The ongoing development of lasers with integrated beam-shaping features offers new opportunities for research in the field of laser beam welding. Main challenges for laser welding of aluminum alloys, such as AW-5083 or AW-6082, are pore formation and cracking. The locally adapted power distribution has a major influence on the keyhole required for deep penetration welding and therefore on occurring weld defects. To determine the reasons, the use of synchrotron radiation during the welding process enables the visibility of the keyhole shape. This investigation contains an analysis of the keyhole and melt pool shape based on the high-speed video images of the synchrotron radiation. The variation of the power ratio of center beam to ring allows a comparison of the influence of the beam shaping method. To stabilize the keyhole, a temporal power modulation is used for the ring. The results show an influence of the ring mode on the keyhole depth and the melt pool shape. The videos allow an analysis of different mechanisms for pore formation, such as the collapse of the keyhole.
Laser welding as a tool for manufacturing highly precise parts for electronic and electro mobility components is gaining worldwide importance. The precise control of energy input is one paramount challenge of welding highly reflective materials with high thermal conductivity such as copper and its alloys. Laser beam wavelengths in the visible range show an increase in absorptivity from < 5% (1030 nm) to ≥ 40% (515 nm) on copper at room temperature and open new options in material processing technologies. This paper presents the in situ observation of laser welding processes on Cu-ETP and CuSn6 with laser beam sources of 1030 nm and 515 nm wavelength using synchrotron radiation at DESY Petra 3 Beamline P07 EH4. The influence of laser power from 1 kW up to 4 kW and feed rates from 50 mm/s up to 500 mm/s on vapor capillary geometry and dynamics with same focal diameters is compared. For the investigations, a synchrotron beam of 2x2 mm2 in size with a photon energy of 89 keV is used for investigation. The material samples are analyzed by means of material phase contrast method to show boundaries between solid, liquid, and gaseous material phases. It is found, that both welding processes show a different geometry of the vapor capillary. A different sensitivity to changes of the feed rate of the welding process is observed. The vapor capillary of the 1030 nm welding process tends to be more sensitive on feed rate changes while showing an overall better weld seam quality. When welding with 515 nm, comparatively higher feed rates lead to better welding results.
The laser beam welding process is not commonly used for joining interconnectors on metallized substrate such as Printed Circuit Board (PCB) due to the presence of the vapor capillary and high energy input which exceed the thermal destruction threshold of the substrate. To perform a welding process between interconnectors and PCBs, a metallization with sufficient thermal mass is required. The cold gas spraying process is used to spray a copper layer on a thin metallization to increase its thickness and the thermal mass. In this paper, a copper interconnector is laser-welded on a metallization of PCB which is cold gas sprayed with copper powders. The characterization and transfer of the welding technology to the joining of spray layer is investigated. The main challenges of the welding process on spray layer on substrate are the uncontrolled surface roughness and the inhomogeneous heat distribution of the spray layer compared to the bulk material. The influence of the surface roughness on the void formation is investigated by considering roughness values of the sprayed layer. A correlation between the void formation and the surface roughness is shown. Also, the void formation at the weld joint increases with the higher laser beam power. The increased laser beam power leads to a deeper vapor capillary and it is assumed that the inhomogeneous heat distribution of the lower joining partner induces varying solidifications speed. By reducing the surface roughness value and lower laser beam power, we could significantly reduce the void formation at the weld root.
Due to the increasing power, contacting of high-power semiconductor components requires ever larger cross sections, which can no longer be handled by conventional joining processes such as ultrasonic wire and ribbon bonding. To generate larger cross sections than those that can be joined by an ultrasonic bonding process, an alternative joining method must be selected. Laser beam welding offers the possibility of contactless joining without additional external force. Due to the process, however, a minimum thickness of the lower joining partner is required, on the one hand to prevent a through-weld and on the other hand to reduce the thermal stress for sensitive layers below the lower joining partner. A joining process that can also be used for contacting thin metallizations is laser-based soldering. An advantage of this method is the lower thermal load on sensitive components. However, disadvantages are on the one hand a higher contact resistance at the joining point and on the other hand a poor solderability of some materials (e.g. stainless steel, aluminum) when using a soft soldering process. In the context of this work, first results from the development of a combined laser-based joining process of freely combinable welding and soldering technology are presented. The contacting on a substrate to be soldered is done by means of a tin-plated strip connector and the contacting on the metallized semiconductor is done as laser welding. In both cases, the contact material or the connector is designed as a tin-plated ribbon material. This provides the user with a process with which the connection can be carried out either as welding, as soldering or in a combination of welding and soldering.
