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Micro Technology

E 030
Absorber-free Laser Beam Welding of Transparent Thermoplastics
While laser welding of polymers is used in many industrial applications, an infrared absorber is usually required for laser transmission welding. However, absorber-free laser beam welding can be utilized in a large number of applications primarily in medical device technology or in high-tech products.

Successful welding without an IR absorber is primarily attributed to the availability of new laser sources at specialized wavelengths. Analysis of the absorption spectra of polymer compounds shows particular wavelength ranges at which sufficient IR absorption occurs to enable welding. To generate a heat source in the joining area, the intensity distribution and the wavelength of the laser must be aligned to the absorption characteristics of the polymer compound. The usage of special optics with high numerical aperture keeps the laser intensity on top of the material and below the melting threshold. Only in the welding area does the intensity reach the necessary value to determine the welding of the transparent components.

Contact Person
Dipl.-Ing. Andreas Roesner
Phone +49 241 8906-158
Fraunhofer Institute for Laser Technology ILT

E 030
Compact Turn Key System for Microwelding of Plastics and Electrical Contacts
Direct diode lasers are now available with sufficient brightness and power to effectively perform microwelding and plastic bonding. The short wavelength in the range of 800nm to 1,000nm is much better absorbed by highly reflective metals, such as copper or gold. This enables efficient pulsed welding of electrical contacts.

A compact turn key system with a 100W diode laser and scanner will be presented. The footprint of the table top system is 25cm by 25cm to include the laser safe enclosure. Sample welding of plastics and thin metals will be performed. The system operates on 220V and does not require any water cooling.

Contact Person
Dr. Stefan Heinemann
Phone +1 734 738-0500
Fraunhofer USA

E 032
Glass Soldering by Laser Radiation
In industrial manufacturing glass solders are mainly applied in electro technology and electronics especially for the closure of electrode feedthrough and housing. The durability and the mechanical load of a glass solder joint depends on the mechanical stresses. Because of the problems with mechanical stresses the most joining processes require a temperature-time-profile which causes a thermal impact for the whole componentry. Often the required temperature sequence damages sensible components inside the housing by diffusion processes. Thus a soldering technology which works with reduced temperature input and a local heating is needed.

Glass soldering by laser radiation is an alternative to reduce the thermal input because of the localised energy absorption. The absorption of the laser radiation by the glass solder is an essential condition for a successful soldering process. This requirement is also performed by leadfree solders recently. By absorption the laser radiation the necessary temperature for a constant heating, melting and crack free soldering is achieved.

Contact Person
Dipl.-Ing. Heidrun Kind
Phone +49 241 8906-490
Fraunhofer Institute for Laser Technology ILT

E 113.3
High Speed Micro Structuring by In-volume Selective Laser Etching
High speed 3D micro structuring of transparent materials is possible by in-volume selective laser etching (ISLE). Using high repetition rate lasers like fs fiber lasers and high power slab amplifiers productive 3D modification is possible with sub micrometer precision. The modified material is selectively removed by wet chemical etching.

Micro channels, 3D micro parts and shaped micro holes in glass and sapphire are demonstrated. High power fs-laser radiation (100W) is used to demonstrate the scaling of the ISLE process.

Contact Person
Dr. Jens Gottmann
Phone +49 241 8906-406
Fraunhofer Institute for Laser Technology ILT

E 032
Laser Soldering for Flexible Interconnection of Self-Bonding Copper Wire
Currently, the interconnection of self-bonding copper wires is soldered manually for electronic products due to a lack of automation facilities. The quality of the solder connection strongly depends upon the person conducting it. This method is not only time consuming, but also harbors a danger: the section of wire to be connected can tear when very thin self-bonding wires, e.g. < 100?m, are used, or a sound electrical interconnection cannot be established. To increase the process speed and reproducibility, an automated laser soldering process has been developed that not only enhances the manufacturing flexibility, but also offers great potential for further miniaturization. With this process, the enamel removal and the interconnection take place in one single process step. By using cost-effective diode laser systems this soldering process is even economically worthwhile compared to competing selective soldering processes.

