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This study used electroless nickel‐immersion gold surface finish. The lead free solder used are tin‐silver‐copper 305 and tin‐silver‐copper 307 solder alloys. The difference in copper composition will affect the intermetallic compound′s microstructure after the laser soldering process. The intermetallic compound formation analysis reveals that only (Cu, Ni)6Sn5 was observed at the solder joint interface for both solders after laser soldering. The grain microstructure of tin‐silver‐copper 305 formed is rounded‐shaped and bar‐shaped, while tin‐silver‐copper 307 shapes are oval‐shaped and flake‐like. However, for cross‐sectioned analysis, the intermetallic compound grain microstructure formed at the solder joint formation was (Ni, Cu)3Sn4 and (Cu, Ni)6Sn5 presented in dendrite‐like and scale‐like shapes. This result shows that copper content in solder composition is directly affected the intermetallic compound grain microstructure. When exposed to the ageing process, the intermetallic compound thickness will increase directly with ageing time. The intermetallic compound thickness for tin‐silver‐copper 305 was increased from 0.98 μm to 8.34 μm while tin‐silver‐copper 307 was increased from 1.54 μm to 8.76 μm. The result also shows that nano‐sized of Ag3Sn grain particle was formed on the intermetallic compound surface after an ageing process for both samples, tin‐silver‐copper 305 and tin‐silver‐copper 307. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to investigate the influence of different solder alloy materials on passive devices during laser soldering process. Solder alloy material has been found to significantly influence the solder joint's quality, such as void formation that can lead to cracks, filling time that affects productivity and fillet shape that determines the solder joint's reliability. Design/methodology/approach: Finite volume method (FVM)-based simulation that was validated using real laser soldering experiment is used to evaluate the effect of various solder alloy materials, including SAC305, SAC387, SAC396 and SAC405 in laser soldering. These solders are commonly used to assemble the pin-through hole (PTH) capacitor onto the printed circuit board. Findings: The simulation results show how the void ratio, filling time and flow characteristics of different solder alloy materials affect the quality of the solder joint. The optimal solder alloy is SAC396 due to its low void ratio of 1.95%, fastest filling time (1.3 s) to fill a 98% PTH barrel and excellent flow characteristics. The results give the ideal setting for the parameters that can increase the effectiveness of the laser soldering process, which include reducing filling time from 2.2 s to less than 1.5 s while maintaining a high-quality solder joint with a void ratio of less than 2%. Industries that emphasize reliable soldering and effective joint formation gain the advantage of minimal occurrence of void formation, quick filling time and exceptional flowability offered by this solution. Practical implications: This research is expected not only to improve solder joint reliability but also to drive advancements in laser soldering technology, supporting the development of efficient and reliable microelectronics assembly processes for future electronic devices. The optimized laser soldering material will enable the production of superior passive devices, meeting the growing demands of the electronics market for smaller, high-performance electronic products. Originality/value: The comparison of different solder alloy materials for PTH capacitor assembly during the laser soldering process has not been reported to date. Additionally, volume of fluid numerical analysis of the quality and reliability of different solder alloy joints has never been conducted on real PTH capacitor assemblies. [ABSTRACT FROM AUTHOR]

This study introduces a novel method for integrating aluminum flexible printed circuit boards (FPCBs) and copper FPCBs into battery management systems (BMS) using and instantaneous large area facial laser source soldering. Achieving a robust bonding strength of 65 MPa involved applying 600 W of laser power for 2 s, enhancing atom diffusion and promoting intermetallic compound (IMC) growth. Finite Element Method (FEM) simulations revealed variations in heat transfer between Al and Cu, affecting IMC thickness at interfaces. Formation of the (Cu, Ni)3Sn4 phase within solder, and variations in laser output significantly influenced solder joint orientation and Al electrode nucleation. Excessive laser power (>800 W) caused critical damage, such as delamination at the Al-PI interface, altering fracture modes and bonding strength. Furthermore, with a detailed examination of the laser soldering phenomenon through both experimental and numerical investigations, this study provides a thorough understanding of the different soldering mechanisms in conventional reflow soldering compared to instantaneous uniform large-area heat source laser soldering. These insights provide new design and material considerations to replace the conventional wiring harness with Al/Cu FPCB lap joints which optimize the circuitry and reducing BMS volume.

