Microelectronics Reliability

Transcription

1 Microelectronics Reliability 49 (2009) Contents lists available at ScienceDirect Microelectronics Reliability journal homepage: Interfacial microstructure and shear strength of Ag nano particle doped Sn 9Zn solder in ball grid array packages Asit Kumar Gain a, Y.C. Chan a, *, Ahmed Sharif b, N.B. Wong c, Winco K.C. Yung d a Department of Electronic Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong b Department of Materials and Metallurgical Engineering, Bangladesh University of Engineering and Technology, Dhaka-100, Bangladesh c Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong d Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong article info abstract Article history: Received 14 January 2009 Received in revised form 8 May 2009 Available online 3 June 2009 Sn 9Zn solder joints containing Ag nano particles were prepared by mechanically mixing Ag nano particles (0.3, 0.5 and 1 wt%) with Sn 9Zn solder paste. In the monolithic Sn Zn solder joints, scallop-shaped AuZn 3 intermetallic compound layers were found at their interfaces. However, after the addition of Ag nano particles, an additional uniform AgZn 3 intermetallic compound layer well adhered to the top surface of the AuZn 3 intermetallic compound layer was found. In addition, in the solder ball region, fine spherical-shaped AgZn 3 intermetallic compound particles were observed as well as Zn-rich and b-sn phases. With the addition of Ag nano particles, the shear strengths consistently increased with an increase in the Ag nano particle content due to the uniform distribution of fine AgZn 3 intermetallic compound particles. The shear strength of monolithic Sn Zn and 1 wt% Ag nano particle content Sn Zn solder joints after one reflow cycle were about 42.1 MPa and 48.9 MPa, respectively, while their shear strengths after eight reflow cycles were about 39.0 MPa and 48.4 MPa, respectively. The AgZn 3 IMCs were found to be uniformly distributed in the b-sn phase for Ag particle doped Sn 9Zn composite solder joints, which result in an increase in the tensile strength, due to a second phase dispersion strengthening mechanism. The fracture surface of monolithic Sn Zn solder exhibited a brittle fracture mode with a smooth surface while Sn Zn solder joints containing Ag nano particles showed a typical ductile failure with very rough dimpled surfaces. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Due to the inherent toxicity of lead (Pb), environmental regulations and health concerns around the world have been targeted to eliminate the usage of Pb-bearing solders in electronic assemblies [1 5]. This has prompted a search for Pb-free solders and enhanced the research activities in this field. As a result, the development of new lead-free solders and their composites, in addition, is also driven by the continual miniaturization of integrated circuits and the quest for better performance and reliability from interconnections. In general, the reliability of solder joints is greatly influenced by the interfacial reaction between the substrate and solder. During a reflow process, intermetallic compound (IMC) layers are formed inevitably at the interface between the solder and substrate. Moreover, due to solid-state diffusion, the intermetallic compound (IMC) layer becomes thicker and thicker with more reflow cycles and a thermal aging stage. The properties of solder joints as well as the reliability of the whole package are very sensitive to the thickness and morphology of the IMC layers at the * Corresponding author. Tel.: ; fax: address: eeycchan@cityu.edu.hk (Y.C. Chan). interface of the joints [6]. Although the formation of an IMC layer is important for good wetting and bonding, an excessively thick layer is harmful because of its brittle nature which makes it prone to mechanical failure even under a low load [7]. To replace Pb Sn solder, many Sn-based solders such as Sn Ag, Sn Cu, Sn Zn, Sn Ag Cu etc. have been developed as candidates for lead-free solders. Among them, Sn Zn solder has recently been considered as a suitable candidate for a Pb-free solder material because of its low melting point (198 C) as compared with other Snbased solders, e.g., Sn Cu (227 C), Sn Ag (221 C), Sn Ag Cu (217 C) as well as its low cost [8 10]. In general, the higher melting temperature, in the range of C associated with solders (Sn Cu (227 C), Sn Ag (221 C)), can damage the other electronic components mounted on the circuit board while reflowing [11]. However, some important issues such as inferior wettability, easy oxidation and micro-void formation need resolving to increase the practical use of these solder alloys [12,13]. It is well known that the poor oxidation resistance of the Sn Zn eutectic alloy is due to the oxidation of Zn, which exists in both primary and eutectic phases. If the amount of Zn-phase in the Sn Zn eutectic alloy can be reduced or fixed by forming IMCs, it is expected that the oxidation resistance can be improved. Therefore, much /$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi: /j.microrel

