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The composition and thickness of surface oxide of solder particles is extremely important to the quality of interconnect and reliability of packaged system. The purpose of this paper is to develop an observable measurement to research the issue.

AES (Auger electron spectroscopy), XPS (X‐ray photoelectron spectroscopy), TEM (transmission electron microscopy) and STEM (scanning transmission electron microscopy) were employed to examine the oxide layer on microscale solder powders. Conventional techniques and FIB (Focus Ion Beam) were employed for the TEM sample preparation. High angle annular dark field (HAADF) pattern was applied to distinguish the oxide layer and the solder matrix by the contrast of average atomic number. The results were confirmed by AES and XPS measurement.

The solder powders were exposed to air (70% relative humidity) at 150°C for 0, 120 and 240 h for the accelerated growth of oxide. The surface oxide thickness was 6 nm and 50 nm measured by TEM for 0 h and 120 h samples, respectively. It was found that the increase in surface oxide thickness of solder particles is proportional to the rooting of time. The elemental distribution along the oxide was quantified by line scanning using STEM and the atomic ratio of Sn to O in the oxide layer nearer to the outer, the middle, and the inner (adjacent to the solder matrix) was found to be 1:2, 2:3 and 1:1, respectively. The result was validated using XPS which gave Sn to O ratio of 1:2 at 5 nm depth of surface oxide.

This is the first time FIB technology has been used to prepare TEM specimens for solder particles and TEM pictures shown of their surface oxide layer. Though requiring more care in sample preparation, the measurements by TEM and STEM are believed to be more direct and precise.

This paper aims to present a robust prediction method for estimating the quality of electronic products assembled with pin-in-paste soldering technology. A specific board quality factor was also defined which describes the expected yield of the board assembly.

Experiments were performed to obtain the required input data for developing a prediction method based on decision tree learning techniques. A Type 4 lead-free solder paste (particle size 20–38 µm) was deposited by stencil printing with different printing speeds (from 20 mm/s to 70 mm/s) into the through-holes (0.8 mm, 1 mm, 1.1 mm, 1.4 mm) of an FR4 board. Hole-filling was investigated with X-ray analyses. Three test cases were evaluated.

The optimal parameters of the algorithm were determined as: subsample is 0.5, learning rate is 0.001, maximum tree depth is 6 and boosting iteration is 10,000. The mean absolute error, root mean square error and mean absolute percentage error resulted in 0.024, 0.03 and 3.5, respectively, on average for the prediction of the hole-filling value, based on the printing speed and hole-diameter after optimisation. Our method is able to predict the hole-filling in pin-in-paste technology for different through-hole diameters.

No research works are available in current literature regarding machine learning techniques for pin-in-paste technology. Therefore, we decided to develop a method using decision tree learning techniques for supporting the design of the stencil printing process for through-hole components and pin-in-paste technology. The first pass yield of the assembly can be enhanced, and the reflow soldering failures of pin-in-paste technology can be significantly reduced.

This paper aims to evaluate the morphology and thickness of oxides that form on the surfaces of tin whiskers. The problems related to the growth of tin whiskers are stated, and the relevance of oxide layers adhering to whiskers is discussed.

Modern laboratory methods including focused ion beam sectioning, energy dispersive spectroscopy and X-ray photoelectron spectroscopy have been used to characterise the composition of oxides present on the surfaces of 48-year-old whiskers. These very old whiskers had nucleated and grown on electronic equipment stored at ambient temperatures. They were compared to the oxide layers on newly grown 2-week-old whiskers.

A dual oxide film, consisting of stannous and stannic oxides, was found present on both the old and the new whiskers. Measurements of oxide thickness were established for both generations of whiskers and these were noted to be similar to those films present on pure, cleaned bulk tin.

Only very new and very old whiskers, and their oxide films, were the focus of this investigation. However, sufficient data were gained to predict the effect both kinds of oxide films would have during whisker bridging between conductors and the risk of short circuits. Thick oxide films (order of 30 nm) may have a greater resistance to shorting, but they will be more difficult to remove during solder dipping (with respect to whisker mitigation).

A knowledge of the oxide thickness on growing/gyrating tin whiskers will provide the electronics industry with data useful for establishing the risk of short circuits. It will also be useful during the forensic work associated with component and assembly failure analysis.

The data resulting from this study are unique. They are of value to others who may require knowledge of the morphology, composition and thickness of oxides present on tin whiskers of different vintage.

