Microstructure Of Solder Research Articles

Evaluation of the microstructure and whisker growth in Sn–Zn–Ga solder with Pr content

Abstract

Rate-dependent behavior of Sn alloy–Cu couples: Effects of microstructure and composition on mechanical shock resistance

Solders serve as electrical and mechanical interconnects in electronic packaging. The mechanical shock behavior of a Pb-free solder joint is quite complex, since the influences of solder microstructure, intermetallic compound (IMC) layer thickness, and strain rate on the overall dynamic solder joint strength need to be quantified. Dynamic solder joint strength is hypothesized to be controlled by two factors. At low strain rates it should be controlled by the bulk solder, whereas at high strain rates it may be controlled by the brittle intermetallic compound layer. In this paper, the dynamic solder joint strength of Sn–3.9 Ag–0.7 Cu solder joints was experimentally measured over the strain rate range 10−3–12s−1. The influences of changes in solder microstructure and IMC layer on dynamic solder joint strength were quantified, and visualized in three dimensions. Fracture mechanisms operating in the solder-controlled and IMC layer-controlled dynamic strength regimes are discussed. Finally, qualitative numerical simulations were conducted, which accurately depict the experimentally observed fracture behaviors.

Evolution of Ag3Sn compounds and microhardness of Sn3.5Ag0.5Cu nano-composite solders during different cooling rate and aging

This paper presents the microstructure and Vickers microhardness of Sn3.5Ag0.5Cu solder doped with trace amounts of TiO2 nanopowders, obtained with different cooling rate and aging conditions. The experiment results that the coupling effect by cooling rate and TiO2 nanopowders additions significantly affected primary β-Sn phase, Ag3Sn grain size and spacing of the Ag3Sn phase, as well as the morphology of Ag3Sn. Ag3Sn was relatively spherical at the water-cooling rate and had a needle-like morphology at the air-cooling rate. However, the Ag3Sn IMC not obviously roughed after aging time at 125°C for 7days. Due to both nano-Ag3Sn IMC and uniform microstructure of the nano-composite solders, the Vickers microhardness improved, in good agreement with the prediction of the classic theory of dispersion strengthening. It appears that adding trace TiO2 nanopowders are an efficient way to develop novel high-performance solders.

Effect of Zn on properties and microstructure of SnAgCu alloy

The microstructures, wettabilities and mechanical properties of SnAgCu-xZn (x = 0, 0.5, 0.8, 1.0, 1.2, 2.0, 2.5, 3.0) solders were investigated, respectively. The results indicated that adding small amount of Zn can evidently improve the wettability, mechanical properties and refine the microstructure of SnAgCu lead-free solder. However, there existed an effective range for the Zn addition, the best Zn content was found to be 0.8 % in the current study. Moreover, the presence of Zn in the solders plays a major role in inhibiting the growth of Cu–Sn intermetallic layer in the solder/Cu interface. Based on thermal-cycling tests, it is demonstrated that the addition of Zn can enhance the thermal-fatigue properties of SnAgCu solder joints.

The constitutive response of three solder materials

As increasing worldwide demand for portable consumer electronics drives development of smaller, faster, more powerful electronic devices, components in these devices must become smaller, more precise, and more robust. Often, failure of these devices comes as a result of failure of the package (i.e. when a mobile phone is dropped) and specifically comes as a result of failure of solder interconnects. As a result, stronger more reliable solder materials are needed. In this paper, the constitutive responses of three solder materials (Sn63Pb37, Sn62Pb36Ag2, and Sn96.5Ag3Cu0.5) are analyzed as a function of temperature (−196°C to 60°C) and strain rate (10−3 to >103s−1). The lead-free Sn96.5Ag3Cu0.5 possessed the highest yield stress of the three solders at all tested strain rates and temperatures, and all solder microstructures which displayed a mechanical response that was sensitive to temperature exhibited grain coarsening with increasing plastic strain, even at room temperature.

