Effects of small addition of In on the structure of the rapidly cooled Sn–Ag–Zn solder

The effect of small additions of In, up to 1 wt.%, on the microstructure of the eutectic Sn–3.7 wt.%Ag–0.9 wt.%Zn solder was investigated. As observed by microstructural analysis, the increase of In content made β-Sn easy to form but suppressed the formation of the AgZn phase in the Sn–3.7Ag–0.9Zn solder. After annealing at 473 K for 20 and 50 h, the microstructure varied a lot in the morphology of the investigated Sn–Ag–Zn–In solder. The β-Sn dendrites grew coarser but dimmer accompanied with the segregation of the intermetallic compounds (IMCs) along their boundaries. Furthermore, the suppressed Ag–Zn IMCs formed in the Sn–3.7Ag–0.9Zn–1In solder. And the coarsening of the β-Sn dendrites and the growth of IMCs particles in the microstructure of the samples brought a significant softening during annealing of the investigated Sn–Ag–Zn–In alloys.     

Interfacial reactions between Sn–8Zn–3Bi–xAg lead-free solders and Cu substrate

The formation and the growth of the intermetallic compounds (IMCs) at the interface between the Sn–8Zn–3Bi–xAg (x = 0, 0.5, and 1 wt.%) lead-free solder alloys and Cu substrate soldered at 250 °C for different durations from 5 to 60 min were investigated. It was found that Cu₅Zn₈ and CuZn₅ formed at Sn–8Zn–3Bi/Cu interface, and Cu₅Zn₈ and AgZn₃ formed at the solder/Cu interface when the solder was added with Ag. The thickness of IMC layers in different solder/Cu systems increased with increasing the soldering time. And the growth of the IMCs was found to be mainly controlled by a diffusion mechanism. Additionally, the growth of the IMC layers decreased with increasing content of Ag in the soldering process.     

Comment on the paper “Controlling intermetallic compound formation reaction between Sn and Ni-P by Zn addition” by X.F. Zhang, J.D. Guo, J.K. Shang, J. Alloys Compd. 479 (2009) 505–510

Zhang et al. recently reported about the formation of Ni₄(Sn,Zn) in the interlayer of a Sn–Zn/Ni(P) solder joint. This phase is claimed to be based on the binary Ni₄Sn phase. However, this phase as described in the literature by Mikulas and Thomassen, was ruled out for any existing phase diagram version. It could be proved that the diffraction pattern from Mikulas and Thomassen was composed of Ni and Ni₃Sn low-temperature phase. Thus the interpretation of their X-ray diffraction results is incorrect and the phase “Ni₄Sn” is an artefact. The indexing of Ni₄(Sn,Zn) by Zhang et al. is based on this artefact and therefore is incorrect, too. Furthermore, Tai et al. investigated IMC formation in Sn–3Ag–0.5Cu/Ni–8Zn–8P joints and could not observe any interdiffusion of Zn as stated by Zhang et al.     

Study on the properties of Sn–9Zn–xCr lead-free solder

The influences of different Cr content to lead (Sn)–Zn solder were investigated. Sn–9Zn–xCr shows finer and more uniform microstructure than Sn–9Zn. Thermal gravimetric analysis (TGA) and Auger electron spectroscopy (AES) results show that adding Cr significantly improves the oxidation resistance of Sn–9Zn solder, and reduces the thickness of oxidation film of Sn–9Zn–xCr solder. When Cr content is 0.1%, the Sn–9Zn–0.1Cr solder have the best oxidation resistance. In addition, the effect of Cr addition on the wettability, melting point and mechanical properties of Sn–9Zn solder was discussed.     

Effect of surface finish on the fracture behavior of Sn–Ag–Cu solder joints during high-strain rate loading

This study assesses the reliability of eutectic Sn–Pb, Sn–1.0Ag–0.5Cu, Sn–3.0Ag–0.5Cu and Sn–4.0Ag–0.5Cu solder bumps on three different pad surface finishes (ENIG, electrolytic Ni/Au and Cu-OSP) with and without an aging treatment at 150 °C for 100 h. This study focused primarily on how the pad surface finish and solder alloy composition affects the reliability of solder joints using a high-speed ball pull test method. The fracture forces and failure mechanisms were also examined. The results showed that the electrolytic Ni/Au surface finish had the highest fracture forces for all four different solder alloys with and without the aging process.     

