Anelling effect on the lower melting point ternary solder Alloy Sn-Bi-Zn

Transcription

1 Anelling effect on the lower melting point ternary solder Alloy Sn-Bi-Zn Tarik talib Issa & Dunia K.M.Al-Nasrawy, University of Baghdad, College of Science, Department of Physics Abstract ---A ternary solder alloy of composition Sn 42 having a lower melting point has been studied by (DSC) technique. The eutectic alloy Sn-Bi-Zn melts sharply at approximately 136 C. a alloy were found to annealing soften at 150 C for 12 hours, the x-ray diffraction pattern and optical micrographs shows the microstructure changes accordingly. The hardness of produced alloy has been found for both as cart and annealed as a soften metal. INTRODUCTION Solder is metal alloy consisting of distinct percentages of two or more metals. In electrical work, the alloy is usually tin (Sn) and lead (pb). However, silver (Ag), Zinc (Zn), and Antimony (Sb) are used for special soldering alloys, solder that uses lead has lower melting point than pure lead. However, some solder contain no lead. A eutectic alloy is a composition of one or more metals that has one sharp melting point and no intermediate plastic stage [1]. According to the European union waste Electrical and Electronic Equipment Directive (WEEE) and Restriction of hazardous Substances, Directive (ROHS), lead had to be eliminated from electronic system by July 1, 2006[2]. Lead solder was still used until the 1980 because it was thought that the amount of lead that could leach into waster from the solder was negligible. Since even small amounts of lead have been found detrimental to health. Alternative solder alloy with lower melting points than those of eutectic Sn-pb are often considered for many applications [3]. After establishing an optimum ternary composition of Sn-pb-Bi, quaternary additions were examined for additional beneficial effects on the melting character [4]. Silver, Copper, Indium, Aluminum and Zinc elements replacement pb element to establish lead free solder alloy has been investigated. The thermal, micro structural and mechanical properties The aim of this work was to determine a ternary Sn_Bi_Zn,alloy that not only melted at least40 C,below the eutectic Sn_Pb, but also of shape homogenized microstructure and improved hardness. EXPERIMENTAL PROCEDURE The Sn 42 used were mixed for pure elements (99.9 wt %) and melted using temperature furnace under inert atmosphere of 0.5 lit/hr flow argon and caste in Alumina boat. Two alloys were prepared for sake at comparison with its properties obtained in the studied systems. The melting behavior was determine using diffraction scanning calorimetry (DSC) upon heating r 5 C / min to determine the heat extraction that are conductor the onest, peak, Endset, melting point. The product alloy were annealed at 150 C for 12 hours, the alloys was examined before and after annealing by XRD technique to identify the phases Sn-Bi-, Sn-Zn respectively. The solder alloys microstructure was evaluated by optical microscopy. Brinell hardness testes were performed on selected alloys at applied load 30 Kgm and loading time was 20 sec.2 > RJSSM: Volume: 02, Number: 05, September-2012 Page 10

2 RESULTS AND DISCUSSION The melting behavior was determined in the Sn 42 ternary composition. Figure 1.a is tropical DSC profile of the alloy. The profile shows the temperature region, a long portion at alloy melts sharply at approximately ~ C (onest). This solidus temperature is followed by continuity in the DSC curve that is indicate of initial liquids temperature at ~ C (peak), the majority of the alloy volume remains solid until approximately 130 C, denoted in figure 1.a by a slope change on premelting (solid-state diffusion ) portion of the second heat extraction well. This temperature of130 C is, in effect, a second solidus temperature for the remaining solid portion of the alloy. The majority of the alloy finally becomes molten at approximately C (Endest). This comparison having excess bismuth results in the ~ 140 C melting phase, wile excess zinc results lowering in the melting point at the alloy ~ 136 C[ 6]. The thermal behavior did not shows extremely change after annealing. However, a minor effect was observed at the endo thermal melting point peak (more sharpness), as shown in figure 1.b. Figure 1a :- Typical differential scanning calorimetric (DSC) profile for Sn 42 ternary alloy before annealing. > RJSSM: Volume: 02, Number: 05, September-2012 Page 11

