Cu6Sn5 Phase Research Articles

Electrochemical deposition mechanism of copper-zinc-tin alloy and structural characterization

The electrodeposition of Cu-Sn-Zn coating (CZT) was investigated. The bath consisted of aqueous solution of Cu, Sn and Zn sulphate in the presence of sodium citrate (NaC6H5Na3O7) as complexing agent. The pH was set between 4 and 5.5 to stabilize the bath. Cyclic voltammetry exhibited four peaks during cathodic scan corresponding to the reductions of metal ions and adsorbed hydrogen. Impedance measurements were made at each potential peak. The effect of the metal salts concentration and the potential scan rate were studied. The deposit mechanism is controlled by mass transfer in parallel with a faradaic reaction. For the deposition of Cu-Sn and Cu-Sn-Zn alloys, the average diffusion coefficients of Cu2+ and Sn2+ ions and Cu2+, Sn2+ and Zn2+ ions were calculated. At E = -1.5 V, a Cu-Sn-Zn deposit is obtained with 55 at% copper, 25 at% tin and 20 at% zinc. The X-ray diffraction pattern shows the characteristic peaks of Cu, Cu6Sn5 and Cu3Zn2 phases. The deposit morphology was characterized by SEM.

Effect of post-heat treatment on the thermophysical and compressive mechanical properties of Cu-Ni-Sn alloy manufactured by selective laser melting

This study investigated the effect of heat treatment on the microstructure, room- and high-temperature mechanical properties, and thermal properties of selective laser melted Cu-Ni-Sn alloy. Initial microstructural observation confirmed that the as-fabricated sample was composed of Cu, Cu6Sn5, Cu3P and undissolved Ni phases, and then the heat-treated sample was composed of CuNi solid solution, (Cu, Ni)3Sn and (Cu, Ni)3P. Room- and high-temperature compression tests (25 °C ~ 500 °C) were performed, and the yield strengths at room temperature measured 230.4 MPa and 346.0 MPa for as-fabricated and heat-treated materials, which indicates an approximately 50% increase in strength after heat treatment. Furthermore, as temperature increased, a phenomenon where the yield strength inverts occurred for both materials, and the cause of such a phenomenon was identified to be due to the difference in strengthening mechanisms. Thermal diffusivity is lower in heat-treated sample at all temperatures, but on the other hand, thermal conductivity interestingly is higher in heat-treated sample than as-fabricated sample (As-fabricated sample: 30.7–44.0 W/m∙K, heat-treated sample: 32.8–49.6 W/m∙K). The reason for this is identified to be due to microstructure evolution and defect control after heat treatment. Correlations between initial microstructures and mechanical- and thermophysical-properties were also discussed based on these findings.

Effect of Zn addition on Cu3Sn formation in Sn-10Cu alloys

Sn-Cu alloys have generated interest as potential candidates for high-temperature soldering applications, as they are economically feasible and environmentally safe. Sn-Cu alloys with copper contents beyond 7.6wt.% solidify with a primary Cu3Sn phase, followed by peritectic and eutectic reactions. Typically, phases which form as elongated needles are undesirable, as they tend to be more brittle and in turn reduce the strength and toughness of the alloy. The effect of Zn on the peritectic reaction and phase formation in a Sn-10wt.%Cu alloy is investigated through cooling curves and microstructural analysis using optical and electron microscopy. Zn was alloyed in the range of 0.1-1wt.% to the base Sn-10Cu alloy system. The results indicate that the amount of the primary Cu3Sn phase that forms is inversely proportional to the concentration of Zn. Although complete suppression of Cu3Sn was not observed, there was a clear effect of Zn reducing the amount of the primary Cu3Sn phase, with the greatest reduction of Cu3Sn occurring with a 1wt.% Zn addition. The reduction of the elongated needle-shaped primary Cu3Sn phase may find application in the development of more reliable bulk solder microstructures.