The purpose of this paper is to investigate the creep properties of Sn‐0.7Cu composite solder joints reinforced with optimal nano‐sized Ag particles in order to improve the creep performance of lead‐free solder joints by a composite approach.

The composite approach has been considered as an effective method to improve the creep performance of solder joints. Nano‐sized Ag reinforcing particles were incorporated into Sn‐0.7Cu solder by mechanically mixing. A systematic creep study was carried out on nano‐composite solder joints reinforced with optimal nano‐sized Ag particles and compared with Sn‐0.7Cu solder joints at different temperatures and stress levels. A steady‐state creep constitutive equation for nano‐composite solder joints containing the best volume reinforcement was established in this study. Microstructural features of solder joints were analyzed to help determine their deformation mechanisms during creep.

The creep activation energies and stress exponents of Ag particle‐enhanced Sn‐0.7Cu lead‐free based composite solder joints were higher than those of matrix solder joints under the same stress and temperature. Thus, the creep properties of nano‐composite solder joints are better than those of Sn‐0.7Cu solder joints.

The findings indicated that nano‐sized Ag reinforcing particles could effectively improve the creep properties of solder joints. A new steady‐state creep constitutive equation of nano‐composite solder joints was established. Deformation mechanisms of Sn‐0.7Cu solder and nano‐composite solder joints during creep were determined.

This study aims to summarize the effects of minor addition of Ho REE on the structure, mechanical strength and thermal stability of binary Sn- Ag solder alloys for high-performance applications.

This study investigates the effect of a small amount of holmium addition on the microstructure, thermal stability, mechanical behaviour and wettability of environmentally friendly eutectic melt-spun process Sn – Ag solder alloys. Dynamic resonance technique, X-ray diffraction (XRD) and scanning electron microscopy were carried to study stiffness, identification of the phases and the morphology features of the solder. Structure and microstructure analysis indicated that presence of rhombohedral ß-Sn phase in addition to orthorhombic IMC Ag₃Sn phase dispersed in Sn-matrix. Also, the results showed that Ho rare earth addition at a small trace amount into Sn-Ag system reduces and improves the particle size of both rhombohedral ß-Sn and orthorhombic IMC Ag₃Sn based on the adsorption effect of the active RE element. The adsorption of Ho at grain boundaries resulted in Ag₃Sn more uniform needle-like which is distributed in the ß-Sn matrix. The fine and uniform microstructure leads to improvement of mechanical strength. The microstructure refinement is due to the high surface free energy of IMC Ag₃Sn grains, and it prevents the dislocation slipping. This maybe enhance the micro-hardness and micro-creep hence delays the breaking point of the solder. Ho (RE) trace addition could enhance the melting temperature and contact angle up to 215°C and 31°, Respectively, compared with plain solder. All results showed that Ho trace addition element has an effective method to enhance new solder joints.

Effect of rare earth element Ho particles on the microstructure and mechanical behavior of eutectic Sn-3.5Ag solder alloy was studied. Some important conclusions are summarized in the following: microstructure investigations revealed that the addition of Ho particles to eutectic Sn-3.5Ag inhibited in reducing and refines the crystallite size as well as the Ag3Sn IMC which reinforced the strength of plain solder alloy. The mechanical properties values such as Young’s modulus, Vickers microhardness of Sn-3.5Ag solder alloy can be significantly improved by adding a trace amount of Ho particles compared with plain solder due to the existence of finer and higher volume fraction of Ag3SnIMC. These variations can be understood by considering the plastic deformation. The strengthening mechanism of the Sn-3.5Ag-Ho solder alloy could be explained in terms of Ho harden particles and finer IMC, which are distributed within eutectic regions because they act as pinning centres which inhibited the mobility of dislocation that concentrated around the grain boundaries. The results show that the best creep resistance is obtained when the addition of Ho 0.5 is compared to plain solder. The addition of Ho on Sn-3.5Ag lead-free solder alloy decreases the melting temperature to few degrees.

Development of holmium-doped eutectic Sn-Ag lead-free solder for electronic packaging.

This study aims to study the impact of intermetallic compound on microstructure, mechanical characteristics and thermal behavior of the melt-spun Bi-Ag high-temperature lead-free solder.

