Multi Material Micro Manufacture Network of Excellence - polymers

Micro injection moulding: an experimental study on the relationship between the filling of micro parts and runner designs

Mon, 04 Aug 2008 13:10:07 +0000

C.A. Griffiths, S.S. Dimov, E.B. Brousseau
Manufacturing Engineering Centre, Cardiff University, CF24 3AA, UK

Abstract

To increase productivity and thus reduce the unit cost, often micro moulding tools incorporate multiple cavities. For this a runner design must be selected, the main function of the runner system is to facilitate the flow of molten material from the injection nozzle into the mould cavity. Therefore, the micro injection filling process depends on the optimum design of runner systems. In this context, the paper reports an experimental study that investigates the flow behaviour of the polymer melts in micro cavities with a particular focus on the relationship between the filling of micro parts and the size of the runner system. In particular, the runner size effects on the micro injection moulding process were investigated. The filling performance of spiral-like micro cavities was studied as a function of runner size in combination with melt temperature, mould temperature, injection speed and holding pressure time employing the design of experiment approach. In addition, the results were analysed further to identify the effects of the runner

Machining of polystyrene by UV laser radiation for patch clamping device fabrication

Wed, 30 Jul 2008 12:34:35 +0000

S. Wilson (a),(b), W.Pfleging (c), A. Welle (d), P.Kirby (b), M.Przylbyski (e)

(a) Institute for Microstructure Technology, Forschungszentrum Karlsruhe, 76344 Eggenstein-L, DE
(b) School of Applied Sciences., Cranfield University, Cranfield, Beds. MK43 0AL, UK
(c) Institute for Materials Research 1, Forschungszentrum Karlsruhe, 76344 Eggenstein-L, DE
(d) Institute for Biological Interfaces, Forschungszentrum Karlsruhe, 76344 Eggenstein-L, DE
(e) ATL Lasertechnik GmbH, Burger Str. 48, 42929 Wermelskirchen, Germany

Abstract

Laser patterning is of interest for MST applications; direct ablation of polymer material for generating 2D and 3D shapes such as microfluidic channels, curved shapes or micro-holes and alternatively photo-induced change of chemical or physical surface properties. Correct laser choice and process parameters enables new approaches for the fabrication of lab-on-chip devices with integrated functionalities. Laser-assisted ablation and modification of polystyrene (PS) is introduced with respect to the fabrication of polymer devices for high throughput planar patch clamping - a method of measuring the electrical activity of a cell currently a focus for high throughput systems (HTS). There are currently no marketed systems using novel materials that have surface modifications for either individual cell placement, or for dealing with cell networks, a physiologically important consideration for tissue engineering and understanding cell to cell interactions.
Within 4M, a design jointly proposed by FZK and Cranfield University for the fabrication of a polymer patch clamping system, laser micro-drilling of PS and subsequent surface functionalisation for cell adhesion has been investigated as a function of laser and process parameters. High power ArF laser with a pulse of 20 ns as well as high repetition ArF excimer laser sources with pulse lengths of 4-6 ns were used in order to study the influence of laser pulse length on laser drilling and laser induced surface modification. Micro-drilling of PS with diameters down to 1.5 μm have been demonstrated. Furthermore, localized formation of chemical structures suitable for improved single cell and cell network adhesion has been achieved on PS surfaces.

Batch Fabrication Methods for Polymer Based Active Microsystems using Hot Embossing and Transfer Bonding Technologies

Tue, 29 Jul 2008 11:51:28 +0000

T. Grund, M. Heckele and M. Kohl
Forschungszentrum Karlsruhe GmbH, Institute for Microstructure Technology (IMT),Postfach 3640, 76021 Karlsruhe, Germany

Abstract

A batch compatible process flow to overcome the costly piece by piece assembly of hybrid microsystems is shown. Hot embossing is used to fabricate microstructured polymer layers. Wafer scale compatible bonding tasks are carried out by ultrasonic welding and heat activated bonding with micromachined bonding foils. As demonstrator device, a shape memory alloy (SMA) actuated polymer microvalve is introduced. The valve concept, fabrication technologies and device characteristics are discussed.

