Molding of Pb and Zn with microscale mold inserts

Molding of Pb and Zn metal plates with LiGA (Lithographie, Galvanoformung, Abformung) fabricated Ni microscale mold inserts was carried out at 300 °C. Both as fabricated Ni inserts and Ni inserts conformally coated with Ti-containing hydrocarbon (Ti-C:H) coatings were used. The molding performance was characterized both in terms of feature generation on the metal plates and insert condition after molding. The present results demonstrate that, in cases where significant metal/insert chemical interactions exist, surface engineering of the mold insert is necessary to obtain satisfactory performance, and that conformal deposition of suitably engineered ceramic coatings onto Ni microscale mold inserts is an effective means for achieving high temperature micromolding of reactive metals. WJM gratefully acknowledges partial project support from NSF through grant DMI-0124441, Louisiana Board of Regents through contracts LEQSF(2001–04)-RD-A-07 and LEQSF(2000–03)-RD-B-03, and NASA SBIR contract NAS5–01179 through a subcontract with Mezzo Systems Inc.     

Metal micromolding: further experiments and preliminary finite element analysis

We report results of instrumented microscale compression molding experiments on Al with Ta mold inserts. The Ta inserts have high-aspect-ratio microscale structures fabricated by micro-electrical-discharge-machining. These microscale structures were further surface engineered by electrochemical polishing, followed by deposition of a conformal amorphous hydrogenated carbon based coating. The molding response of Al, in terms of molding force versus insert displacement, was measured in situ with a high-vacuum, instrumented, compression molding apparatus, and rationalized with a simple model on the mechanics of molding. Molding response was further studied numerically through finite element analysis.     

High-temperature instrumented microscale compression molding of Pb

Compression molding of Pb plates with LiGA (Lithographie, Galvanoformung, Abformung) fabricated Ni microscale mold inserts was carried out in the temperature range of 100–300 °C. In-situ measurements of compressive molding force, demolding friction force and insert displacement were carried out with a custom-built, high-vacuum, high-temperature, instrumented molding machine. Microscale features generated on Pb plates and insert condition after repeated molding runs were examined. The in-situ force monitoring capability enabled compressive stresses needed for molding and frictional stresses generated by demolding to be measured as a function of temperature. Our results demonstrate that, in cases where no significant metal/insert chemical interactions exist, present LiGA fabricated Ni inserts possess adequate mechanical properties for repeated micromolding of low melting temperature metals.We gratefully acknowledge partial project support from NSF through grant DMI-0124441, Louisiana Board of Regents through contracts LEQSF(2001–04)-RD-A-07 and LEQSF(2000–03)-RD-B-03. Ni inserts used in this work were purchased from Mezzo Systems Inc.     

Fabrication of high-aspect-ratio microscale Ta mold inserts with micro electrical discharge machining

We report fabrication of microscale Ta mold inserts by micro-electrical-discharge-machining (μEDM). Morphology, chemistry, and structure of the near-surface region of as-μEDMed Ta blanks have been characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. A TaC surface layer forms on as-μEDMed Ta surfaces. This altered surface layer was removed by electro-chemical-polishing. Further modification of Ta insert surfaces was accomplished by deposition of a conformal Ti-containing hydrogenated carbon coating. We demonstrate successful replication of high-aspect-ratio microscale structures in Al and Cu by compression molding with such surface-engineered Ta mold inserts.     

Study of Hot Embossing Using Nickel and Ni–PTFE LIGA Mold Inserts

Hot embossing is one of the main process techniques for polymer microfabrication, which helps X-ray lithography, electroplating, and molding (LIGA) to achieve low-cost mass production. Most problems in polymer micromolding are caused by demolding, especially for hot embossing of high-aspect-ratio microstructures. The demolding forces are related to the sidewall roughness of the mold insert, the interfacial adhesion, and the thermal shrinkage stress between the mold insert and the polymer. The incorporation of polytetrafluoroethylene (PTFE) particles into a nickel matrix can have the properties such as antiadhesiveness, low friction, good wear, etc. To minimize the demolding forces and to obtain high-quality polymer replicas, a Ni-PTFE composite microelectroforming has been developed, and the hot embossing process using Ni and Ni-PTFE LIGA mold inserts has been well studied in this paper. The morphologies, sidewall roughness, and friction coefficient have been explored in the fabricated Ni-PTFE LIGA mold insert. Finally, the comparison of embossed microstructures with various aspect ratios and the comparison of the embossing lifetimes of mold inserts have been carried out between Ni and Ni-PTFE mold inserts, which show a better performance of the Ni-PTFE mold and its potential applications.     

