polymers

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

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.

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.

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.

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.