Fabrication of Sn-Cu alloy solder by pulse electroplating on the metalized Si wafer

Sn-Cu alloy solder was deposited on the Au metalized Si wafer by pulse electroplating using tri-ammonium citrate based Sn-Cu co-electroplating aqueous solution. The influences of plating parameters, aging and reflowing on the morphologies, compositions, phases and microstructures of the Sn-Cu alloy solder were investigated. The current density of 10 mA/cm2 and the reverse time of 100 ms can be used to obtain a high-quality Sn-Cu alloy layer. During aging at room temperature, Cu6Sn5 formed gradually in the Sn-Cu alloy layer. After reflowing at 230 °C, the Sn-Cu alloy solder is well distributed on the Si substrate, in which (Cu,Au)6Sn5 and AuSn4 particles are randomly embedded in the Sn matrix.

Effects of microstructure and temperature on corrosion behavior of Sn–3.0Ag–0.5Cu lead-free solder

The heterogeneous microstructure of solder could be obtained when cooling rate of the solder joint was not even, which would affect the corrosion behavior of solder during service. The ambient temperature would also affect the corrosion behavior of solder joint. In this paper, the effects of microstructure and temperature on the corrosion behavior of Sn–3.0Ag–0.5Cu (SAC305) lead-free solder were investigated. The various microstructures of SAC305 lead-free solder were obtained by cooling specimens in air and furnace. Compared to the fine-fibrous Ag3Sn phase inside the commercial SAC305 solder, platelet-like Ag3Sn formed as cooling speed decreasing. The polarization behavior of SAC305 solders in 3.5 wt.% NaCl solution was not significantly affected by various microstructures, but sensitive to temperature.

Wettability and shear strength of active Sn2Ti solder on Al2O3 ceramics

PurposeThe purpose of this paper is to investigate the wettability of an active Sn2Ti solder on an Al2O3 ceramic material at temperatures of 700°C and higher. Based on the results of the wettability study, soldered joints of Al2O3 ceramics/Sn2Ti solder/steel type AISI 321 were fabricated and the variation of shear strength with time was determined.Design/methodology/approachFor determining melting points, differential scanning calorimetry analysis was performed. The wetting angle of Sn2Ti solder on Al2O3 ceramics was measured using specially developed equipment with a 10‐3 Pa vacuum at temperatures of 700, 800, 850 and 900°C. The wetting angle on AISI 321 steel at a temperature of 850°C was also determined. The joints of Al2O3 ceramics/Sn2Ti solder/steel type AISI 321 were prepared at 900°C, in a vacuum for times 5, 10, 15 and 20 min.FindingsThe best wettability of Sn2Ti solder was achieved at a temperature of 900°C. The wetting angle at the parameter of 900°C/ for 15 min was 47.5°. The joints of Al2O3 ceramics/Sn2Ti solder/steel type AISI 321 attained a strength of 18.3 MPa. It was found that the microstructure of Sn2Ti solder consists of a tin matrix with the presence of a αTi6Sn5 phase.Originality/valueThe results of the work are of significance for the further development of soldering with active solders in a vacuum, as well as with the application of power ultrasound. The possibility of soldering Al2O3 ceramics with SnTi‐based solders was thus demonstrated.

Die attach properties of Zn–Al–Mg–Ga based high-temperature lead-free solder on Cu lead-frame

Several candidate alloys have been suggested as high-temperature lead-free solder for Si die attachment by different researchers. Among them, Zn-Al based alloys have proper melting range and excellent thermal/electrical properties. In this study, Zn-Al-Mg-Ga solder wire was used to attach Ti/Ni/Ag metallized Si die on Cu lead-frame in an automatic die attach machine. Die attachment was performed in a forming gas environment at temperature ranging from 370 to 400 C. At the interface with Cu lead- frame, CuZn4 ,C u 5Zn8 and CuZn intermetallic compound (IMC) layers were formed. At the interface with Si, Al3Ni2 IMC formed when 200 nm Ag layer was used at the die back and AgZn and AgZn3 IMC layers when the Ag layer was 2,000 nm thick. Microstructure of the bulk solder consists of mainly two phases: one with a brighter contrast (about 80.9 wt% Zn) and the other one is a mixture of light (about 73.7 wt% Zn) and dark phases (about 45 wt% Al). Zn-Al-Mg-Ga solder wetted well on Cu lead-frame, covered entire die area and flowed in all directions under the Si die. Less than 10% voids were found in the die attach samples at die attach temperatures of 380 and 390 C. Die shear strength was found within the acceptable limit (21.8-29.4 MPa) for all the die attach temperatures. Die shear strength of standard Pb-Sn solder was also measured for comparison and was found to be 29.3 MPa. In electrical test, maximum deviation of output voltage after 1,000 thermal cycles was found 12.1%.

