Influence of titanium dioxide nanopowder addition on microstructural development and hardness of tin–lead solder

In this study, varying weight percentages of multiwalled carbon nanotubes were successfully incorporated into 95.8Sn-3.5Ag-0.7Cu solder to synthesize novel lead-free composite solders. The composite solders were synthesized using a powder metallurgy route consisting of blending, compaction, sintering, and extrusion. The extruded materials were then characterized for their physical, thermal, and mechanical properties. With the addition of increasing weight percentage of carbon nanotubes, the composite solders experienced a corresponding decrease in density values and an improvement in wetting properties. The melting temperatures of the composite solders were found to be unchanged with additions of carbon nanotubes. However, improvements in the mechanical properties, in terms of microhardness and tensile properties, were observed with increasing weight percentages of carbon nanotubes.

Lead-free solder reinforced with multiwalled carbon nanotubes

Composite solders were prepared by mechanically dispersing 15v% of Cu or Ag particles into the eutectic Sn‐3.5Ag solder. The average sizes for the nominally spherical Cu and Ag particles were 6 and 4 microns, respectively. Two different processing methods were used to prepare the composite solders: blending the powdered particles with solder paste, and adding particles to the molten solder at 2808C. The composite solders were characterised by studying the morphology, size and distribution of the reinforcing phase. Particular interest and emphasis are given towards the modifications of the reinforcements during the reflow process. Microstructural features and chemical analysis of the composite solders were studied using optical and scanning electron microscopy (SEM), and energy dispersive x‐ray (EDX) analysis. The effect of reflow and isothermal ageing on the microstructure as well as the morphological changes in the interfacial IM layer of the composite solders were extensively analysed. A mechanism for IM layer growth is proposed for solid state isothermal ageing.

Microstructural characterisation of reflowed and isothermally‐aged Cu and Ag particulate reinforced Sn‐3.5Ag composite solders

The influence of copper nanopowders on microstructure and hardness of lead-tin solder

Mossbauer spectroscopy was used to characterize dispersion-strengthened composite solder powders that were formed through hot gas spray atomization. To perform quantitative measurements, we first measured the relative recoilless fractions of eutectic solder and three intermetallic compounds: Cu3Sn, Cu6Sn5, and Ni3Sn4. These results were then used to determine the concentrations of intermetallic species present in various composite solder samples. Mossbauer spectroscopy was shown to be an effective tool in the analysis of dispersion-strengthened composite solders and was preferentially sensitive to the presence of tin-based intermetallics and oxides.

A Mössbauer study of tin-based intermetallics formed during the manufacture of dispersion-strengthened composite solders

Previous chapters of this book have discussed the wetting behavior of near-eutectic Sn-Pb solders. These alloys are the most common in electronic applications and are deserving of the greatest attention. However, there are many applications where the properties of these alloys can be improved. A composite solder, or a solder that contains second-phase dispersions of particles, could improve solder joint properties. The area where composite solders could have the greatest impact is in improving the mechanical properties of the joint. However, the wetting behavior of the solder cannot be compromised for the sake of the mechanical properties -good wetting behavior is a necessity. Therefore, for a composite solder to be useful for electronic packaging applications mechanical properties, wetting and manufacturability must be optimized.

G. Kuo

Papers

The Properties of Composite Solders