2 A.K. Gain et al. / Microelectronics Reliability 49 (2009) research has been concentrated on the addition of other micrometer sized elements such as Bi, In, Ag, Al, Fe and Co into the Sn Zn solder so as to obtain better solder alloys and a controlled fine microstructure [14,15]. With the development of nano technology, nano-sized Ag particles were selected as reinforcements in manufacturing composite solders. Mohan et al. [16] prepared Sn Pb composite solders by the addition of single wall carbon nano-tubes (SWCNT) as a reinforcing agent and their mechanical properties such as hardness, yield strength and ultimate tensile strength were shown to be superior to the unreinforced solder, while the melting point was not appreciably altered. Mavoori and Jin [17] used 5 nm TiO 2 and 10 nm Al 2 O 3 particles as reinforcement for a conventional 63Sn 37Pb solder and reported significant enhancement in creep resistance and other mechanical properties. Moreover, the nano-sized metallic particle (Ni, Cu, and Mo) reinforced composite solders were developed, and the results showed that the mechanical properties, such as microhardness and creep resistance were increased [18]. Shen et al. [19] successfully prepared a ZrO 2 reinforced composite solder by mechanically dispersing ZrO 2 particles into a eutectic Sn 3.5Ag solder paste, and the composite solders had an improved microhardness and a refined microstructure. Tai et al. [20] reported that nano-sized Ag reinforced Sn 0.7Cu composite solders and their joints showed better wettability and mechanical properties, as well as longer creep-rupture lives, than Sn 0.7Cu solder. However, the result of a literature search revealed that no studies have been made so far to develop lead-free Sn Zn solders containing Ag nano particles for use on Au/Ni metalized Cu pads. Accordingly, the aim of the present study is to synthesize lead-free Sn Zn solder joints with different weight percentages of Ag nano particles. During the reflow process, Ag nano particles will react with the Zn-phase and form Zn-based intermetallic compounds. In addition, monolithic solder joints and those containing Ag nano particles were characterized for their interfacial microstructure and shear strengths on Au/Ni metallized Cu pads as a function of the number of reflow cycles and the content of Ag nano particles. 2. Experimental procedure To prepare solder balls approximately 0.76 mm diameter, Sn 9Zn (Showa Denko JUFFIT-E 9ZSN10M) solder paste was taken from the refrigerator where it had been held for 1 h at room temperature, and mixed with different weight percentages (0.3, 0.5 and 1) of Ag nano particles (Shenzhen Junye Nano Material Co., China). The mixture was blended manually for 30 min. Then, the paste mixtures were printed on alumina substrates using a stainless steel stencil with a thickness of 0.15 mm and reflowed in a reflow oven (BTU VIP-70N) at 245 C. A solder mask-defined copper bond pad on the flexible substrate of a BGA package was used as a base for the electrodeposition of Ni and Au. The solder mask-opening diameter was 0.6 mm with a 7 lm thick Ni layer on the ball pad. The average thickness of the Au layer was 0.5 lm. Lead-free solder balls with a diameter of 0.76 mm, were placed on prefluxed Au/Ni/Cu bond pads of the substrates and reflowed at a temperature of 245 C with a belt speed of 60 cm/min in a convection reflow oven (BTU VIP-70N). To characterize the microstructures, the reflowed samples were cross sectioned and mounted in resin, then ground with different grit sizes of emery papers and polished with 0.5 lm Al 2 O 3 powder. Finally, the interfacial morphology at the solder alloy/bga substrate interface was observed using a scanning electron microscope (SEM, Philips XL 40 FEG) using the backscattered electron (BSE) imaging mode and an energy dispersive X-ray spectrometer (EDAX International, Model No. DX-4) was utilized for determining the chemical composition of the intermetallic compounds (IMC). Before SEM observations, the samples were sputter coated with Au to avoid effects due to charging. Transmission electron microscopy Fig. 1. Bright field TEM images (a and b) of Ag nano particles and (c) a selected area diffraction pattern of Ag nano particles.