Influence of thermal cycling on shear strength of Cu–Sn3.5AgIn–Cu joints with various content of indium

This work presents an investigation on the influence of thermal cycling of Cu–Sn3.5AgIn–Cu joints for various content of indium. Solders Sn–3.5Ag containing 0, 6.5 and 9 mass% In were prepared by rapid quenching of appropriate alloys. Joints Cu–solder–Cu were prepared in furnace at 280 °C and 1800 s. Thermal cycling was in the interval room temperature (RT)–150 °C up to 1000 cycles and in the interval RT–180 °C for 500 cycles. The shear strength of the joints with indium-free solder decreases with increasing number of cycles. On the contrary shear strength of joints with indium containing solders increases with increasing number of cycles. It is related with the thickness of Cu₆Sn₅ phase which makes the interface between Cu substrate and solder. In the first case the thickness of this phase is growing with increasing number of cycles, in the second case the amount of this phase is reducing with increasing the number of cycles due to the support of dissolution of copper from Cu₆Sn₅ phase into the Sn–Ag–In solder by indium. X-ray diffraction analysis of original solders as well as of uncycled and 1000 times cycled joints made with all three kinds of solders is given.     

Influence of indium addition on structure, mechanical, thermal and electrical properties of tin–antimony based metallic alloys quenched from melt

The melt-spinning processes of binary Sn–10 wt.% Sb and ternary Sn–10 wt.% Sb–In were analyzed using X-ray diffractometer and differential thermal analysis (DTA). The results showed that supersaturated solid solution and new intermetallic compound In₃Sn were produced during melt-spinning technique not found under equilibrium conditions. It is also found that a small amount of In addition significantly lowers the melting point of the Sn–10 wt.% Sb alloy and reduce the crystal size to ≈60 nm. Also, tin–antimony solder doped with In exhibits good mechanical properties, Vickers hardness and mechanical strength due to refined microstructure. This work was performed to study the influence of rapid solidification and indium addition on structure and properties of tin–antimony based alloys.     

Investigations of interfacial reactions of Sn–Zn based and Sn–Ag–Cu lead-free solder alloys as replacement for Sn–Pb solder

The interfacial reactions of Sn–Zn based solders and a Sn–Ag–Cu solder have been compared with a eutectic Sn–Pb solder. During reflow soldering different types of intermetallic compounds (IMCs) are found at the interface. The morphologies of these IMCs are quite different for different solder compositions. As-reflowed, the growth rates of IMCs in the Sn–Zn based solder are higher than in the Sn–Ag–Cu and Sn–Pb solders. Different types of IMCs such as γ-Cu₅Zn₈, β-CuZn and a thin unknown Cu–Zn layer are formed in the Sn–Zn based solder but in the cases of Cu/Sn–Pb and Cu/Sn–Ag–Cu solder systems Cu₆Sn₅ IMC layers are formed at the interface. Cu₆Sn₅ and Cu₃Sn interfacial IMCs are formed in the early stages of 10 min reflow due to the limited supply of Sn from the Sn–Pb solder. The spalling of Cu–Sn IMCs is observed only in the Sn–Ag–Cu solder. The size of Zn platelets is increased with an increase of reflow time for the Cu/Sn–Zn solder system. In the case of the Sn–Zn–Bi solder, there is no significant increase in the Zn-rich phases with extended reflow time. Also, Bi offers significant effects on the wetting, the growth rate of IMCs as well as on the size and distribution of Zn-rich phases in the β-Sn matrix. No Cu–Sn IMCs are found in the Sn–Zn based solder during 20 min reflow. The consumption of Cu by the solders are ranked as Sn–Zn–Bi > Sn–Ag–Cu > Sn–Zn > Sn–Pb. Despite the higher Cu-consumption rate, Bi-containing solder may be a promising candidate for a lead-free solder in modern electronic packaging taking into account its lower soldering temperature and material costs.     

