This contribution presents a phenomenological, analytical model for laser welding of polymers which is suited for a quick process quality estimation for the practitioner. Besides material properties of the polymer and processing parameters like welding pressure, feed rate and laser power the model is based on a simple few parameter description of the size and shape of the laser power density distribution (PDD) in the processing zone. The model allows an estimation of the weld seam tensile strength. It is based on energy balance considerations within a thin sheet with the thickness of the optical penetration depth on the surface of the absorbing welding partner. The joining process itself is modelled by a phenomenological approach. The model reproduces the experimentally known process windows for the main process parameters correctly. Using the parameters describing the shape of the laser PDD the critical dependence of the process windows on the PDD shape will be predicted and compared with experiments. The adaption of the model to other laser manufacturing processes where the PDD influence can be modelled comparably will be discussed.
This work is motivated by the observation that the shape of a laser power density distribution (PDD) significantly influences the manufacturing quality in numerous laser processes. Lacking appropriate PDD shape parameters this influence, however, is not described quantitatively by few characteristic figures of the PDD. The paper presents a new quantitative, application adapted few parameter characterisation of PDD shape. For nearly circular PDDs the localisation as just one additional parameter on top of the common characteristics beam power and PDD radius is introduced and proven as meaningful. The localisation is based on the fourth moment of the PDD. This ensures simple optical transformation properties and thus easy adjustability of the localisation of the laser beam as manufacturing tool. Together with beam power and radius the localisation allows to determine the power fractions in the central and ring-like outer region of the PDD as well as the fraction outside the PDD radius. This will be shown by application of evaluation functions which evaluate the spatial regions of the PDD with different weights. Applications to real beams used for laser manufacturing will be demonstrated. For the examples of surface dominated laser processes it will be shown briefly that this approximate shape description with one additional parameter allows an estimate of PDD influence on manufacturing quality. An outlook on further shape characterising parameters is given.
Micro-joining and hermetic sealing of dissimilar and biocompatible materials is a critical issue for a broad spectrum of products such as micro-electronics, micro-optical and biomedical products and devices. Today, biocompatible titanium is widely applied as a material for orthopedic implants as well as for the encapsulation of implantable devices such as pacemakers, defibrillators, and neural stimulator devices. Laser joining is the process of choice to hermetically seal such devices.
Laser joining is a contact-free process, therefore minimizing mechanical load on the parts to be joined and the controlled heat input decreases the potential for thermal damage to the highly sensitive components. Laser joining also offers flexibility, shorter processing time and higher quality. However, novel biomedical products, in particular implantable microsystems currently under development, pose new challenges to the assembly and packaging process based on the higher level of integration, the small size of the device's features, and the type of materials and material combinations. In addition to metals, devices will also include glass, ceramic and polymers as biocompatible building materials that must be reliably joined in similar and dissimilar combinations. Since adhesives often lack long-term stability or do not meet biocompatibility requirements, new joining techniques are needed to address these joining challenges. Localized laser joining provides promising developments in this area. This paper describes the latest achievements in micro-joining of metallic and non-metallic materials with laser radiation. The focus is on material combinations of metal-polymer, polymer-glass, metal-glass and metal-ceramic using CO2, Nd:YAG and diode laser radiation. The potential for applications in the biomedical sector will be demonstrated.
