Laser Microwelding Research Articles

Quality improvement of copper welds by laser microwelding with the usage of spatial power modulation

Laser welding of copper is gaining more and more importance to create electrical contacts due to the high temperature resistance and high achievable mechanical loads. However, laser welding of copper in the past was always associated with low process stability. By using high brightness fiber laser sources, small laser spots can be generated which allows keyhole-based deep penetration welding even in copper with high quality. Unfortunately, a small spot size and keyhole welding lead to a small connection area between the two joining partners. To avoid this, spatial power modulation—a linear feed with superposed circular motion—has been introduced. By using an additional parameter, oscillation frequency, and amplitude, in conjunction with spatial power modulation, we can increase not only the connection area but also the stability of the laser welding process and quality characteristics of the welds. In addition to the conformity of the weld depth, the surface roughness of the weld is a measure of the quality. Especially in interconnection of lithium ion cells and high power electronics, the consistency of the weld depth influences the connection area, which is essential for the current-carrying capacity. The quantity of weld defects and irregularities has a direct impact on the surface roughness of the weld. This paper presents recent results on the influence of the spatial power modulation on quality characteristics during laser microwelding by analyzing the weld via three-dimensional longitudinal cross sections and via laser measuring of the weld surface. Experimental investigations are supplemented by finite element simulations which enable a detailed analysis of the influence of the laser scanning strategy on the geometry of the fusion zone.

Interface modification based ultrashort laser microwelding between SiC and fused silica.

It is a big challenge to weld two materials with large differences in coefficients of thermal expansion and melting points. Here we report that the welding between fused silica (softening point, 1720°C) and SiC wafer (melting point, 3100°C) is achieved with a near infrared femtosecond laser at 800 nm. Elements are observed to have a spatial distribution gradient within the cross section of welding line, revealing that mixing and inter-diffusion of substances have occurred during laser irradiation. This is attributed to the femtosecond laser induced local phase transition and volume expansion. Through optimizing the welding parameters, pulse energy and interval of the welding lines, a shear joining strength as high as 15.1 MPa is achieved. In addition, the influence mechanism of the laser ablation on welding quality of the sample without pre-optical contact is carefully studied by measuring the laser induced interface modification.

A stainless-steel-based implantable pressure sensor chip and its integration by microwelding

A stainless-steel (SS) chip of capacitive pressure sensor and its integration method are developed with a focus on smart implant applications. The sensors are entirely microfabricated with biocompatible materials, through thermal bonding of gold-polyimide diaphragm film to the chip dies made of medical-grade SS. The reference cavity design with dead-end holes created in the SS die is both theoretically and experimentally verified to enhance pressure sensitivity. Laser microwelding is investigated as an alternative integration path for this type of SS-based sensors to establish permanent and reliable bond onto SS-based platform devices. The microwelded bond is revealed to provide twice the mechanical strength and ∼6×electrical conductance compared with a conventional conductive epoxy case. The microwelded sensors exhibit an average sensitivity of 110ppm/mmHg close to its pre-welding level. The microwelding integrations of fabricated chips with the SS antenna stent and hypodermic needle are demonstrated. The results suggest not only that the developed pressure sensor is compatible with laser microwelding, but also that micowelding is a promising packaging technique for SS-based biomedical and implant microdevices that require long-term bond reliability.

Investigations of laser microwelding using low power fibre laser for thin 304 stainless steel sheets

Investigations of laser microwelding using low power fibre laser for thin 304 stainless steel sheets

Investigations of laser microwelding using low power fibre laser for thin 304 stainless steel sheets

Experimental investigation of laser beam butt welding of thin 304 stainless steel sheets (200 μm) using low power Yb-doped fibre Laser of 1090 nm wavelength is reported. Effect of various process parameters on ultimate tensile strength (UTS), width and depth are obtained. The laser power has been varied in order 60 (5) 85 W to understand its effect on the weld strength at different scanning speeds 4(2.0)10:00 mm/s. Beam spot diameter was varied between 200 (50) 300 μm. These governing parameters have been combined in the form of energy density (J/mm2) to present the results. It is observed that with an increase in the energy density the weld strength increases and reaches to maxima at around 80 J/mm2. At same value, the ratio of spot diameter to depth (D/d) is = 1.0 which is in tune with a value of energy density for maximum weld strength.

