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In the present study, nanoindentation studies of the 95.8Sn-3.5Ag-0.7Cu lead-free solder were conducted over a range of maximum loads from 20 mN to 100 mN, under a constant ramp rate of 0.05 s^-1. The indentation scale dependence of creep behavior was investigated. The results revealed that the creep rate, creep strain rate and indentation stress are all dependent on the indentation depth. As the maximum load increased, an increasing trend in the creep rate was observed, while a decreasing trend in creep strain rate and indentation stress were observed. On the contrary, for the case of stress exponent value, no trend was observed and the values were found to range from 6.16 to 7.38. Furthermore, the experimental results also showed that the creep mechanism of the lead-free solder is dominated by dislocation climb.

One of the most pressing challenges facing today's electronics packaging industry is to identify reliable and cost-effective solder alloys to replace toxic lead containing solder. Besides evaluating new alloy compositions and improving the soldering process, it is important to understand how surface finishes applied to the copper metallization affect the joint characteristics. The characterization of intermetallics during the early stages of nucleation and the growth is hindered by the nanoscopic grain size and layer thickness. This study investigates the impact of PCB finish and solder type on the interfacial intermetallics. Five types of solder and four types of finishes were used: Sn37Pb (SP), Sn3.5Ag (SA), Sn3.5Ag0.7Cu (SAC), Sn2Ag0.5Cu4Bi (SACB) and Sn3Bi8Zn (SBZ) solders, combined with immersion Silver (I–Ag), electroless Nickel-immersion Gold (ENIG), Organic Solderability Preservative (OSP) and immersion Tin (I–Sn). It was shown that both the SP and SAC solders follow a parabolic growth model and that the surface finish has a significant effect on the intermetallic morphology and growth kinetics. A combined SEM and XRD investigation was shown to be a suitable method for characterizing nanoscale intermetallics.

In this study, Sn-Ag-Cu based nanocomposites with carbon nanotubes (CNTs) as reinforcements were successfully synthesized via the powder metallurgy technique. Lead-free solder powders were firstly blended together with varying weight percentages of CNTs. The materials were then compacted, sintered and finally extruded at room temperature. The extruded materials were characterized for their microstructural, thermal and mechanical properties. The porosity of the nanocomposites was observed to increase with increasing weight percentages of CNTs, accordingly the density of the nanocomposites was reduced. Thermomechanical analysis of the solder nanocomposites showed that the use of CNTs as reinforcements decreased the average coefficient of thermal expansion of the solder matrix. Furthermore, the results of mechanical properties characterization revealed that the addition of CNTs aids in enhancing the microhardness and the overall strength of the nanocomposite solder. An attempt is made in the present study to correlate the variation in weight percentages of the carbon nanotubes with the properties of the resultant nanocomposite materials.

In the present study, 0.05 wt.% of Ni-coated multi-walled carbon nanotubes (Ni-CNTs) were successfully incorporated into the 95.8Sn–3.5Ag–0.7Cu solder using the powder metallurgy technique, to synthesize a new lead-free composite solder. Its mechanical property (in terms of hardness) was investigated at room temperature using the nanoindentation method. The results revealed that the nanoindentation hardness increased by 14.3% with the incorporation of 0.05 wt.% of Ni-coated CNTs. This observation is in good agreement with the microhardness test results. Moreover, the addition of Ni-CNTs improved the creep resistance of the composite solder. The test results established that nanotechnology coupled with composite technology in electronics solders can result in the enhancement of mechanical properties. These advanced interconnect materials will thus benefit the microelectronics assembly and packaging industry.

Effects of Mn-doped TiO₂ nanoparticles on the wettability, printability and thickness of intermetallic layer of SAC30 on a Cu substrate were studied in this paper. Concentration of Mn-doped TiO₂ nanoparticles was varied from 0.05 wt.% to 1wt.%. The wettability was evaluated in terms of contact angle of solder on the copper substrate and the printability was measured from the volume ratio of printed solder on the copper substrate to volume of stencil opening. The experimental results showed that 0.10wt.% Mn-doped TiO₂ led to the lowest contact angle while the printability was decreased with the increase of the added nanoparticles and the thinnest intermetallic layer was found at 0.50wt.% Mn-doped TiO₂ nanoparticles. Mn-doped TiO₂ concentration was then optimized using a desirability function to find optimal values for the three responses. It was found that 0.07wt.% was the optimal concentration for the three metrics — wettability, printability and thickness of the intermetallic layer.

With the development of lead-free solders in the electronic packing industry, Sn–Ag–Cu solders are one of the most promising lead-free alloys to be applied due to their outstanding mechanical property and wettability. By performing indentation experiments, the effect of cooling rate on the mechanical properties of Sn–3.0Ag–0.5Cu (SAC305) solder is investigated in typical cooling conditions (i.e., furnace cooled and water quenched) and compared with the as-machined samples of bulk solder bars from the industry. Based on continuous stiffness measurement technique, Young’s modulus and hardness are reduced by 2.3–3.9GPa and 0.053–0.085GPa, respectively, after annealing treatment for the indentation depth between 1000nm and 1100nm in samples after cooling, however, the value of hardness is independent of cooling condition. By defining the contact stiffness to represent residual stress in solder samples after cooling and annealing process, an exponential-based Oliver–Pharr model is employed to fit the unloading responses of indentation. It is found that the smaller cooling rate induces less contact stiffness and thus less residual stress. Despite different cooling conditions, the contact stiffness of unannealed and annealed solder samples are 711.8–842.5$\mu$N/nm and 655.2–673.4$\mu$N/nm, respectively. Thus, annealing treatment of 210${}^{\circ }$C for 6h can effectively alleviate residual stress to a similar level for SAC305 solder samples with different cooling conditions. This conclusion is supported by the alleviation of pile-up deformation in the residual indentation after annealing treatment.