Micro-machining of Metals, Ceramics and Polymers using Nanosecond Lasers

Tue, 20 May 2008 09:34:50 +0000

M.R.H Knowles, G. Rutterford, D. Karnakis, A. Ferguson
Oxford Lasers Ltd, Unit 8, Moorbrook Park, Didcot, OX11 7HP, UK

Abstract

Laser micro-processing is an enabling technology that facilitates component minaturization and improved performance characteristics. It is being applied across many industries – semiconductor, electronics, medical, automotive, aerospace, instrumentation, and communications. Laser ablation of metals, ceramics and polymers is a complex process and the exact nature of the interaction is specific to the material and laser processing parameters used. Ablation is usually a combination of evaporation and melt expulsion. In order to achieve the highest quality results it is often desirable to minimize the degree of melting involved and short pulse lasers show certain advantages in this respect. We discuss the benefits of high laser intensity (GW/cm)^2 on target for efficient laser micro-fabrication in metals and ceramics. At such high irradiance conditions, material properties are approaching their critical limits and ablation mechanisms are becoming even more complicated but can be exploited to our advantage in particular for high aspect ratio micro-drilling and micro-cutting.

High aspect ratio micron-sized vias in "flex" and polymer foils using ion irradiation

Mon, 19 May 2008 14:21:11 +0000

H. Yousef, M. Lindeberg, K. Hjort
Department of Engineering Sciences, Uppsala University, Box 534, 75121 Uppsala, Sweden

Abstract

As the call for higher wiring density in packaging and interconnection technologies rapidly evolves, the need for smaller dimensions in vias and interconnects must be met. The frontier of advanced high aspect ratio technologies is today often found within microelectronics and MEMS. The process described in this paper stems from advanced MEMS and allows micromachining of deep, vertical vias in polyimide based foils and flexible-PCBs. The process is superior with respect via throughput and size compared with traditional via manufacturing techniques such as chemical etching, drilling, dry etching and laser ablation.

The technique makes use of ion irradiation to enhance the selectivity and directionality of the chemical etching technique. Within the areas exposed to the ion irradiation, small sub-micron pores (capillaries) are created, one for every ion. If etching is prolonged, the pores become merged. Conventional electrodeposition from a metallic seed layer is used to fill these structures with metal. The smallest achievable size of the vias is only limited by the resolution of the mask; vias of below 10 μm in diameter can readily be achieved in a 75 μm thick polyimide foil. It is possible to obtain two inherently different types of via structures using this process: (1) conventional solid vias, and (2) vias consisting of bundles of sub-micron wires (having a specified metal density between 0.2 and 20%). As the individual sub-micron wires have aspect ratios of several hundreds, this allows fabrication of truly vertical via structures, allowing ultra high-density wiring.

Characterization of polymers for improved shrinkage prediction in micromolding.

Mon, 19 May 2008 14:17:28 +0000

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.

Fabrication Chain for Prototyping of Microfluidic Chips in Polymers

Mon, 19 May 2008 14:09:50 +0000

T. Brenner, C. Müller, H. Reinecke, R. Zengerle, and J. Ducrée
IMTEK – University of Freiburg, Georges-Koehler-Allee 106, D-79110 Freiburg, Germany

Abstract

We established an integrated prototyping chain for rapid fabrication of microfluidic chips in polymers comprising fabrication of masters made from elastomers, replication into polymers by soft embossing, surface modification and thermal sealing. Our techniques enable rapid and precise fabrication of fully functionalized microfluidic chips featuring typical minimum lateral dimensions of 50 μm and aspect ratios smaller than one.

Study of Factors Affecting Aspect Ratios Achievable in Micro-injection Moulding

Mon, 19 May 2008 14:01:50 +0000

B. Sha, S.S. Dimov, D.T. Pham and C. A. Griffiths
Manufacturing Engineering Centre, Cardiff University, Cardiff CF24 3AA, UK

Abstract

Micro-injection moulding is one of the key technologies for micro-manufacture because of its mass-production capability and relatively low component cost. The replication of micro-features is an important issue in broadening the use of this technology. The aspect ratios achievable in replicating such features are one of the most important process characteristics and constitute a major manufacturing constraint in applying injection moulding in a range of micro-engineering applications. This research studies the effects of five process factors and one size factor on the achievable aspect ratios, and the role they play in producing micro components in different polymer materials. In particular, the following factors are considered: barrel temperature, mould temperature, injection speed, holding pressure, the existence of air evacuation, and the size of micro features. The study revealed that the barrel temperature and the injection speed are the key factors affecting the aspect ratios of micro features replicated in PP and ABS. In the case of POM, in addition to these two factors, the mould temperature is also an important factor for improving the replication capabilities of the micro-injection moulding process. For all three materials, an increase of feature sizes improves the melt flow. However, the melt fill of micro features does not increase linearly with the increase of their sizes.

