Background and Aim: Soldering is used in fixed prosthodontics, for different purposes such as connecting separate parts of the bridge, recontouring proximal and occlusal contacts and repairing casting voids. The aim of this study was to compare the flexural resistance of two rod and paste solders used in base metal alloys. Materials and Methods: Thirty rectangular specimens (1×4×30 mm) were made using super cast base alloy. The samples were sectioned into two equal parts and were placed in a soldering investment as pairs with 0.3 mm gaps between them. They were divided into 2 groups and soldered with rod solder in one group and paste solder in the other. The samples were subjected to a flexure test on a Universal Testing Machine. Statistically analysis was performed using F- and t-tests. Results: The minimum and maximum flexural resistance was 107.2N and 301.2N for the rod- and 62.8N and 109.3N for the paste solders, respectively. The mean flexural resistance was 196.5N in the rod solder group and 89.8N in the paste solder group. A significant difference in flexural resistance was observed between the two study groups (P=0.001). Conclusion: The results of this study indicated that flexural resistance of the rod solders was significantly higher than the paste solders.

The aim of the present study is to produce Sn base Lead-free nanocomposite solders reinforced by nanoparticles with rapid solidification technique and compare their mechanical, electrical and thermal properties with conventional SAC (Sn-3.8Ag-0.7Cu) solder. Therefore, four Lead-free soldering alloys Sn-3.8Ag-0.7Cu-XAl (X = 0, 0.25, 0.5, 1) were alloyed using a vacuum arc remelting (VAR) furnace. Then with melt spinning technique ribbons of nanocomposite solders reinforced with Cu6Sn5 and Ag3Sn intermetallic compounds nanoparticle were manufactured. The microstructural, mechanical, electrical and thermal properties of these nanocomposite solders were investigated using scanning electron microscopy, X-ray diffraction, Vickers hardness method, four-point resistance measurement method and differential scanning calorimetry (DSC). The results showed the uniform distribution of nanoparticles intermetallic compounds Cu6Sn5 and Ag3Sn in the solder matrix and a 30% significant increase of micro-hardness, negligible variation in the specific electrical resistance, and a 3 degrees increase in the melting temperature of the new nanocomposite solder compared to conventional SAC solder.

Development of electronic industries, compression of electronic equipment, and removing lead from electronic circuits for environmental issues, resulted in a significant challenge in design and development of tin-based Lead-free solders with physical and mechanical properties similar to old tin-lead alloys. In this regard, the set of Sn-Ag-Cu alloys with eutectic and near eutectic compositions have been proposed to replace Sn-Pb solders. As a Lead-free solder alloy, low melting point, high reliability, and compatibility with various fluxes are among the properties of this category of alloys. In order to improve the properties of the joint, these solders are sometimes reinforced with different nanoparticles. In this study, Sn0. 3Ag0. 7Cu compound reinforced with graphene nanosheets with different weight percentages (0, 0. 05, 0. 1, and 0. 2) was studied. Microstructure of the alloys was investigated by scanning electron microscopy(SEM) and optical microscopy. Melting temperature, wetting behavior and electrical resistivity of the solders were evaluated. According to the results, by adding graphene nanosheets, the wetting angle of the solder first decreased and then increased. This parameter showed the optimal amount for sample containing %0. 1 graphene nanosheets with a %10 reduction. The melting point and electrical resistance of the solder alloy did not change significantly with compositing. With the addition of graphene nanosheets, the thickness of the intermetallic compounds Cu6Sn5 present at the interface between copper and solder was reduced up to %30.

In today's technological landscape, the push for miniaturization in electronic devices is greater than ever, driven by technological advancements.The challenges of electromigration and thermomigration have arisen due to the need to establish new electronic connections under conditions characterized by creeping temperatures, originating from the low melting point of solders and high current density.  Therefore, recently, alloying and composite materials have been employed to enhance the resistance of electronic connections to electromigration. In this study, efforts to enhance the resistance to electromigration using a composite SAC0307 Lead-free solder alloy incorporating cobalt microparticles. The presence of cobalt in the intermetallic composition of the interface causes more stability of the intermetallic composition of the interface and prevents the reduction of the thickness of the intermetallic composition of the interface during the time of the electromigration test; As a result, the stability and electronic connection of the sample soldered with composite solder alloy is more than that of non-composite solder alloy. On the other hand, due to the fine grain structure and the increase in grain boundary density in the composite solder alloy, the lattice diffusion mechanism in the non-composite solder alloy has been changed to the grain boundary diffusion mechanism; As a result, due to the consumption of copper atoms flowed from the cathode side to the anode by the intermetallic compounds present in the grain boundaries, non-uniform microstructural was observed in the composite solder alloy during the time of electromigration test.