So far, the main approach to weld absorber-free thermoplastics is exploiting their intrinsic absorption by choosing a
proper wavelength of the laser. In order to melt the joining partners spatially restricted at the interface usually optics with
a high numerical aperture are used. However, practice shows that the heat affected zone (HAZ) extends over a large area
along the beam axis regardless of the optics used. Without clamping or convective cooling thermally induced expansion
of the material can cause blowholes or deformation of the irradiated surface. To reduce the thermal stress on the part
surface a dynamic beam superposition is investigated with the laser beam performing a precession movement.
Joining fiber reinforced polymers is an important topic for lightweight construction. Since classical laser transmission welding techniques for polymers have been studied and established in industry for many years joint-strengths within the range of the base material can be achieved. Until now these processes are only used for unfilled and short glass fiber-reinforced thermoplastics using laser absorbing and laser transparent matrices. This knowledge is now transferred to joining long glass fiber reinforced PA6 with high fiber contents without any adhesive additives. As the polymer matrix and glass fibers increase the scattering of the laser beam inside the material, their optical properties, changing with material thickness and fiber content, influence the welding process and require high power lasers. In this article the influence of these material properties (fiber content, material thickness) and the welding parameters like joining speed, laser power and clamping pressure are researched and discussed in detail. The process is also investigated regarding its limitations. Additionally the gap bridging ability of the process is shown in relation to material properties and joining speed.
Within the plastic industry laser transmission welding ranks among the most important joining techniques and opens up
new application areas continuously. So far, a big disadvantage of the process was the fact that the joining partners need
different optical properties. Since thermoplastics are transparent for the radiation of conventional beam sources (800-
1100 nm) the absorbance of one of the joining partners has to be enhanced by adding an infrared absorber (IR-absorber).
Until recently, welding of absorber-free parts has not been possible.
New diode lasers provide a broad variety of wavelengths which allows exploiting intrinsic absorption bands of
thermoplastics. The use of a proper wavelength in combination with special optics enables laser welding of two optically
identical polymer parts without absorbers which can be utilized in a large number of applications primarily in the
medical and food industry, where the use of absorbers usually entails costly and time-consuming authorization processes.
In this paper some aspects of the process are considered as the influence of the focal position, which is crucial when both
joining partners have equal optical properties. After a theoretical consideration, an evaluation is carried out based on
welding trials with polycarbonate (PC). Further aspects such as gap bridging capability and the influence of thickness of
the upper joining partner are investigated as well.
In this contribution we evaluate laser scanning approaches for the interconnection of the 31 electrical contacts of a MWT
back-contact solar cell. The selective energy deposition with a laser system allows the minimization of thermomechanical
stress in the wafer, but requires adapted scanning strategies to prevent damages in the solar cell top layer.
The laser scanning process of the MWT solar cell is conducted in combination with a composite foil as an interconnector
and a pre-dispensed solder paste. This approach is evaluated regarding the joining quality of the interconnection as a
function of the scanning strategy.
Plastics play an important role in almost every facet of our lives and constitute a wide variety of products, from everyday
products such as food and beverage packaging, over furniture and building materials to high tech products in the
automotive, electronics, aerospace, white goods, medical and other sectors [1].
The objective of PolyBright, the European Research project on laser polymer welding, is to provide high speed and
flexible laser manufacturing technology and expand the limits of current plastic part assembly. New laser polymer
joining processes for optimized thermal management in combination with adapted wavelengths will provide higher
quality, high processing speed up to 1 m/s and robust manufacturing processes at lower costs. Key innovations of the
PolyBright project are fibre lasers with high powers up to 500 W, high speed scanning and flexible beam manipulation
systems for simultaneous welding and high-resolution welding, such as dynamic masks and multi kHz scanning heads.
