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Issue Title: Special Sections: Pb-free Solders and Materials for Emerging Interconnect and Packaging Technologies; Phase Stability, Phase Transformations, and Reactive Phase Formation in Electronic Materials XIII; and Advanced Materials for Power Electronics and Power Conditioning Systems We have investigated the effect of small amounts of Cu on suppression of metastable [beta]Sn-NiSn^sub 4^ eutectic growth in solder joints between Sn-3.5Ag-xCu solders and Ni-based substrates. For Sn-3.5Ag/electroless nickel immersion gold (ENIG) and Sn-3.5Ag/Ni solder joints we showed that the eutectic mixture contains [beta]Sn, Ag^sub 3^Sn, and metastable NiSn^sub 4^. It was found that addition of only 0.005 wt.% Cu to Sn-3.5Ag-xCu/ENIG or Sn-3.5Ag-xCu/Ni joints promoted formation of a stable [beta]Sn-Ni^sub 3^Sn^sub 4^ eutectic and that both Ni^sub 3^Sn^sub 4^ and NiSn^sub 4^ occur in the eutectic at this Cu level. We also showed that for complete prevention of formation of metastable NiSn^sub 4^ during eutectic solidification of the solder joint, addition of at least 0.3 wt.% Cu was required.

Purpose In the production processes of electronic devices, production activities are interrupted due to the problems caused by soldering defects during the assembly of surface-mounted elements on printed circuit boards (PCBs), and this leads to an increase in production costs. In solder paste applications, defects that may occur in electronic cards are usually noticed at the last stage of the production process. This situation reduces the efficiency of production and causes delays in the delivery schedule of critical systems. This study aims to overcome these problems, optimization based deep learning model has been proposed by using 2D signal processing methods. Design/methodology/approach An optimization-based deep learning model is proposed by using image-processing techniques to detect solder paste defects on PCBs with high performance at an early stage. Convolutional neural network, one of the deep learning methods, is trained using the data set obtained for this study, and pad regions on PCB are classified. Findings A total of six types of classes used in the study consist of uncorrectable soldering, missing soldering, excess soldering, short circuit, undefined object and correct soldering, which are frequently used in the literature. The validity of the model has been tested on the data set consisting of 648 test data. Originality/value The effect of image processing and optimization methods on model performance is examined. With the help of the proposed model, defective solder paste areas on PCBs are detected, and these regions are visualized by taking them into a frame.

Traditional methods for closing gastrointestinal (GI) surgery incisions, like suturing and stapling, present significant challenges, including potentially life-threatening leaks. These techniques, especially in robot-assisted minimally invasive surgery (RAMIS), require advanced manual skills. While their repetitive and time-consuming nature makes them suitable candidates for automation, the automation process is complicated by the need for extensive contact with the tissue. Addressing this, we demonstrate a semi-autonomous contactless surgical procedure using our novel Robot-assisted Laser Tissue Soldering (RLTS) system on a live porcine bowel. Towards this in-vivo demonstration, we optimized soldering protocols and system parameters in ex-vivo experiments on porcine bowels and a porcine cadaver. To assess the RLTS system performance, we compared the pressure at which the anastomosis leaked between our robotic soldering and manual suturing. With the best setup, we advanced to an in-vivo Heineke Mikulicz closure on small bowel incision in live pigs and evaluated their healing for two weeks. The five pigs that successfully completed the procedure, survived without leaks and histology indicated mucosal regeneration and fibrous tissue adhesion. This marks the first in-vivo semi-automated contactless incision closure, paving the way for automating GI surgery incision closure which has the potential to become an alternative to traditional methods.

Fluxes have a negative impact on the environment; as a result, fluxless soldering has become a promising method in electronic packaging. However, detailed studies on fluxless soldering are very rare, especially those involving the use of electroless nickel immersion gold (ENIG) substrate under formic acid (FA) atmosphere that can effectively reduce the majority of solders. In this work, the characteristic parameters of FA reflow soldering performed by combining Sn–3.5Ag–0.5Cu (SAC305) solder and ENIG substrate are compared with the soldering conducted using liquid rosin mildly activated (RMA) flux. It is found that the wettability of FA-exposed solder is greater than that of RMA-containing solder because the former spreads across the interfacial layer of intermetallic compounds (IMCs) produced before the melting of SAC305. Additionally, the interfacial reactions of FA-exposed solder resemble those of RMA solder before and after the thermal aging at 150 °C. Therefore, the impact strengths of these two solders are almost the same due to the similarity of their microstructures and close growth rates of (Cu,Ni)6Sn5 IMC layers during thermal aging. The findings of this study suggest that FA reflow soldering is a promising environmentally friendly technique for electronic packaging.