The miniaturization and compaction trends in electronic equipment and the removal of lead (Pb) element from solder alloys due to environmental considerations have created a great challenge in the field of designing and developing of new solder alloys. Therefore, researchers have recently focused on composite solder alloys using reinforcing particles to improve the reliability of Lead-free solders. In this research, SAC0307 solder alloys (99 wt. % Sn, 0. 3 wt. % Ag, and 0. 7 wt. % Cu) with different percentages of cobalt microparticles were made by the Accumulative Roll Bonding (ARB) method. Then, the effect of the particles on wettability, microstructures and mechanical characteristics of solder alloys was investigated. The lowest contact angle was 23◦in 0. 2 wt. % cobalt sample. By adding cobalt to the solder matrix, the size of intermetallic compounds (IMCs), Cu6Sn5 and Ag3Sn, decreased and the percentage of eutectic phases increased. The shape of the interfacial intermetallic compounds changed from scallop to layer shape by adding cobalt, and their average thickness increased about 13-71% in composite samples. The shear strength of solders increased up to 38% by enhancement of cobalt microparticles in the solder alloy containing 0. 4 wt. % cobalt, however, shear strength was decreased in the composite solder containing 1 wt. % cobalt due to the agglomeration of microparticles. The shear fracture surfaces showed that the nature of the fracture changed from ductile fracture in the form of elongated dimples to brittle fracture in the form of cleavage with the increase in the percentage of cobalt microparticles. The composite solder alloys containing 0. 2-0. 4 wt. % Co have the best wettability behavior and tensile shear strength.

Soldering plays a crucial role in the electronics industry, driving the need for constant improvements in physical and mechanical properties and the management of intermetallic compound formation. Research in composite materials aims to achieve a uniform distribution of reinforcing particles within solder matrix to enhance their performance. This study investigates the integration of cobalt microparticles into SAC0307 Lead-free soft solder alloy using the accumulative roll bonding (ARB) method. Microstructural analysis confirmed a homogeneous dispersion of cobalt particles within the solder after three ARB passes. Moreover, increasing cobalt content led to a reduction in the size of Cu6Sn5 intermetallic compounds, from 9 µm to 5 µm with 1% cobalt by weight. Examination of β-Sn grain morphology revealed the impact of cobalt particles on recovery and recrystallization kinetics in the solder. Mechanical testing indicated a 20% decrease in interlayer strength within composite solder sheets. Tensile tests showed a 28% increase in strength and a 31% decrease in elongation for composite solder alloy containing 1% cobalt. Differential scanning calorimetry (DSC) results revealed minimal change in the melting temperature of composite solder foil.

The progress in scientific and technical products and increasing needs for advanced electrical and electronic devices have motivated researchers to investigate new ideas in this field. One of the main challenges in this way is the connection between microchips and other parts of electrical boards. Leadbased alloys, especially tin-lead solders are the conventional materials which have destructive effects on living organisms and the environment. Electrical conductive adhesives, used as replacement for lead-based solders, are composites comprised of a polymer matrix as adhesive material and conductive fillers for conduction of electricity. In this research conductive adhesives were prepared using diglycidyl ether of bisphenol A epoxy resin as the polymer matrix and various amounts of silvercoated copper powder as conductive filler. The copper powder was coated with silver using electroless plating. The structural properties of the filler was characterized by inductivity coupled plasma analysis. The morphology of the samples was investigated by scanning electron microscopy. The conductive properties, shear strength and thermal stability of adhesives were also evaluated. The conductive adhesive containing 70 percent by weight of silver-coated copper powder showed optimum properties. For this sample an electrical resistivity of 2.8×10-2  W.cm and a shear strength of 10.77 MPa were obtained. In addition, the weight loss during thermogravimetric reduction was 23.69% for the optimum sample, while it was 88.71% for the sample with no filler, indicating an improvement in thermal stability due to adding filler.