KEYWORDS: Laser welding, Signal processing, Semiconductor lasers, High power diode lasers, Laser scattering, Process control, Polymers, Absorption, Scattering, Carbon
Current product development showing an ever shrinking physical volume is asking for new, reliable joining technologies. Laser beam technologies conceal innovative solutions to overcome limitations of conventional joining technologies. Laser beam welding of thermoplastics offers several process technical advantages. The joining energy is fed contact-less into the joining area, avoiding mechanical stress and thermal load to the joining partners. The energy is supplied spatially (seam width on the order of 100 μm) and timely (interaction time on the order of ms) very well defined. Different process strategies are possible leading to flexibility, product adapted irradiation, short process times and high quality weld seams as well as to high integration abilities and automation potentials. During the joining process no vibration, no thermal stress, no particle release takes place. Therefore, destruction of mechanically and electronically highly sensitive components, such as microelectronics, is avoided. The work place pollution is neglectable compared to other joining technologies, such as gluing (fume) or ultrasonic welding (noise, pieces of fluff). Not only micro-components can be welded in a reproducible way but also macro-components while obtaining a hermetic sealing with good optical appearance. In this publication firstly, an overview concerning process technical basis, aspects and challenges is given. Next, results concerning laser penetration welding of polymers using high power diode lasers are presented, while comparing contour and simultaneous welding by experimental results and the on-line process monitoring.
Laser welding of polymers using high power diode lasers offers specific process advantages over conventional technologies, such as short process times while providing optically and qualitatively valuable weld seams, contactless yielding of the joining energy, absence of process induced vibrations, imposing minimal thermal stress and avoiding particle generation. Furthermore this method exhibits high integration capabilities and automatization potential. Moreover, because of the current favorable cost development within the high power diode laser market laser welding of polymers has become more and more an industrially accepted joining method. This novel technology permits both, reliable high quality joining of mechanically and electronically highly sensitive micro components and hermetic sealing of macro components. There are different welding strategies available, which are adaptable to the current application. Within the frame of this discourse scientific and also application oriented results concerning laser transmission welding of polymers using preferably diode lasers are presented. Besides the used laser systems the fundamental process strategies as well as decisive process parameters are illustrated. The importance of optical, thermal and mechanical properties is discussed. Applications at real technical components will be presented, demonstrating the industrial implementation capability and the advantages of a novel technology.
Laser welding of polymers using high power diode lasers offers specific process advantages over conventional technologies, such as short process times while providing optically and qualitatively valuable weld seams, contactless yielding of the joining energy, absence of process induced vibrations, imposing minimal thermal stress and avoiding particle generation. Furthermore, this method exhibits high integration capabilities and automatization potential. Moreover, because of the current favorable cost development within the high power diode laser market laser welding of polymers has become more and more an industrially accepted joining method. This novel technology permits both, reliable high quality joining of mechanically and electronically highly sensitive micro components and hermetic sealing of macro components. There are different welding strategies available, which are adaptable to the current application. Within the frame of this discourse scientific and also application oriented result concerning laser transmission welding of polymers using preferably diode lasers are presented. Besides the sue laser system the fundamental process strategies as well as decisive process parameters are illustrated. The importance of optical, thermal and mechanical properties is discussed. Applications at real technical components will be presented, demonstrating the industrial implementation capability and the advantages of a novel technology.
Miniaturization is one of the keywords for the production of customer oriented and highly integrated consumer products like mobile phones, portables and other products from the daily life and there are some first silicon made products like pressure sensors, acceleration sensors and micro fluidic components, which are built in automobiles, washing machines and medical products. However, not all applications can be covered with this material, because of the limitations in lateral and 3-dimensional structuring, the mechanical behavior, the functionality and the costs of silicon. Therefore other materials, like polymers have been selected as suitable candidates for cost effective mass products. This holds especially for medical and optical applications, where the properties of selected polymers, like biocompatibility, inert chemical behavior and high transparency can be used. For this material laser micro processing offers appropriate solutions for structuring as well as for packaging with high flexibility, material variety, structure size, processing speed and easy integration into existing fabrication plants. The paper presents recent results and industrial applications of laser micro processing for polymer micro fluidic devices, like micro analysis systems, micro reactors and medical micro implants, where excimer radiation is used for lateral structuring and diode lasers have used for joining and packaging. Similar technologies have been applied to polymer waveguides to produce passive optoelectronic components for high speed interconnection with surface roughness less than 20 nm and low attenuation. The paper also reviews the technical and economical limitations and the potential of the technology for other micro products.
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