Morphologies of Primary Cu6Sn5and Ag3Sn Intermetallics in Sn–Ag–Cu Solder Balls

This article focuses on the morphologies of primary Cu6Sn5 and Ag3Sn intermetallics in small Sn–Ag–Cu (O $270~\mu \text{m}$ ) solder balls. The Cu6Sn5 phase showed a large variety of different shapes and sizes, ranging from facetted hexagonal rods, to partly facetted splitting crystals and parallel growing branches, to dendritic crystals without facets. The results of electron backscatter diffraction (EBSD) measurements confirm [0001] as the major growth direction and the { $10\bar {1}0$ } planes as facets of the hexagonal rods. The formation of crystals splitting parallel to the { $10\bar {1}0$ } planes may be caused by a slight deviation of the major growth direction toward $\langle 2\bar {1}\bar {1} 0\rangle $ . Primary Ag3Sn intermetallics showed less morphology variations and solidified as typical plate structures with a planar and an irregular side. Sixfold star-shaped formations of multiple plates arranged around a common center have been investigated by EBSD. All plates appear to have the same hexagonal orientation and possible growth directions are parallel to the { $10\bar {1}0$ } planes. However, these pseudohexagonal structures showed color differences between plates of different growth directions, if investigated with polarized light microscopy. Those orientation differences were not detectable by EBSD. Possible interpretations are discussed on the basis of the orthorhombic distorted lattice and by possible twinning mechanisms.

Brazing of porous copper foam/copper with amorphous Cu-9.7Sn-5.7Ni-7.0P (wt%) filler metal: interfacial microstructure and diffusion behavior

In this work, brazing of porous copper foam (PCF) to copper (Cu) using amorphous Cu-9.7Sn-5.7Ni-7.0P (in weight, wt%) filler metal has been performed. PCF with different pore densities of 15 pore per inch (PPI), 25 PPI, and 50 PPI were sandwiched in between amorphous Cu-9.7Sn-5.7Ni-7.0P filler/Cu based plate. A brazed joint of Cu/Cu using amorphous Cu-9.7Sn-5.7Ni-7.0P filler was prepared for comparison purposes. The interfacial microstructures and mechanical properties of the brazed joint were investigated to study the joint ability after the brazing process. Scanning electron microscope (SEM) confirmed the interfacial microstructure by the formation of the diffusion layer (shown in light shaded area) and filler layer (gray island-shaped) for both Cu/Cu and Cu/PCF/Cu brazed joint. The X-ray diffraction (XRD) patterns identified the brittle phases of Cu3P and Ni3P, Cu and Cu6Sn5 phases at the diffusion layer. In the shear test, the strength value decreases with increase in the pore densities of PCF. The decreasing shear strength observed with an increase in the number of PPI in PCF is due to the formation of more cavities in Cu/PCF as the number of PPI in Cu/PCF increases.

The thermal cycling reliability of copper pillar solder bump in flip chip via thermal compression bonding

In this paper, the thermal-mechanical reliability of flip chip on board (FCOB) with copper pillar solder joint is investigated. By increasing the temperature and time of the thermal compression bonding (TCB) process, the copper pillar solder joint with intermetallic compound (IMC) as the main body is obtained. Then the Cu pillar/Sn-Ag/Cu pad and Cu pillar/IMC/Cu pad joint structures are carried out the thermal cycling test separately. It is observed that the crack of the Sn-Ag solder joint caused by ductile fracture, which is leaded by fatigue and then extension through microvoids caused by creep. And the crack of IMC joint is mainly caused by the brittle fracture along the Cu6Sn5 and Cu3Sn phase interface. At the same time, two constitutive of viscoplasticity and elastic-plastic-creep and life prediction models are compared. The effect of underfill on the thermal-mechanical reliability of copper pillar solder joint is evaluated by comparing the underfills filled with different weight ratio filler particles.

Rapid Formation of Kinetically Sprayed Cu-Sn Intermetallic Film

The kinetically spraying method was used to fabricate an in situ copper- (Cu-) tin (Sn) intermetallic compound (IMC) film with its thickness of approximately 1 μm using a Cu-Sn mixed powder. Microsized Cu (~5 μm) and Sn (~10 μm) powders were mixed at its ratio of 45 : 55 wt.%, respectively, and then deposited onto a silicon substrate, forming an IMC layer. The actual composition of the deposited film was measured to be at a Cu : Sn ratio of 36 : 64 wt.% (in situ kinetically sprayed at 200°C). This kinetically sprayed process uses the energy source of collision and heat energy simultaneously, leading to the formation of an IMC phase. The IMC phase of Cu6Sn5 was formed successfully within 3 minutes of in situ deposition. Moreover, we obtained a Cu6Sn5 phase when the thin film was annealed in a furnace for 1 hour immediately after kinetically spraying at room temperature. However, an IMC phase was not formed in the thin film when kinetically sprayed at room temperature followed by heating on a hot plate for 3 minutes. It seems that the simultaneous supply of collision and heat energy is crucial to result in phase formation. Therefore, we have proven that the kinetically spraying process is capable of fabricating a super-thin layer of IMC film within a short time.