Leaching of heavy metal elements in solder alloys

Leaching behavior of heavy metal elements from Sn–3.5Ag–0.5Cu, Sn–9Zn, and Sn–37Pb solder alloys and their joints was investigated in typical H₂SO₄, NaCl and NaOH solutions. The leaching amount of Sn from solder joints was more than that from solder alloys and the leaching amount of Sn from Sn–3.5Ag–0.5Cu solder joint in the NaCl solution was the most. The surface corrosion products on the solder and their joints were composed of oxide, oxide hydroxide or oxychloride of the component element. Much more surface oxides for the samples treated in the NaCl solution produced than that in the NaOH and H₂SO₄ solutions.     

Formation and thermal stability of new Zr–Cu-based bulk glassy alloys with unusual glass-forming ability

The simultaneous addition of Al and Ag to Zr–Cu binary alloys increased in the stabilization of supercooled liquid, the reduced glass transition temperature and γ value, leading to greatly enhance the glass-forming ability (GFA). The Zr–Cu–Ag–Al glassy alloy samples with diameters above 15 mm were obtained in the wide composition range of 42–50 at% Zr, 32–42 at% Cu, 5–10 at% Ag, and 5–12 at% Al. The best GFA was obtained for Zr₄₈Cu₃₆Ag₈Al₈ alloy, and the glassy samples with diameters up to 25 mm were fabricated by an injection copper mold casting. The Zr₄₈Cu₃₆Ag₈Al₈ glassy alloy exhibited high tensile and compressive fracture strength of over 1800 MPa.     

Interfacial interaction of solid nickel with liquid Pb-free Sn–Bi–In–Zn–Sb soldering alloys

The dissolution process of nickel in liquid Pb-free 87.5% Sn–7.5% Bi–3% In–1% Zn–1% Sb and 80% Sn–15% Bi–3% In–1% Zn–1% Sb soldering alloys has been investigated by the rotating disc technique at 250–450 °C. The temperature dependence of the nickel solubility in soldering alloys obeys a relation of the Arrhenius type c_s = 4.94 × 10² exp(−39500/RT)% for the former alloy and c_s = 4.19 × 10² exp(−40200/RT)% for the latter, where R is in J mol⁻¹ K⁻¹ (8.314 J mol⁻¹ K⁻¹) and T is in K. Whereas the solubility values differ considerably, the dissolution rate constants are rather close for these alloys and fall in the range (1–9) × 10⁻⁵ m s⁻¹ at disc rotational speeds of 6.45–82.4 rad s⁻¹. Appropriate diffusion coefficients vary from 0.16 × 10⁻⁹ to 2.02 × 10⁻⁹ m² s⁻¹. With both alloys, the Ni₃Sn₄ intermetallic layer is formed at the interface of nickel and the saturated or undersaturated melt at dipping times of 300–2400 s. The other Ni–Sn intermetallic compounds are found to be missing. A simple mathematical equation is proposed to evaluate the Ni₃Sn₄ layer thickness in the case of undersaturated melts. The tensile strength of the nickel-to-alloy joints is 94–102 MPa, with the relative elongation being 2.0–2.5%.     

Effects of sulfide-forming element additions on the Kirkendall void formation and drop impact reliability of Cu/Sn–3.5Ag solder joints

Ternary Pb-free solders, Sn–3.5Ag–X, containing 0.5 wt.% of Zn, Mn and Cr, were reacted with Cu UBM, which was electroplated using SPS additive. Characteristics of Cu–Sn IMCs and Kirkendall void formation at the Cu/Sn–3.5Ag solder joints were significantly affected by the third element, and the potency to suppress Kirkendall voids at the solder joint increased in the order of Cr, Mn, Zn, which was indeed the order of the drop reliability improvement. From the AES analyses, it was suggested that the sulfide-forming elements in the solder diffused into the Cu UBM and reduced the segregation of S atoms to the Cu/Cu₃Sn interface by scavenging S, which led to the suppression of Kirkendall void nucleation at the Cu/Cu₃Sn interface and the drop reliability improvement. In the case of the Zn-containing solder joint, Cu₃Sn phase, known to be a host of Kirkendall voids, did not form at all even after extended aging treatments. The magnitude of the tensile stress at the Cu₃Sn/Cu interface which drove the Kirkendall void growth was estimated to be 10–100 MPa.     

