Wilhelm Pfleging

Laser micromachining of mold inserts for replication techniques: state of the art and applications

The rapid fabrication of microcomponents made from polymers will be presented. The whole fabrication process is divided into three main steps: First, direct patterning of polymers with excimer laser radiation enables the fabrication of first prototypes. Second, laser assisted micromachining using Nd:YAG and KrF-Excimer laser allows a rapid manufacturing of microstructured mold inserts. Third, the application of light induced reaction injection molding (UV-RIM) gives the access to the replication of the previously fabricated mold insert. The fabrication of prototypes made of polymer is carried out highly precisely with excimer laser radiation. With the aid of a motorised aperture mask, CAD data are transmitted directly into the polymeric surface. With an appropriate pretreatment of the polymer surface the debris formation can be drastically reduced. A promising method of micropatterning of mold inserts made of steel is called laser microcaving. This processing technique enables a clean patterning process with only a small amount of debris and melt. The etch rate and surface quality strongly depend on the chemical composition of the steel and the process parameters. Surface qualities with a roughness of about 300 nm can be achieved. Microstructures composed of polymers or ceramic-composites are successfully demolded by using the UV-RIM technique with aspect ratios up to 10. Capillary Electrophoresis-Chips made of PMMA are fabricated, and the functionality of the CE-Chips is demonstrated.

Rapid fabrication of microcomponents

In the macroscopic world different rapid-technologies like Rapid Prototyping, Rapid Manufacturing or Rapid Tooling have been established for a fast prototype or molding tool development. In all cases CAD-data can be transformed in a model or prototype directly using a laser which polymerizes reactive resin layer by layer to a final 3D mold within a short period. In this work the rapid fabrication of micro components made from polymers or composites will be presented. The whole fabrication process is divided into two main steps: Firstly laser assisted micro machining using Nd:YAG and KrF-Excimer laser allows a rapid manufacturing of micro structured cemented carbide or steel mold inserts. Secondly the application of light induced reaction injection molding using reactive monomer/polymer resins gives access to the replication of the previously fabricated mold insert. The total processing period starting from CAD until the modeled micro structured part is less than one week.

Laser Micromachining of Metallic Mold Inserts for Replication Techniques

The laser microcaving (LMC) of steel is performed with cw Nd:YAG laser radiation. LMC enables a “clean” patterning process with only a small amount of debris and melt. During LMC the formation of a Ni-enriched interface layer and an oxide surface layer may be observed. The formation of these reaction layers as well as the etch rate and the surface quality strongly depend on the chemical composition of the steel and the process parameters. Surface qualities with an roughness of about R a (center line average)=300 nm can be realised. The ablation rates are in the range of 10 6 µm 3 /s. With excimer laser radiation a further improvement of surface topographies can be achieved via laser planarisation. Mold inserts are manufactured by LMC, and microstructures composed of PMMA are successfully demolded by using the Ultraviolet light induced Reaction Injection Molding (UV-RIM) or Photomolding technique. CE(Capillary Electrophoresis)-Chips made of PMMA are successfully demolded, and the functionality of the CE-Chips is demonstrated.

Comparing roll-to-roll and laser-assisted hot embossing for micro- and nanofabrication

We demonstrate the suitability of two cost efficient technologies, namely roll-to-roll hot embossing and laser-assisted hot embossing, to fabricate arrays of structures in the microscale down to the sub-100 nm range. We therefore employ polymers with a relatively moderate glass transition temperature, e.g., cyclic olefin copolymer (COC) and polystyrene (PS). We compare the two replication processes regarding their precision and cost using different 1D and 2D nanostructure gratings and microfluidic channels. All nickel shims used for the replication are fabricated in combination of electron beam or UV lithography and nickel electroforming. The replicated structures are used in different applications. The nanopillar arrays are coated with gold and integrated in the hot embossed microfluidic channels for lab-on-a-chip (LoC) surface-enhanced Raman analysis. We evaluate the as-fabricated 2D nanopillar arrays for surface-enhanced Raman spectroscopy (SERS) using solutions of rhodamine 6G as exemplary analytes. The influence of the geometrical parameters like diameter and pitch of the polymer structures as well as the influence of the gold layer thickness are discussed. 1D-gratings will be used as resonators for organic distributed feedback (DFB) lasers. Both elements, the SERS chips and the organic DFB lasers as tunable excitation source can be combined in the future to form one Raman-on-Chip optofluidic platform for sensitive detection of low-concentrated analytes in water.

Laser in battery manufacturing: impact of intrinsic and artificial electrode porosity on chemical degradation and battery lifetime

The main goal is to develop an optimized three-dimensional (3D) cell design with improved electrochemical properties, which can be correlated to a characteristic lithium distribution along 3D micro-structures at different State-of-Health (SoH). 3D elemental mapping was applied for characterizing the whole electrode as function of SoH. It was demonstrated that fs-laser generated 3D architectures improves the battery performance regarding battery power and lifetime. It was quantitatively shown by laser-induced breakdown spectroscopy that 3D architectures act as attractor for lithium-ions. Furthermore, lateral intrinsic porosity variations were identified to be possible starting points for lithium plating and subsequent cell degradation. Results achieved from post-mortem studies of cells with laser structured electrodes (intrinsic and artificial porosity variation), and unstructured lithium-nickel-manganese-cobalt-oxide electrodes will be presented.

Laser-Materials Processing for Energy Storage Applications

This chapter will review the use of laser-based material processing techniques, such as pulsed laser deposition (PLD), laser-induced forward transfer (LIFT), and material processing via 3D laser structuring (LS) and laser annealing (LA) techniques for energy nstorage applications. PLD is a powerful tool for fabricating highquality layers of materials for cathodes, anodes, and solid electrolytes for thin film microbatteries. LIFT is a versatile technique for printing complex materials with highly porous structures for the fabrication of micropower sources, such as ultracapacitors and thick-film batteries. LS is a recently developed technique for modifying the active material by forming advanced 3D electrode architectures and increasing the overall active surface area. LA is a rapid technology for nadjusting the crystalline battery phase and for controlling the grain size on the micro- and nanoscale. This chapter will review recent work using these laser processing techniques for the fabrication of micropower sources and lessons learned from the characterization nof their electrochemical properties.