Microstructure Of Solder Alloys Research Articles

Influence of Fe and Ho additions on Sn-3.0Ag-0.5Cu solder alloy: Microstructure, electrochemical and mechanical properties

In this work, the microstructure, electrochemical and mechanical properties of Sn-3.0Ag-0.5Cu solder alloy with Fe and Ho additions were studied. The results demonstrated that adding of Fe and Ho improved the microstructure of solder alloy and formed FeSn2 phase and Ho5Sn3 phase. Besides, the addition of Fe weakened the microhardness and tensile properties of the solder alloy, which was ascribed to a weak interface between FeSn2 and β-Sn matrix. The microhardness and tensile properties of solder alloy were enhanced by adding Ho owing to the improvement of microstructure and the strengthening of the second phase. Electrochemical tests and atomic force microscopy (AFM) results showed that comparing to the base solder alloy, higher corrosion current densities and rougher surfaces after corrosion were found in the solder alloys with the Fe and Ho additions.

Effect of multi-walled carbon nanotubes on the microstructure and properties of Sn-58Bi solder alloys

The influence of multi-walled carbon nanotube (MWCNT) content on the melting properties, wettability, microstructure, and intermetallic compounds (IMCs) of Sn-58Bi-xMWCNT (x = 0, 0.01, 0.02, 0.03, 0.05, and 0.10 wt.%) and the effects of MWCNT on the tensile strength of Cu/Sn-58Bi-xMWCNT/Cu solder joint were analyzed. The results show that MWCNT addition at a small trace amount into Sn-58Bi solder could increase the spreading area of Sn-58Bi solder, refine the solder matrix microstructure, inhibit the growth of interfacial IMCs, and significantly improve the tensile strength of Sn-58Bi solder joints. However, the melting point and melting range remained the same or slightly changed. The wettability of Sn-58Bi alloys increased first and then decreased with the addition of MWCNT. The spreading area and the tensile strength of solder joint were the maximum when the MWCNT content was 0.01 wt.%, and they were 42.23 mm2 and 50.07 MPa, respectively. The reason may be related to the improved microstructure of solder alloys and the morphology of IMCs due to MWCNT addition at trace level.

Pattern Formation by Spinodal Decomposition in Ternary Lead-Free Sn-Ag-Cu Solder Alloy

In comparison to Pb-based solders which have a toxic effect, the tin-silver-copper (SAC) family of alloys have relatively strong reliability and are widely used in the electronics industry. Phase separation and coarsening phenomenon on the surface of 96.5 wt. % Sn-3.0 wt. % Ag-0.5 wt. % Cu (SAC305) solder products exhibit special microstructural features and offer opportunities for the microstructure control of microelectronic interconnects. However, the formation mechanism of such morphological patterns is still unknown. Here, we applied a combination of experimental and phase field methods to study how such patterns form. It was observed that the pattern was Sn-rich and exhibited the characteristic morphology of spinodal decomposition. Contrary to earlier findings that only binary systems like Sn-Pb and Sn-Bi experienced such phenomena, spinodal decomposition was firstly observed in ternary solder system Sn-Ag-Cu. Morphology of Sn-rich patterns depended on whether the spinodal decomposition reacted completely. SAC305 solder alloy was easily decomposed by Sn component after being heated to roughly 260 °C. The above conclusions could offer theoretical support for quantitatively controlling the microstructure of solder alloys and would enhance the quality of related products.

The influences of reactive nanoparticles alloying on grain boundary and melting properties about Sn3.0Ag0.5Cu solder

Herein, we prove that alloying of reactive nanoparticles can improve nanoparticles/β-Sn interfacial bonding and influence the solder alloy's melting point. Furthermore, the alloying effect can enhance the creep resistance of solder alloy. 0-0.5 wt% Ag nanoparticles (NPs) were added to Sn3.0Ag0.5Cu (SAC305) solder paste by mechanical stirring for the preparation of composite solder alloys, which were then extracted from the composite solder pastes. The joints were observed by scanning electron microscope and transmission electron microscope. The elementary composition of the prepared alloys was analyzed by electron dispersive spectrometer. The melting properties of alloys were tested by differential scanning calorimeter. The influences of Ag NPs as reactive nanophase on solder microstructure and melting properties were studied. The results indicated the existence of transition layer at the interface between Ag NPs and β-Sn. Additionally, the interfacial bonding improved after Ag NPs converted to Ag3Sn NPs. Due to Ag NPs alloying and solder alloy microstructure refinement being affected, melting points of alloys increased with 0-0.2 wt% addition of Ag NPs and decreased with 0.2–0.5 wt% addition.