iSoldering_wetting software was used to simulate the solder wetting process in laser soldering. Based on the simulation, the range of process parameters was initially determined, and the orthogonal experimental method was used to study the impact of each process parameter on solder wetting and connection quality. Then, the components were connected to the printed circuit board (PCB) using laser soldering equipment, and the welding seam morphology was analyzed to verify the reliability of the software. Pull-out experiments were carried out to test their connection strength using a universal testing machine. The results show that the simulation of the solder wetting process using iSoldering_wetting software is reliable. Laser power 16 w, wire speed 10 mm/s, and welding time 0.7 s are the process parameters with the best wettability of Sn-based solder, and the connection strength between the component and PCB is the highest using these process parameters. [ABSTRACT FROM AUTHOR]

The electric vehicle (EV) industry challenges battery joining technologies by requiring higher energy density both by mass and volume. Improving the energy density via new battery chemistry would be the holy grail but is seriously hindered and progresses slowly. In the meantime, alternative ways, such as implementing more efficient cell packaging by minimising the electrical resistance of joints, are of primary focus. In this paper, we discuss the challenges associated with the electrical characterisation of laser-soldered joints in general, and the minimisation of their resistive losses, in particular. In order to assess the impact of joint resistance on the overall resistance of the sample, the alteration in resistance was monitored as a function of voltage probe distance and modelled by finite element simulation. The experimental measurements showed two different regimes: one far from the joint area and another in its vicinity and within the joint cross-section. The presented results confirm the importance of the thickness of the filler material, the effective and total soldered area, and the area and position of the voids within the total soldered area in determining the electrical resistance of joints. [ABSTRACT FROM AUTHOR]

Laser soldering has attracted attention in microbumps joining field due to its noncontact and localized heating, a short joining time, fluxless and easy automation. In this study, Sn-3.0Ag-0.5Cu/Ni–P microbumps were prepared by laser soldering and reflow soldering respectively, then the effects of isothermal aging and multiple reflowing on microstructure and shear properties of the microbumps were compared and analyzed. The results show that a small granular and loose (Cu, Ni)6Sn5 intermetallic compounds and striated Sn grains were formed in laser-soldered microbumps, while a long and needlelike (Cu, Ni)6Sn5 intermetallic compounds and intertwined twins Sn grains were generated in reflow-soldered microbumps. During isothermal aging at 150 °C, the morphology of (Cu, Ni)6Sn5 particles changed to scallop with a large aspect ratio in the laser-soldered microbumps, which evolve to short rod-like in reflow-soldered microbumps, and the IMCs thickness in laser-soldered microbumps was always much thinner than that in reflow-soldered microbumps. The shear strength of as-soldered microbumps by laser soldering was slightly higher than that by reflow soldering ones, which sharply decreased from 0 to 100 h for both cases, and then was maintained at a similar level with increasing aging time. During multiple reflowing, the thickness of IMCs gradually increased in both cases, and the morphology of (Cu, Ni)6Sn5 particles changed to a dense short rod in laser soldered microbumps, which evolved to an irregular lumpy and long rod-like in reflow soldered microbumps. The shear strength for both laser and reflow soldered microbumps decreased with increasing reflowing times, but the decrease amplitude was all small. Moreover, the (Cu, Ni)6Sn5 IMCs transformed from granular to rod-like related to the content Ni atoms, and which critical value was evaluated to be 6–10 at%, based on the Jackson parameter α. Therefore, laser soldering is effective for reducing the thickness of IMCs and ensuring the mechanical property after isothermal aging and multiple reflowing of the microbumps was similar to reflow soldering.

The growing prominence of the electric vehicle industry, fueled by environmental concerns, has demanded innovation in various aspects of battery technologies with special emphasis on increasing the efficiency of both electric storage and its retrieval. An unexplored area of this is to identify the possibilities and limits of laser soldering. Here, we reveal the effects of surface pretreatment conditions and the amount of filler, along with the laser power and irradiation time on the characteristics of laser-soldered joints, by simultaneously evaluating the electrical and mechanical behavior of laser-soldered nickel-plated steel sheets (Hilumin®). By describing the morphological characteristics of the resolidified solder and the electrical and mechanical properties of the joints, we identify three, characteristically different morphological appearances and highlight the optimal one, where uniform and mostly void-free solder can be produced. Furthermore, we report a correlation between the threshold of upper sheet melting (either expressed as laser power or irradiation time) and joint deterioration in terms of the electrical and mechanical properties of the joint. We conclude that laser soldering can create joints with outstanding electrical conductance and adequate mechanical stability that meets the critical specifications of battery joining technologies when the surface pretreatment condition and processing parameters are properly optimized. [ABSTRACT FROM AUTHOR]

