Micro-hot Embossing Research Articles

Effects of Different Backing Materials of Hybrid Rapid Tooling on the Demolding Time in the Hot Embossing Process

Fresnel lenses are becoming more and more important because they are widely used as optical elements for concentrating solar power. Micro-hot embossing is a promising approach to fabricate Fresnel lenses. Precision optical elements must be more quickly and cheaply introduced to the market due to the pressure of global competition. The thermal conductivity of Aluminum (Al)-filled epoxy resins is lower than that of conventional mold steel materials. This work demonstrates a technique for fabricating hybrid rapid tooling with different backing materials to investigate the demolding efficiency in the hot embossing process. It was found that the Al was strongly recommend as backing material for fabricating hybrid rapid tooling due to cost, demolding time efficiency and dimensional accuracy of the embossed parts. Demolding efficiencies for the hot embossing mold with backing materials of copper, aluminum and steel about 78 %, 68 % and 50 % can be enhanced compared to that of the conventional rapid tooling. The replication rate exceeding 96 % in the hot embossing mold manufacturing process can be reached. The transcription rate exceeding 93 % in the hot embossing process can be obtained.DOI: http://dx.doi.org/10.5755/j01.ms.24.3.13897

Development of a precision hot embossing tool with microstructures for microfabrication

Hot embossing molding is a promising method to fulfill fabrication of microstructures. The surface flatness of a hot embossing tool is the key parameter affecting the transcription rate significantly of the micro-hot embossing process. This study demonstrated a technology for fabricating a precision hot embossing tool using hybrid materials. The silicone rubber mold was chosen as a bridge tooling, which is the key process for fabricating a precision hot embossing tool using hybrid materials. The mold plate can improve the surface flatness of the fabricated hot embossing tool during post-curing. The surface flatness of the hot embossing tool around 46.38% can be improved and a cost reduction around 69.61% can be achieved.

Development and Application of Hybrid Mold with Microfeatures in Micro-Hot Embossing

Micro-hot embossing is a highly effective process for fabricating microdevices with microfeatures in polymeric materials. One of the most troublesome problems in precision machinery industry is the time and expense needed to produce a mold for microreplication. This study presents an approach of manufacturing a hybrid mold with microfeatures that is fast, cost-effective, and easy to produce. A precision second silicone rubber mold is a key technology for fabricating a precision hybrid mold with microfeatures in the proposed optimal manufacturing process. Aluminum 6061 alloy was chosen as a backing mold plate in the hybrid mold for reducing the manufacturing cost and improved the thermal conductivity of epoxy resin composites. A hybrid mold was equipped with conformal cooling channels to reduce the cycle time in the micro-hot embossing cycles. The developed hybrid mold can be used to fabricate precision micro-optical components using micro-hot embossing molding.

Micro-Hot Embossing of Fresnel Lens Using Precision Micro-Featured Mold

Micro-hot embossing process has been widely used in the micromanufacturing. Development of a simple and cost-effective method for fabricating the micro-featured mold insert for micro-hot embossing molding is an important issue. Several techniques such as Si-based micromachining technology, lithographie galvanoformung abformung (LIGA), laser micromachining, micro-electro-discharge machining, micromachining, and deep reactive ion etching have been proposed for fabricating the micro-featured mold insert. However, these methods have some limitations including high cost, complex manufacturing processes, and long processing time. In this study, a simple and cost-effective method for fabricating micro-featured mold with micro-features for microfabrication of polymer was proposed. Effects of micro-hot embossing process parameters on the embossed accuracy of microfeatures were investigated. Results showed that the embossed accuracy of microgroove depth and width increased with both the embossing load and embossing temperature until a saturation value is reached. Based on both cycle time and green manufacturing, an approximately perfect Fresnel lens can be replicated under the embossing load of 50 Kgf and the embossing temperature of 170°C.

A cost‐effective method to fabricate micro‐featured mold for microstructures replication

AbstractThis study demonstrated a method for manufacturing a micro‐featured mold insert of Fresnel lens. The transcription rate of this process is about 92.5%. A plastic Fresnel lens was fabricated using micro‐hot embossing process. The transcription rate of the embossed part is about 95.1%. The micro‐featured mold insert not only reduces the fabrication cost, but has higher form accuracy as well. In comparison with conventional method for fabricating a pair of mold insert, a cost reduction of 60.4% can be achieved using the hybrid method proposed in this study.