Effects of gallium, phosphorus and nickel addition in lead-free solders: A review

Ever since the start of the electronic age, soldering has been an important interconnecting method in microelectronic packaging. Since the 1960 s, development of information technology (IT)-infrastructure has witnessed rapid advancement owing to development of novel electronic equipment. This, in turn, has led to growth and progression of industries and improved human lifestyle. Present-day electronic gadgets are highly sophisticated and comprise several components. Sn–Pb based solder alloys have always delivered excellent results, offering several amazing benefits, namely, easy handling, low melting temperature, good working condition, ductility, and exceptional wetting on Cu and its alloys. Owing to its lethal and harmful effects on health and the environment, the US Congress introduced the legislation on the limited use of Pb in 1990. Consequently, alternatives to lead free solders are being developed for last three decades. This literature review discusses the effect of Gallium, Phosphorus and Nickel addition on solder alloy microstructure and mechanical properties.

Effect of addition of Cu on the properties of eutectic Sn-Bi solder alloy

Abstract The present work reports the effect of Cu addition on the melting point, hardness and electrical resistivity of Sn-57 wt.% Bi eutectic solder alloy. Both binary eutectic Sn-57 wt.% Bi and ternary Sn-(57-x)Bi-xCu (x = 0.1, 0.3, 0.5, 0.7 and 1 wt.%) alloys containing various amounts of Cu were developed by melting casting route. The microstructure of the various solder alloys was analyzed using an optical microscope and a SEM. The variation in melting point, hardness and electrical resistivity of the Sn-Bi eutectic solder alloys with the addition of Cu was determined. The melting point of the eutectic Sn-Bi solder alloy was found to decrease up to the addition of 0.7 wt.% Cu. However, further addition of Cu led to an increase in the melting point of the alloy. Addition of Cu led to an increase in the hardness of the eutectic Sn-Bi solder alloy whereas the electrical resistivity of this alloy was found to increase up to the addition of 0.7 wt.% of Cu beyond which a decrease in the electrical resistivity was observed. A change in the microstructure of the solder alloy was observed when it was reheated above the melting temperature.

Electrical and Thermal Characterisation of Millscale Modified Sn-Cu Lead-Free Solders

Lead-free solders are gaining much attention as a result of legislation against the inclusion of lead and other hazardous materials in solders used in joining electronic components. This study investigated the effect of iron millscale (IMS) modified tin-copper (Sn-Cu) alloy on the electrical resistivity, electrical, and thermal conductivities of the solder samples under increasing applied current. The input materials consist of tin, zinc and iron millscale while the copper was varied from 0.2 – 1.0 wt. %. Fabrication of the alloy employed metal casting technique followed by relevant test samples preparation for characterisation in terms of microstructure, electrical, and thermal conductivities. Results show that the sample with 1 wt. % Cu addition exhibited the highest electrical and thermal conductivity values of 9967.9 S/m and 11.24 x 10-5 W/mK respectively at applied current value of 600 A with the lowest resistivity of 1 x 10-4 (Ωm). The solder alloy microstructure confirmed the presence of Cu6Sn5-FeO intermetallic phase dispersed in Sn matrix forming a continuous network. Contribution to the overall desirable performance of the solder alloy may have stemmed from the strong and coherent inter-crystal cohesion between the Cu6Sn3 and FeO phases which resulted in improved electrical and thermal conductivities of the as cast solder. The grade of solder alloy fabricated is adjudged suitable for assembling electronic components in industrial plant control panels.

Effects of post-reflow cooling rate and thermal aging on growth behavior of interfacial intermetallic compound between SAC305 solder and Cu substrate

The interfacial reactions between Cu and Sn3Ag0.5Cu (SAC305) solder reflowed under various cooling rates were investigated. It is found that the cooling rate is an important parameter in solder reflow process because it influences not only microstructure of solder alloy but also the morphology and growth of intermetallic compounds (IMCs) formed between solder and Cu substrate. The experimental results indicate that only scallop-like Cu6Sn5 IMC layer is observed between solder and Cu substrate in case of water cooling and air cooling, while bilayer composed of scallop-like Cu6Sn5 and thin layer-like Cu3Sn is detected under furnace cooling due to sufficient reaction time to form Cu3Sn between Cu6Sn5 IMC and Cu substrate which resulted from slow cooling rate. Samples with different reflow cooling rates were further thermal-aged at 423 K. And it is found that the thickness of IMC increases linearly with square root of aging time. The growth constants of interfacial IMC layer during aging were obtained and compared for different cooling rates, indicating that the IMC layer thickness increased faster in samples under low cooling rate than in the high cooling rate under the same aging condition. The long prismatic grains were formed on the existing interfacial Cu6Sn5 grains to extrude deeply into solder matrix with lower cooling rate and long-term aging, and the Cu6Sn5 grains coarsened linearly with cubic root of aging time.