Study of the effect of Sn grain boundaries on IMC morphology in solid state inter-diffusion soldering

This paper reports on 3D phase field simulations of IMC growth in Co/Sn and Cu/Sn solder systems. In agreement with experimental micrographs, we obtain uniform growth of the CoSn3 phase in Co/Sn solder joints and a non-uniform wavy morphology for the Cu6Sn5 phase in Cu/Sn solder joints. Furthermore, simulations were performed to obtain an insight in the impact of Sn grain size, grain boundary versus bulk diffusion, IMC/Sn interface mobility and Sn grain boundary mobility on IMC morphology and growth kinetics. It is found that grain boundary diffusion in the IMC or Sn phase have a limited impact on the IMC evolution. A wavy IMC morphology is obtained in the simulations when the grain boundary mobility in the Sn phase is relatively large compared to the interface mobility for the IMC/Sn interface, while a uniform IMC morphology is obtained when the Sn grain boundary and IMC/Sn interface mobilities are comparable. For the wavy IMC morphology, a clear effect of the Sn grain size is observed, while for uniform IMC growth, the effect of the Sn grain size is negligible.

Wetting properties, recrystallization phenomena and interfacial reactions between laser treated Cu substrate and SAC305 solder

Effect of laser treatment has been studied on the wetting ability of Cu substrate during soldering with SAC305 solder paste. The contact angle of molten solder drops on Cu substrate changes when the substrates treated with different Nd:YAG laser powers. The correlations between the extraordinary change of wetting angle and the surface interaction between the melt pool of solder alloy and Cu plates are studied. A texture formation was found in the laser treated Cu substrate, which supports the diffusion of the Sn atoms. The thickness of Cu3Sn interface layer is increasing with increasing laser power helping the formation of Cu6Sn5 phase, and resulting a better metallic bonding in solder joints.

Two-Phase η′ + η Region in Cu6Sn5 Intermetallic: Insight into the Order–Disorder Transition from Diffusion Couples

The ongoing electrification and miniaturization increase the quality demands on solder joints. A bottleneck for solder joint reliability can be the intermetallic Cu6Sn5 phase, which undergoes a phase transition, implying a volume change in a relevant temperature range. There are contradicting reports on the sign and magnitude of this volume change, which possibly implements stresses and cracks in solder joints. To clarify the characteristics of the phase transition, different samples were manufactured by applying industrial-like standards and isothermal heat treatments around the predicted phase transition temperature. Using x-ray diffraction, a coexistence of ordered η′ and disordered η was detected in samples treated at 438–445 K. The lattice parameters show that the volume of the disordered η phase is approximately 0.64–0.65% smaller than the one of the ordered η′ phase. A comparison with order–disorder transitions in structurally related phases shows that the volume change based on order–disorder transitions is normally of opposite sign and around 0.1–0.2%. Therefore, an effect of different compositions is considered responsible for the volume change. Adopting the exact composition Cu6Sn5 (Cu1.20Sn) for the η′ phase, it was estimated, based on density functional theory calculations from the literature, that the coexisting η phase assumes lower Cu content of Cu1.171Sn at 438 K and Cu1.174Sn at 445 K. In contrast, the lattice parameters of η′, generated at different temperatures, imply a largely temperature-independent composition of Cu1.20Sn. This leads to adjustments of the Cu-Sn phase diagram.

Improved microstructure and bonding strength via MIG arc brazing in Sn-based Babbitt layer for bearing fabrication

A SnSb12Cu6 Babbitt layer was prepared for bearing applications by both metal inert-gas (MIG) arc brazing and centrifugal casting methods. The microstructure and interface bonding strength were investigated systematically. The results showed that fine microstructure without segregation was observed for the MIG method where a large number of diamond-shaped SnSb phases and dendrite Cu6Sn5 phases embedded in α-Sn matrix. In contrast, severe microstructure segregations with three distinct regions were observed in the Babbitt layer prepared by centrifugal casting method. The average interface bonding strength between the Babbitt layer and carbon steel of the MIG arc brazed samples was about 79 MPa, being two times larger than that of the centrifugal casting samples. The fracture mechanisms were discussed in terms of the fractural mechanics theory, and the refining microstructure was found to be primarily responsible for enhanced bonding strength. These findings provided a novel strategy for developing high quality Babbitt bearings with homogeneous microstructure and with high bonding strength.

