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Effect of the TiO2 Nanoparticles on the Growth Behavior of Intermetallics in Sn/Cu Solder Joints
Shengyan Shang,Anil Kunwar,Jinye Yao,Yanfeng Wang,Haitao Ma,Yunpeng Wang 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.2
In order to investigate the effect of TiO2 nanoparticles on growth behavior of interfacial Cu6Sn5 intermetallics compounds(IMCs) in Pb-free Sn/Cu system, the solder joints are fabricated by using flux doped with different content (0.0–2.0 wt% offlux) and particle diameter (5 nm and 50 nm) of TiO2 . In context of isothermal reflow soldering at 250 °C and subsequentair cooling, the increase in reflow duration from 10 to 120 s was characterized with an increment in IMC layer thicknessand grain size, due to the enhancement of Cu flux contribution for Ostwald ripening during constant temperature reflow andprecipitation kinetics during cooling. The increased proportion of TiO2 nanoparticles in flux was found to reduce the growthof IMC layer and grain size. The suppression effect on IMC was more pronounced for 5 nm particles as compared to the 50nm TiO2 . The TiO2 nanoparticles, adsorbed on IMC plane can retard the growth of the latter. Presence of sufficient amountof a given sized TiO2 nanoparticles among IMCs, by increasing the effective stress at the localized interfaces, and causingthe breaking of brittle Cu6Sn5 during growth stage; can help in the inhibition of IMC whisker formation. Particle diameterand mass proportion of TiO2 nanoparticles are important for soldering materials design.
Shengyan Shang,Anil Kunwar,Yanfeng Wang,Jinye Yao,Yingchao Wu,Haitao Ma,Yunpeng Wang 대한금속·재료학회 2019 ELECTRONIC MATERIALS LETTERS Vol.15 No.2
Solder ball of initial diameter 1.4 mm, was refl ow soldered with Cu substrate at 523.15 K using fl ux doped with Cu@Agcore–shell nanoparticles (NPs) in the proportion 0–2 wt%. The solders were then air cooled to room temperature. The use ofNPs, by reducing the base height (H) of the solder and enhanced the diameter (W) of the solder, caused an overall increase inthe spread ratio of the solder. The altered magnitudes of heat and mass transfer in these geometrically diff erent but constantvolume specimens were analyzed using fi nite element method. The occurrence of diff erential concentration gradient, radialthermal gradient and velocity magnitudes, in solders with diff ering geometry were numerically elaborated. The Cu6Sn5 intermetalliccompound (IMC) formed at the Cu/Sn interface, was obtained to be the thickest for the specimen using undopedfl ux, whereas it was found to be smallest for the sample processed with fl ux containing 0.5% NPs. From the growth kineticsstudy, it has been inferred that IMC thickness is linearly proportional to the geometrical parameter H and Wb , with b < 1.