Wetting behavior and interfacial characteristics of In–Sn alloy on CuZr-based bulk metallic glass

The wettabilities of In–Sn alloy on Cu₄₀Zr₄₄Al₈Ag₈ BMG substrate were investigated using the sessile-drop method at different temperature. The result shows that the equilibrium contact angle decreased with increasing temperature. The interfacial reaction of the active Sn atoms in molten In–Sn alloy and the active Zr atoms in Cu₄₀Zr₄₄Al₈Ag₈ BMG caused crystallization reaction. Ion beam sputtering profiling in combination with AES technique was employed to investigate the Sn diffusion in Cu₄₀Zr₄₄Al₈Ag₈ BMG. Between 473 K and 673 K, the diffusion coefficients vary from 0.7 × 10⁻¹⁶ m²/s to 12.9 × 10⁻¹⁶ m²/s. It is concluded that the interfacial reaction is favorable to the crystallization and then the crystallization also promotes Sn diffusion.     

Microstructural evolution of intermetallic compounds in Sn–3.5Ag–X (X = 0, 0.75Ni, 1.0Zn and 1.5In)/Cu solder joints during liquid aging

In this paper, the microstructural evolution of IMCs in Sn–3.5Ag–X (X = 0, 0.75Ni, 1.0Zn, 1.5In)/Cu solder joints and their growth mechanisms during liquid aging were investigated by microstructural observations and phase analysis. The results show that two-phase (Ni₃Sn₄ and Cu₆Sn) IMC layers formed in Sn–3.5Ag–0.75Ni/Cu solder joints during their initial liquid aging stage (in the first 8 min). While after a long period of liquid aging, due to the phase transformation of the IMC layer (from Ni₃Sn₄ and Cu₆Sn phases to a (Cu, Ni)₆Sn₅ phase), the rate of growth of the IMC layer in Sn–3.5Ag–0.75Ni/Cu solder joints decreased. The two Cu₆Sn₅ and Cu₅Zn₈ phases formed in Sn–3.5Ag–1.0Zn/Cu solder joints during the initial liquid aging stage and the rate of growth of the IMC layers is close to that of the IMC layer in Sn–3.5Ag/Cu solder joints. However, the phase transformation of the two phases into a Cu–Zn–Sn phase speeded up the growth of the IMC layer. The addition of In to Sn–3.5Ag solder alloy resulted in Cu₆(Sn_x,In_1?x)₅ phase which speeded up the growth of the IMC layer in Sn–3.5Ag–1.5In/Cu solder joint.     

Kinetic peculiarities of anodic dissolution of silver and Ag–Au alloys under the conditions of oxide formation

The kinetics of anodic dissolution of silver and Ag–Au alloys (X_Au = 0.1–30 at.% Au) in aqueous alkaline solution under the conditions of the formation of silver oxides has been examined. The techniques of cyclic voltammetry, chronoammetry, and photopotential measurements have been used. It was established that the anodic formation and cathodic reduction of Ag₂O on silver and alloys are controlled by migration in the oxide layer. Ag₂O oxide is an n-type semiconductor with an excess of silver atoms. Oxide layers formed on monocrystalline Ag(1 1 1) and Ag(1 1 0) are more stoichiometric than the layer formed on polycrystalline Ag.     

Experimental study of Ti–Sn–Y system phase equilibria at 473 K

The phase equilibria of the Ti–Sn–Y ternary system at 473 K have been investigated mainly by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA). The existences of 10 binary compounds, Ti₃Sn, Ti₂Sn, Ti₅Sn₃, Ti₆Sn₅, Ti₂Sn₃, Sn₃Y, Sn₂Y, Sn₁₀Y₁₁, Sn₄Y₅ and Sn₃Y₅ were confirmed. The 473 K isothermal section was found to consist of 13 single-phase regions, 23 two-phase regions and 11 three-phase regions. There is no new ternary compound found in the work. None of the phases in this system reveals a remarkable homogeneity range at 473 K.     

