4M Knowledge base - papers

S. Geißdörfer, U. Engel, M. Geiger
Chair of Manufacturing Technology, University of Erlangen-Nuremberg, 91058 Erlangen, Egerlandstr. 11, Germany

Abstract

At microscale, the large ratio between mean grain size of the material and specimen dimension cause an increasing influence of single grain forming behaviour on the overall forming process. Thus the forming behaviour of these parts can no longer be regarded as to be homogeneous. This leads to a change in the material behaviour resulting in a large scatter of forming results, e.g. varying cup height in a cup backward extrusion process or varying spring-back angles in a micro bending process. Moreover, some correlation between the integral flow stress of the workpiece and the scatter of the process factors on the one hand and the mean grain size and its standard deviation on the other hand has been detected in experiments. Conventional FE-simulation which is by its nature size independent, is not able to consider these effects observed when scaling down processes, in particular represented by a reduction of the flow stress, an increasing scatter of the process factors and a local material flow being different to that obtained in the case of macro parts. Therefore, a new simulation model is being developed in order to take into account the identified effects and to determine the scatter of the process factors. The so-called mesoscopic model provides the discretisation of the simulated material into individual objects which represents the grain structure of the real material. To each object an individual flow curve is assigned, calculated on the basis of metal physics given by Hall-Petch and Ashby’s theory. The computational grain structure generation is based on the theory of a Monte Carlo Potts growth law.

The present paper deals with the theoretical background of the new mesoscopic model, its characteristics like synthetic grain structure generation and the calculation of micro material properties - based on conventional material properties. The verification of the simulation model is done by carrying out various experiments with different mean grain sizes and grain structures but the same geometrical dimensions of the workpiece.

J. Dalin (a), J. Wilde (a), A. Synodinos (b), P. Lazarou (b)and N. Aspragathos (b)

(a) University of Freiburg – IMTEK, Department of Microsystems Engineering, Georges-Köhler Allee 103, 79110, Freiburg, Germany, contact: Johan.Dalin@imtek.uni-freiburg.de
(b) Robotics Group, Department of Mechanical Engineering and Aeronautics, University of Patras, Greece, contact: Lazarou@mech.upatras.gr

Abstract

Self-assembly is relatively unused in industrial micro-fabrication, although it offers opportunities to simplify processes and to lower manufacturing costs. A variety of self-assembly procedures have been introduced that take advantage of various forces, e.g. capillary, gravitational, electro-static. In this paper a concept for the alignment of micro-parts on a substrate using fluidic-self-assembly with electro-static attraction is presented. Further, FEM-simulations for the electro-static alignment force are performed and its dependence on several geometric parameters, e.g. the width of the binding sites and the distance between micro-part and substrate at the binding sites, is investigated. Based on results an analytic model is extracted. Furthermore, simulations are also performed to estimate capillary alignment forces, acting on micro-parts that are self-aligned. Finally, the magnitude of electro-static and capillary forces is compared. This novel assembly concept, where the alignment of the component at the binding site is achieved due to electro-static energy minimisation and, optionally, in combination with capillary alignment, could be beneficial in the manufacturing of heterogeneously integrated MEMS, such as optical and RF micro-systems.

P. Lazarou (a), N.A. Aspragathos (a), E. Jung (b)

(a) Robotics Group, Department of Mechanical Engineering and Aeronautics, University of Patras, Patras T.K. 26500, Greece
(b) Chip Interconnection Technologies, Fraunhofer IZM Berlin, Germany

Abstract

Micromanipulation is a very important issue in several fields of technology (microelectronics, optoelectronics & MEMS device packaging). Current implementations do not provide both sub-micron accuracy and movement of parts over centimeter-scale to a ~100μm final alignment precision. A micropart-inside-a-liquid-droplet manipulation concept that manages to bridge the gap from meso via the micro to the sub-micron scale in a fully contained process has been previously introduced by integrating the phenomena of electrowetting, dielectrophoresis and fluidic self-assembly. In this paper, an investigation of the electric fields that drive the manipulation of the droplet and micropart during the stages of electrowettng and dielectrophoresis is presented. Information for critical factors such as electrostatic force, Maxwell stress and surface charge density distribution is provided. Their effect on the manipulation process is verified, in accordance to theory.

P.J. Bolt, J.E. Bullema, R. Korbee, R. Kusters
TNO Science and Industry, Eindhoven, The Netherlands

Abstract

This paper concerns the feasibility of polymer capping of RF-MEMS devices, replacing traditional silicon solutions. The advantage would be less costs and potential for both further miniaturisation and integration of electrical functions in the cap. One of the challenges is the resistance against expoxy overmoulding as part of the traditional back-end process chain. This involves temperatures of 175oC and pressures of 10MPa, which the cap has to withstand. Calculations are made and experiments carried out to investigate the feasibility of selected polymers. It is shown that nanofillers will lift the polymers mechanical properties comfortably above the minimum established demands.

G. Tosello (a), A. Schoth (b), H.N. Hansen (a)

(a) Technical University of Denmark (DTU), Department of Mechanical Engineering, Produktionstorvet, Building 427S, DK-2800 Kgs. Lyngby, Denmark
(b) Laboratory for Process Technology, Department of Microsystems Engineering (IMTEK), University of Freiburg, George-Koehler-Allee 103,79110 Freiburg, Germany

Abstract

In polymer micro manufacturing technology, software simulation tools adapted from conventional injection moulding can provide useful assistance for the optimization of moulding tools, mould inserts, micro component design, and process parameters. Conventional implementation methods of simulation are not suitable for micro injection (μIM) application and are limiting the possibility to extend the use of existing packages for the modelling and the simulation of polymer micro parts. Different strategies optimized for the set-up the simulation of a miniaturized part with micro features are presented. Model design and mesh issues are discussed, as well as dynamic implementation of the flow constrains for the creation of an effective interface between the machine and the polymer flow in the simulation software. The results of the different methods are evaluated by means of a quantitative study which compares the simulated results and the actual micro injection moulding experiments.