Influence of pulsation in thermo-mechanical analysis on laser micro-welding of Ti6Al4V alloy

The pulse parameters of laser heat source have a definite effect on the weld joint structure. However, the complexity in parameter selection increases many folds with reduction in geometric dimensions of the specimen. Hence, an attempt has been made to investigate the laser microwelding of 500µm thick Ti6Al4V alloy in butt joint configuration using pulse Nd:YAG laser. The influence of laser scanning speed and pulse energy is analyzed to produce a defect-free joint. High peak power is actually dampen by pulsation of laser cratered to use in microwelding process. The feasible range of process parameters like laser scanning speed of 3–7mm/s and peak power of 1–5kW produces high quality weld joint using other favorable conditions that mainly diminishes the formation of oxides in welding of titanium alloy. A sophisticated numerical model is always beneficial to capture the thermo-mechanical behavior under differential influence of process parameters. A 3D finite element based sequentially coupled thermo-mechanical model is developed by considering the pulse mode of heat flux. There is considerably variation in temperature profile using actual pulse mode of heat flux as compared to average laser power. Typical hourglass heat source for over penetrated weld is developed for the simulation of microwelding process. Large-displacement theory is considered to predict the weld-induced distortion for laser microwelding process. The computed results are well agreed with experimentally measured values and show the robustness of the present numerical model used for micro scale welding process.

Conditioning of copper material surfaces increasing the efficiency of continuous wave laser microwelding

Major challenges in the welding of copper are high reflectivity for infrared wavelengths and insufficient reproducibility of the welds. Studies have shown that the surface conditioning of copper materials with pulsed green laser radiation stabilizes process conditions, as well as significantly increases absorption of pulsed infrared laser radiation. Experimental results are presented, which illustrate how advantages of this conditioning can be transferred to welding with continuous IR radiation. It is possible to significantly reduce the necessary IR laser power and to optimize the weld appearance. In this regard, the influence of inert gas and the conditioning parameters is analyzed.

An investigation of heat transfer and fluid flow on laser micro-welding upon the thin stainless steel sheet (SUS304) using computational fluid dynamics (CFD)

A transient three-dimensional model is numerically developed using the method of computational fluid dynamics (CFD) to characterize some thermal phenomena and characterization of heat transfer and fluid flow in laser micro-welding by considering the heat source and the material interaction leads to rapid heating, melting and thermal cycles in the heating zone. The application of developed thermal models has demonstrated that the laser parameters, such as laser power, scanning velocity and spot diameter, have considerable effects on the peak temperature and resulted weld pool. The heat source model is consisted of surface heat source and adaptive volumetric heat source that could be well represented the real laser welding as the heat penetrates into the material. In the computation of melt dynamics, mass conservation, momentum and energy equations have been considered to compute the effects of melt flow and the thermo-fluid energy heat transfer. The simulation results have been compared with two sets of experimental research to predict the weld bead geometry and solidification pattern, which laser welds are made on thin stainless steel sheet (SUS304). The shape comparison describes those parameters relevant to any changes in the temperatures and melt dynamics are of great importance on the heat distribution and formation of weld pool during laser micro-welding process. The fair agreement between simulated and experimental results, demonstrates the reliability of the computed model.

Thermo-Mechanical Analysis on Thermal Deformation of Thin Stainless Steel in Laser Micro-Welding

In the present study, a three-dimensional finite element model has been developed to simulate the temperature, stress and deformation fields in continuous wave (CW) laser micro-welding of thin stainless steel sheet. The welding deformation was experimentally evaluated using a single-mode fiber laser with a high-speed scanning system. Application of developed thermal model demonstrated that the laser parameters, such as laser power, scanning velocity and spot diameter have a significant effect on temperature field and the weld pool. In the case of welding deformation, numerical simulation was carried out by an uncoupled thermo-mechanical model. The welding stress and deformation are generated by plastic deformation during the heating and cooling periods. It was confirmed that the residual stress is higher than yield strength and has strongest effect upon the welding deformation. The numerical simulated results have proved that the developed finite element model is effective to predict thermal histories, thermally induced stresses and welding deformations in the thin material.

Investigations of welding instabilities and weld seam formation during laser microwelding of ultrathin metal sheets

During laser microwelding, the melt pool behavior and the formation of the weld seam depend on various process parameters. In this paper, the authors performed tests to clarify the influence of laser power P, the feeding rate vf, the focal diameter df, the foil thickness s, and the thermophysical material properties. Ultrathin metal foils such as stainless steel, aluminum, and titanium in thicknesses of 50 and 100 μm were welded in bead-on-plate welds in order to generate a full penetration weld. For this purpose, focal diameters between 25 and 78 μm were applied. By means of high-speed videography and micro-cross-sections, the observations were analyzed depending on the feeding rate. Imperfections such as root defects, surface structures, and humps were described and evaluated. Moreover, the influence of melt pool behavior prior to the appearance of humping is illustrated for full penetration microwelding in contrast to insufficient welds. The Rayleigh theory of the instability of a free suspended liquid cylinder is discussed. A correlation between the length of the melt pool L and the spot size df is examined to define the humping threshold for stainless steel. Due to the different thermophysical properties of the applied materials, weld seam formation and process behavior are changed.