3 748 A.K. Gain et al. / Microelectronics Reliability 49 (2009) (TEM, CM 20, Philips) were used for the observation of Ag nano particles. To measure the shear strength, ball shear tests were performed on reflowed samples using a shear testing machine (PTR-1000, Rhesca Co. Ltd., Japan) with a 100 lm shear tool height and a 550 lm/s shear speed. The average strength of twenty solder joints with the minimum and maximum values removed was taken for each condition. After ball shear testing, the fracture surfaces and composition were investigated thoroughly using SEM and EDX. 3. Results and discussion Fig. 1a and b shows bright field TEM images of Ag nano particles and (c) a selected area diffraction pattern of Ag nano particles. In Fig. 2. SEM micrographs of (a) Sn Zn, (b) Sn Zn/1 wt% Ag solder joints after one reflow cycle and EDS spectra (c) and (d) from regions marked P and Q in Fig. 1b. Fig. 3. SEM micrographs of Sn Zn solder joints after one reflow cycle depending on the nano Ag content; (a) 0 wt%, (b) 0.3 wt%, (c) 0.5 wt% and (d) 1 wt%.

4 A.K. Gain et al. / Microelectronics Reliability 49 (2009) the TEM image, the spherical shaped Ag nano particles about nm in diameter are clearly observed. In the low magnification TEM observation (Fig. 1a), it seems the nano particles inside one cluster are in good contact. Actually when the sample was tilted and observed at a higher magnification, between the particles there was often some space as shown in Fig. 1b. Fig. 2 shows cross-sectional backscatter electron micrographs of (a) monolithic Sn Zn solder and (b) 1 wt% Ag nano particles added Sn Zn solder joints after one reflow cycle. In monolithic Sn Zn solder joints (a), scallop-shaped AuZn 3 intermetallic compound layers were clearly observed at their interfaces. However, at their interfaces some micro-voids were found as indicated with arrow heads in Fig. 2a. After the addition of Ag nano particles, an additional intermetallic compound layer with a dark contrast was seen to be well adhered on the top surface of the AuZn 3 layer with a dense lamellar structure. At their interfaces no defects such as cracks, voids etc were found. EDS spectra (c and d) were taken from regions marked P and Q in Fig. 2b. From the EDS spectra, it was confirmed that the dark contrast top intermetallic compound formed was the AgZn 3 phase and the bright contrast bottom phase formed was an AuZn 3 intermetallic compound. Fig. 3 shows cross-sectional backscattered electron micrographs of Sn Zn solder joints depending on the nano Ag content; (a) 0 wt%, (b) 0.3 wt% (c) 0.5 wt% and (d) 1 wt% after one reflow cycle which were taken from the solder ball region. In monolithic Sn Zn solder joints (a), a fine acicular-shaped Zn-rich phase was clearly observed in the b-sn matrix. However, after the addition of Ag nano particles, fine AgZn 3 intermetallic compound particles as indicated with arrow heads in Fig. 3b d were found to be homogeneously distributed, suggesting that the blending the Ag nano particles was successful as well as fine acicular shaped-zn-rich and b- Sn phases. In addition, with an increase in the Ag nano particle content, the AgZn 3 intermetallic compound size was increased due to agglomeration of Ag nano particles. Fig. 4 shows cross-sectional backscattered electron micrographs of Sn Zn solder joints depending on the nano Ag content; (a) 0 wt%, (b) 0.3 wt% (c) 0.5 wt% and (d) 1 wt% after eight reflow cycles. In monolithic Sn Zn solder joints (a), no intermetallic com- Fig. 4. SEM micrographs of Sn Zn solder joints after eight reflow cycles depending on the nano Ag content; (a) 0 wt%, (b) 0.3 wt%, (c) 0.5 wt% and (d) 1 wt%. Fig. 5. SEM micrographs of solder ball region of (a) Sn Zn and (b) Sn Zn/1 wt% Ag solder joints after eight reflow cycles.

