Journal of Welding Science

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.

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.
 

Eutectic tin-zinc solder can be a suitable replacement for tin-lead solder due to its low cost, suitable melting temperature, and desirable mechanical properties. However, due to the high vapor pressure of zinc, manufacturing this alloy using the melt method is very difficult and expensive. In this study, Sn-8.9%Zn lead-free solder was fabricated using the angular accumulative extrusion method of tin sheets and zinc powder in 10, 12, and 15 passes, and characterized. Microstructural investigations were performed using optical and scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction spectroscopy. The shear strength and hardness of the solders were also measured. The results showed that after 12 passes, the dispersion of zinc powder in the tin matrix was improved, and the dissolution of zinc was confirmed by a decrease in the XRD peak intensities. However, after 15 passes, cracks appeared in the structure. The shear strength of the tin-zinc solder joint was about 60% higher than that of commercial tin-lead solder. The wetting angle of this solder on copper was measured to be 21 degrees, and its electrical resistance was measured to be 4.1 nanoohms, which is within the acceptable range for electronic applications, although it has a weaker performance compared to tin-lead solder.