In this paper, a new group of lead-free high-temperature Pb-free solder bearing alloys with five weight percentages of different silver additions, Bi-Ag_x (x = 3.0, 3.5, 4.0, 4.5 and 5.0 Wt.%) have been developed by rapidly solidification processing (RSP) using melt-spun technique as a promising candidate for the replacement of conventional Sn-37Pb common solder. The effect of the addition of a small amount of Ag on the structure, microstructure, thermal and properties of Bi-Ag solder was analyzed by means of X-ray diffractometer, scanning electron microscopy, differential scanning calorimetry and Vickers hardness technique. Applying the RSP commonly results in departures from conventional microstructures, giving an improvement of grain refinement. Furthermore, the grain size of rhombohedral hexagonal phase Bi solid solution and cubic IMC Bi_0.97Ag_0.03 phase is refined by Ag addition. Microstructure analysis of the as soldered revealed that relatively uniform distribution, equiaxed refined grains of secondary IMC Bi_0.97Ag_0.03 particles about 10 µm for Bi-Ag_4.5 dispersed in a Bi matrix. The addition of trace Ag led to a decrease in the solidus and liquidus temperatures of solder, meanwhile, the mushy zone is about 11.4°C and the melting of Sn-Ag_4.5 solder was found to be 261.42°C which is lower compared with the Sn-Ag₃ solder 263.60°C. This means that the silver additions into Bi enhance the melting point. The results indicate that an obvious change in electrical resistivity (?) at room temperature was noticed by the Ag addition. It was also observed that the Vickers microhardness (H_v) was increased with Ag increasing from 118 to 152 MPa. This study recommended the use of the Bi-Ag lead-free solder alloys for higher temperature applications.

Silver content is very important for the soldering process and solder joint reliability. Based on the present investigations described in this study, several conclusions were found regarding an evaluation of microstructural and mechanical deformation behavior of various Bi-Ag solders. The effect of Ag and rapid solidification on the melting characteristics, and microstructure of Bi-Ag alloys were studied. In addition, the mechanical properties of Bi with different low silver were investigated. From the present experimental study, the following conclusions can be drawn. The addition of Ag had a marked effect on the melting temperature of the lead-free solder alloys, it decreases the melting temperature of the alloy from 263.6 to 261.42°C. Bi-Ag solders are comprised of rhombohedral Hex. Bi solid solution and cubic Ag_0.97Bi_0.03 IMC is formed in the Bi matrix. The alloying of Ag could refine the primary Bi phase and the Bi_0.97Ag_0.03 IMC. With increasing Ag content, the microstructure of the Bi-Ag gradually changes from large dimples into tiny dimple-like structures. The refinement of IMC grains was restrained after silver particles were added into the matrix. The inhibition effect on the growth of IMC grains was most conspicuous when solder was doped with Ag particles. As a result, the Vickers microhardness of the Bi-Ag lead-free solder alloys was enhanced by more than 100% ranging from 118.34 to 252.95 MPa. Bi-Ag high-temperature lead-free solders are a potential candidate for replacing the tin-lead solder (Sn-37Pb) materials which are toxic to human and the environment and has already been banned.

This study recommended the use of the Bi-Ag lead-free solder alloys for high-temperature applications.

The purpose of this paper is to study the melting temperature of the nanoparticles of the new developed Sn‐0.4Co‐0.7Cu (wt%) lead‐free solder alloy.

Nanoparticles of Sn‐0.4Co‐0.7Cu lead‐free solder alloy were prepared by the self‐developed consumable‐electrode direct current arc technique, where ultrasonic vibration was applied during the manufacturing of the particles. X‐ray diffraction and field emission scanning electron microscope were employed to analyze the crystal structure and morphology of the nanopartiles, respectively. Differential scanning calorimetry was used to investigate the melting temperature of both the bulk alloy and as‐prepared nanoparticles.

The melting temperature of the nanoparticles was approximately 5°C lower compared to that of the bulk alloy.

As a novel developed lead‐free solder alloy, the Sn‐0.4Co‐0.7Cu (wt%) alloy provides a cost advantage compared to the extensively used Sn‐Ag‐Cu system. Some limitations still exist, however, mainly due to its relatively higher melting temperature compared to that of eutectic Sn‐37Pb solder. In view of this situation, the attempt to lower its melting temperature has recently attracted more attention based on the knowledge that the melting temperature for pure metals is reduced when the particle size is decreased down to a few tens of nanometers.