5 750 A.K. Gain et al. / Microelectronics Reliability 49 (2009) Fig. 6. Shear strength of monolithic Sn Zn solder and Ag nano particles added Sn Zn solder joints as a function of the number of reflow cycles. pound was found at their interfaces. However, the AuZn 3 intermetallic compound was moved to the solder region. The detachment of the AuZn 3 IMC layer was presumably due to the weak adhesion between the AuZn 3 IMC layer and the Ni layer caused by the depletion of the Au layer during the reflow process. The detachment of the AuZn 3 IMC layer enhanced the brittleness of the solder joints as well as leading to a decrease in the solder shear strength. On the other hand, at their interfaces a very uniform intermetallic compound layer with a lamellar structure was found in solder joints containing Ag nano particles as shown in Fig. 4b d. The bottom AuZn 3 intermetallic compound layer appeared in bright contrast and the top AgZn 3 intermetallic compound layer appeared in dark contrast. As the number of reflow cycles were increased as well as with an increase in the Ag nano particle content, the interfacial intermetallic compound layer thicknesses were not significantly changed as shown in Figs. 2b and 4b d. However, a few spherical-shaped AgZn 3 intermetallic compound particles were found near the top layer. Fig. 5 shows cross-sectional backscattered electron micrographs of (a) Sn Zn and (b) 1 wt% Ag nano particle content Sn Zn solder joints after eight reflow cycles which were taken from the solder ball regions. In the monolithic Sn Zn solder joints after eight re- Fig. 7. SEM fracture surfaces of Sn Zn solder joints doped with Ag nano particles after one reflow cycle; (a and b) 0 wt%, (c and d) 0.5 wt% and (e and f) 1 wt% Ag nano particles.

6 A.K. Gain et al. / Microelectronics Reliability 49 (2009) flow cycles, the acicular-shaped Zn-rich phase size was increased as compared with that in one reflow cycle solder joints. On the other hand, fine spherical-shaped AgZn 3 intermetallic compound particles were found in the solder ball region as well as the Znphase and b-sn phase. In the SEM image shown as Fig. 5b, it was observed that in the Ag added Sn Zn solder joint the amount of acicular shaped Zn-phase is decreased. The explanation here is that with more Ag, more Zn reacts with the Ag to form AgZn 3 compounds and the solder becomes depleted in Zn. Furthermore, the formation of AgZn 3 intermetallic compound particles will enhance the oxidation resistance of solder joints in service. From a reliability test, it is reported that after exposing Sn Zn solder to 85 C/ 43%RH (relative humidity) and 85 C/85%RH atmospheres, the oxidation of Sn Zn solder is attributed to the oxidation of Zn, which diffuses to the Sn grain boundaries and forms ZnO. These oxides are liable to give rise to cracks along the Sn grain boundaries. Tai et al. [20] reported that if the amount of Zn-phase in the Sn Zn eutectic alloy can be reduced or fixed by forming IMCs, it is expected that the oxidation resistance can be improved. The addition of Ag or Cu into the Sn Zn eutectic alloy is observed to have an effect on the oxidation resistance during thermal and humidity exposure tests. Furthermore, Hsuan and Lin [21] found that the formation