With this initial step, PolyBright will break new paths in processing of advanced plastic products overcoming the quality
and speed limitations of conventional plastic part assembly. Completely new concepts for high speed processing,
flexibility and quality need to be established in combination with high brilliance lasers and related equipment.
PolyBright will thus open new markets for laser systems with a short term potential of over several 100 laser
installations per year and a future much larger market share in the still growing plastic market. PolyBright will hence
establish a comprehensive and sustainable development activity on new high brilliance lasers that will strengthen the
laser system industry.
Recently, since the size of component becomes smaller, then the welding of thin metal sheet has been required. Besides, the flexibility of process is important according to the accessibility especially for small components. Fraunhofer Institute for Laser Technology had developed the SHADOW® welding technology, in which the high speed joining with small distortion is possible using pulsed Nd:YAG laser. The possibility of high speed and high quality welding had been reported by using single-mode fiber laser. The combination of micro beam and high speed laser scanning has the advantages for thin metal sheet welding. Therefore, the characteristics of micro-welding for thin metal sheet were investigated by high speed laser scanning, in which the welding was carried out by high speed scanner system with single-mode fiber laser and pulsed Nd:YAG laser. The proper welding region was narrow by the laser beam with a large focus diameter of 160 μm without pulse control, while a small focus diameter of 22 μm can control the welding state widely. A small focus diameter can perform the excellent welding seam from the extreme beginning without pulse control. The penetration depth can be controlled by the energy density with a small focus diameter of 22 μm at the energy densities less than 1 J/mm2. Besides, the unique periodic structure appeared at the high velocity of beam scanning with a small focus diameter. Moreover, the overlap welding of 25 μm thickness sheet can be performed regardless of small gap distance between two sheets by the laser beam with a small focus diameter of 22 μm.
The joining processes in electronic device manufacturing are today still dominated by conventional joining techniques like press fitting, crimping and resistance welding. Laser beam joining techniques have been under intensive investigations and subsequently new processes for mass manufacturing and high accuracy assembling were established. With the newly developed SHADOW(R) welding technology technical aspects such as tensile strength, geometry and precision of the weld could be improved. This technology provides highest flexibility in weld geometry with a minimum welding time as well as new possibilities in using application adapted materials. Different parts and even different metals can be joined by a non-contact process. The application of a relative movement between the laser beam and the part to be joined at feed rates of up to 60 m/min produces weld seams with a length from 0.6 mm to 15.7 mm using a pulsed Nd:YAG laser with a pulse duration of up to 50 ms. Due to the low energy input, typically 1 J to 6 J, a weld width as
small as 50 μm and a weld depth as small as 20 pm have been attained. This results in low distortion of the joined watch
components.
Within this paper this new welding process will be explained and several examples of joined components will be presented with respect to fundamentals and the sustainable implementation of the SHADOW (R) welding technique into watch manufacturing and electronic industry. For microsystem applications the laser joining technology is modified to join even silicon and glass parts without any melting based on the formation of a thermally induced oxygen bond. New fields of applications for joining different materials such as steel to brass or steel to copper for electrical interconnects will be discussed. Here the SHADOW(R) welding technique offers new possibilities for the combination of good electrical properties of copper with high mechanical stiffness of steel. The paper will give a closer look to microjoining applications especially using the SHADOW(R) welding technique. Basics of the process as well as its application on dedicated examples will be shown for small parts such as axis-wheel combinations and electrical connectors.
