Experimental and numerical analyses of laser remelted Sn–0.7 wt%Cu solder surfaces Bismarck Luiz Silva • Jose ´ Eduardo Spinelli • Manuel V. Cante ´ • Felipe Bertelli • Noe ´ Cheung • Rudimar Riva • Amauri Garcia Received: 11 December 2014 / Accepted: 31 January 2015 / Published online: 8 February 2015 Ó Springer Science+Business Media New York 2015 Abstract Numerous studies on the effects of solidifica- tion thermal parameters, microstructure and reliability of Sn–Cu solder alloys can be found in the literature, however only a very limited number of investigations deal with the application of laser surface remelting (LSR) in soldering processes. One of the key advantages of the LSR rapid solidification conditions relies on the reduction in size and the more homogeneous distribution of intermetallic parti- cles. This study aims to analyze the effect of LSR process parameters on microstructural changes and hardness evo- lution in the remelted region of a Sn–0.7 wt%Cu alloy. Optical and SEM microstructures were used for determi- nation of geometrical and dimensional aspects of the remelted pool profile such as depth (d) and width (w) as a function of the laser beam speed (V b ). Both dimensions are shown to vary linearly with V b . Hardness varied noticeably with V b (from 11.5 to 19.5 HV for Vb varying in the range 2.4–9.0 m/min) caused by the fineness of the eutectic mixture and the corresponding more homogeneous distri- bution of intermetallic Cu 6 Sn 5 particles. The theoretical predictions provided by a heat transfer numerical model are shown to represent the dimensions of the laser-remelted Sn–0.7 wt%Cu alloy pool. A growth law is proposed re- lating the microstructural interphase spacing to the cooling rate, encompassing both directional solidification and LSR. 1 Introduction The increasing environmental and health concerns, has led the use of Pb to be banned in the manufacture of electronic goods by the international legislation (EU RoHS) in 2006. Since then intensive efforts are taking place to develop lead-free solder alloys [1]. Sn–Cu alloys of near eutectic compositions are already used as a commercial alternative for soldering of microelectronic parts due to satisfactory features such as adequate wettability, good mechanical strength, ductility and manufacturability, besides low cost [2, 3]. The Sn–Cu eutectic reaction, which governs the structural development of the Sn–0.7 wt%Cu alloy, occurs at 227 °C in equilibrium between the faceted Cu 6 Sn 5 phase and the non-faceted Sn-rich phase [4]. The Cu 6 Sn 5 phase usually grows in form of fibers embedded in a continuous Sn-rich matrix. During the last few years, the soldering industry be- comes highly interested in rapid solidification processes for soldering due to cost reduction and microstructure refine- ment. One of the challenging aspects in electronics industry is to implement laser soldering. Laser processing is known by its unique features such as localized and noncontact heating, rapid rise and fall in temperature, and ease of automation as compared with the reflow soldering process [5]. The alignment of all these aforementioned figures strongly advises a wide investigation on laser-soldered Sn– Cu specimens. Emphasis on practical inter-relations of size of the treated zones, the scale of the phases forming the microstructure and mechanical properties is expected to be B. L. Silva Á J. E. Spinelli (&) Department of Materials Engineering, Federal University of Sa ˜o Carlos, UFSCar, Sa ˜o Carlos, SP 13565-905, Brazil e-mail: spinelli@ufscar.br M. V. Cante ´ Á F. Bertelli Á N. Cheung Á A. Garcia Department of Manufacturing and Materials Engineering, University of Campinas, UNICAMP, PO Box 6122, Campinas, SP 13083-970, Brazil R. Riva Institute for Advanced Studies, General Command for Aerospace Technology, PO Box 6044, Sa ˜o Jose ´ Dos Campos, SP 12228-970, Brazil 123 J Mater Sci: Mater Electron (2015) 26:3100–3107 DOI 10.1007/s10854-015-2802-0