of AgZn 3 intermetallic compounds occurs at the grain boundaries. In our present study, the formation of fine spherical-shaped AgZn 3 intermetallic compound particles can improve the oxidation resistance of the Sn Zn solder. During soldering, the Zn-rich phase will react with Ag nano particles and form intermetallic compound particles and reduce the Zn-phase in solder joints. In addition, these intermetallic compound particles will form in the grain boundaries and later on block the penetration of water vapor and oxygen, which in turn reduces the formation of ZnO along the grain boundaries. Since solder joints are often subjected to mechanical loading during processing and system use, the mechanical properties of solder joints, such as shear strength and the creep resistance, are crucial to the reliability of solder joints. Therefore, a ball shear test is essential to evaluate the effect on the solder joints as a function of the number of reflow cycles. Fig. 6 shows the variation of ball shear strength of monolithic Sn Zn and Ag nano particle containing Sn Zn solder joints depending on the number of reflow cycles. The shear strength of monolithic Sn Zn solder joints after one reflow cycle was about 42.1 MPa while the shear strength after eight reflow cycles was about 39.0 MPa. On the whole, the shear strength of solder joints containing Ag nano particles changed very little as a function of the number of reflow cycles, regardless of the uniform intermetallic compound layer as well as the fine AgZn 3 intermetallic compound particles. However, the Sn Zn solder joints with a high percentage of Ag nano particles exhibited consistently higher strengths than that of solder joints with a lower Ag nano particle content for each reflow cycle due to the formation of fine spherical-shaped AgZn 3 particles. With a larger amount of Ag particles, the amount of AgZn 3 compounds formed was also larger. Later some of the AgZn 3 IMCs agglomerate together to form micrometer-sized AgZn 3 IMCs in the bulk solder. Due to a second phase dispersion strengthening mechanism [22] of AgZn 3 intermetallic compound particles, the Ag doped solder showed a higher strength than the undoped solder. The shear strength of 0.3 wt% and 1 wt% Ag nano particles content solder joints after one reflow cycle were about 45.8 MPa and 48.9 MPa, respectively. However, in the solder joints containing Ag nano particles, the shear strengths were not significantly changed after eight reflow cycles. In this study, uniform intermetallic compound (IMC) layers were found at their interfaces in the solder joints containing Ag nano particles and these even increased with the number of reflow cycles as shown in Figs. 2b and 4b d. The shear strength of solder joints containing 0.3 wt% and 1 wt% Ag nano particles after eight reflow cycles were about 44.9 MPa and 48.4 MPa, respectively. For the nano-ag doped solder, the fracture occurred through the bulk of the solder and the strength of the solder joint thus depends on that of the bulk solder. Due to a second phase dispersion strengthening mechanism, the Fig. 8. SEM fracture surfaces of Sn Zn solder joints doped with Ag nano particles after eight reflow cycles; (a and b) 0.5 wt% and (c and d) 1 wt% Ag nano particles.