Purpose: Laser soldering has attracted attention as an alternative soldering process for microsoldering due to its localized and noncontact heating, a rapid rise and fall in temperature, fluxless and easy automation compared to reflow soldering. Design/methodology/approach: In this study, the metallurgical and mechanical properties of the Sn3.0Ag0.5Cu/Ni-P joints after laser and reflow soldering and isothermal aging were compared and analyzed. Findings: In the as-soldered Sn3.0Ag0.5Cu/Ni-P joints, a small granular and loose (Cu,Ni)6Sn5 intermetallic compound (IMC) structure was formed by laser soldering regardless of the laser energy, and a long and needlelike (Cu,Ni)6Sn5 IMC structure was generated by reflow soldering. During aging at 150°C, the growth rate of the IMC layer was faster by laser soldering than by reflow soldering. The shear strength of as-soldered joints for reflow soldering was similar to that of laser soldering with 7.5 mJ, which sharply decreased from 0 to 100 h for both cases and then was maintained at a similar level with increasing aging time. Originality/value: Laser soldering with certain energy is effective for reducing the thickness of IMCs, and ensuring the mechanical property of the joints was similar to reflow soldering. [ABSTRACT FROM AUTHOR]

High demands for precision laser soldering technologies arise as digital devices move towards volume downsizing. Laser soldering is a very complicated thermodynamic chemical process, and controlling the temperature also becomes challenging. Based on experimental data, a thermodynamic model for the soldering process is developed in this study, taking into account variables like laser power, spot size, and heating duration, among others. A novel feedforward-PI control algorithm is proposed using the model which includes a target temperature curve-based feedforward algorithm to help the PI feedback control to achieve precise temperature control during the laser soldering process. Experiments and comparisons are used to demonstrate the efficacy of the suggested model and control approach. The outcomes show that the suggested model is capable of effectively describing the dynamics of laser soldering. The temperature standard deviation of the proposed control technique is shown to be lower than 55%-60% of the classic PID control approach, while the former has higher precision. [ABSTRACT FROM AUTHOR]

Purpose: Pb-free solders have been developed to replace the standard Sn–Pb eutectic solder since the prohibition on Pb used in solders. The Sn–Ag–Cu series of lead-free solders is the most extensively used in the electronics industry. The Ag3Sn, which forms during isothermal ageing, can significantly degrade solder joint reliability. Sn–Ag–Cu solder's high price further hindered its use in the electronics industry. This paper aims to investigate different copper percentages into Sn–xCu solder alloy to improve its microstructure and strength performance. Design/methodology/approach: The solder alloys used in this work were Sn–xCu, where x = 0.0, 0.3, 0.5, 0.7, 1.0 Wt.%, which was soldered onto electroless nickel immersion gold (ENIG) substrate using carbon dioxide (CO2) gas laser. Then these samples were subjected to isothermal aging for 0, 200, 500, 1,000 and 2,000 h. The Sn–xCu solder alloy was fabricated through a powder metallurgy process. Findings: Microstructure characterization showed that Cu addition resulted in fine and rounded shape of Cu–Sn–Ni particles. Shear strength of Sn–xCu solder joints was increased with increasing Cu content, but at aging duration of 1,000 h, it dropped slightly. It is believed that the strength improved due to the increment of diffusion rate during isothermal aging. Practical implications: In a Cu–Sn solder, the recommended amount is 1.0 Wt.% of Cu. In extensive aging procedures, it was discovered that Sn1.0Cu solder improved the reliability of solder joints. The findings indicated that the innovative solder alloys might satisfy the needs of high-reliability applications. Originality/value: The study shows that the right amount of Cu enhances the solidification of Sn–Cu solder, increasing the shear force of the Cu–Sn solder joint. The Sn1.0Cu exhibits a ductile fracture on the top microstructure, improving the joint's average shear strength. [ABSTRACT FROM AUTHOR]

Laser soldering is a crucial soldering technique in the realm of electronic assembly. The temperature of the solder joint is intimately connected with the quality of the solder. This paper introduces an adjustable power upper limit variable-structure Proportional–Integral–Derivative (PID) intelligent control method for regulating the temperature of the solder joint during laser soldering. Distinct laser power limits are employed for workpieces with varying heat capacities. The solder joint temperature is monitored through an infrared thermometer, which enables closed-loop temperature control via a variable-structure PID algorithm. Residual neural network (ResNet) models are utilized to predict key soldering process parameters. This method has been executed and validated on a practical testing platform. Compared to other laser soldering control techniques, the proposed method demonstrates a low overshoot, rapid dynamic response, and swift adjustment capabilities, effectively enhancing the soldering quality and production efficiency. [ABSTRACT FROM AUTHOR]

