by a nickel electroforming onto the mother microstructure. In order to demonstrate the proposed method, a polymeric high aspect ratio microstructure having smaller square microstructures on its top surface was fabricated. The fabricated two-level microstructure shows fine vertical sidewalls, which is a characteristic feature of the deep X-ray lithography. In addition, a metallic mold insert for a mass replication was fabricated by a nickel electroforming process.     

Rapid-manufacturing of micro-structured devices based on MWCNTs/PP composites by using hot embossing replication process

Carbon nanotubes have attracted the fancy of many scientists since their first discovery in 1991. Their small dimensions, strength and remarkable physical properties make them a very unique material with a whole range of promising applications. The most important application of carbon nanotubes based on their important mechanical properties will be as reinforcements in composite materials, especially nanotube-filled polymer composites are an obvious materials application area. In this work, the micro-structured devices in range of micro meter have been manufactured based on polymer/carbon nanotubes composites by using hot embossing replication process. Firstly, the carbon nanotubes with different loading rate (0.1, 1 and 10 %) have been mixed with polypropylene (PP) in molten state to obtain the composite, the rheological properties of MWCNTs/PP composites with different CNT loading ratios were investigated by means of rheometer with a cone-and-plate geometry, the improvement of dispersion of the CNT particles in polypropylene matrix were observed by scanning electronic microscopy. Afterwards, the obtained composite were granulated in particles and used in hot embossing process to realize the replication of micro structured; in this step, a Al mould with micro-motif on surface obtain by machining with computer numerical control machine tools has been used. Finally, the micro-structured motifs on the mould have been successfully transferred with the details on the MWCNTs/PP substrate under the embossing pressure.     

声表面波气体传感器聚合物敏感膜材料的选择

聚合物敏感膜材料是声表面波（SAW）气体传感器应用最为广泛的膜材料。该文就聚合物敏感膜材料的吸附原理、物理性质以及线性溶解能关系（LESR）予以论述。给出了筛选和设计特种性能聚合物膜的方法．旨在为声表面波气体传感器选择或设计合适的聚合物敏感膜材料提供依据。     

Reduction of mechanical stress in micromachined components caused by humidity-induced volume expansion of polymer layers

 Polymer layers frequently used in microsystem technology tend to absorb water from ambient humid air which typically results in swelling of the polymer layers. Depending on the specific component design, this volume expansion may cause changes in the mechanical stress, or even displacement of device structures. In most applications, these effects limit performance and reliability, and should therefore be minimized. The present paper describes an approach for the investigation of swelling phenomena in thin polymer layers. Polyimide PI2540 was chosen as a model polymer. After extensive characterization of the polymer layer properties, static and dynamic sorption behavior was investigated by different means. Based on our experimental results, we have developed linearized models to accurately describe the swelling behavior. Several polymers were characterized. Although the micro-physical mechanisms responsible for the humidity-induced swelling are still poorly understood, we are – based on our data – able to effectively reduce humidity induced stress by selecting suitable polymers and optimizing processing procedures. Received: 25 August 1997/Accepted: 19 December 1997     

Replication of micro components by different variants of injection molding

In microsystems technology, components made by micro injection molding are applied to an increasing extent. The variety of materials, low costs, the high number of sub-variants, and the relatively easy shaping are decisive factors. As further improvement, special variants like micro multi-component injection molding or micro powder injection molding are currently under development at Forschungszentrum Karlsruhe. The goals of these research activities are not only to increase economic efficiency but also to expand the range of materials to metals and ceramics.These R+D activities were mainly sponsored by the Deutsche Forschungsgemeinschaft (DFG) and the Federal Ministry of Education and Science (BMBF). We also wish to thank our industrial partners, namely STEAG microParts, Zumtobel Staff, and all colleagues at Forschungszentrum Karlsruhe for their always helpful assistance.     

Microscale molding replication of Cu- and Ni-based structures

Microdevices and microsystems made of metals can possess unique functionalities. Metal-based high-aspect-ratio microscale structures (HARMS) are basic building blocks of such microdevices and microsystems. Cost-effective fabrication of metal-based HARMS is paramount to the economic viability of such devices and systems. Microscale molding replication promises low-cost, high-throughput production of metal-based HARMS. In this paper, results on molding replication of Cu- and Ni-based HARMS are reported. Molding response of Cu was measured as a function of temperature. Attempts were made to rationalize measured molding responses with companion high-temperature tensile testing. Fabrication of Ni-based HARMS by compression molding is demonstrated successfully for the first time.     

High aspect ratio micro tool manufacturing for polymer replication using μEDM of silicon, selective etching and electroforming

Mass fabrication of polymer micro components with high aspect ratio micro-structures requires high performance micro tools allowing the use of low cost replication processes such as micro injection moulding. In this regard an innovative process chain, based on a combination of micro electrical discharge machining (μEDM) of a silicon substrate, electroforming and selective etching was used for the manufacturing of a micro tool. The micro tool was employed for polymer replication by means of the injection moulding process.     

Materials selection in micromechanical design: an application of the Ashby approach

The set of materials available to microsystems designers is rapidly expanding. Techniques now exist to introduce and integrate a large number of metals, alloys, ceramics, glasses, polymers, and elastomers into microsystems, motivating the need for a rational approach for materials selection in microsystems design. As a step toward such an approach, we focus on the initial stages of materials selection for micromechanical structures with minimum feature sizes greater than 1 /spl mu/m. The variation of mechanical properties with length scale and processing parameters is discussed. Bounds for initial design values of several properties are suggested and the necessity for the measurement of other properties (especially residual stresses and intrinsic loss coefficients) is discussed. Adapting the methods pioneered by Ashby et al., materials indices are formulated for a number of properties and materials selection charts are presented. These concepts are applied to illustrate initial materials selection for shock-resistant microbeams, force sensors, micromechanical filters, and micromachined flexures. Issues associated with the integration of materials into microsystems are briefly discussed.     

Micro assembly injection moulding with plasma treated inserts

Injection moulding is one of the most common manufacturing processes for thermoplastics. By injection moulding, polymer micro components can be produced in large numbers at low costs. Micro assembly injection moulding as a combination of multi-component injection moulding and micro injection moulding enables to avoid offline process steps, as joining is already accomplished in the mould by overmoulding. In case of joint hybrid micro structures, the bonding strength between two components affects the stability of the micro system and is thus important for the part quality. Investigations carried out at the Institute of Plastics Processing (IKV), Aachen, Germany, deal with methods to increase the bonding strength of a plastic and a non-plastic part joint. As shown in the following, a plasma treatment of the inserts is an appropriate approach for this aim.