Agradecimentos: The authors are grateful to FAPESP-São Paulo Research Foundation, Brazil (Grants: 2017/16058-9, 2017/15158-0 and 2017/12741-6), Capes-Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brazil (Funding Code 001), CNPq-National Council for Scientific and Technological Development (Grant 408576/2016-2) and FAPEAM (Amazonas State Research Foundation) for their financial support. The authors would like to thank the Brazilian Nanotechnology National Laboratory— LNNano for allowing us to use its facilities Ver menos

Directional solidification experiments coupled with mathematical modelling, drop shape analyses and evaluation of the reaction layers were performed for three different types of joints produced with the Sn-0.7 wt.%Cu solder alloy. The association of such findings allowed understanding the mechanisms affecting the heat transfer efficiency between this alloy and substrates of interest. Nickel (Ni) and copper (Cu) were tested since they are considered work piece materials of importance in electronic soldering. Moreover, low carbon steel was tested as a matter of comparison. For each tested case, wetting angles, integrity and nature of the interfaces and transient heat transfer coefficients, ‘h’, were determined. Even though the copper has a thermal conductivity greater than nickel, it is demonstrated that the occurrence of voids at the copper interface during alloy soldering may decrease the heat transfer efficiency, i.e., ‘h’. Oppositely, a more stable and less defective reaction layer was formed for the alloy/nickel couple. This is due to the suppression of the undesirable thermal contraction since the hexagonal Cu6Sn5 intermetallics is stable at temperatures below 186°C in the presence of nickel Ver menos