This paper aims to develop a thermal fluid–structure interaction (FSI) methodology to study the effect of different Cu pillar bump diameters on thermal and mechanical performance during the reflow soldering process. The desktop reflow oven is modeled in ANSYS FLUENT, while the ball grid array (BGA) package assembly is modeled in ANSYS STATIC STRUCTURAL. The accuracy of the simulated reflow temperature profile has been verified by comparing it with the experimental temperature data, according to JEDEC standards. The temperature distributions of solder and Cu pillar bumps are compared. A parametric study has been conducted to analyze the effect of different Cu pillar diameters on the reflow soldering process. By coupling the thermal loads with the structural analysis using thermal FSI, Cu pillar bumps with a diameter of 0.20 mm are found to exhibit the lowest reflow temperature, minimum temperature difference, and minimum deformation and thermal stress, making them the most suitable interconnection joints for flip chip technology. The study also examines the effect of soldering materials on the Cu pillar bump. The findings of this research provide valuable insights into the effects of varying Cu pillar diameters on the reflow soldering process, which can help in the development of more reliable electronic assemblies.

In surface mount technology, development toward green manufacturing by converting all leaded soldering processes to lead free soldering process has created a lot of challenges mainly in wave soldering process which led to copper dissolution to assemble board causing it to be scrapped if not contained. The paper aims to propose a workable and practical solution to reduce extensive copper dissolution in assemble board and expand the cycle of allowable rework in assemble board. The work was carried out using Six Sigma methodology with defining the problem and research goals, measure the details in various aspects of current process, analyse data to identify potential root cause in a process, improve the process and control the process through experimental approaches. Main factors contributing to copper dissolution were identified and analysed. Total of five factors were identified namely the printed circuit board (PCB) finishing and copper layer construction in PCB, component terminal and led finishing, soldering flux usage and solder alloy composition, environment control with the use of Nitrogen tunnelling and the last factor was on the process itself which was from the in-contact process with molten turbulence soldering or non-contact process with intrusive soldering. Combined controlled factors contributing to minimization of copper dissolution by reducing the direct contact time to molten solder with optimize solder alloy composition and process control was formulated. An increase of sixty percentage of boards with lower copper dissolution going through the lead free wave soldering and rework soldering were obtained, another forty percent reduction of board being scrapped were also obtained with boards going through the molten solder up to triple times.

The main purpose of the software application is to simulate the temperature field in the process of induction pack of elements of machine-building structures of the fuel profile, which will further improve the quality of connections. The program simulates the flange heating process during the induction brazing process. The purpose of the developed module is to provide experimental studies of the induction soldering process. The program provides graphic information during the technological process, provides the ability to adjust the technological parameters, and allows the development of the technological process.

This research aimed to study a Bi–Ag–Mg soldering alloy and the direct soldering of Al2O3 ceramics and Ni–SiC composites. Bi11Ag1Mg solder has a broad melting interval, which mainly depends on the silver and magnesium content. The solder starts to melt at a temperature of 264 °C. Full fusion terminates at a temperature of 380 °C. The microstructure of the solder is formed by a bismuth matrix. The matrix contains segregated silver crystals and an Ag (Mg, Bi) phase. The average tensile strength of solder is 26.7 MPa. The boundary of the Al2O3/Bi11Ag1Mg joint is formed by the reaction of magnesium, which segregates in the vicinity of a boundary with a ceramic substrate. The thickness of the high-Mg reaction layer at the interface with the ceramic material was approximately 2 μm. The bond at the boundary of the Bi11Ag1Mg/Ni–SiC joint was formed due to the high silver content. At the boundary, there were also high contents of Bi and Ni, which suggests that there is a NiBi3 phase. The average shear strength of the combined Al2O3/Ni–SiC joint with Bi11Ag1Mg solder is 27 MPa.

This paper investigates the effect of soldering temperature on solder joint voids and reliability of flip-chip LED chips during reflow soldering. Lead-free solder SAC305 was used as solder paste. The void ratio of the flip-chip LED solder joint at 250°C, 260°C, 270°C, 280°C, and 290°C reflow soldering temperatures was detected by x-ray detector. Shear tests were conducted to evaluate the influence of interfacial reactions on the mechanical reliability of solder joints. The distribution of voids in the shear section was observed by scanning electron microscope (SEM). Next, the photoelectric and thermal properties of FC-LED filament were tested and analyzed. Finally, a high-temperature and high-humidity aging experiment was carried out to test the reliability of the LED filament. The results show that the void ratio of the LED filament soldering joint is the lowest when the soldering temperature is 270°C. The small void ratio of the solder joints results in lower steady-state voltage and junction temperature of the flip-chip LED filament. As the void density in the solder joint decreases, the shear strength of the solder joint increases. At this time, the shear resistance and mechanical reliability are the highest.

In this paper, the factors affecting the reliability of small-size PBGA with low thermal expansion coefficient are determined by theoretical and simulation analysis. The simulation results are verified by reliability test, dye penetration, metallographic section, and electron microscope scanning analysis, revealing that the height and diameter of solder joints are reliable with low CTE small size PBGA. The high-reliability welding process method of this kind of device is obtained, which is of great significance for the quality assurance of aviation and aerospace electronic products.