7 752 A.K. Gain et al. / Microelectronics Reliability 49 (2009) Fig. 9. Schematic diagram for dimple formation mechanism of (a) Sn Zn and (b) Ag nano particle added Sn Zn solder joints after shear tests with a scheme of the crack propagation. solder retained its high strength (reliability) even after multiple reflows. On the other hand, the shear strength of a Sn Ag Cu solder after one reflow cycle was about 1680 g (36.3 MPa) [23]. The detailed fracture behavior of monolithic Sn Zn solder and solder joints containing Ag nano particles may be revealed by extensive fractrographic observations. Fig. 7 shows SEM images of fracture surfaces of (a and b) Sn Zn solder and Sn Zn solder joints containing different weight percentages of Ag nano particles can be seen in Fig. 7c f having (c and d) 0.5 wt% and (e and f) 1 wt% Ag nano particle content. The fracture surface of monolithic Sn Zn solder joints exhibited a brittle fracture mode with a smooth surface as shown in Fig. 7a and b. On the other hand, Sn Zn solder joints containing Ag nano particles showed ductile failure with very rough dimpled surfaces due to the formation of fine AgZn 3 intermetallic compound particles as shown in Fig. 7c f. Micrographs of fracture surfaces of Sn Zn solder joints containing different weight percentages of Ag nano particles after eight reflow cycles are shown in Fig. 8. Fig. 8a and b are fractographs of Sn Zn solder joints with 0.5 wt% addition of Ag nano particles, while in Fig. 8c and d the solder contained 1 wt% Ag nano particles. From these SEM micrographs it is clear that the fracture mode was ductile with the characteristic with rough dimpled surfaces. However, the dimple size increased with an increase in the number of reflow cycles due to an increase in the size of the AgZn 3 intermetallic compound phase. Since the fracture occurred inside the solder, the difference in shear strength should be dependent on the interfacial structure. After the addition of Ag nano particles, the shear strength consistently increased with an increase in the Ag nano particle content as a result of the uniform distribution of fine AgZn 3 intermetallic compound (IMC) particles. In addition, the fracture surface of Sn Zn solder joints containing Ag nano particles appeared to be ductile with very rough dimpled surfaces due to the fine AgZn 3 intermetallic compound (IMC) particles as represented schematically in Fig Conclusions In the present study, the interfacial reactions, the morphology of intermetallic compound (IMC) particles and the shear strength of monolithic Sn Zn solder and solder joints containing different weight percentages of Ag nano particles with Au/Ni metallized Cu pad BGA substrates were investigated for up to eight reflow cycles. The results of this study are summarized as follows: 1. At the interfaces between monolithic Sn Zn solder and Au/Ni metallized Cu pads, scallop-shaped AuZn 3 intermetallic compound layer was found. However, after the addition of Ag nano particles, an additional uniform AgZn 3 intermetallic compound layer was observed at the top surface of the AuZn 3 layer. The intermetallic layer thickness did not significantly change with an increase in the number of reflow cycles. 2. In monolithic Sn Zn solder joints, acicular-shaped Zn-rich phases were found in the b-sn matrix in the solder ball regions. However, in solder joints containing Ag nano particles, additional fine AgZn 3 intermetallic compound particles were found as well as Zn-rich phases in the b-sn matrix. The AgZn 3 intermetallic compound layer thickness increased with an increase in the number of reflow cycles. 