Effect of polymer orientation on pattern replication in a micro-hot embossing process: experiments and numerical simulation

The hot embossing process has been identified as a promising technique for fabricating micro- and nanostructures for polymer-based biological and chemical MEMS (micro electro mechanical systems). However, there has not been any investigation of the effect of polymer chain orientation in the base polymer substrate on replication during the micro-embossing process. Such effects could prove important because polymer chain orientation may develop in the polymer substrates during their production. In this investigation, it was observed that the degree and ease of microchannel replication are significantly influenced by the molecular chain orientation in injection-molded polymer substrates. Microchannels aligned along the flow direction of the polymer replicate easily compared to microchannels aligned across the flow direction of the polymer. The replication fidelity during hot embossing was investigated using a white-light confocal microscope. The anisotropy of injection-molded polymer plays a dominant role in the replication fidelity of microchannels, and the ability to model the anisotropic behavior of the material will enable understanding and prediction of the hot embossing process. Therefore, a material model that reflects the directionality was utilized to simulate the experimental embossing results obtained both along and across the flow direction of the polymer. By comparing experimental results with simulations, we observed that the model is reasonably realistic.

Development and Study of Applications Combining Nanopowder Imprint Lithography and Array-Type UV-Curing Technology for Micro-Lens Molding

This study developed creative imprinting technology, combining nano-imprint lithography and array-type UV-curing technology. It used nanopowders as the method to transmit imprint force, and integrated technical features, such as soft lithography, light-curing resistant and gas-assisted imprint technology, in order to study the development of technological processes of micro-lens array manufacturing, and mature the application and technology of nano-imprinting. According to research results, SUS 304 stainless steel sheet with a micro-hole array could be smoothly fabricated into an original micro-lens array mold upon gas-assisted micro-hot embossing. At the same time, a micro-lens array structure with a complementary external form could be precisely remolded and reproduced by PDMS. Complete molding of micro-lens could be effectively achieved by combining imprints of gas-assisted lithography developed in this study, and even UV-NIL. The effective imprinting area and reproducibility of transfer printing could be greatly improved when a micro-lens contacts perfectly with a substrate surface. Moreover, since PDMS soft molds have short remolding times, and are easily feathered during manufacturing, production costs could be effectively reduced through features such as, low surface free energy, resistant to adhering to the mold during imprinting, and collocation of gas-assisted nanopowder imprinting of micro-structural processes.

Manufacturing of an aluminum alloy mold for micro-hot embossing of polymeric micro-devices

In micro-hot embossing of polymeric micro-devices, e.g. microfluidic devices, the quality of the mold plays an important role in determining not only the product quality but also the overall production cost. Often the mold is made of silicon, which is brittle and fails after producing a limited number of parts. Metallic molds produced by micro-machining have a much longer life; however, the surface finish of the mold is not ideal for producing polymeric devices that require good surface finish. The metallic glass mold produced by micro-hot embossing with a silicon master is a recent development, which could produce high quality and high strength molds with long life span. However, metallic glasses are rather costly. In an attempt to reduce the production cost of the mold with acceptable quality, strength and life span, we explore here the manufacture of an aluminum alloy (AA6061-T6) mold by hot embossing using a silicon master. Using a set of channels to be produced on the aluminum alloy as the benchmark, we examine the orientation effect of the channels on the AA6061-T6 mold produced by hot embossing. Finally, to examine the effectiveness of the AA6061-T6 mold, it is employed for the hot embossing of polymeric (TOPAS 8007) substrates.

Structural and microfluidic analysis of hollow side-open polymeric microneedles for transdermal drug delivery applications