Effect of wavelength and pulse duration on laser micro-welding of monocrystalline silicon and glass

Micro-welding characteristics of silicon and glass by pulsed lasers are described. In this study, four types of laser beam, which are nanosecond pulsed laser and picosecond pulsed laser of 532 and 1064 nm in wavelength, were used for joining monocrystalline silicon and glass. Influence of wavelength and pulse duration on micro-welding of monocrystalline silicon and glass was experimentally investigated under the same spot diameter, and the molten area of monocrystalline silicon and glass was characterized. Finally, the breaking strength was evaluated for the overlap weld joint with different pulse duration and wavelength. A splash area of molten silicon around the weld bead line was obvious in the nanosecond pulsed laser. On the other hand, there was no remarkable molten splash around the weld bead line in the picosecond pulsed laser. Breaking strength of specimens with 1064 nm wavelength was higher than with 532 nm wavelength in nanosecond laser, whereas breaking strength of laser-irradiated specimen by picosecond pulse duration was higher than that by nanosecond pulse duration. It is concluded that the combination of picosecond pulse duration and infrared wavelength leads to the stable molten area appearance of the weld bead and higher breaking strength in micro-welding of glass and monocrystalline silicon.

Implantable diamond capsules for electro stimulation and recording

Event Abstract Back to Event Implantable diamond capsules for electro stimulation and recording Kumaravelu Ganesan1, 2, David J. Garrett1, Nick Opie2 and Steven Prawer1 1 University of Melbourne, School of Physics, Australia 2 SmartStent PTY LTD, Australia Introduction: Implantable electronic devices must necessarily adhere to a very strict set of standards before they can be approved for clinical use. One of these standards is the requirement that electronically active components such as microprocessors must be encapsulated hermetically to protect the body from the toxicity of conventional electronic components and as well as to protect the components from the harsh environment inside the body which leads to accelerated device failure. This article provides an overview of an all-diamond hermetic capsule for retinal as well as cortical implants for electrostimulation and recording. Materials and Methods: Diamond Microelectrode array: Diamond microelectrode array of 3-D surface electrodes as shown in fig1a and fig 1.b was fabricated using conventional as well as unconventional fabrication techniques. The microelectrodes are nitrogen incorporated unltrananocrystalline diamond and the body is polycrystalline diamond[1]. CMOS chip integration: Lithographically defined Indium bumps and flip chip bonding technique was used to bond the CMOS processor to the electrode to make one-to-one connection. Electrical feedthrough: An active braze alloy of 95% gold was brazed in vacuum environment to form the electrical feedthrough, electrical contacts as well as the braze line for final laser welding. Laser Microwelding : Pulsed Laser welding technique was used to join the two halves together hermetically. Fig. 1. (a) Components of the diamond/gold encapsulation with high-density diamond electrode array (2) flip-chip bonded to a 256 channel stimulator application specific integrated circuit (ASIC) (1) and a diamond box with integrated feedthroughs for power and data transfer (3). The two diamond components are sealed by welding around the outer edges of the braze seam (b).[2] (c)Diamond cortical implant for recording. This is approximately half the size of the retinal implant shown in (b) and has the dimension of 2X0.7X0.3mm. A receiver Rx coil in fabricated on the diamond body. Results and Discussion: An all diamond 256 channel retinal implant was fabricated and tested successfully. A cortical recording implant is under development with the wireless power and data transfer facilities. Conclusion: A new hermetic encapsulation paradigm for a medical implant , using polycrystalline diamond, was presented. The new packaging technology uses high-conductivity gold braze feedthroughs for power and data input and a laser welded seam of Gold-ABA braze joining the diamond shell components. This work was funded in part from Australian Research Council through its Special Research Initiative (SRI) in Bionic Vision Science and Technology grant to Bionic Vision Australia (BVA); ARC Linkage grant 2015(SMARTSTENT PTY LTD)

Laser micro-welding of Cu-Al dissimilar metals

To study laser micro-welding technology of dissimilar metals, experimental research has been conducted on laser micro-welding of a fine copper wire to an Al pin of an integrated circuit chip. The results show that a Nd:YAG pulse laser welding system with a maximum output power of 300 W can successfully join a fine copper wire of 0.25-mm diameter with an Al pin. The process parameters include a single pulse energy of 3.3 J, a defocusing amount of −0.5 mm, and a peak power of 0.7 kW. During the laser micro-welding process, the laser beam illuminates the surface of the fine copper wire, which has high melting temperature and good fluidity, melting it so that the Al pin becomes submerged in the copper melt, attaining common defects such as blowholes and cracks and exhibiting poor fluidity and high oxidability. Solution-diffusion welding is conducted, and good metallurgical bonding is obtained between the fine copper wires and the Al pins with the decrease of their temperature.

