4M Knowledge base - papers

Characterization of polymers for improved shrinkage prediction in micromolding.

M.H.E. van der Beek (a), G.W.M. Peters (b), H.E.H. Meijer (b)
a Department of Design & Manufacturing, TNO Science and Industry, Eindhoven 5600 HE, the Netherlands
b Department of Materials Technology, Eindhoven University of Technology, Eindhoven, 5600 MB, the Netherlands

Abstract

The (bulk) specific volume of polymers is one of the main material properties determining the dimensional accuracy of polymer products, i.e. product shrinkage and warpage. Shrinkage can cause considerable problems in the replication of microstructures (e.g. crack-formation, misalignment), during ejection of the product (e.g product shrinkage around mold features), and in back-end processes (e.g. mismatch in the dimensions of parts during assembly). This explains the importance of specific volume data for use in simulations for mold design and process optimization. In micro molding, the polymer is subjected to high cooling rates and high shear rates because of the small dimensions and the relatively large surface to volume ratio of micro features. These processing parameters are known to influence the specific volume of the polymer. However, standard experimental techniques to measure the specific volume of polymers only take the influence of temperature and pressure into account (PVT-behavior) and are known to lead to large deviations in the prediction of shrinkage, dependent on processing conditions. In this study we present a custom designed dilatometer to measure quantitatively the specific volume of semi-crystalline polymers for an unusual combined wide range of cooling rates, elevated pressures, and shear rates, covering (micro)molding conditions, i.e. cooling rates up to 35 C/s, pressures up to 60 MPa, and shear rates up to 80 1/s. This new approach of measuring specific volume gives better understanding of the volumetric changes occurring in the polymer during molding and if used as input for processing simulation software will lead to improved shrinkage and warpage predictions.

Submitted on May 19, 2008 - 14:17.

Characterization of Pulses in Micro EDM Milling Based on Wear and Material Removal

G. Bissacco(a), J. Valentincic(b), B.D. Wiwe(a), H.N. Hansen(a)
a: Department of Manufacturing Engineering and Management (IPL), Technical University of Denmark (DTU), Produktionstorvet 2800 Kgs. Lyngby, Denmark
b: Laboratory for Alternative Technologies, Faculty of Mechanical Engineering, University of Ljubljana

Abstract

This paper presents an investigation on wear and material removal in micro EDM milling for selected process parameters combinations typical of rough and finish machining of micro features in steel using state of the art equipment. Based on discharge counting and volume measurements, electrode wear unit and material removal unit are measured for several energy levels. The influence of the accuracy of volume measurements on the electrode wear unit and material removal unit are discussed and the issues limiting the applicability of real time wear sensing in micro EDM milling are presented.

Submitted on November 12, 2007 - 16:23.

Chemical Bonds of Nanoscale Materials – Reasons for Various Applications

Iovka Dragieva
Bulgarian Academy of Sciences, Inst. Electrochem. Energy Systems, 10, Ac. G. Bonchev Str., 1113 Sofia, Bulgaria

Submitted on November 12, 2007 - 16:23.

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Applications

Concept for Fluidic Self-Assembly of Micro-Parts Using Electro-Static Forces

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.

Submitted on July 30, 2008 - 10:36.

Concept for Packaging of a Silicon based Biochip

T. Velten (a), M. Biehl (a), T. Knoll (a), W. Haberer (a)
(a) Fraunhofer Institute for Biomedical Engineering, Ensheimer Strasse 48, 66386 Sankt Ingbert, Germany

Abstract

We report on a concept for packaging of a silicon-based biochip for integration with a fluidic cartridge, thus forming a lab-on-chip (LOC). The biochip, which has dimensions of 2 mm x 2 mm, comprises a central membrane having a diameter of 200 μm, and 20 bond pads with metal tracks leading to the membrane. The packaged biochip provides a fluidic interface to the cartridge as well as electrical interfaces to the biochip electronics being located in a readout instrument. The packaging method ensures the strict separation between the wet sensing area and the electrical contacts. The challenge is that the biochip has a freely moving membrane, additionally with a delicate biological coating, and this membrane is positioned on the same side of the silicon chip as the bond pads for the electrical interconnection. For packaging, the biochip is mounted into a recess of a rigid printed circuit board (PCB). The biochip is electrically connected with the PCB using a proprietary MicroFlex interconnection (MFI) technology, thus resulting in a flat surface towards the reaction chamber of the fluid cartridge. After the realization of the electrical contacts between the sensor chip and the PCB, the entire chip is encapsulated with an epoxy layer, leaving the membrane of the biochip uncovered. To protect the membrane against the fluidic epoxy, a specially shaped silicone casting-mould is used. In a last step, the biochip with the epoxy layer is glued on the bottom side of the cartridge.

Submitted on July 29, 2008 - 15:41.

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