Microstructure and Mechanical Properties of Tin-Bismuth Solder Reinforced by Aluminum Borate Whiskers

Tin-bismuth solder has emerged as a promising lead-free alternative to tin-lead solder, especially for low-temperature packaging applications. However, the intrinsic brittleness of tin-bismuth solder alloy, aggravated by the coarse bismuth-rich phase and the thick interfacial intermetallic layer, notably limits the mechanical performance of the bonded joints. In this work, the microstructure and mechanical performance of solder joints were improved by adding 3.2 vol.% aluminum borate whiskers to the tin-bismuth solder alloy. This whisker-reinforced composite solder was fabricated through a simple process. Typically, 25-μm to 75-μm tin-bismuth particles were mixed with a small amount of aluminum borate whiskers with diameter of 0.5 μm to 1.5 μm and length of 5 μm to 15 μm. The addition of whiskers restrained the formation of coarse brittle bismuth-rich phase and decreased the lamellar spacing from 0.84 μm to 7.94 μm to the range of 0.22 μm to 1.80 μm. Moreover, the growth rate of the interfacial intermetallic layer during the remelting treatment decreased as well. The joint shear strength increased from 19.4 MPa to 24.7 MPa, and only declined by 4.9% (average, −5.9% to 15.8%) after the tenth remelting, while the shear strength of the joint without whiskers declined by 31.5% (average, 10.1–44.1%). The solder alloy was reinforced because of their high strength and high modulus and also the refinement effect on the solder alloy microstructure.

Influence of Ni addition on the mechanical properties of Bi-5Sb-8Sn solder alloys

In this paper, the microstructures of solder alloys were improved by adding trace elements of Ni to BiSbSn solder to enhance Bi-based solder alloys mechanical properties. The spreading areas, tensile strengths and shear strengths of the Bi-5Sb-8Sn-xNi solders with various Ni contents were characterised. The results revealed that after Ni was added to the BiSbSn solder, two new phases occurred: Ni3Sn4 and NiSb2. When the Ni content was 1%, the solder tensile strength was at the highest. When the Ni content was less than 3%, the shear strength increased as the Ni content increased. When the Ni content was more than 3%, the shear strength decreased gradually, primarily owing to the large amounts of impurities and pores introduced by the internal aggregation effect. In summary, when the Ni content was between 1 and 3%, the solders had the most-usable overall properties.

Enhancement of the impact toughness in Sn–Ag–Cu/Cu solder joints via modifying the microstructure of solder alloy

In this research, the impact toughness of Sn–3.0Ag–0.5Cu/Cu (wt%, SAC305/Cu) solder joints is efficiently improved via controlling the solidification step of reflow process. During solidification step of reflow process, the solder joints were annealed under various heating time and temperature. A high speed shear tester was used to evaluate the impact reliability of these solder joints. Noteworthily, the annealing at higher temperature (210°C) for a short time (100s) can enhance the average impact toughness of SAC305/Cu solder joints up to 30%. The improvement of impact toughness was attributed to the evolution of microstructure in the solder alloys. In the annealed solder, the phase precipitation within the solder varied from a dot type toward a network type. Additionally, the β-Sn grain structure was altered from interlaced grains to larger grains due to the redistribution of Cu in the solder.

Microstructure and mechanical properties of Sn–Zn–Bi–Cr lead-free solder

In this paper, the effect of trace addition of Cr on the mechanical properties and reliability on Sn–8Zn–3Bi solder alloys was investigated. It has been demonstrated that the microstructure of solder alloys was refined after doping traces of Cr. The elongation reaches up to 40.63% after doping 0.1% Cr; and the fracture mechanism converts from quasi-cleavage fracture into ductile fracture. With aging time of 0, 4, 9 and 16days, mechanical property of Sn–8Zn–3Bi–0.3Cr alloy was improved slightly. It was found that the Sn–Zn–Cr phase was increased and Zn in alloy was consumed after aging, so that the amount of primary Zn phase was reduced and microstructure was improved.

