Unsteady and steady solidification of monophasic and peritectic Sn-Sb and Sn-Sb-(Ag,Cu) alloys: microstructural evolution, wettability and mechanical properties

Author(s)

José Marcelino da Silva Dias Filho

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Mecânica
• Defense date: 2016-10-17

Examining board members

Amauri Garcia; Antonio Celso Fonseca de Arruda; Cecília Amélia de Carvalho Zavaglia; Eduardo Netto de Souza; Maria Aparecida Pinto

• Advisor: Noé Cheung; Amauri Garcia

Abstract

Considerable effort is being made to develop lead-free solders for assembling in environmental-conscious electronics, due to the inherent toxicity of Pb. The search for substitute alloys of Pb¿Sn solders has increased in order to comply with different soldering purposes. The solder must not only meet the expected levels of electrical performance but may also have appropriate mechanical strength, with the absence of cracks in the solder joints. The Sn¿Sb alloy system has a range of compositions that can be potentially included in the class of high temperature solders. This study aims to establish interrelations of solidification thermal parameters, microstructure and mechanical properties of Sn¿Sb (2.0 wt.%Sb, 5.5 wt.%Sb and 10 wt.%Sb) and Sn-5.5 wt.%Sb-1 wt.%(Cu,Ag) alloys samples, which were directionally solidified (DS) under cooling rates similar to those used in industrial practice. A complete high-cooling rate cellular growth is shown to be associated with the Sn¿2.0 wt.%Sb and Sn-10 wt.%Sb alloys. A reverse dendrite-to-cell transition is observed for the Sn¿5.5 wt.%Sb and Sn¿5.5 wt.%Sb-1 wt.%Ag alloys, while a complete dendrite growth is shown to be associated with the Sn¿5.5 wt.%Sb-1 wt.%Cu alloy. The solute concentrations along the length of the DS castings were determined by X-ray fluorescence and macrosegregation trends have not been detected. The primary and secondary phases (within the intercellular and interdendritic regions), were identified by X-ray diffraction analysis. Strength and ductility of the Sn¿2.0 wt.%Sb and Sn-10 wt.%Sb alloys are shown not to be affected by the scale of the cellular spacing. On the other hand, a considerable variation in these properties is associated with the cellular region of the Sn¿5.5 wt.%Sb and Sn¿5.5 wt.%Sb-1 wt.%Ag alloys casting. For the Sn¿5.5 wt.%Sb-1 wt.%Cu alloy, the ultimate tensile strength and the yield tensile strength increase with the decrease in the primary dendrite arm spacing, however, the elongation remained constant. On the other hand, the cellular and dendrite spacings are shown not to affect significantly the hardness along the length of the DS castings. The wettability was analyzed for all the alloys against a steel substrate by using a goniometer. The spreading areas of these alloys on a copper substrate were evaluated after hot dipping procedures at different temperatures. About 95% of the surface area of the substrate is shown to be covered for any alloy examined (AU)

• FAPESP's process: 13/09267-0 - Microstructural evolution in the transient solidification of monophasic and peritectic Sn-Sb solder alloys (and Sn-Sb-X) and in solder/substrate interfacial layers
• Grantee: José Marcelino da Silva Dias Filho
• Support Opportunities: Scholarships in Brazil - Doctorate