The joining processes in watch manufacturing industry are today still dominated by conventional joining techniques like press fitting or crimping. Laser beam micro welding provides consistent joining and high flexibility. Different parts and even different metals can be joined in a non-contact process. The application of a relative movement between the laser beam and the part to be joined at feed rates of up to 60 m/min produces weld seams with a length from 0.6 mm to 15.7 mm using a pulsed Nd:YAG laser with a pulse duration of up to 20 ms. Due to the low energy input, typically 1 J to 6 J, a weld width as small as 50 μm and a weld depth as small as 20 μm have been attained. This results in low distortion of the joined watch components. Since the first applications of laser beam micro welding of watch components showed promising results, the process could be further enhanced using the SHADOW welding technique. Aspects of the technique such as tensile strength, geometry and precision of the weld been improved. Within the scope of this paper this new welding process will be explained and several examples of joined watch components will be presented with respect to fundamentals and the sustainable implementation of the SHADOW welding technique into watch manufacturing. New fields of applications for joining different materials such as steel to brass or steel to copper for electrical interconnects will be discussed. Here the SHADOW welding technique offers new possibilities for the combination of good electrical properties of copper with high mechanical stiffness of steel. The paper will give a closer look to micro joining applications especially using the SHADOW welding technique. Basics of the process as well as its application on dedicated examples will be shown for small parts such as axis-wheel combinations.
The combination of dissimilar materials like brass and stainless steel is often needed in watch movements due to tribologic aspects. For mass production in automotive applications, a joining technique for alloyed copper with alloyed steel is needed. Laser beam micro welding offers an alternative to conventional joining techniques like press fit or soldering. Depending on the joining geometry, two different welding techniques are investigated: seam and spot welding. High strength and reproducibility are the main objective of joining dissimilar metals. Cracks and spillings are affected by the metallic continuity and should be avoided. Lap- and T-joints can be produced by the SHADOW-Welding technique. The length of the continuous welding seams are up to 15.7 mm at a feed rate of up to 60 m/min with a pulsed laser source. The weld width attained ranges from 50 to 250 μm and a weld depth from 20 to 150 μm. This low energy joining process with minimized heat input results in low distortion of the parts joined. Applying spot welding, the pulse forming capability is needed especially for highly reflective metals like copper. The welded joints have a higher strength than the basic material.
Laser beam soldering (LBS) is a non-standard manufacturing process for electronic packaging and interconnection technology today. Due to the actual trend towards complex and cost intensive products, LBS gains more attention for certain applications in this field. For mass production in automotive applications a fully automated and temperature controlled LBS process was developed. The achieved results are discussed with respect to quality, reliability and process efficiency and compared to established micro flame (hydrogen) soldering technology. The development of the LBS process is presented. The process window is optimized using High Speed Video Imaging. Temperature signals are logged by means of pyrometry. The processed parts are evaluated with metallographical assessment of solder joint quality. Especially cross sections reveal the fine grained structure and the shape of the meniscus of the solder joints. The reliability is proven using shear strength tests and thermally induced strain cycles. Conclusively, LBS is a stable, reproducible process for applications requiring controlled and locally restricted heat input. The thermal and mechanical stress is reduced in comparison to conventional techniques.
Conventional joining techniques like press fitting or crimping require the application of mechanical forces to the parts which, in combination with the tolerances of both parts to be joined, lead to imprecision and poor tensile strength. In contrast, laser beam micro welding provides consistent joining and high flexibility and it acts as an alternative as long as press fitting, crimping, screwing or gluing are not capable of batch production. Different parts and even different metals can be joined in a non-contact process at feed rates of up to 60 m/min and with weld seam lengths from 0.6 mm to 15.7 mm. Due to the low energy input, typically 1 J to 6 J, a weld width as small as 50 μm and a weld depth as small as 20 μm have been attained. This results in low distortion of the joined watch components. Since the first applications of laser beam micro welding of watch components showed promising results, the process has further been enhanced using the SHADOW technique. Aspects of the technique such as tensile strength, geometry and precision of the weld seam as well as the acceptance amongst the -mostly conservative- watch manufacturers have been improved.
The increasing demands in MEMS fabrication in the past led to new requirements in production technology for these devices. Especially the packaging and assembly of optical devices like high power diode lasers require high accuracy in positioning and high reproducibility in combination with low production costs. Conventional assembly technology and mechanical adjustment methods are time consuming and exspensive. Therefore a need of new assembly procedures arose. Each component of the system has to be positioned and fixed. The equipment for manipulating is very expensive. Also adjustment of the parts after joining requires additional mechanical devices that need to be accessible after joining. The decreasing dimensions of the microsystems cause problems in assembly and increase dramatically the tolerance conditions
The laser beam micro forming as a non-contact tool offers the possibility of active adjusment after the assembly is completed.