Numerical simulation and fabrication of microscale, multilevel, tapered mold inserts using UV-Lithographie, Galvanoformung, Abformung (LIGA) technology

Techniques for economic fabrication of high-aspect-ratio microscale structures (HARMS) are being investigated intensely. Microdevices employing metal-based HARMS are of particular interest for mechanical, electro-mechanical, and chemical applications. In many applications, HARMS with two or more heights are needed. Fabrication of these multi-level HARMS by compression molding requires two-level or multi-level mold inserts. In addition, tapered mold inserts would help achieving easy insert-part separation. This paper reports a process for fabricating two-level tapered mold inserts by combining UV-lithography of SU-8 resist, one-step metal electrodeposition, polish and level, followed by SU-8 resist removal. Without tilting and rotation during the lithography step, tapered plating molds are obtained by employing characteristics of UV-lithography and resist development. The SU-8 removal method used does not reduce the strength of the electrodeposited mold insert. Efficacy of our approach is demonstrated with a two-level mold insert prototype.     

Direct microscale imprinting of Al at room temperature with Si inserts

For direct imprinting of metals, hard materials such as diamond and SiC have been used to construct mold inserts in preference to Si, despite the ease in fabricating Si-based micro-/nano- scale structures. In this communication, we demonstrate that micron scale Al structures can be replicated with good fidelity at room temperature by compression molding with Si inserts without incurring insert damage. We further report on results of a finite element analysis of the mechanics of the molding process. The finite element results provide some understanding of the observed lack of damage to the Si inserts.     

Low temperature deposited titanium boride thin films and their application to surface engineering of microscale mold inserts

Titanium boride thin films were deposited at low temperatures by balanced magnetron sputtering and inductively coupled plasma (ICP) assisted balanced magnetron sputtering. The chemical composition, surface morphology, structure, and mechanical properties of titanium boride thin films were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy, and instrumented nanoindentation. As compared to titanium boride films deposited by balanced magnetron sputtering, the increase in plasma density surrounding the substrate surface during film growth afforded by the ICP assist causes significant film densification and mechanical property improvement. The morphology of titanium boride thin films deposited onto microscale non-flat Ta substrates and their effectiveness as barrier coatings for microscale compression molding of Al was characterized by focused ion beam sectioning and SEM. The present results show the potential of low-temperature deposited, conformal, titanium boride thin films for engineering surfaces of microscale mold inserts for microscale pattern replication in reactive metals by compression molding.     

Manufacture of a micro-sized piezoelectric ceramic structure using a sacrificial polymer mold insert

There have been technical limitations to manufacture microstructures due to difficulty of demolding during replication process of high aspect ratio microstructure in mass production technologies. In the present study, the fabrication of a novel sacrificial micro mold insert and powder injection molding process using such a micro mold insert is proposed and developed. It utilizes a synchrotron radiation to fabricate the shape of polymer based sacrificial mold inserts and then these mold inserts were exposed at X-ray once more to adjust its solubility. This second X-ray exposure facilitates dissolving of mold inserts instead of demolding process which have difficulties like pattern collapses or defects in case of precise replication process. In this manner, severe problems of demolding process in conventional mass production technologies can be efficiently overcome. To verify the usefulness of the proposed technique, polymer based micro mold inserts with several tens of micrometer sized structure for piezoelectric sensor applications were fabricated using X-ray micromachining process radiated synchrotron. The solubility of mold inserts were optimized by the second X-ray exposure without an X-ray mask and then subsequent powder injection molding process was utilized with a piezoelectric based material. Finally, piezoelectric ceramics with micrometer-scale and high aspect ratio of 5 were successfully fabricated, verifying that the present sacrificial mold system is useful for the precise replication process such as the fabrication of microstructure with high aspect ratio or complicated structure.     

High aspect ratio multi-level mold inserts fabricated by mechanical micro machining and deep etch X-ray lithography

 Complex microstructures can be fabricated in large quantities by thermoplastic molding processes. The shape of the microstructures is determined mainly by the mold insert. Until now, multi-level mold inserts have been fabricated either by deep etch X-ray lithography and electroforming, Harmening et al. (1992), or by milling of a brass substrate, Schaller et al. (1995). In both cases there are limitations on structuring either by the fabrication effort or by the sizes of the smallest available milling heads. To avoid these limitations on structuring, a new process for manufacturing multi-level mold inserts has been developed at Forschungszentrum Karlsruhe. Milling, drilling, deep etch X-ray lithography and electroforming have been combined to manufacture a mold insert which is characterized by high aspect ratios with small lateral dimensions and various level heights. Samples with two levels and an aspect ratio of 15 have been manufactured. Much higher aspect ratios seem to be achievable. This paper covers the fabrication process, first tests, and experimental results of manufacturing a multi-level mold insert for molding three-dimensional components of a microvalve system. Received: 30 October 1995 / Accepted: 17 January 1996     