A computational modeling is employed for quantitative assessment of weld formation and area of tissue temperature necrosis during the human skin laser soldering. The evaluation is carried out depending on the components composition of using solders, including bovine serum albumin (BSA), indocyanine green (ICG), and carbon nanotubes (CNTs), as well as the angle of incidence of laser light and its pulse duration. The influence of CNT on the change of thermodynamic characteristics of albumin denaturation and the rate of formation of the laser weld is investigated. The obtained results suggest to limit the duration of laser light pulse by temperature relaxation time to minimize transfer of thermal energy to reduce the heating of human skin tissues. The developed model has a great potential for further optimization of laser soldering of biological tissues technology with greater efficiency in minimizing the weld area. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to review the effect of copper percentage in Sn-based solder alloys (Sn-xCu, x = 0–5 Wt.%) on intermetallic compound (IMC) formation and growth after laser soldering. Design/methodology/approach: This study reviews the interfacial reactions at the solder joint interface, solder joint morphology and the theory on characterizing the formation and growth of IMCs. In addition, the effects of alloying and strengthening mechanism, including wettability, melting and mechanical properties are discussed. Findings: This paper presents a comprehensive overview of the composition of tin-copper (Sn-Cu) solders with a potential to enhance their microstructure, mechanical characteristics and wettability by varying the Cu percentage. The study found that the best Cu content in the Sn-xCu solder alloy was 0.6–0.7 Wt.%; this composition provided high shear strength, vibration fracture life value and ideal IMC thickness. A method of solder alloy preparation was also found through powder metallurgy and laser soldering to improve the solder joint reliability. Research limitations/implications: This study focuses on interfacial reactions at the solder joint interface, solder joint morphology, modelling simulation of joint strength and the theory on characterising the formation and growth of IMC. Originality/value: The paper comprehensively summarises the useful findings of the Sn-Cu series. This information will be important for future trends in laser soldering on solder joint formation. [ABSTRACT FROM AUTHOR]

Identification of laser soldering of lead-free solder Sn-3.0Ag-0.5Cu (SAC305) in electronic packaging was still an enormous challenge. It was difficult to detect defects in large-scale production. This work proposed an identification model based on multi-information fusion convolutional neural network (MIFCNN) for inspecting laser soldering process. In this method, the forty images in chronological order and the temperature data were combined as the input to be utilized in detecting defects. The results demonstrated that MIFCNN had best accuracy for three types of joints with accuracy of 98.28 % due to the combination of images and temperature information. The ICNN and TCNN had poor recognition accuracy for the warpage defect with 73.9 % and the poor wetting defect with 66.5 %, respectively. This was because the images and temperature information were the key to identifying the poor wetting defects and warpage defects, respectively. The poor wetting defect could be recognized by difference of contact angle, while the warpage defect could be significantly detected by maximum temperature. This work could help detecting defects of laser soldering in the actual production and widen the application of MIFCNN in the field of laser soldering. • A novel multi-information fusion model is proposed for defects identification. • The images and temperature information are collected simultaneously as inputs. • The reasons of better performance are investigated for the proposed model. [ABSTRACT FROM AUTHOR]

• Metal surface texturing is used to reduce the dispersity and void rate of solder in narrow gaps. • Gradient design of surface texture through different ultrafast laser scanning speeds is realized. • Based on the present method, the welding strength of 10.4 MPa is achieved. Obvious voids in the solder in a narrow gap is a common problem that greatly affects the reliability of mechanical connections. Due to its high heating rate, laser soldering causes more severe voids and even evolves into dispersion of the solder. A method of metal surface texturing is put forward, in which the texture gradient is used to directionally transport solder for lower dispersity, and the pattern design of texture is used to reduce the void rate. The directional transport of solder is realized through the differences in oxidation degree and microstructure of stainless steel surface under different ultrafast laser scanning speeds. The discharge of voids in the solder is achieved through the reservation of the central area in the solder and the oscillation during the laser heating process. Based on the present method, the aggregation of solder is achieved, with the void rate of 18 % and the joining strength of 10.4 MPa. [ABSTRACT FROM AUTHOR]

Laser soldering is a crucial soldering technique in the realm of electronic assembly. The temperature of the solder joint is intimately connected with the quality of the solder. This paper introduces an adjustable power upper limit variable-structure Proportional–Integral–Derivative (PID) intelligent control method for regulating the temperature of the solder joint during laser soldering. Distinct laser power limits are employed for workpieces with varying heat capacities. The solder joint temperature is monitored through an infrared thermometer, which enables closed-loop temperature control via a variable-structure PID algorithm. Residual neural network (ResNet) models are utilized to predict key soldering process parameters. This method has been executed and validated on a practical testing platform. Compared to other laser soldering control techniques, the proposed method demonstrates a low overshoot, rapid dynamic response, and swift adjustment capabilities, effectively enhancing the soldering quality and production efficiency.

