Showing 3 results for Nourmohammadi
M.h. Nourmohammadi, M. Movahedi, A.h. Kokabi, M. Tamizi,
Volume 9, Issue 1 (Journal OF Welding Science and Technology 2023)
Abstract
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.
Dr Mojtaba Movahedi, Dr Amir Hossein Kokabi, Engineer Mohammad Hadi Nourmohammadi,
Volume 9, Issue 2 (Journal OF Welding Science and Technology 2024)
Abstract
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 matrices 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
Engineer M. H. Nourmohammadi, M. Movahedi, A. H. Kokabi ,
Volume 10, Issue 1 (Journal OF Welding Science and Technology 2024)
Abstract
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.