Manufacturing of high quality micro prototypes by injection molding using hybrid mold technology

Mon, 19 May 2008 13:52:40 +0000

A. Frick (a), C. Stern (a), U. Berger (b)
a Polymer Sciences and Processing, Aalen University of Applied Sciences AAUAS, Aalen 73430, Germany
b Department of Mechatronics, Aalen University of Applied Sciences AAUAS, Aalen 73430, Germany

Abstract

A larger number of polymeric prototypes with special material properties are often demanded for research and development. Thereby, it is most essential that the prototypes are made from the target material and the related processing technique. A sophisticated and fast possibility to obtain a mold for replicating parts (prototypes) by injection molding is making inserts for hybrid molds, using a rapid prototyping (RP) technique. RP technique (e.g. stereolithography) allows shaping complex mold cavity geometries as well as curved cooling conducts, what is not possible by conventional manufacturing.

The manufacturing of high quality micro parts by injection molding requires a plasticizing unit with small screw channel volume to reduce the residence time of the polymeric melt. Nowadays, the minimal commercially available screw diameter is 14 mm. A newly developed plasticizing unit with a screw diameter of 12mm, which was done at AAUAS in collaboration with ARBURG, permits a gentle processing of polymers, spending only half of the residence time. This is an advantage when micro prototypes are manufactured in a single-cavity mold.

The present work points out, how the combination of the benefits of stereolithography and micro injection molding can be successfully used for producing micro prototypes. By means of some examples, it is shown that the performance of small plastic products (part mass in the milligram range) can be optimized by choosing the right material and processing technique. Thus the spectrum of application of micro parts can be extended.

A new approach in polymer waveguide fabrication

Mon, 19 May 2008 13:44:46 +0000

Severin Dahms, Frederik Bundgaard and Oliver Geschke
MIC - Department of Micro and Nanotechnology, Technical University of Denmark (DTU), Building 345 East, 2800 Kgs. Lyngby, Denmark

Abstract

Waveguides are an excellent means of integrating sensor components in single use microfluidic polymer systems. However, most processes for producing on-chip waveguides require several process steps, some of which are not suited for mass production. We report a simple procedure in which two different grades of the cyclic olefin copolymer (COC) Topas® are used as substrate and core layer. In a spin coating process a Topas® grade with high refractive index is spin coated onto the injection moulded substrate with lower refractive index, thereby generating a core layer. A simple hot embossing process enables simultaneous structuring of waveguides and microfluidic channels in the core layer. In a final step the microfluidic structures can be closed with a lid, either by thermal bonding or by laser transmission welding.

The refractive index and glass transition temperature Tg can be altered by changing the ratio between the two copolymers of Topas®. The low optical transmission loss of the material, along with its chemical resistance and low water absorption, makes Topas® a good choice for making integrated optics in microfluidic systems.

Polymer technology for disposable microfluidics

Mon, 19 May 2008 13:11:26 +0000

R. Jurischka (a), Ch. Blattert (a), I. Tahhan (a), A. Schoth (a), H. Reinecke (a),
a Laboratory for Process Technology, Institute of Microsystem Technology, University of Freiburg, 79110 Freiburg, Germany

Abstract

Present main applications of microfluidic devices are within the life sciences or chemical analysis. Polymers are ideally suited for these applications due to their material properties and their applicability for high volume production. In this study, we developed a rapid manufacturing technology for disposable microfluidic devices using UV-LIGA and injection molding. Exchangeable inserts for the molding tool were fabricated by a modified UV-LIGA technology. The UV-LIGA process is based on a SU-8 lithography with a metal substrate, which allows for a reduction of the nickel electroplating time. These inserts enable a cost effective structuring of polymers. Different prototypes of chips for microfluidic applications with channel dimensions down to 10 μm and aspect ratios of 8 have been fabricated. The electroplated nickel structure has a hardness of 800 Vickers and an excellent top surface roughness of Ra < 20 nm. Taper angles of 3-8 degrees result in low demolding forces. The main advantage of our rapid processing technology is the availability of the geometry, the specific target material and manufacturing technology right from the start of the development to a cost effective high volume production of microfluidic devices.