High aspect ratio multi-level mold inserts fabricated by mechanical micro machining and deep etch X-ray lithography

Complex microstructures can be fabricated in large quantities by thermoplastic molding processes. The shape of the microstructures is determined mainly by the mold insert. Until now, multi-level mold inserts have been fabricated either by deep etch X-ray lithography and electroforming, Harmening et al. (1992), or by milling of a brass substrate, Schaller et al. (1995). In both cases there are limitations on structuring either by the fabrication effort or by the sizes of the smallest available milling heads. To avoid these limitations on structuring, a new process for manufacturing multi-level mold inserts has been developed at Forschungszentrum Karlsruhe. Milling, drilling, deep etch X-ray lithography and electroforming have been combined to manufacture a mold insert which is characterized by high aspect ratios with small lateral dimensions and various level heights. Samples with two levels and an aspect ratio of 15 have been manufactured. Much higher aspect ratios seem to be achievable. This paper covers the fabrication process, first tests, and experimental results of manufacturing a multi-level mold insert for molding three-dimensional components of a microvalve system. The development of this technology has been supported by the European Community as part of the Esprit project IMICS.     

Fabrication of high-aspect-ratio microscale mold inserts by parallel μEDM

The micro-electrical-discharge-machining (μEDM) technique is an alternative to LiGA (Lithographie, Galvanoformung, Abformung) for fabricating metal-based high-aspect-ratio microscale structures (HARMS). Traditional μEDM is a serial subtractive machining technique in which cuts are performed sequentially, and is therefore difficult to use for generating complex micropatterns on surfaces. In this paper, we report results of a hybrid microfabrication approach, combining micropattern definition with LiGA fabricated Ni HARMS with parallel micropattern generation with μEDM. Multiple micropatterns with some geometrical complexity were successfully generated in parallel on elemental Ta and 304 stainless steel. The hybrid LiGA/parallel-μEDM strategy offers a credible alternative to conventional LiGA regarding fabrication of meso- and micro- scale mold inserts, and enables them to be fabricated out of high-temperature metals/alloys not achievable with electrodeposition.     

Fabrication, Assembly, and Testing of Cu- and Al-Based Microchannel Heat Exchangers

Metal-based microchannel heat exchangers (MHEs) are of current interest due to the combination of high heat transfer performance and improved mechanical integrity. Efficient methods for fabrication and assembly of functional metal-based MHEs are essential to ensure the economic viability of such devices. In this paper, the results on fabrication, assembly, and heat transfer testing of Cu- and Al-based MHE prototypes are reported. Efficient fabrication of Cu- and Al-based high-aspect-ratio microscale structures (HARMSs) has been achieved through molding replication using surface-engineered metallic mold inserts. Replicated metallic HARMSs were assembled through eutectic bonding to form entirely Cu- and Al-based MHE prototypes, on which heat transfer tests were conducted to determine the average rate of heat transfer from electrically heated Cu blocks placed outside the MHEs to water flowing within the molding replicated microchannel arrays. Experimentally observed heat transfer rates are higher as compared to those from previous studies on microchannel devices with similar geometries. The potential influence of microchannel surface profile on heat transfer rates is discussed. The present results illustrate the potential of metal-based MHEs in wide-ranging applications.$hfill$[2007-0170]      

The lifetime comparison of Ni and Ni-PTFE moulding inserts with high aspect-ratio structure

Micro molding is the key process of LIGA (UV-LIGA) technique for low-cost mass production. It is difficult to demold for high aspect ratio of the structure fabricated by LIGA technique due to adhesion and friction force between the side-walls of the molding inserts and the thermoplastic material (PMMA). In this paper, the life times of the molding inserts made of Nickel (the material usually used for LIGA) and Ni-Teflon (PTFE) compound material are studied. The experiment shows the lifetime of Ni-PTFE molding insert is longer than the one of Ni for across pattern.This work was supported by the national High technology Research and Development Program of China (863 Program, No. 2002 AA404130), and National Natural Science Fundation of China (No. 10375058)     

Fabrication of High-Aspect-Ratio Electrode Arrays for Three-Dimensional Microbatteries

Silicon-micromachining techniques have been combined with conventional material-synthesis methods to develop microelectrodes for 3-D microbatteries. The resulting electrodes feature an organized array of high-aspect-ratio microscale posts fabricated on the current collector to increase their surface area and volume for a given footprint area of the device. The diameter of the posts ranges from a few micrometers to a few hundred micrometers, with aspect ratios as high as 50. The fabrication approach is based on micromolding of the electrode materials and subsequent etching of the mold to release the electrode structures. Deep reactive-ion-etching or photo-assisted anodic etching has been used to form an array of deep holes in the silicon mold. Electroplating or colloidal-processing method has been used to fill the mold with battery-electrode materials. Measurements on electrochemical half-cells indicated that the 3-D electrode arrays, which are composed of vanadium oxide nanorolls or carbon, exhibited much greater energy densities (per-footprint area) than that of the traditional 2-D electrode geometries. The use of electroplating enabled us to fabricate 3-D interdigitated arrays of nickel and zinc; and battery operation was demonstrated. [2006-0293].     

