Design of a Multicomponent Alloy for Application in Electronic Components Solder

In 2006, directive 2002/95/EC came into force in the European Union, which contemplates restrictions on hazardous substances for electronic products. Since then, the development of solder substitutes has increased substantially [1]. Thus, research into new types of solders is essential [2]. Studies on adding Bi and In in solders based on high entropy or multicomponent alloys have been developed recently [3]. However, studies that allow an understanding of this type of system are currently under constant development. Hence, the present study shows a microstructural characterization of a multicomponent alloy that will work as an alternative for electronic components solder. A multicomponent solder was prepared using high purity (>99.9%) Sn, Bi, In, Cu and Zn with an atomic proportion of (SnBiIn)80Zn10Cu10 in an electric furnace. Initially, the elements with the lowest melting point (Sn, Bi, In and Zn) were melted at 350°C. Cu was added to the molten metal, the furnace temperature was increased to 720°C, and the alloy was solidified on a steel mold. The wetting behavior was studied using polished Cu sheets with alumina. A solder piece was placed on a Cu sheet and reflowed at 220°C for 5 min in an electric furnace. Later, samples were air-cooled at room temperature and cleaned with pure ethanol. The samples were mounted in polychrome resin and cross-section cut for their metallographic analysis. The samples were prepared by conventional metallographic processing. The microstructure was analyzed by scanning electron microscopy (SEM) using a HITACHI SU3500 device, coupled with backscattered electrons (BSE) and energy dispersion spectrometer (EDS) detectors. Figure 1 shows the EDS-SEM elemental mappings analysis of the multicomponent solder. A homogeneous distribution of three phases in the microstructure is observed. The elemental mappings allowed to identify the phases as BiIn (Zn) (light tone), Sn (InBi) (light gray tone) and CuZn (SnIn) (dark gray tone). Figure 2 shows BSE-SEM cross-section micrographs obtained of the solder/substrate joint (a–b) and EDS-SEM elemental mappings analysis (c). The contact angle (θ°) was 51.26°. The contact angle value obtained indicates that the weld has an acceptable wettability according to the reported values, 0° < θ° < 30° – very good wetting, 30° < θ° < 40°– good wetting, 40° < θ° < 55° – acceptable wetting, 55° < θ° < 70° –poor wetting, and θ° > 70° – very poor wetting [4]. In addition, one of the most critical factors influencing solder joint reliability is the intermetallic compound (IMC) layer [5]. Since the thickness of the IMC layer was not uniform throughout the interface, the mean value of the thickness (Y) of IMC was obtained from the equation: Y=A/L, where A is the total area of the IMC layer in the image, and L is the length of the IMC in the interface direction [6]. The average IMC layer thickness was 3.45 µm, where <4 µm constitutes an acceptable measure within the electronics industry [7]. The elemental mapping analyses show that Bi does not diffuse in IMC due to the significant size difference between atoms of Bi and Cu, which restricted their mutual solubility [8]; meanwhile, Cu is the dominant diffusion element. EDS-SEM elemental mappings analysis of the multicomponent solder. EDS-SEM elemental mappings analysis of the solder/substrate joint