Contact Person
Dipl.-Ing. Felix Schmitt
Phone +49 241 8906-322
Fraunhofer Institute for Laser Technology ILT

E 030
Laser Transmission Bonding
In the fabrication of hybrid micro-devices and systems consisting of different single components silicon is usually used as a base material. Conventionally these components are joined by bonding methods such as Silicon Direct Bonding and Anodic Bonding. The disadvantages of these joining methods are causing a high thermal stress and using the entire bond surface. As an alternative to these conventional areal bonding methods laser transmission bonding offers an unique opportunity to realize continuous selective bonding through a localized application. The exact energy deposition minimizes the heat affected zone and the thermal load of sensitive components can be reduced. Furthermore a locally selective joining is enabled. In addition to bonding dissimilar material combinations like silicon-glass, laser transmission bonding can also be applied to join similar material combinations like silicon-silicon and glass-glass. Thereby the laser energy is absorbed by a metallic interlayer in the joining zone.

Contact Person
Dipl.-Ing. Anselm Wissinger
Phone +49 241 8906-500
Fraunhofer Institute for Laser Technology ILT

E 100.K1
Microstructuring with Excimer Lasers
Microstructuring with excimer lasers is particularly interesting for patterning organic materials like plastics or bio tissues. Due to the short wavelengths in the deep UV-range and the extremly high absorption of most organic materials, a very clean ablation is realized with excimer lasers. At optimized parameters thermal effects can be neglected. Excimer lasers have a high beam diameter and a tophead profile. Therefore, they are often used in mask projection setups, enabling to micropattern a relatively large area. By using masks with respectively small apertures, the setup can be used to drill holes with diameters of less than 5?m. The ablation depth per pulse can be easily adjusted by varying the fluence. Ablation depths of 100nm per pulse can be realized, allowing a very acurate patterning.

Patterning with excimer lasers is a rather slow process, due to small repetition rates of often only 200Hz. The excimer laser used here stands out with its high repetition rate of 2kHz.

Contact Person
Dipl.-Phys. Moritz Schaefer
Phone +49 241 8906-305
Fraunhofer Institute for Laser Technology ILT

E 160.1
Tool Generation and Modification by Ablation with Ps-lasers
Complex replication tools for injection moulding or hot embossing are produced by generating the ablation geometry in a 3D-CAD-model and slicing the material with sclices of less than 1?m thickness. Especially with picosecond lasers, the accuracies of the laser ablation can be dramatically increased. Due to the very high pulse powers, the material is ablated only by vaporization and there is almost no residual melting layer on the surface. With this technology the slicing thickness can be reduced to several 100nm and therefore highly accurate moulding tools can be produced.

Contact Person
Dipl.-Ing. Andreas Dohrn
Phone +49 241 8906-220
Fraunhofer Institute for Laser Technology ILT

E 030
TWIST - New Process and SystemTechnlogy for the Laser Welding of Bio-medical Products
The development of new laser sources with almost ideal beam quality e.g.fibre lasers and disc lasers is bringing new opportunities for the laser welding of polymers. The latest research results show that using a recently developed welding method called TWIST® – Transmission Welding by an Incremental Scanning Technique and taking advantage of the high focusability of these laser sources, high quality weld seams at high processing speed can be achieved. Beside the process related benefits, the TWIST® approach enables the development of a new generation of compact and cost effective laser systems for the welding of polymers. Due to very high beam quality, the necessary optical equipment like scanner and focusing device can be miniaturized while keeping the ability to achive spot sizes down to several 10?m. Therefore, the new TWIST® process and the corresponding welding station developed provide higher process flexibility and precision for various bio-medical products such as Microfluidics.

Contact Person
Dipl.-Ing. Andrei Boglea
Phone +49 241 8906-217
Fraunhofer Institute for Laser Technology ILT
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