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.     

Application of the inclined exposure and molding process to fabricate a micro beam-splitter with nanometer roughness

This paper successfully used inclined exposure technology to fabricate a wafer-level 3D micro cube beam splitter with a 45° optical grade surface (~1.4 mm thick). This research also tests the effect of solvent loss percentage of the SU-8 3035 polymer material (85.45 % solvent removal) to optimum surface roughness on the surface roughness of inclined surfaces. The smallest surface roughness achieved in the experiments using SU-8 3035 material with a thickness of 1.4 mm was less than 34 nm (400 × 400 μm area). And the reflective surface roughness of the molding cube beam-splitter is below 2 nm. The optical power of the fabricated cube beam splitter is about 60.55 and 39.44 % for transmission and reflection, respectively. This type of micro cube beam-splitter can be used as a key component in Pico-projectors, Interferometers, bio detection systems, data storage systems, and linear encoder optic systems. And this novel technology also has the characteristics of high throughput and wafer-level assembly.     

A novel approach to realize the local precise variotherm process in micro injection molding

Variotherm is special mould temperature controlling concept which realizes the rapid heating/cooling of mould during material processing in order to extend the freezing time of materials. A novel variotherm concept based on silicon wafer combined with micro electric resistance heating structures is purposed and prototyped in this study. The manufacture process of this variotherm unit was introduced and its heating/cooling performance was tested and analyzed by thermal graphic method, which indicate that the new variotherm concept has excellent thermal control efficiency and precise temperature distributions.     

Fabrication of micro gear by micro powder injection molding

Micro components made from polymers can be easily processed but they may not be suitable for all applications. One example is where good mechanical properties are required. Thus, the fabrication of micro components from non-polymeric materials such as metals and ceramics is essential. In this paper, the fabrication of 316L stainless steel micro gear by micro powder injection molding is reported. The specifications of the green micro gear were: 10 teeth, module of 0.08, outer diameter of 1 mm and a length of 1 mm. Injection molding was conducted on a conventional injection molding machine with a small screw diameter of 14 mm. The green micro gear was well replicated. The debound micro gear retained its shape and the teeth were well defined. After sintering, the shape was also retained but with some surface irregularities. The process differences between μPIM and PIM, such as the use of smaller particle size and higher mold temperature are also highlighted.     

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.

     

Analysis of demolding in micro metal injection molding

In this paper micro metal injection molding (μMIM) is being studied to produce 316L stainless steel microstructures. Experimental work showed that demolding failure was a serious hindrance to the success of μMIM as a suitable technology to produce small microstructures. Thus, a theoretical analysis of microstructure demolding in μMIM is needed in order to understand the demolding behavior theoretically and how to avoid demolding failure in μMIM. In this paper, theoretical analysis of the demolding of 24×24 (totally 576) microstructures was conducted with the help of Abaqus finite element analysis software. The analysis was involved in two factors that possibly lead to demolding failure: one is the shear stress during ejection of the microstructure due to contact pressure between the microstructure and the microcavity, the other is thermally-induced stress due to cooling of the microstructure. The analysis shows that the following factors have significant influence on the demolding: aspect ratios of the microstructure, the coefficient of friction between the microstructure and the microcavity, demolding temperature and holding pressure. And the microstructure that is farther away from the centerline of the round part with microstructures undergoes higher stress and more easily subject to breakage. The moment when the microstructure is the most possibly subject to breakage during demolding is always the onset of ejection.     

Adaptive control of the filling velocity of thermoplastics injection molding

Injection velocity, a key variable in injection molding, was controlled via an adaptive controller using a self-tuning regulator (STR) scheme. The pole-placement design was employed first, together with the performance enhancement techniques of anti-windup estimation, feed-forward control, and cycle-to-cycle adaptation. The pole-placement design with the enhancement techniques was found experimentally to work very well over different molding conditions. However, this design was also found to be sensitive to the model mismatch. To overcome this problem, a new adaptive controller based on a generalized predictive control (GPC) principle was designed to make the controller more robust. Experiments have shown that the adaptive GPC control of injection velocity has inherently good set-point tracking performance and excellent tolerance to model structure mismatch.     

Performance and simulation of thermoplastic micro injection molding

 Originally developed for the replication of high aspect ratio LIGA structures, micro injection molding is presently on its way to become an established manufacturing process. Enhanced technological products like micro optical devices are entering the market. New developments like the different kinds of injection molding with several components open up opportunities for increasing economic efficiency as well as for new fields of applications. Software tools for the simulation of the thermal household of the molding tool and/or the moldfilling process itself can provide useful but not wholly sufficient assistance for the optimization of micro injection molding. Received: 10 August 2001/Accepted: 24 September 2001     

Dimensional measurement of micro mechanical components with HAR

This paper describes a new type of interferometer which may be used for 2D and 3D surface profiling of optically rough surfaces. The system uses a wide band, low coherence light for this purpose. The brightness of the interference fringes falls from a peak to zero on profile amplitude differences which are greater than the coherence length of the light used. The brightness variations within the interference packet are digitally signal processed to extract surface position information. In addition a surface measurement system based around an autofocus sensor will be described.     