UV nano embossing for polymer nano structures with non-transparent mold insert

In recent years, UV nano embossing (or imprinting) process has been widely used for mass replication of nano structures. Most of the UV embossing machines use a UV transparent mold insert (e.g. quartz or glass). However, when a master of nano structures of interest could be realized only in a UV non-transparent mold material, it would be desirable to have a UV embossing machine which could be operated with such a UV non-transparent mold insert. In this regard, we have designed and manufactured a new UV embossing system in such a way that UV non-transparent (e.g., metal or ceramic) mold inserts can also be used as the master for the mass replication of nano structures. For the new UV embossing system, we fabricate several metal mold inserts: a nickel electroformed mold insert having grating nano structures and two AAO (anodic aluminum oxide) mold inserts having dimple nano structures and high-aspect-ratio nanopores. Finally, corresponding nano structures are successfully replicated via the UV nano embossing machine developed in this study.     

Micro-injection molding using a polymer coated mold

We applied an insulating polymer layer to the surface of mold cavity to injection-mold large plastic parts with a microsized thickness. Polyimide (PI) was coated on the mold wall using spray coating method. A thin light guide plate (LGP) was designed and fabricated via micro-injection molding. The polymeric coating layer could enhance the fluidity of polymer melt in the cavity during filling stage by minimizing the formation of the skin layer during injection molding. The surface roughness and pattern transfer rate of the LGPs were analyzed experimentally. In addition, numerical simulation was carried out to understand the insulation effect of the layer in the injection molding.

     

Rapid fabrication of microcomponents – UV-laser assisted prototyping, laser micro-machining of mold inserts and replication via photomolding

 The rapid fabrication of microcomponents made from polymers or composites will be presented. The whole fabrication process is divided into three main steps: first, direct patterning of polymers with excimer laser radiation enables the fabrication of first prototypes. Second, laser assisted micromachining using Nd:YAG or KrF-Excimer laser radiation allows a rapid manufacturing of microstructured mold inserts made of steel or polymer. Third, the application of UV-light-induced reaction injection molding (UV-RIM, photomolding) process using reactive monomer/polymer resins gives the access to the replication of the previously fabricated mold insert. For mold insert fabrication, the development of different process strategies is in progress in order to meet the best fit for three dimensional shapes (e.g., steep walls or slowly inclined walls). The development of mold inserts made of polymers is performed via UV laser ablation. This is a new promising method for the rapid manufacturing of microcomponents. Received: 10 August 2001/Accepted: 24 September 2001 We are grateful to our colleagues A. Sporrer and P. Severloh for her technical assistance in SEM/EDX. We also thank M. Blumhofer for his support in laser profilometry and H. Besser and W. Hoffmann for helpful discussions. This paper was presented at the Fourth International Workshop on High Aspect Ratio Microstructure Technology HARMST 2001 in June 2001.     

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.     

Replication of large scale micro pillar array with different diameters by micro injection molding

The capillary force is always used as the driving force of microfluidic chips. In this study, the capillary force of blood smart diagnostic microfluidic chip which fabricated by micro-injection molding (μ-IM) is offered by the structure of micro pillar array. And the detection effect of blood smart diagnostic microfluidic chips is affected by the replication and height distribution of large scale micro pillar array. So the effect of process parameters on the micro-structure and the height distribution of micro pillar is studied. The mold design is also an important factor affecting micro parts properties. In this study, a steel mold insert with almost 15,500 micro blind cavities was fabricated by milling, electrical discharge machine and Femtosecond Laser process. Polymethyl methacrylate -Polystyrene copolymer (SMMA NAS 30) was used as the molding material. The single factor trail and orthogonal experiment approach were adopted to investigate the effect of several process parameters and the significant effect factors affecting the replication of micro pillar. And the height distribution of micro pillar array was investigated by scanning electron microscope (SEM) and universal tool-measuring microscope to measure the replication quality. The results reveal that the replication of micro pillar is sensitive to the flow direction of the polymer melt. The height of micro pillar increases with the increase of mold temperature and injection speed. Moreover, the height distribution of micro pillar along and against flow direction was tightly related to the thermomechanical history of material during the molding process.