3 Fig 1b :- Typical differential scanning calorimetric (DSC) profile for Sn 42 ternary alloy after annealing at 150 C for 12h The solder alloy microstructure was evaluated by x-ray diffraction pattern given in figure 2a, as casting. The diffraction peaks of Sn-Bi alloy are conspicuous near the interface between the antimony and zinc resulting the Sn-Zn phase in the thermal diffraction temperature range 250 C to 350 C Sn is considered to take place. Figure 2b, shows the behavior of the overheating process, the change in structure was clearly identified from the x-ray diffraction pattern. The diffraction peaks of both Sn- Bi, Sn-Zn alloy are sharper and can be distinguishing easily. From the Sn-Zn binary alloy phase diagram[7]. It is evident that Zn melts significantly in the Sn liquid. The phase diagram also show that 35 atomic percent Zn melts in the Sn liquid at 300 C. this value is equivalent to the proportion the all Zn melts in Sn liquid in the case of the Sn-Bi-Zn annealed ternary alloy. Figure 2a:- x-ray diffraction pattern of the Sn 42 ternary alloy the numerical number indicate the phases present no.1 Sn-Bi, no.2 Sn-Zn. Figure 2b:- x-ray diffraction pattern of the Sn 42 ternary alloy after annealing at 150 C for 12h. The change on the microstructure of the Sn 42 ternary alloy was clearly observed before and after annealing process. Figure 3.a shows the microstructure of the Sn-Zn eutectic alloy consisted of both an acicular structure, formed as a primary crystal(black Spots), and a fine eutectic structure, formed in Sn-rich and Zn-rich solid solutions. The microstructure was changed during the annealing at 150 C for 12 hours, as shown in figure 3b as compared to the microstructure. Wile the microstructure > RJSSM: Volume: 02, Number: 05, September-2012 Page 12

4 of Sn-Bi eutectic alloy consisted of a primary phase and mixture of Bi-rich solid solution (bright colored area) and Sn-rich solid solution (dark colored area), as shown in figure 4.a. remarkable microstructure changes were observed during annealing for 12h as compared to the observed microstructure before annealing has shown in figure 4.b. its clearly be observed the homogeneity distribution of Sn-rich solidsolutionby Bi phase (whitespots). Thisis becomeof thesolid solubility ofbi in Sn-richsolid solutiondecreases remarkablyas annealingwere done [8]. Figure 3: Optical micrographs of (a):-the microstructure of Sn-Zn eutectic, (b): The microstructure of Sn-Zn, eutectic after annealing at 150 C for 12h. Figure 4: Optical micrographs of (a):- The microstructure of Sn-Bi eutectic, (b):- The icrostructure of Sn-Bi, eutectic after annealing at 150 C for 12h. The Brinell hardness valueb10 HRB forthe ternary alloy Sn-Bi-Zn as castwas calculated at room temperature. Itappears thatthe hardening of microstructure wascased bysolid solution of Biin to Sn-rich solid solution and byprecipitation of Bi in the Sn-rich solid solution. On the other hand,softening of microstructure coarsening forthesn-bi-zn system assumed that the hardening overcomes softening. Thehardness of the alloy did not changes afterannealingat 150 Cfor 12 h. however, the microstructure of SN-Bi, Sn-Zn eutecticalloycoarsenedduring the annealing [9].usually. CONCLUSION 1.The meltingpoint ofthesn42-bi57.3-zn0.7ternary alloywas found at~136 Candno changes were observed at the annealing process. > RJSSM: Volume: 02, Number: 05, September-2012 Page 13

5 2.The micro structural changes of the Sn-Bi and Sn-Zn eutectic solder alloywas achieved as cast and asannealed. 3.it wasfound that the alloyof leas free solder having thesoftening hardness as cast and asannealedbecause of the solid solution of Bi into Sn-rich solid solution. REFERENCES [1] David L.Pippen:A primer and hard soldering electrical corrections,(the Technology Interface,1997) pp.1-9. [2] T.Yamarroto et al : Assembly technology using lead free solid, FOSTSO Sci.Tech.January.,January 2007 [3] M.T.McCormack, Y.Dgani,H.S.Chan, and W.R.Gesick: A lower-melting point solder alloy for surface mounts, J.JOM,48(5)(1996)PP [4] IPC-SM-786A, Procedures for characterizing adhering of microstructure /Reflan Sensitive ICS (Lin colnwood, 1L 1995). [5] VIANCO Paul;REJENT,erome GRANT Richard -: Dexetropment of Sn-based low melting temperature Pb-free solder allyos, Material transactions JIM ISSN ,2004, Vol- 45.No.7,pp [6] Mnyazawa, Y.Arige.T, Microstructural changes and hardness lead free solder alloys, ECO Desigen apos; Firs, International symposium on volume, issue, 3-3 Fab-1999, pp [7] Massalssci T.B. "Binary Alloy phase Diagrams, American Society for metals,metals park,dhio (1990)pp [8] T.B.Massaiskci, H.Okamoto, P.R.subramanion and L.Kacprzak : Binary alloy phase diagram second edition (ASM) Internet, Materials park,1990,pp [9] M.Kitajima et al -: Development of Sn-Zn-Al lead free solder allos. FUSITSO Sci. Tech.J.41-2, PP , > RJSSM: Volume: 02, Number: 05, September-2012 Page 14