11:15am - 11:30am
OCT keyhole depth measurement in copper micro welding
Robert Bosch GmbH, Germany
The transition of the powertrain from combustion to electric systems increases the demand for reliable copper connections. For such applications, laser welding has become a key technology. Due to the complexity of laser welding, especially at micro welding with small weld seam dimensions and short process times, reliable in-line process monitoring has proven to be difficult. By using a green laser (515 nm), the welding process of copper benefits of the increased absorption, resulting in a shallow and stable deep penetration welding process. In this contribution, the monitoring of the capillary depth in micro copper welding, with welding depth of up to 1 mm, was performed coaxially, using an optical coherence system with a measurement wavelength of 840 nm. By comparing the measured capillary depth and the actual welding depth, independently of the investigated process parameters and the stability, a good correlation between two measured values could be shown.
11:30am - 11:45am
Determination of thermophysical process limitations for the laser-based droplet brazing process using different droplet and substrate materials
1Bayerisches Laserzentrum GmbH (blz), Konrad-Zuse-Straße 2-6, 91052 Erlangen, Germany; 2Institute of Photonic Technologies (LPT), Friedrich-Alexander-Universität Erlangen-Nürnberg, Konrad-Zuse-Straße 3-5, 91052 Erlangen, Germany; 3Erlangen Graduate School in Advanced Optical Technologies (SAOT), Paul-Gordan-Straße 6, 91052 Erlangen, Germany
The demand for microelectronic components is rising constantly over the last few decades due to the progress in digitalization. Along with this, the requirements for joining technologies are growing since they are highly responsible for progress in microelectronics. Laser-based droplet brazing shows unique features like a quasi-force-free joining process and high-temperature stable connections and is therefore on the way to its industrial implementation. While the first developments have been limited to the contacting of silver metallizations on piezo actuators, today the transferability of the process with regard to different solder and substrate materials is a major goal. In this work the relation between the solidification time of the droplet and diffusion processes depending on the substrate layout and material properties is investigated via highspeed imaging and EDX analysis. Based on the thermophysical behaviour of the process, the scalability for future applications can be derived for different material combinations.
11:45am - 12:00pm
Temporally and spatially highly resolved reconstruction of vapor capillary geometry during laser beam welding using synchrotron radiation
1RWTH Aachen University, Chair for Laser Technology LLT, Germany; 2Fraunhofer Institute for Laser Technology LLT, Germany; 3University of Stuttgart, Institut für Strahlwerkzeuge IFSW, Germany; 4RWTH Aachen University, Nonlinear Dynamics of Laser Manufacturing Processes NLD, Germany
Welds of electrical components made of aluminum and copper need high electrical and mechanical quality. Process instabilities do not allow a continous reproducibility. To generate a deeper understanding of the process and to evaluate process dynamics, it is possible to use modern in situ analysis methods.
In this work, in situ phase-contrast high-speed videography using synchrotron radiation is presented. The phase contrast method reveals the phase boundaries between solid, liquid and gaseous phases. A spatial resolution down to <20 µm is possible due to the high coherence of the synchrotron beam, which allows to observe small vapor capillaries of fiber lasers with <100 µm diameter. 3D capillary geometries are reconstructed from 2D image data of welds on aluminum using a fiber laser and disc laser. Ray tracing is performed using this reconstruction, which allows the time resolved tracking of the laser beam inside the vapor capillary for quantitative estimations.
12:00pm - 12:15pm
Direct welding of glass and copper with a large gap by femtosecond laser pulse bursts
1Institute of Applied Physics, Abbe Center of Photonics, Friedrich Schiller University Jena, Albert-Einstein-Straße 15, 07745 Jena, Germany; 2Fraunhofer Institute for Applied Optics and Precision Engineering IOF, Center of Excellence in Photonics, Albert-Einstein-Straße 7, 07745 Jena, Germany
We report on the welding of borosilicate glass to copper using bursts of femtosecond laser pulses with a pulse duration of 265-fs and a wavelength of 1030-nm. The systematical analysis demonstrated in this paper represents a fundamental step towards the robust laser micro-welding of glass-to-metal.
The highest bonding strength is achieved with a laser fluence 2.5 times higher than the laser-induced damage threshold of the glass sample. Moreover, the glass-metal interface must be located within the Rayleigh range of the focused laser beam representing a focal diameter of 3.7-µm, and the gap size between both components must be less than 2-µm. The highest value, in the region of 14-MPa, compares well with proof-of-principle demonstrations published before. However, in contrast to previous achievements, no clamping is required. Consequently, the presented work demonstrates an easy glass-to-metal welding approach as an alternative to traditional bonding techniques based on adhesives or sample-pretreatments.
12:15pm - 12:30pm
Investigations on the influence of the material selection of the clamping device during laser transmission welding of multi-layer polymer films with wavelength-adapted laser beam sources
Fraunhofer-Institut für Lasertechnik ILT, Germany
In lasertransmissionwelding process of polymers with wavelength adapted laser beam sources, the joining partners are fixed in an overlap arrangement. A sufficient energy absorption is ensured by addressing the material-dependent intrinsic absorption bands. The fixing is realized by a clamping device to achieve a technical zero gap between the joining partners in order to ensure heat exchange and melt permeation. The materials are in direct contact with the polymers and influence the heat dissipation as well as the propagation of the laser beam. While the upper material must be transparent for the laser radiation, a variety of materials are available for the lower part. Hence, it is investigated how the individual material combinations affect the process.To investigate the influence of material combinations as well as the influence of roll-to-roll processing or possible process limits welding tests are performed. The weld seam is analyzed by cross sections and tensile tests.