Dimensional measurement of micro mechanical components with HAR

This paper describes a new type of interferometer which may be used for 2D and 3D surface profiling of optically rough surfaces. The system uses a wide band, low coherence light for this purpose. The brightness of the interference fringes falls from a peak to zero on profile amplitude differences which are greater than the coherence length of the light used. The brightness variations within the interference packer are digitally signal processed to extract surface position information. In addition a surface measurement system based around an autofocus sensor will be described.     

Micromachining of buried micro channels in silicon

A new method for the fabrication of micro structures for fluidic applications, such as channels, cavities, and connector holes in the bulk of silicon wafers, called buried channel technology (BCT), is presented in this paper. The micro structures are constructed by trench etching, coating of the sidewalls of the trench, removal of the coating at the bottom of the trench, and etching into the bulk of the silicon substrate. The structures can be sealed by deposition of a suitable layer that closes the trench. BCT is a process that can be used to fabricate complete micro channels in a single wafer with only one lithographic mask and processing on one side of the wafer, without the need for assembly and bonding. The process leaves a substrate surface with little topography, which easily allows further processing, such as the integration of electronic circuits or solid-state sensors. The essential features of the technology, as well as design rules and feasible process schemes, will be demonstrated on examples from the field of μ-fluidics     

Three-dimensional finite element method for the filling simulation of injection molding

With the development of molding techniques, molded parts have more complex and larger geometry with nonuniform thickness. In this case, the velocity and the variation of parameters in the gapwise direction are considerable and cannot be neglected. A three-dimensional (3D) simulation model can predict the filling process more accurately than a 2.5D model based on the Hele–Shaw approximation. This paper gives a mathematical model and numeric method based on 3D model to perform more accurate simulations of a fully flow. The model employs an equal-order velocity–pressure interpolation method. The relation between velocity and pressure is obtained from the discretized momentum equations in order to derive the pressure equation. A 3D control volume scheme is used to track the flow front. During calculating the temperature field, the influence of convection items in three directions is considered. The software based on this 3D model can calculate the pressure field, velocity field and temperature field in filling process. The validity of the model has been tested through the analysis of the flow in cavities.     

Automation of the powder injection molding process

Powder injection molding (PIM) offers a high potential for fabrication of micro-mechanical parts manufactured in metal or ceramic material providing a large variety of properties. To ensure an economical micro-PIM production in large lot sizes and high quality automation of the process beginning with demolding, handling, debinding and ending with sintering is a necessity. Within the field of automation research focus is to optimize critical processes like sprue separation, demolding and handling as well as the set-up of an autonomous and automated process-chain which are presented in this article.This work is based upon the Collaborative Research Centre SFB 499 funded by the German Research Foundation (DFG)     

A visual mold with variotherm system for weld line study in micro injection molding

In order to study the weld line developing process and its influence on mechanical properties in micro injection molding, a visual mold with variotherm system mold was designed and fabricated. In this mold, a visualization design and a rapid heating/cooling system were integrated, and specimens with different cross section shape and micro dimensions could be molded for weld line study. The building process for the visual and variotherm mold was presented and the experiments were executed. The specimens for weld line study of micro injection molding were produced applying different processing parameters. A problem of flash in molded specimens needs to be solved.     

Fabrication of the plastic component for photonic crystal using micro injection molding

In this decade, many techniques have been introduced to fabricate photonic crystal in optical applications. Most of the processes used to fabricate the photonic crystal are time consuming and not cost effective. This study demonstrates an efficient method to fabricate photonic crystals. A polymer-based photonic crystal slab has been developed by embedding mixture with a high dielectric constant. Photonic crystals have patterned structures in which periodicity of dielectric properties can manipulate electromagnetic waves. The operation wavelength is about half of the characteristic dimension. Technique of injection molding is applied to make polymer parts with the photonic crystal pattern. Then mixture of barium titanate powder and epoxy is embedded on the patterned structure of the polymer part. The contrast of dielectric coefficients between mixture and polymer can constitute a structure with some photonic band gap. By means of polymer processing, mass production of photonic crystal devices like optical switch, optical waveguide, optical filter and so forth can be realized in a cost effective way.     

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.     

Micro molding for double-sided micro structuring of SU-8 resist

Advances in micro and nano fabrication technologies for MEMS require high-level measurement techniques with regard to sampling and sensitivity. For this purpose at the Institute of Microtechnology (IMT) highly sensitive piezoresistive 3D force sensors based on SU-8 polymer have been developed. In this paper we present an improved micro fabrication process for a double-sided micro structured design. The sensors are produced by multilayer processing techniques such as UV lithography and coating methods. The double-sided micro structured design demands a photoresist application method which simultaneously features a top side structuring and a casting from a mold. We use a new micro molding process to meet the demands. The micro fabrication technology is described, focusing on the development of the molding structure for shaping of the bottom side and a capable release process for the detachment of the molded structures. The fabrication process of the SU-8 mold layer is optimized to fabricate molding structures with heights from a few μm up to 350 μm. Therefore different SU-8 formulations, namely with classification numbers 5, 25, 50, and 100, have been used. The fundamental limitations for the mold design result from the lithography process, which defines the smallest lateral resolution, and from the characteristics of a molding process, e.g. the impossibility to realize an undercut. To allow for reliable release, the molding structures have to be coated with a sacrificial layer. Silicon nitride is deposited onto the substrate with accompanying monitoring of the deposition temperature during the PECVD process.