In this paper, we present a new design of hollow, out-of-plane polymeric microneedle with cylindrical side-open holes for transdermal drug delivery (TDD) applications. A detailed literature review of existing designs and analysis work on microneedles is first presented to provide a comprehensive reference for researchers working on design and development of micro-electromechanical system (MEMS)-based microneedles and a source for those outside the field who wish to select the best available microneedle design for a specific drug delivery or biomedical application. Then, the performance of the proposed new design of microneedles is numerically characterized in terms of microneedle strength and flow rate at applied inlet pressures. All the previous designs of hollow microneedles have side-open holes in the lumen section with no integrated reservoir on the same chip. We have proposed a new design with side-open holes in the conical section to ensure drug delivery on skin insertion. Furthermore, the present design has an integrated drug reservoir on the back side of the microneedles. Since MEMS-based, hollow, side-open polymeric microneedles with integrated reservoir is a new research area, there is a notable lack of applicable mathematical models to analytically predict structural and fluid flow under various boundary conditions. That is why, finite element (FE) and computational fluid dynamic (CFD) analysis using ANSYS rather than analytical systems has been used to facilitate design optimization before fabrication. The analysis has involved simulation of structural and CFD analysis on three-dimensional model of microneedle array. The effect of axial and transverse loading on the microneedle during skin insertion is investigated in the stress analysis. The analysis predicts that the resultant stresses due to applied bending and axial loads are in the safe range below the yield strength of the material for the proposed design of the microneedles. In CFD analysis, fluid flow rate and pressure drop in the microneedles at applied inlet pressures are numerically and theoretically investigated. The CFD analysis predicts uniform flow through the microneedle array for each microneedle. Theoretical and numerical results for the flow rate and pressure drop are in close agreement with each other, thereby validating the CFD analysis. For the proposed design of microneedles, feasible fabrication techniques such as micro-hot embossing and ultraviolet excimer laser methods are proposed. The results of the present theoretical study provide valuable benchmark and prediction data to fabricate optimized designs of the polymeric, hollow microneedles, which can be successfully integrated with other microfluidic devices for TDD applications.

Development of ultrasonic micro hot embossing technology

We succeeded in precise replication of patterns by impressing ultrasonic vibration besides heat and the loading force on the micro hot embossing (MHE). A Ni electroformed mold with micro patterns with seven sizes of entrance from 100 μm 2 to 1.2 mm 2 was used. The experiment was executed on a polycarbonate (PC) sheet while impressing longitudinal wave of ultrasonic vibration at maximum amplitude of 1.8 μm. The effect that bubble defect in the pattern was diminished or completely disappeared was observed by impressing ultrasonic vibration. Moreover, it was clarified that ultrasonic vibration assisted softened PC to move to the center of the pattern area in a mold. We found that the effect of ultrasonic vibration was well pronounced at low contact force. Perhaps very high contact force may be obstructing the progression of ultrasonic vibration.

Multi-layer microstructure fabrication by combining bulk silicon micromachining and UV-LIGA technology

A novel method for fabrication of multi-layer microstructures of microelectro-mechanical system (MEMS) devices is described. This technique, which combines bulk silicon micromachining technique and UV-LIGA technique can overcome some shape limitations of single technique on complex microstructures. To demonstrate this combination, the SU-8 microstructure fabricated in the etched silicon grooves is presented. In this fabrication process, a SU-8 removal method by fuming sulfuric acid was introduced and a novel type of plastics PETG was tried in microhot embossing process. The proposed fabrication process can be applied to fabricating a high-aspect-ratio microstructure for a large displacement actuator and precision sensors. Moreover, this combined process enables the fabrication of more complex structures, which cannot be fabricated by bulk micromachining or UV-LIGA alone.

研削加工によるカーボン型を用いたガラス材料の大面積マイクロ成形

研削加工によるカーボン型を用いたガラス材料の大面積マイクロ成形

Micro Hot Embossing for Replication of Microstructures

This paper reports the development of a micro-hot embossing process for high-quality microstructure transfer from molds to polymer materials. Polycarbonate was selected as the structural material. Replications of rectangular reflecting mirrors with dimensions of 500 µm (L) × 100 µm (W) × 220 µm (H) were performed. To replicate such microstructures with vertical sidewall surfaces, a combination of temperature of 185°C and pressure of 1.7 kg/mm2 was necessary. The finished vertical surfaces were sufficiently smooth to be used in an optical switch as reflection mirrors. Replications of micro V-grooves and microlens cavities for passive alignment of optical fibers and microlenses were carried out as well. It can be concluded that a combination of embossing temperature above 175°C and applied pressure above 5 kg/mm2 is necessary to achieve a perfect replication of such microstructures with tapered surfaces. The executive results of this research demonstrated that micro hot embossing is a promising technology for fabricating high precision microstructures with polymer materials and allows the low-cost production of microcomponents.