Properties and microstructure of Sn–0.7Cu–0.05Ni solder bearing rare earth element Pr

Effects of trace amount of rare earth element Pr on properties and microstructure of Sn–0.7Cu–0.05Ni solder were investigated in this paper. The solderability of Sn–Cu–Ni–xPr alloy and shear strengh of Sn–Cu–Ni–xPr soldered micro-joints were determined by means of the wetting balance method and shear test, respectively. Moreover, microstructure of solder alloys bearing Pr, as well as intermetallic compound (IMC) layer formed at solder/Cu interface after soldering were observed. It was concluded that the major benefits of rare earth element Pr on Sn–Cu–Ni lead-free solder are: improving solderability, refining microstructure, and depressing IMC (IMC) growth, which exhibited improved mechanical properties. It also revealed that (Cu,Ni)6Sn5 is the majority IMC phase at the interface of Sn–Cu–Ni–xPr/Cu solder joints. Ni added into the solder effectively suppressed the growth of Cu3Sn and consequently also the total IMC layer thickness. Above all, the thickness and morphology of the interfacial (Cu,Ni)6Sn5 IMC were optimized due to alloying Pr. It can be inferred that Pr and Ni would play an important role in improving the reliability of Sn–Cu–Ni lead-free solder joints.

217 電子実装基板用はんだの粘塑性変形と微細組織(材料力学(3))

217 電子実装基板用はんだの粘塑性変形と微細組織(材料力学(3))

Effect of post-reflow cooling rate on intermetallic compound formation between Sn–3.5 Ag solder and Ni–P under bump metallization

Cooling rate is an important parameter in solder reflow process because it influences not only microstructure of solder alloy but also the morphology and growth of intermetallic compounds (IMC) formed between solder and its metallization. All these ultimately affect the mechanical integrity of the joint. In this work, the effect of cooling rate on IMC growth is studied in Sn–3.5 Ag solder/Ni–P under bump metallization (UBM) system. Morphology and growth kinetics of the formed Ni 3Sn 4 IMC under different cooling rates are studied. Needle-type, boomerang-type and chunk-type of Ni 3Sn 4 IMCs have been observed between solder and Ni–P UBM under various cooling conditions. The amount of the needle-type and boomerang-type grains decreases with the increase of reflow time. Prolonged reflow results in continuous layer of chunk-type IMC grains with no obvious effect from the cooling rate. Samples with different post-reflow cooling rate are further annealed. It is found that the IMC layer thickness increases faster in samples under fast cooling rate than the slow ones under the same annealing condition.

Microstructure changes in Sn-3.5Ag solder alloy during creep

Experimental data on behavior of the Sn-3.5Ag solder alloy microstructure during tensile creep deformation and subsequent failure is described. Depending upon applied stress, the nucleation and further development of grain boundary defects that start at an earlier stage in the deformation process was revealed. A discussion is presented on possible micromechanisms of the crack formation process.

Tensile test for estimation of thermal fatigue properties of solder alloys

A tensile test is proposed to evaluate the thermal fatigue resistance of solder alloys. The test is based on the strain rate change method to obtain the strain rate sensitivity index, m. The m value is obtained at various strains during the tensile test. The plots of m and strain where m is measured showed a linear relation; therefore, the m value at zero strain, m0, and the gradient, k, are obtained by extrapolation. The m value at zero strain related to the coarseness or fineness of solder alloy microstructure; m0 becomes lower with coarsening of the microstructure. The solder alloys with low m0 and low k have excellent thermal fatigue resistance when compared with alloys with high m0 and high k. m0 and k would be good measures to estimate the thermal fatigue properties of solder alloys; highly resistant alloys have low m0 and low k.

Modeling joining materials for microelectronics packaging

Modeling of solder-substrate interactions together with careful experimental work can provide a good basis for developing new materials such as conductive adhesives and Pb-free solders as well as fluxless soldering processes for microelectronics packaging. The modeling of the solder-substrate interactions will in effect lead to a rationalization of the trial and error methods commonly employed and hence minimize the number of experiments required. It provides useful information on the chemical reactions, stabilities of various microstructures and growth rates of reaction products during joining or in use of electronic devices. This is of particular importance in the case of small solder volumes, since the compositions and microstructures of solder alloys can be entirely altered by the solder-substrate reactions during the joining. As specific examples the solder-substrate reactions have been investigated in the Sn-Bi/Cu and Sn-Bi-Zn/Cu systems with and without adhesives. The solder-substrate-environment interactions under high purity reducing gases have been studied also with the meniscograph. The reduction of surface oxides, formation and the stability of the intermetallic layers, Cu/sub 3/Sn and Cu/sub 6/Sn/sub 5/, and the growth of brittle Bi layer in the microjoints due to the change of the composition of the solder filler was studied both theoretically and experimentally. Moreover, an explanation concerning the strong dewetting effect of zinc-containing solders found experimentally is given. An emphasis was placed also on the solder-substrate-environment interaction by studying the effect of humidity on chemical stability of microjoints in an epoxy-based adhesive.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>