• A method of reliable bonding of copper-coated glass and metal by continuous-wave laser soldering is proposed. • The maximum shearing force of 3239 N and the maximum shearing strength of 39.17 MPa are obtained. • The effects of welding parameters on the shearing force, shearing strength and welding area are discussed systematically. • The bonding mechanism of copper-coated glass and metal is explained. The research on laser welding of glass and metal mainly focuses on ultrashort pulse laser or nanosecond laser, since continuous wave (CW) laser cannot be directly applied to the welding of glass and metal. In this paper, a method of reliable bonding of copper-coated glass and stainless steel by laser soldering is proposed. The effects of welding parameters including laser power and irradiation time on the shearing force, shearing strength and welding area are discussed systematically. It can be concluded that the increase of laser power and irradiation time is beneficial to the improvement of welding strength. However, excessive heat input will lead to glass fragmentation and serious peeling of copper coating, causing the decrease of welding strength. At the welding parameters of laser power of 85 W and irradiation time of 50 s, the maximum shearing force of 3239 N and the maximum shearing strength of 39.17 MPa are obtained by laser irradiation on stainless steel. [ABSTRACT FROM AUTHOR]

Cu-based component/aluminum substrate solder joint is achieved through laser soldering technology in this paper. The solder wettability on aluminum substrate and microstructure-properties of Cu-based component/aluminum substrate laser soldering joint are studied. The results show that the presence of the high melting point Al2O3 oxide film (∼18.45 nm thickness) isolates the contact between the molten Sn-based solder and the aluminum substrate, which results in the poor wetting properties of aluminum substrate. The surface modification of aluminum substrate can significantly improve wettability (110°→14°). Anisotropic Sn dendrites appear in the brazing area of laser soldering joints, and Ag3Sn is precipitated in the β-Sn matrix. The (Cu, Ni)6Sn5 IMC is formed near the Ni layer side. Due to the extremely fast cooling rate, the IMC thickness is less than 5 μm, and a continuous (Cu, Ni)6Sn5 region with a thickness of less than 1 μm appears at the interface near the Ni layer side. The average maximum linear load of the laser soldering joints is 95.2 N/mm. The laser soldering joint fracture occurs along the brittle (Cu, Ni)6Sn5 IMC formed at the Ni layer interface, and the fracture mode is mainly ductile fracture.

The Sn-Pb solder is a conventional solder used in electronic assembling applications which needs replacement due to environmental concerns and legislation. In this study it was found that Pb-free Sn-Ag-Cu (SAC) solder was able to replace Sn-Pb solders. The soldering process was successfully performed with SAC305 by applying modulated pulse laser technique in the duty cycle of a 1070 nm fiber laser under ambient atmospheric pressure. The laser power is set at a constant of 85 W and the pulse frequency was 250 Hz with different duty cycles of 99, 90, 80, 70, 60 and 50%. There was a surface finish of electroless nickel immersion gold (ENIG) located between solder ball and Cu substrate. The formation of (Cu,Ni)6Sn5 as an intermetallic compound (IMC) layer at the SAC305/ENIG interface were observed using a scanning electron microscope (SEM) fitted with and energy dispersive spectroscopy (EDS). As a result, the modulated pulse affected the growth behaviour of interfacial layer. Also, a Ni3P layer is formed as the interfacial layer. Finally, the results showed that the hardness values fluctuated according to the duty cycle percentage. [ABSTRACT FROM AUTHOR]

Laser soldering has been widely used in electronic industries due to its excellent metallurgical bonding behaviour. In this research an investigation of intermetallic compound (IMC) formation at the interface between SAC405/Cu joint during laser soldering using different set of combined parameters was performed. As a comparison, reflow soldering was used. The characterization and microstructure analysis of samples were evaluated by using optical microscopy and a scanning electron microscope (SEM) equipped with an energy dispersive X-ray (EDX) analysis. The properties of each solder joints were analysed. The results revealed that Parameter (II) was selected as the best results due to excellent joining properties and less formation of voids at both interface and bulk solder. The IMC formed at the interface was identified as η-Cu6Sn5 while ε-Ag3Sn at the bulk solder. For the IMC thickness, the IMC layer of SAC405/Cu using Parameter (II) was thinner than IMC of SAC405/Cu after reflow soldering. Upon the revelation of these observations, using laser as a soldering method can reduce the growth of IMC layer thickness when compared to conventional reflow soldering. [ABSTRACT FROM AUTHOR]