This paper describes this new technology pointing out the used mechanisms of laser induces deformation:
From the basic mechanisms dedicated structures are derived to achieve the desired degrees of freedom for the adjustment process. Based on the upsetting mechanism the positioning of a cylindrical lens in front of a high power diode laser is shown. The adjustment in two degrees of freedom can be realized by irradiating the actuating structure from one direction. The achieved accuracy is in the micron range.
The knowledge transfer to a tube-like actuator will be demonstrated. The tilting of a mirror in two rotational movements will be shown.
The results to be presented have partially been achieved within the Collaborative Research Center (SFB) 440 "Assembly of Hybrid Microsystems" which was financially supported by the Deutsche Forschungsgemeinschaft DFG.
After the invention of the laser principle and its first application for drilling of jewels in watch movements, the laser was only used for marking. The still ongoing trend of miniaturization and automation opened a new field of application: laser beam micro welding. This paper gives an overview of the new application of laser beam welding in watch industry. The combination of dissimilar materials like brass and stainless steel is often needed in watch movements due to tribologic aspects. Here, laser beam micro welding offers an alternative to conventional joining techniques like press fit or gluing. Since the watch components are very small the locally limited heat input of the laser beam offers the possibility of weld seam widths < 200 micrometers . The depth and the width of the closed weld seam as well as the surface quality can be influenced especially at the end of the seam using the pulse forming capability of a pulsed Nd:YAG laser. Several watch components could be joined by means of laser beam micro welding. The width of the seam could be reduced to 100-200 micrometers . The joining geometries of an axis/wheel combination are in the range of 100 micrometers to 1 mm diameter of the axis and about 200 micrometers wheel thickness. The process of laser beam micro welding could be integrated in a fully automated assembly machine for watch movement parts. This paper will give an overview about some results of a European research project where the welding of microparts was investigated. The aim was to decrease contamination and distortion of the parts during the mending process. The work to be presented has been funded by the European Commission in a project under the contract BRPR-CT- 0634.
The new welding technique 'SHADOW ' is introduced. SHADOW means the use of a single pulse to generate a quasi continuous weld of several millimeters in length. HET processing time is defined by the pulse duration of the pulsed laser. At present, a state-of-the-art laser is capable of a maximum pulse duration of 20 ms. The variation of the laser power depend on time is a vital capability of the pulsed laser to adapt the energy deposition into the workpiece. Laser beam welds of several watch components were successfully performed. Similar metals like crowns and axes made out of stainless steel have been welded using pulsed laser radiation. Applying a series of about 130 single pulses for the crown-axis combination the total energy accumulates to 19.5 J. The use of the SHADOW welding technique reduces the energy to 2.5 J. While welding dissimilar metals like stainless steel and bras, the SHADOW welding reduces drastically the contamination as well as the distortion. Laser beam welding of copper has a low process reliability due to the high reflection and the high thermal conductivity. SHADOW welds of 3.6 mm length were performed on 250 micrometers thick copper plates with very high reproducibility. As a result, a pilot plant for laser beam welding of copper plates has been set up. The work to be presented has partly been funded by the European Commission in a project under the contract BRPR-CT-0634.
The production of microsystems and miniaturized devices often requires joining technologies, which meet the demands of ultra clean manufacturing. Especially for optical and medical products low pollution and distortion joining processes are necessary to guarantee the quality and the function of the device. For this applications laser welding with fiber lasers at laser powers of up to P = 10 W and focus dimensions < 30 micrometers have been used for welding micro mechanical devices. At intensities I > 106W/cm2 welding depths of 100 micrometers can be achieved with minimized pollution of the parts and smooth and clean appearance of the surface of the welds. For joining polymers and dissimilar materials high power diode lasers have been used providing even better conditions regarding pollution of the joining partners. By using material adapted laser wavelengths the heating of the material can be concentrated to the inner joining area of an overlap material joint. With this technique, thermoplastic polymer compounds and silicon glass compounds have been joined with low temperature and no influence on the quality of the parts with joining widths of less that 100 micrometers .
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