Surface Microstructure Replication in Injection Moulding

Mon, 19 May 2008 13:06:25 +0000

H. N. Hansen, U. A. Theilade
Department of Manufacturing Engineering and Management, Technical University of Denmark, Building 427, Produktionstorvet, DK-2800 Kgs. Lyngby, Denmark

Abstract

In recent years polymer components with surface microstructures have been in rising demand for applications such as lab-on-a-chip and optical components. Injection moulding has proven to be a feasible and efficient way to manufacture such components. In injection moulding the mould surface topography is transcribed onto the plastic part through complex mechanisms. This replication however, is not perfect, and the replication quality depends on the plastic material properties, the topography itself, and the process conditions. This paper describes and discusses an investigation of injection moulding of surface microstructures. Emphasis is put on the ability to replicate surface microstructures under normal injection moulding conditions, notably with low cost materials at low mould temperatures. The replication of surface microstructures in injection moulding has been explored for Polypropylene at low mould temperatures. The process conditions were varied over the recommended process window for the material. The geometry of the obtained structures was analyzed. Evidence suggests that step height replication quality depends linearly on structure width in a certain range. Further it was found that in this range, the replication quality depends strongly on process conditions. It was concluded that the achieved step height varies linearly with the mould groove width.

Study of the rheological properties of poly(methylmethacrylate) (PMMA) and cyclo-olefin-copolymer (COC) to optimize the hot-embossing process

Mon, 19 May 2008 12:54:06 +0000

M. Sahli (a,c), C. Roques-Carmes (a), R. Duffait (b) and C. Khan Malek (c)
a Laboratoire de Microanalyse des Surfaces (LMS), ENSMM, 26 Rue de l’Epitaphe,
b Centre de Transfert des Micro et Nanotechnologies (CTMN), 39 Avenue de l’Observatoire,
c Laboratoire FEMTO-ST, CNRS UMR 6174, Département LPMO, 32 Avenue de l’Observatoire, 25000 Besançon, France.

Abstract

A study of the rheological properties of two types of amorphous polymeric materials (PMMA and COC) was conducted in order to optimize the operating conditions for the hot embossing of the polymers. The glass transition temperature (Tg), the melt flow index (IF), and the viscosity as a function of shear stress were determined. These intrinsic properties were related to the aptitude of the polymers to reproduce the geometrical shape and surface states of a microstructured mould. The flow imposed to the polymeric material in shear or elongational mode was correlated to this rheological approach.

Multiphoton assisted micro- and nanoprocessing of materials

Mon, 19 May 2008 12:38:48 +0000

H. Schucka, Th. Veltena, T. Anhuta, D. Sauera, R. Le Harzicb, K. Königa
a Fraunhofer-Institute for Biomedical Engineering, D-66386 St. Ingbert, Germany
b JenLab GmbH, D-07745 Jena, Germany

Abstract

Sub-micrometer structuring has been performed on polymers, metal films and semiconductors using near 3
infrared, 90 MHz femtosecond laser pulses at <3 nJ pulse energy. A compact (65x62x48 cm ) multiport laser scanning microscope FemtoCut (JenLab GmbH) has been employed. A tuneable turn-key, one-box Chameleon (tunable from 720 - 930 nm) has been used as laser source.

Pulse energies in the sub-3 nJ range are sufficient to induce multiphoton ionisation when using a high NA 2
objective (e.g. NA = 1.3) in order to obtain transient TW/cm laser intensities. By exploiting this multiphoton effect, we were able to perform patterning of several types of material with sub-micron resolution. Depending on the pulse energy, cut widths of 350 nm and 900 nm have been achieved in 30 nm thin gold films. In polyimide Pyralin PI2611 (HD microsystems) we reached cut widths of 570 nm. Direct laser processing of silicon wafers resulted in cut widths of about 500 nm. Interestingly, besides the 500 nm cut we found two types of additional nanostructures. A first superficial layer contained non-homogenously distributed laser-induced nanocones which represent non-coherent structures. After removing this layer by etching with ammonium fluoride, a second highly coherent “ripple” structure became obvious. Most interestingly, these symmetric features possessed a wavelength (distance) of 50 – 70 nm. A clear dependence of the ripple structures on the polarization was proven.

Double hot-embossing with polymeric intermediate mould

Mon, 19 May 2008 12:33:38 +0000

Chantal Khan Maleka, Gaël Thuilliera, Roland Duffaitb , Laurent Guyoutc
a Laboratoire FEMTO-ST, CNRS UMR 6174, Département LPMO, 32 Avenue de l’Observatoire, 25044 Besançon Cedex, France.
b Centre de Transfert des Micro et Nanotechnologies (CTMN), 39 Avenue de l’Observatoire, BP 1445-25007 Besançon Cedex 3, France.
c Department of Applied Mechanical Engineering, University of Franche Comté, 16 Route de Gray, 25030 Besançon Cedex, France.

Abstract

Our approach uses a two-step replication process for hot embossing and a rigid polymeric intermediate mould. This process overcomes some geometrical limitations in microstructured mould fabrication, enables positive-tone imprinting, prolongs the lifetime of the master, and lowers the overall cost of the replication process.