Sn-Ag3.5-Cu0.7 Pb-free solder bumps were successfully fabricated on a copper clad laminate (CCL) surface by using a fiber laser system. The parameters of the laser apparatus used in the fabrication were laser power of 12 W, pulse frequency of 500 kHz, pulse duty factor of 50% and spot diameter of 0.03 mm. The fabrication result shows that the solder bumps formed by laser soldering were sufficiently and uniformly melted and securely joined with good properties. In this study, the spherical cap-type appearance of the solder bumps was theoretically interpreted from the perspective of the degree of lattice interface matching and it was demonstrated by non-spontaneous metal nucleation theory that the experimental parameters had been reasonably selected. [ABSTRACT FROM AUTHOR]

Suturing of corneal incisions requires significant skill. We demonstrate a noncontact method that will simplify the bonding process. 5-mm-long penetrating vertical and slanted incisions were made in corneas of eyes, extracted from dead piglets. A fiber-optic laser system was used for laser soldering of the incisions, under close temperature control, using albumin solder. The burst-pressure PB immediately after the soldering was found to be PB ≈ 92 and 875 mmHg, for vertical and slanted incisions, respectively. PB = 875 mmHg is an exceptionally high figure, ≈10 times the clinically acceptable value for sutured incisions. Laser soldering was then performed on penetrating incisions made in the corneas of live healthy piglets, of weight ≈10 Kg. After a healing period, the eyes were extracted, and the corneas were examined by histopathology and by optical coherence tomography. Our method immediately generated watertight and strong bonding without noticeable corneal shape distortion. These results would be beneficial for cataract surgery and for corneal transplantations. The fiber-optic system makes it much easier to bond corneal incisions. In the future, laser soldering could be automated and efficiently used by less experienced surgeons, thereby reducing the workload on the experienced ones. [ABSTRACT FROM AUTHOR]

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The magnitudes of input power and scan speed of laser heat source can affect the morphology and size of interfacial Cu 6 Sn 5 intermetallic compound (IMC) formed or grown in Sn/Cu and Sn-3.5Ag-0.5Cu/Cu (SAC/Cu) joints. Experimentally, it has been observed that greater power and smaller scan speed can create temperature field of higher magnitude, thereby enhancing the interfacial reaction. The occurrence of conglomerated, prismatic (faceted) and scalloped IMC morphologies in the specimens corresponding to designated laser processing parameters, has been explained with the help of Jackson parameter. The heat and mass transfer phenomena during laser soldering, is modeled using finite element analysis. Enthalpy method is applied in the FEM based computational model to describe the phase change based heat transfer at the melting regime of the solder. With an attainment of transient temperature profiles at several scan speeds through the numerical analysis, the values of interfacial reaction temperature at solder/substrate interface and diffusion phenomenon based mass transfer of Cu into solder are then utilized to explain the experimental results of IMC size. In comparison to pure Sn solder, SAC solder type is characterized with the formation of thicker IMC at laser power of 50 W and scan speeds below 180 mm/min. [ABSTRACT FROM AUTHOR]

The work dealt with the soldering of ceramic substrates by the application of laser beam heating using ultrasound assistance. The joints were fabricated at a laser beam power of 2 kW and ultrasound frequency of 40 kHz. The Bi11Ag2La alloy was applied as the solder, which wetted both substrates, namely Al2O3 and ZrO2. Wetting of the ZrO2 substrate was significantly better, attaining a wetting angle of 45.5°. In the case of Al2O3 the wetting angle attained just 73° under the same conditions. Neither a new transition layer, nor any contact interlayer were observed on the interface in either substrate. In spite of that, the fabricated joints achieved satisfactory quality and showed no cracks or irregularities. [ABSTRACT FROM AUTHOR]

Introduction: Laser tissue soldering using albumin and indocyanine green dye (ICG) is an effective technique utilized in various surgical procedures. The purpose of this study was to perform laser soldering of rat skin under a feedback control system and compare the results with those obtained using standard sutures. Material and Methods: Skin incisions were made over eight rats’ dorsa, which were subsequently closed using different wound closure interventions in two groups: (a) using a temperature controlled infrared detector or (b) by suture. Tensile strengths were measured at 2, 5, 7 and 10 days post-incision. Histological examination was performed at the time of sacrifice. Results: Tensile strength results showed that during the initial days following the incisions, the tensile strengths of the sutured samples were greater than the laser samples. However, 10 days after the incisions, the tensile strengths of the laser soldered incisions were higher than the sutured cuts. Histopathological examination showed a preferred wound healing response in the soldered skin compared with the control samples. The healing indices of the laser soldered repairs (426) were significantly better than the control samples (340.5). Conclusion: Tissue feedback control of temperature and optical changes in laser soldering of skin leads to a higher tensile strength and better histological results and hence this method may be considered as an alternative to standard suturing.