A computational analysis of heat transfer and fluid flow in high-speed scanning of laser micro-welding

A transient three-dimensional model is numerically developed using computational fluid dynamics (CFD) method to understand some critical criteria such as temperature fields and melt pool formation by considering the heat source and the material interaction and the effect of laser welding parameters on laser micro-welding process. To gain more implicit insight of fluid dynamics, the issue of circulation of molten metal assisted by the surface tension, buoyancy and recoil pressure forces in the weld pool has been investigated Assuming that atmospheric and vaporised material pressures are balanced at the front of the laser beam. The governing equations from the Navier–Stokes for Newtonian fluid are prepared to estimate the melt flow that influences the rate of temperature distribution in a 3-D domain. The simulation results have been compared with two sets of experimental research to predict the weld bead geometry and solidification pattern which laser welds are made on thin stainless steel sheet (SUS304). The shape comparison describes those parameters relevant to any changes in the melt dynamics and temperatures are of great importance on the formation of weld pool and heat distribution during laser micro-welding. The fair agreement between simulated and experimental results, demonstrates the reliability of the computed model.

Structure, Texture and Magnetic Properties of Laser-Welded Ultrathin Fe–Co–V Foils

This research aims to investigate the effect of pulsed Nd:YAG laser micro-welding on the microstructure, texture and magnetic properties of ultra-thin Fe–Co-7.15 wt% V magnetic alloy. Optical microscopy, scanning electron microscopy and electron backscattered diffraction techniques were used to study the microstructural evolutions. Also, vibrating sample magnetometry was used to characterize the magnetic properties. The results showed that the fractions of low Σ coincidence site lattice boundaries in the fusion zone are higher than those of the base metal. The welded samples experience a significant decrease in their magnetic properties. It was found that the formation of new fiber texture in the fusion zone and grain coarsening are the most important factors affecting the magnetic properties.

403 純チタンの横向き姿勢レーザ微細溶接におけるシールドガス供給方法の検討(生産加工・工作機械+材料加工I)

403 純チタンの横向き姿勢レーザ微細溶接におけるシールドガス供給方法の検討(生産加工・工作機械+材料加工I)

Influence of Bead Geometry on Weld Distortion in Laser Micro-welding of Thin Stainless Steel Sheet with High-speed Scanning

Influence of Bead Geometry on Weld Distortion in Laser Micro-welding of Thin Stainless Steel Sheet with High-speed Scanning

超短脉冲激光微焊接玻璃进展

超短脉冲激光微焊接玻璃进展

Microstructural analysis of laser micro-welds between copper and aluminum

Currently used ultrasonic welded joints for assembly and packaging of Li-Ion batteries have reliability concerns for automotive applications, as the battery is subjected to vibration and other mechanical loads. The sealing of the battery can is very critical for safety. Due to battery weld failures in recent years, the postal service has put ban on shipping Li-ion batteries via regular mail. A laser based alternative joining technology has the potential to offer robust, fast and cost-effective processing of Li-Ion batteries. Before the technology can be fully implemented, it is imperative to understand the effects of various process parameters on the robustness of the weld. In the present analysis, a preliminary study is performed to understand the effect of laser scanning speed on the micro-structural and physical characteristics of the materials in the weld area that ultimately affect the bond quality. Samples are created by welding aluminum and copper in lap shear configuration using a continuous wave fiber laser. Two sets of samples are created using a laser power of 225 W; however, the scanning speeds are 300 and 400 mm/s. Scanning electron microscopy and energy dispersive spectroscopy are performed in the weld area to understand the microstructural and physical characteristics of the joint that may have been affected by the processing parameters.

A laser microwelding method for assembly of polymer based microfluidic devices

This paper presents the development of a laser microwelding method for assembly and packaging of polymer based microfluidic devices. In this approach a diode laser was used to weld two poly(methyl methacrylate) (PMMA) substrates together at the interface using a thin film metal spot based intermediate layer design as a localized absorber. A broad laser beam with a top-hat profile was used to carry out the laser microwelding work. The effects of laser power and processing time on the resultant heated affected zone (HAZ) and the melted zone were investigated. For large area welding, a 2×2 array of thin film metal spots were used to investigate the effect of separation between the spots on the resultant interfacial bond between the two polymer substrates. For comparison, a large area titanium film with a comparable size to that of the 2×2 array was also studied. The results show that the discrete film pattern based design is better than a single large area film in order to reduce the effect of substrate distortion resulting from the higher temperature rise associated with the latter. The tensile strength of the laser welded joints was determined to be about 6MPa for a sample produced using the 2×2 array of circular titanium spot pattern design. The laser microwelding method has been demonstrated successfully in leak-free encapsulation of a microfluidic channel.