Measurement of solder–flux–vapor surface tension by a modified maximum bubble pressure technique

Abstract

While it is widely known that flux is needed to maintain an oxide-free surface during soldering, the fact that flux also reduces the surface tension between solder and ambient is neither widely recognized nor treated extensively in the literature. An apparatus is described which quantitatively evaluates the reduction of surface tension in the presence of flux. Representative data of eutectic lead–tin with water white rosin fluxes are presented.

Three-Dimensional a-Si:H Solar Cells on Glass Nanocone Arrays Patterned by Self-Assembled Sn Nanospheres

“…It is noteworthy that Sn lenses were obtained even at 150 °C, well below the melting temperature. This morphology has not been observed for micrometer scale solder balls. − We believe that it is technologically significant that one can achieve nanoscale templates at such low temperatures, implying great flexibility in choosing polymer and glass substrates for further patterning processes.…”

“…Sn solders are used at length scales of hundreds of micrometers in joining techniques to form ball grid arrays on copper at the back end of the line in a complementary metal-oxide-semiconductor process. − Since Sn-based materials have a strong tendency to be oxidized, a strong antioxidizer, or “flux”, is applied to the Sn to make it dewet from the substrate and transform into spheres (spheroidization) upon annealing around 250 °C. − The flux is typically composed of diethylene triamine pentaacetic acid, tetrakisethylenediamine, and glycerol ethoxylate, which together mechanically crack the surface Sn oxide and inhibit the Sn surface from subsequent oxidation. On a nonwetting surface, this results in the formation of complete Sn spheres upon melting…”

“…For our experiments, we require Sn structures in the tens of nanometers to micrometer range. It is not possible to form spheres out of micrometer thickness Sn layers without applying flux because the Sn oxide surface layer significantly slows diffusion of Sn atoms, preventing rearrangement into the equilibrium shape. − We therefore formed Sn nanospheres by first depositing 10–120 nm thick Sn films on glass substrates using thermal evaporation at room temperature. We then heated the films in a rapid thermal annealing (RTA) furnace under a N 2 flow at temperatures from 150 to 450 °C for 10 s using flux and compared with the same anneal without flux.…”

Solder-based chip-to-tube and chip-to-chip packaging for microfluidic devices

“…The droplet size distribution was subsequently used to determine the specific interfacial areas for each emulsion. With this method, the interfacial areas were found to be 200 cm 21 for CO 2 in water and 600 cm 21 for water in CO 2 . 31 The ductility of the solder alloy as well as the compatibility of the solder joint with organic solvents enabled the construction of a five-port silicon microreactor [Fig.…”

“…Alternatively, the use of rosin fluxes prevents oxidation and enhances solder-wetting. 19,21 In addition, since the melting point of SnPb solder (63%Sn, 37%Pb) is 183 uC and the intermetallic compounds are formed between 200 and 220 uC, connections can realized on laboratory hotplates with no specialized equipment. 22,23 Solder-based connections are compatible with a wide range of organic solvents and conditions.…”