Two sapphire substrates are tightly bonded through a BaTiAl 6 O 12 -glass thin film, by irradiation with a nanosecond laser. After the laser process, the composition of the glass sealant changes, due to incorporation of Al 2 O 3 from the upper substrate. After annealing of the bonded samples (950 °C for 30 minutes) crystalline structures are observed by TEM which are attributed to crystalline BaTiAl 6 O 12 . These crystals together with Al 2 O 3 :Ti centers are the responsible of the observed strong blue luminescence of the laser irradiated region upon UV excitation. The structural and optical characterizations of the bonded samples clarify the laser soldering procedure as well as the origin of the luminescence. Bond quality and bond strength were evaluated by scanning acoustic microscopy (SAM) and tensile tests, which results in a tensile stress of nearly 13 MPa, which is an acceptable value for glass sealants. [ABSTRACT FROM AUTHOR]

In three-dimensional (3D) packaging and assembly technology, Lead-free SnAgCu solder joints inevitably experience multiple reflows. The interfacial compounds of Sn3.0Ag0.5Cu (SAC305)/ Electroless Ni–P/Immersion Au (ENIG) solder bump after laser soldering and subsequent hot air reflows were observed by transmission electron microscopy (TEM), respectively. The initial laser soldering played a key role in interfacial compound evolution during the subsequent multiple reflows. After laser soldering, a thin P-rich layer and an ultrafine scallop-type (Ni, Cu) 3 Sn 4 layer formed at the interface of SAC305/ENIG. The valleys of ultrafine (Ni, Cu) 3 Sn 4 grains served as rapid channels for Ni diffusion, which contributed to the formation of dendritic η -(Cu, Ni) 6 Sn 5 +(Ni, Cu) 3 Sn 2 intermetallic compounds after the first hot air reflow. However, with the number of reflow times increasing, the η -(Cu, Ni) 6 Sn 5 totally transformed to noodle-like (Ni, Cu) 3 Sn 2 owing to their similarly hexagonal lattice structure and the limited Cu supply in solder. [ABSTRACT FROM AUTHOR]

The demand for flexible wearable devices/substrates with miniaturization and improved integration in microelectronic devices has intensified the research interest in low-temperature laser soldering processes as an alternative to conventional reflow soldering processes owing to their advantages, such as local heating, non-contact heating, and short bonding time. In this study, we compared and evaluated the reliability of laser soldered and conventional reflow soldered joints using representative low melting temperature eutectic Sn Bi solder and thin electroless Ni-electroless Pd-immersion Au (ENEPIG)-finished Cu pads. Laser soldering was performed using various laser powers (130, 150, and 170 W) and times (2 and 4 s). Furthermore, an aging test was performed at 110 °C for 2000 h to evaluate the long-term reliability of the soldered joints. The mechanical properties, including the top and cross-sectional views and fracture surfaces, of the soldered joints were analyzed by conducting shear tests after aging. During laser soldering, various intermetallic compounds (IMCs) were formed at the joints depending on the applied energy. The metallization layer and Cu reacted with Sn in the solder after different aging durations, and additional IMCs were formed and grown. After aging for 2000 h, the shear strength decreased, and the interfacial IMC thickness increased. As the aging time increased, the fracture mode changed from an initial ductile fracture to brittle fracture (between the solder and IMCs and/or between IMCs and the Cu pad). The reflow soldered joints exhibited stable shear strength, resulting in ductile fracture until aging for 500 h. However, the shear strength decreased sharply after aging for 1000 and 2000 h, and Bi-segregation was observed after aging for 1000 h, resulting in inferior long-term reliability. After laser soldering at 150 and 170 W for 4 s, the strength of the samples decreased sharply after aging for 1000 and 250 h, respectively, and Bi-segregation was observed after aging for 2000 h. The shear strength of the sample laser soldered at 170 W for 2 s gradually decreased with increasing aging time and maintained a stable shear strength until aging for 2000 h. Therefore, laser soldering at 170 W for 2 s was considered as the optimal condition for long-term reliability. • Soldering properties of laser soldered Sn-58Bi/Au/Pd/Ni-finished Cu joints evaluated. • Laser soldering results were compared with conventional reflow soldered joints. • Various IMCs were formed depending on laser power and irradiation time. • Laser conditions with low applied energy displayed superior long-term reliability. • Selection of the optimal laser conditions is crucial to ensure reliable solder joints. [ABSTRACT FROM AUTHOR]