3. The Sn Zn solder joints containing a high percentage of Ag nano particles showed a higher strength than that of solder joints containing a lower Ag nano particle content after the same number of reflow cycles due to the formation of AgZn 3 intermetallic compound particles as well as a uniform intermetallic compound layer at their interfaces. In addition, the fracture surfaces of solder joints containing Ag nano particles appeared to be typically ductile with very rough dimpled surfaces. Acknowledgements The authors acknowledge the financial support provided by City University of Hong Kong for the Project CERG Grant of Hong Kong Research Grants Council and RGC Ref. No (Development of a nano-activator doped surface modifier for Sn Zn based lead-free soldering). Professor Brian Ralph is thanked for proof reading the manuscript. References [1] Rettenmayr M, Lambeacht P, Kemp B, Graff M. High melting Pb-free solder alloys for die-attach applications. Adv Eng Mater 2005;7(10): [2] Wang FJ, Yu ZS, Qi K. Intermetallic compound formation at Sn 3.0Ag 0.5Cu 1.0Zn lead-free solder alloy/cu interface during as-soldered and as-aged conditions. J Alloys Compd 2007;438: [3] Islam MN, Chan YC, Sharif A, Rizvi MJ. Effect of 9 wt.% in addition to Sn3.5Ag0.5Cu solder on the interfacial reaction with the Au/NiP metallization on Cu pads. J Alloys Compd 2005;396: [4] Anderson IE, Harring JL. Elevated temperature aging of solder joints based on Sn Ag Cu: effects on joint microstructure and shear strength. J Electron Mater 2004;33(12): [5] Sharif A, Chan YC. Investigation of interfacial reactions between Sn Zn solder with electrolytic Ni and electroless Ni(P) metallization. J Alloys Compd 2007;440: [6] Chang TC, Hsu YT, Hon MH, Wang MC. Enhancement of the wettability and solder joint reliability at the Sn 9Zn 0.5Ag lead-free solder alloy Cu interface by Ag precoating. J Alloys Compd 2003;360: [7] Prakash KH, Sritharan T. Interface reaction between copper and molten tin lead solder. Acta Mater 2001;49: [8] Vaynman S, Fine ME. Development of fluxes for Lead free solders containing zinc. Scripta Mater 1999;41(12): [9] Ichitsubo T, Matsubara E, Fujiwara K, Yamaguchi M, Irie H, Kumamoto S, et al. Control of compound forming reaction at the interface between Sn Zn solder and Cu substrate. J Alloys Compd 2005;392: [10] Shih PC, Lin KL. Spallation of interfacial Ag Au Cu Zn compounds in Sn Ag Cu/Sn Zn Bi joints during 210 C reflow. J Alloys Compd 2007;439: [11] Kumar KM, Kripesh V, Shen L, Zeng K, Tay AAO. Nanoindentation study of Znbased Pb free solders used in fine pitch interconnect applications. Mater Sci Eng A 2006;423: [12] Islam MN, Chan YC, Rizvi MJ, Jillek W. Investigations of interfacial reactions of Sn Zn based and Sn Ag Cu lead-free solder alloys as replacement for Sn Pb solder. J Alloys Compd 2005;400: [13] Chou CY, Chen SW. Phase equilibria of the Sn Zn Cu ternary system. Acta Mater 2006;54: [14] Wan JB, Liu YC, Wei C, Gao ZM, Ma CS. Effect of Al content on the formation of intermetallic compounds in Sn Ag Zn lead-free solder. J Mater Sci: Mater Electron 2008;19: [15] Mahmudi R, Geranmayeh AR, Khanbareh H, Jahangiri N. Indentation creep of lead-free Sn 9Zn and Sn 8Zn 3Bi solder alloys. Mater Des 2009;30: [16] Mohan KK, Kripesh V, Tay AAO. Influence of single-wall carbon nanotube addition on the microstructural and tensile properties of Sn Pb solder alloy. J Alloys Compd 2008;455: [17] Mavoori H, Jin S. New, creep-resistant, low melting point solders with ultrafine oxide dispersions. J Electronic Mater 1998;27(11):

8 A.K. Gain et al. / Microelectronics Reliability 49 (2009) [18] Shi Y, Liu J, Xia Z, Lei Y, Fu Guo F, Li X. Creep property of composite solders reinforced by nano-sized particles. J Mater Sci: Mater Electron 2008;19: [19] Shen J, Liu YC, Han YJ, Tian YM, Gao HX. Strengthening effects of ZrO 2 nanoparticles on the microstructure and microhardness of Sn 3.5Ag lead-free solder. Mater Sci Eng A 2006;441: [20] Tai F, Guo F, Xia ZD, Lei YP, Yan YF, Liu JP, et al. Processing and creep properties of SnACu composite solders with small amounts of nanosized Ag reinforcement additions. J Electron Mater 2005;34: [21] Hsuan TC, Lin KL. Effects of aging treatment on mechanical properties and microstructure of Sn 8.5Zn 0.5Ag 0.01Al 0.1Ga solder. Mater Sci Eng A 2007;456: [22] Zhang GJ, Sun YJ, Niu RM, Sun J, Wie JF, Zhao BH, et al. Microstructure and strengthening mechanism of oxide lanthanum dispersion strengthened molybdenum alloy. Adv Eng Mater 2004;6(12): [23] Zhong WH, Chan YC, Alam MO, Wu BY, Guan JF. Effect of multiple reflow processes on the reliability of ball grid array (BGA) solder joints. J Alloys Compd 2006;414: