Microstructural array and solute content affecting electrochemical behavior of Sn-Ag and Sn-Bi alloys compared with a traditional Sn-Pb alloy

A great preoccupation with replacing the traditional Sn-Pb alloy with a Pb-free alloy (“green alloy”) is recognized. There are industrial sectors that demand metallurgical improvements to attain certain unsoundness and adequate properties as a function of imposed operational parameters. In this experimental investigation, two distinctive centrifuged casting alloys (i.e., Sn-2 wt pct Ag and Sn-22 wt pct Pb) are compared. It is found that centrifuged castings have similar microstructure constituents, although distinctive cooling rates and solute contents are considered. It is also found that Ag3Sn intermetallic particles are responsible for attaining similar tensile strength, since more dislocations between Ag3Sn particles and the Sn-rich phase are provided. In order to replace the Sn-Pb alloys with a successor alloy containing sustainability and environmental aspects associated with castability and to guarantee the desired properties, it seems that a green alloy (Pb free) with intermetallic particles finely and homogeneously distributed provides an interesting benefit to various industrial applications.

Microstructural and Hardness Evaluations of a Centrifuged Sn-22Pb Casting Alloy Compared with a Lead-Free SnAg Alloy

Purpose




This paper aims to investigate the effect different fluxes have on the mechanical properties of lead-free solders, specifically Sn-Zn-Bi solder alloy. The solder billets were soldered in between copper substrates and flux was applied. The mechanical tests carried out on the solder alloys were tensile and shear tests. They were experimented on with different fluxes, namely, water-soluble (paste), rosin mildly activated (RMA) and insoluble (RMA) flux. From these experiments, the ultimate tensile strength, shear strength, elongation, yield stress, Young’s modulus and the stress-strain curve are derived. The results showed that solder billets that were soldered onto copper substrates with water-soluble flux yielded the highest ultimate tensile strength and shear strength values of 9.9961 MPa and 118.836 MPa, respectively. Billets soldered using RMA flux had the highest values of elongation and Young’s modulus, 0.306 mm and 50,257.295 MPa, respectively. However, on viewing the failure of all the specimens under an optical microscope and scanning electron microscope (SEM), specimens soldered using water-soluble flux possessed the least deformities, depicting their higher level of mechanical properties, entailing their strength and ductility, deeming them as the most suitable flux for microelectronic applications.




Design/methodology/approach




The solder billets were soldered in between copper substrates and flux was applied. The mechanical tests carried out on the solder alloys were tensile and shear tests. They were experimented on with different fluxes, namely, water-soluble (paste), RMA and insoluble flux (RMA) flux. From these experiments, the ultimate tensile strength, shear strength, elongation, yield stress, Young’s modulus and the stress-strain curve are derived.




Findings




The results showed that solder billets that were soldered onto copper substrates with water-soluble flux yielded the highest ultimate tensile strength and shear strength values of 9.9961 MPa and 118.836 MPa, respectively.




Originality/value




This paper demonstrated that water-soluble fluxes gave the better strength and were most suitable for microelectronics applications.

Effect of fluxes on Sn-Zn-Bi solder alloys on copper substrate

Incorporation of Bi into Sn-0.7Cu-0.08S lead-free solder alloy was applied to investigate its advantages on the melting temperature, wettability, microstructure, mechanical properties and corrosion behaviour. The results indicate that the addition of Bi lowers the melting temperature of the Sn-0.7Cu-0.08S, but enlarges its pasty range. The wettability of Sn-0.7Cu-0.08S on Cu substrate is considerably enhanced with the increase of Bi, as well as the ultimate tensile strength and vickers hardness. The improvement of the mechanical properties can be attributed to the refined microstructure by Bi addition. The corrosion resistance of Sn-0.7Cu-0.08S is obviously increased with the increase of Bi content. Analyses by SEM and XRD indicate that the corrosion product on the solder alloy surface is SnO2.

On the Advantages of Bi Addition into Sn-Cu-S Lead-Free Solder

Sn–Zn based lead free solder is a promising candidate to replace the Sn–Pb eutectic solder due to its low cost and melting temperature (198 °C) near to the Sn–Pb eutectic solder (183 °C). So far eutectic or near eutectic Sn–Pb alloys have been used as solder material but due to harmful effect on environment and human health Pb has to be eliminated from solder and prevent our environment from being polluted. Here the near eutectic composition of Sn-8 wt% Zn has been chosen. Apart from Sn-8 wt% Zn four different alloys containing different wt% of Bi were considered. They are Sn-8Zn-3Bi, Sn-8Zn-6Bi, Sn-8Zn-8Bi and Sn-8Zn-10Bi. The results of the differential scanning colorimetry (DSC) analysis show that addition of Bi to the near eutectic composition of Sn-8 wt% Zn lowers the melting temperature. The microstructure of the alloys were investigated using a scanning electron microscope and energy dispersive x-ray spectroscopy analysis. Tensile test shows that both tensile strength and elongation of the alloys reduce on addition of high wt% Bi to the Sn–8Zn solder alloy.

Development and Characterization of Sn–Zn–Bi Lead Free Solder

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Development and Characterization of Sn–Zn–Bi Lead Free Solder