• The dynamic changes of laser reflectivity in laser soldering can be divided into five stages. • The solder spreading behaviors are revealed. • Laser reflectivity depends on the mechanism of laser reflection and internal heat conduction. • The burn damage of components is caused by high laser reflectivity and concentrated reflection. The random occurrence of component burn damage is a major challenge for laser soldering, but the mechanism has not been clear. In order to find the reason, a new integrating sphere platform was developed to simulate the actual process of laser soldering, and observe the real-time variation of laser reflectivity (LR) from initial fusion to fully spreading out of the solder. The results showed that the whole process is divided into 5 stages, which are initial low LR stage, rapidly rising moment, decreasing stage, re-increasing stage, and stable stage with high LR (around 64%). By analyzing the spreading behaviors and cross microstructures of solder joints, it was found that LR has no direct correlation with the spreading shape or temperature variation of solder paste, but is dependent on the interaction of laser multi-reflections within solder powders, one-time reflection of melt surface, and heat conduction from upper melted liquid to lower unmelted powders. The findings indicated that the burn damage is attributed to the combined effect of high LR and the concentrated reflection caused by crescent solder at the final stage. [ABSTRACT FROM AUTHOR]

Laser tissue soldering is a method of repairing incisions. It involves the application of a biological solder to the approximated edges of the incision and heating it with a laser beam. A pilot clinical study was carried out on 10 patients who underwent laparoscopic cholecystectomy. Of the four abdominal incisions in each patient, two were sutured and two were laser soldered. Cicatrization, esthetical appearance, degree of pain, and pruritus in the incisions were examined on postoperative days 1, 7, and 30. The soldered wounds were watertight and healed well, with no discharge from these wounds or infection. The total closure time was equal in both methods, but the net soldering time was much shorter than suturing. There was no difference between the two types of wound closure with respect to the pain and pruritus on a follow-up of one month. Esthetically, the soldered incisions were estimated as good as the sutured ones. The present study confirmed that temperature-controlled laser soldering of human skin incisions is clinically feasible, and the results obtained were at least equivalent to those of standard suturing. [ABSTRACT FROM AUTHOR]

The laser soldering process was introduced in Micro-USB electronic packaging in this paper. Numerical modeling and analysis was used for laser process parameter design, because experimental measurements of peak temperature and soldering stress are expensive and often intractable. Accurate knowledge of the residual stress and distortion is a prerequisite for the reliability of the electric connector. The present work proposes a three-dimensional transient heat transfer model of Micro-USB package laser soldering process. The calculated thermal cycles and distribution are subsequently used to calculate the distortion and thermal stresses. Meanwhile, the effect of process parameters on residual stress and pin distortion was discussed, and the tensile strength, microstructure, and residual stresses of laser soldering were tested. It can be concluded that the proper laser soldering parameters and power can improve the mechanical property of solder joints on Micro-USB connector. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We propose a new soldering process and a system for a quad flat package IC (QFP-IC). The incident line-formed laser beam converted by this system can realize an external quadrangular form line for the non-contact regional heating, to provide thin and light weight electronic packages as required. The laser beam pumped by an yttrium aluminum garnet (YAG) laser oscillator is split into four beams. Using a galvano motor, which can scan the reflection mirror with high frequencies, the laser beam can change the heating line. The soldering time for QFP-IC of 100 pins with the 0.65 mm pitch was 6 s. As the regional heating just only junctions, the temperature in the resin package was lower than 141 °C after solder fusion. From the experimental result, it is confirmed that this method is less damage to a resin package than a conventional whole heating method. [ABSTRACT FROM AUTHOR]

Although there has been great interest in laser heating for bonding of surgical incisions in tissues, it has not gained wide acceptance by surgeons. We argue that the main obstacle has been the lack of temperature control, which may lead to a weak bonding. We previously developed a laser bonding system based on two infrared transmitting AgBrCl fibers, one for laser heating and one for temperature control. In view of the inherent limitations of such systems observed in many animal experiments, we developed an improved system based on a single infrared fiber. Besides the decreased dimensions, this system offers many advantages over the two-fiber system. It is less sensitive to accuracy of height and tilt of the fiber distal tip above the tissue, ensuring more accurate heating that can potentially lead to stronger bonding with minimal thermal damage. The system is successfully tested in the soldering of 15 corneal incisions, ex vivo. Histopathology shows little thermal damage and good wound apposition. The average burst pressure is 100 30 mmHg. These findings indicate the usefulness of the system for ophthalmic surgery as well as other surgical procedures, including endoscopic and robotic surgery. [ABSTRACT FROM AUTHOR]