Metallurgical Perspective on Alloying Modification of Sn-Ag-Cu Solders

Abstract

pure metal in a vacuum arc melting furnace and subsequently This study investigates the effect of alloying additives on remelting and casting into a Y-shaped graphite mold. the solidification behavior and microstructural characteristics All the specimens were soaked in an oil bath at 1200C for from a metallurgical perspective. Results show that alloying of 1 hr to stabilize the microstructure before testing. Using an Mn and Ti resulted in dramatically reduced undercooling image analyzer, the microstructural characteristics, secondary coarse eutectic structure and extended volume fraction of dendrite arm spacing (SDAS) of Sn and the area fraction of proeutectic Sn of which the dendritic size was refined. Those individual phase, were analyzed quantitatively. Each datum thermal and microstructural changes might be ascribed to the was the average of 15 observations. A scanning electron formation of MnSn2 and Ti2Sn3 intermetallic compounds microscope (SEM) and the energy dispersive X ray (IMCs) appeared respectively in the Mn-doped and Ti-doped spectroscopy (EDS) were used to observe and analyze the samples. Instead of forming heterogeneous IMCs, adding of microstructure. the low temperature solute elements, Bi and Ga, decreases the The thermal behavior of the alloys was investigated using melting point, extends the solidus/liquidus range and causes a differential scanning calorimetry (DSC) analysis. The mixed normal-coarse structure with a varying solute specimens were heated up to above 3000C and then cooled to concentration. Unlike Bi which is only detected in the Sn the ambient temperature, with a constant rate of 2OC/min. matrix, Ga also dissolves in eutectic Ag3Sn and even transforms it into a new intermetallic phase, Ag72Ga28 within Results and discussion the coarse eutectic cells. It is believed that this could give rise Microstructure feature to a specific two-stage nonequilibrium eutectic solidificationThe microstructure of the SnAg sample, Figs. 1(a)(b), feature.illustrates the typical structure of the Sn-Ag eutectic alloyKeywords: Sn-Ag-Cu, transition metals, microstructure, elastic comprising f-Sn dendrites and a eutectic structure with fine modulus.Ag3Sn. The solidification structure of the SnAgBi was nonuniform and the dendritic structure feature was degraded, Introduction Fig. l(c). Some irregular coarse structure was observed to Sn-Ag-Cu alloys (SAC) are considered one of the most surround fine normal regions. Large primary Ag3Sn plates favorable systems as a lead-free solder. However, there are were embedded in the normal structural regions. The still some shortcomings needing to be overcome. Several appearance of primary Ag3Sn corresponds to the phase alloying elements have been proposed for modifying the diagram calculated by Ohnuma et al [5]. As for the SnAgGa microstructure, thermal behavior and interfaces of Sn-Ag-Cu samples, Fig. l(d), the two aforementioned structural regions joints. [1][2][3][4] Most of them can be simply categorized into two were also found and arranged alternatively excep...