Electrochemical Performances of the Sn-Cu Alloy Negative Electrode Materials through Simple Chemical Reduction Method

Sn-Cu alloy powders were prepared <italic>via</italic> a simple chemical reduction method for the negative electrode materials in lithium-ion batteries. The addition of Cu can suppress the growth of Sn particles during synthetic process. Furthermore, the Cu also acts as a matrix phase against the volume change during cycling. With increasing amount of the Cu, a stable Cu6Sn5 phase formed in the Sn-Cu alloy and its cycle performance greatly enhanced depending on the Cu content. To promote the generation of the Cu6Sn5 phase, the synthesis temperature is raised to 60–100°C from the ambient temperature. The Sn-Cu alloy powders prepared at elevated temperatures showed remarkable cycle performances. The Sn-Cu alloy powder obtained at 60°C exhibited a significantly high volumetric capacity of over 2,000 mAh/cc at the 50th cycle.

A Study on the Microstructures and Properties of Selective Laser Melted Babbitt Metals

Babbitt metal cubes were prepared by means of selected laser melting (SLM) process using Sn—11% Sb—6% Cu alloy powders; their microstructures were studied using optical microscope (OM), SEM, EDS, XRD and DSC; and their mechanical properties were tested using Vickers hardness and tensile methods. The results show that fully dense Babbitt metal components can be prepared by using appropriate SLM process parameters and an interlayer staggered laser scanning strategy. Anisotropy characteristics appear in both the microstructure and mechanical properties of SLM-Babbitt cubic specimens. The average hardness was in the range of 32.5 HV0.05 to 35.3 HV0.05. Both tensile strength and elongation were somewhat higher in a direction parallel to the laser scanning speed (Y axis) than in a direction perpendicular to the laser scanning speed (X axis). The strengthening mechanism is suggested to include solid solution strengthening of oversaturated Sb in the Sn matrix, as well as dispersion strengthening of finely dispersed SnSb and Cu6Sn5 particles. The overgrown acicular Cu6Sn5 phases at low laser scanning speeds and void formation at higher laser scanning speeds seriously deteriorate the mechanical properties of the SLM-Babbitt specimens.

The Zn accumulation behavior, phase evolution and void formation in Sn-xZn/Cu systems by considering trace Zn: a combined experimental and theoretical study

The strong effects of Zn addition on the reaction in Sn/Cu systems are widely known. Nevertheless, the micro-mechanism for Zn accumulation behavior, phase evolution and void formation in Sn-xZn/Cu systems remain unclear. In this work, the effect of Zn addition on the interface behavior is investigated. Structures of Sn-xZn/Cu are prepared by the reaction between Sn-xZn solders (x = 0, 0.2, 0.5 and 0.8 wt.%) and the electroplated Cu (EP Cu) joints. During the thermal aging of Sn/EP Cu joints, many voids formed inside the Cu3Sn phase, especially close to the Cu3Sn/EP Cu interface. Whereas the voids were greatly suppressed with Zn addition. During the thermal aging, Zn gradually accumulated near the interface of IMCs/EP Cu. As thermal aging time to168 h and Zn content to 0.8 wt.%, Zn participated in the interface reaction, three layers with different contrasts, (Cu, Zn)6Sn5, Cu6(Sn, Zn)5 and (Cu,Sn)3Zn were formed. Theoretical analysis shows that Zn atom accumulated near the interface of IMCs/EP Cu due to lower diffusion energy barriers (Edf) of Zn than Cu atom. The preferential occupation of Zn atoms in Cu6(Zn,Sn)5 and (Cu,Zn)6Sn5 are Sn3 (4e) and Cu3 (4a) site because of the lowest lattice strain. The diffusion path interstice size for Cu atom via the IMCs layer gradually shrink with the increment of charge transfer in Zn-rich layers, corresponding the Edf of Cu atom gradually rise. As a result, the fluxes of Cu and Sn via the IMCs layer were balanced out, which reduced the Kirkendall voids formation.

A facile and novel method to retard intermetallic compounds formation by inserting Cu3Sn interlayer

An innovative controllable way to mitigate intermetallic compounds (IMC) formation during solid-state aging has been proposed. Interlayers consisting of Cu6Sn5 or Cu3Sn were prepared and inserted between Sn solders and Cu substrates. Results show that all interlayers effectively retard formation of IMC, yet the Cu3Sn interlayer has the best effect. After inserting middle Cu3Sn layer, total IMC thickness formed during the aging process is only half of that in samples without interlayer, and growth rate constant of IMC drops to approximately 25% of that in samples without interlayer. In addition, Cu3Sn phase was consumed, in initial period of solid-state aging, to form Cu6Sn5 phase. This slow and difficult transformation inhibited the formation of IMC by virtue of Cu3Sn’s lower Gibbs energy.