Phase equilibria of the Au–Sn–Zn ternary system and interfacial reactions in Sn–Zn/Au couples

Phase equilibria of the Au–Sn–Zn ternary system and interfacial reactions between Sn–Zn alloys and Au were experimentally investigated at 160 °C. Experimental results reveal that no equilibrium-stated ternary phases were found and the ternary element solubility in the binary phase is insignificant. When the Zn content was less than 3 wt% in the Sn–Zn alloy, only the Au–Sn binary intermetallic compounds (IMCs), such as AuSn, AuSn₂ and AuSn₄ phases, were formed at the Sn–Zn/Au interface. When the Zn content in Sn–Zn alloys was greater than 7 wt%, the AuZn, AuZn₂ and Au₃Zn₇ phases were formed in the Sn–Zn/Au couples at 160 °C. However, both Sn–Zn and Au–Zn IMCs, and the Au–Zn–Sn ternary IMC (T phase) were observed between Au and the Sn–Zn alloys with 3–5 wt% added Zn. This T phase might be the metastable phase. The evolution of IMCs in the Sn–Zn/Au couples is very sensitive to the Zn content in Sn–Zn alloys.     

Interfacial Reactions and Bonding Strength of Sn-xAg-0.5Cu/Ni BGA Solder Joints

The present study details the microstructure evolution of the interfacial intermetallic compounds (IMCs) layer formed between the Sn-xAg-0.5Cu (x = 1, 3, and 4 wt.%) solder balls and electroless Ni-P layer, and their bond strength variation during aging. The interfacial IMCs layer in the as-reflowed specimens was only (Cu,Ni)₆Sn₅ for Sn-xAg-0.5Cu solders. The (Ni,Cu)₃Sn₄ IMCs layer formed when Sn-4Ag-0.5Cu and Sn-3Ag-0.5Cu solders were used as aging time increased. However, only (Cu,Ni)₆Sn₅ IMCs formed in Sn-1Ag-0.5Cu solders, when the aging time was extended beyond 1500 h. Two factors are expected to influence bond strength and fracture modes. One of the factors is that the interfacial (Ni,Cu)₃Sn₄ IMCs formed at the interface and the fact that fracture occurs along the interface. The other factor is Ag₃Sn IMCs coarsening in the solder matrix, and fracture reveals the ductility of the solder balls. The above analysis indicates that during aging, the formation of interfacial (Ni,Cu)₃Sn₄ IMCs layers strongly influences the pull strength and the fracture behavior of a solder joint. This fact demonstrates that interfacial layers are key to understanding the changes in bonding strength. Additionally, comparison of the bond strength with various Sn-Ag-Cu lead-free solders for various Ag contents show that the Sn-1Ag-0.5Cu solder joint is not sensitive to extended aging time.     

Growth Behavior of Intermetallic Compounds at SnAgCu/Ni and Cu Interfaces

The growth behavior of reaction-formed intermetallic compounds (IMCs) at Sn3.5Ag0.5Cu/Ni and Cu interfaces under thermal-shear cycling conditions was investigated. The results show that the morphology of (Cu _x Ni_1–x )₆Sn₅ and Cu₆Sn₅ IMCs formed both at Sn3.5Ag0.5Cu/Ni and Cu interfaces gradually changed from scallop-like to chunk-like, and different IMC thicknesses developed with increasing thermal-shear cycling time. Furthermore, Cu₆Sn₅ IMC growth rate at the Sn3.5Ag0.5Cu/Cu interface was higher than that of (Cu _x Ni_1–x )₆Sn₅ IMC under thermal-shear cycling. Compared to isothermal aging, thermal-shear cycling led to only one Cu₆Sn₅ layer at the interface between SnAgCu solder and Cu substrate after 720 cycles. Moreover, Ag₃Sn IMC was dispersed uniformly in the solder after reflow. The planar Ag₃Sn formed near the interface changed remarkably and merged together to large platelets with increasing cycles. The mechanism of formation of Cu₆Sn₅, (Cu _x Ni_1–x )₆Sn₅ and Ag₃Sn IMCs during thermal-shear cycling process was investigated.