Interfacial Reaction between Sn and Cu-Ti Alloy (C1990HP)

The interfacial reaction between pure tin and substrate with the composition of Cu-4.3 at% Ti (C1990HP) was investigated using the reaction couple technique from 240 °C until 270 °C in the range 0.5~4.0h. The SEM images show the Cu6Sn5 and small precipitated Ti2Sn3 phase formed at the Sn/C1990HP interface. In addition of Ti substantially increased the amount of intermetallic compound (IMC) at the interface which separated parts of Cu6Sn5 compounds with the inner region containing more Ti than the outer. The existence of Sn/C1990HP on the liquid/solid state reaction indicates that spalling occurred with changes in reaction time and temperature. With increased reaction temperature and time, the grain produced an abnormal condition resulting in Cu6Sn5 not accumulating at the interface and spalling into the solder in addition to grain ripening and an increase in total layer thickness. The hexagonal prism-shaped Cu6Sn5 phase is found on the top of the C1990HP substrate when the Cu6Sn5 layer detaches. The reaction phase formation, detachment, and split mechanisms are proposed in this study.

The Evolution of Microstructures and Mechanical Properties of SnAgCu/Cu Weld Interface during Isothermal Aging

Based on the model of the diffusion flux ratio of Cu and Sn at the Cu/Cu3Sn/Cu6Sn5/Sn interface, the evolution of microstructures, the behavior of formation and growth of intermetallic compound (IMC) for Sn95.5Ag3.8Cu0.7 solder aged at 150 °C were studied. The nano indentation was applied to measure the hardness and elastic modulus of the IMC. The tensile strength and the low cyclic fatigue properties of the weld joint were also measured. The results showed that the thickness increments of Cu3Sn and Cu6Sn5 phases of IMC are mainly controlled by diffusion mechanism. The growth rates of Cu3Sn and Cu6Sn5 are 7.86×10-19 m2/s and 7.80×10-17 m2/s, respectively. The hardness and elastic modulus of IMC enhance with increasing aging time. For 24h aging time, the microstructure of the Cu6Sn5 keeps scalloped shape and the elastic modulus of IMC layer are similar to the copper substrate, which result in high fatigue resistance of the welded joint and its tensile strength of 69.50 MPa. With the mechanical hardening cumulative effects resulting from aging and cyclic strain, the fatigue performance and tensile strength of the welded joint gradually worse with the further increase of the aging time.

The influence of high-temperature annealing of electrochemically deposited Cu-Zn-Sn layers on the composition and structure of kesterite films — absorbing layers of solar cells

Cu1−δZn2−xSnxS4 (CZTS) films were prepared by sequential electrochemical deposition on different supports (Ta, Ti, Mo, and glass—Mo). The samples obtained using preliminary annealing in inert nitrogen atmosphere contained a secondary intermetallic phase Cu6Sn5 that did not disappear upon subsequent annealing in reactive sulfur atmosphere at 550 °C for 30 min. The CZTS films prepared without preliminary annealing in inert nitrogen atmosphere contained a minimum amount of secondary phases after the sulfurization step. The samples prepared were characterized by a photovoltaically suitable band gap of 1.5 eV and p-type conductivity.

Two-Side Growth of the Cu9Ga4 Phase during the Interfacial Reactions between Sn–Ag–Cu–Ga Solders and Copper Substrates

Interfacial reactions between Sn–3.0Ag–0.5Cu–1.0Ga/1.5Ga in wt.% solders and Cu substrates have been investigated. The solder and substrate couples were annealed at 180°C for 6, 12, 18, and 24 days. Different layers of intermetallic compounds have been found to form, such as Cu6Sn5 and Cu9Ga4. Sn was also observed within the interfacial layer during the annealing. The Cu6Sn5 phase and the Cu9Ga4 phase were observed to form by turns from the substrate into the solder. The Cu9Ga4 phase grew from both the solder side and the intermetallics side. Growth of the Cu9Ga4 phase was found to depend on the Ga diffusion and the availability of the Cu6Sn5 phase.

Mechanical Properties of Tin-Based Babbitt Alloy using the Direct Extrusion technique

Tin Babbitt is an ideal journal bearing material, because of its microstructural properties, which qualifies these alloys as a bearing material. Effect of the Babbitt die casting (ASTM B23 Alloy 2) on its microstructure and the hardness properties were studied. The forward extrusion type was carried out using cosine profile and the five different reduction area such 5%, 10%, 15%, 20% and 40%. The results show that the refinement of hard phases of Cu6Sn5 and SbSn led to increasing the hardness value after casting, and after extrusion for all reduction percent, except reduction 40%, the dynamic recrystallization is dominant which led to hardness decrease. The result also shows that the extrusion pressure increases with increasing the reduction value. Moreover, cold deformation improved the hardness properties for Babbitt alloy by refinement of the Cu6Sn5 phase.