An investigation of microstructure and mechanical properties of novel Sn3.5Ag0.5Cu–XTiO2 composite solders as functions of alloy composition and cooling rate

Abstract In the present study, the influence of both TiO 2 nanoparticle addition and cooling rate on the melting temperature, microstructure, and mechanical behaviour of Sn3.5Ag0.5Cu (SAC) solder alloys was studied. The composite solders were prepared by mechanical mixing of TiO 2 nanoparticles with SAC solder. With the addition of TiO 2 nanoparticles into the eutectic SAC alloy, a novel SAC composite solder was successfully prepared. The melting temperature for the SAC composite solders was found to be only 1.56 °C higher than that of the SAC solder, indicating that the novel SAC composite solder is fit for existing soldering process. The cooling rate and TiO 2 nanoparticle addition affected the solidification of the microstructure dramatically. Notably, SEM observation of the microstructure of the SAC composite solders under the rapid-cooled condition revealed fine dot-like nano-Ag 3 Sn IMC in the solder matrix. The ultimate tensile strength (UTS), 0.2% yield strength (0.2YS), and microhardness of the SAC composite solder increased with the increase of TiO 2 nanoparticle content by 0.25–1.0 wt.% and the cooling rate, which could be attributed to the dispersion strengthening mechanisms. However, the ductility of the composite solders was found to decrease because of microporosity at the Ag 3 Sn network grain boundary.

Corrosion behavior, whisker growth, and electrochemical migration of Sn–3.0Ag–0.5Cu solder doping with In and Zn in NaCl solution

Corrosion characteristics of Sn–3.0Ag–0.5Cu (SAC) solder doped with In and Zn in NaCl solutions were conducted by sweeping the voltage at a constant rate with a potentiostat. Whisker growth was completed by dipping in 3.5 wt.% NaCl salt solution. Electrochemical migration (ECM) experiment was carried out as a designed program in an electric field with a power supply. Surface morphology and elemental composition of SAC and its doped candidates were determined by SEM, EDAX, XRD techniques. Results showed that when the percent content of Zn was ⩽1%, corrosion current density ( I corr) increased with Zn% increasing, it was up to the highest value when %Zn was 1%. After that, the open circuit potential moved negatively quickly as a function of Zn percent, however I corr increased with Zn percent increasing, also lower than that of doped solder with 1 wt.% Zn, higher than that of no doped solder. The same corrosive law was suitable for SAC candidate with In doping. SEM morphologies showed that whiskers existed in all cases of different In/Zn-concentration alloys. After exposure to severe conditions (3.5 wt.% NaCl solution) for 7 days, the longest whisker for 96.8(Sn–3.0Ag–0.5Cu)–0.2In–3Zn solder was about 300 μm, the average grown rate was evaluated to about 5 Å/s which is higher than the reported result in the former literatures. The possible mechanism was that: after metals reacted with water/ions in water, products or oxidizer in solder expanded to induce compression stress, during the release of stress, Sn extruded out. ECM tests showed that dendrite growth was a result of system under far-equilibrium conditions in sorts of fields as electrical field, thermal field, concentration field, etc., the farer off the equilibrium, the easier that ECM process took place. Dendrite growth rate of SAC solder were faster than those of its candidates with In or Zn dopings, furthermore, rate with Zn doping was larger than that with In doing, which is due to differences on surfaces or different intermetallic compound formations (IMC) on surfaces. Doped with In, dendrites looked like emarcid petals, although they might not look like dendrites, contents on dendrites were mainly Sn. Whereas, dendrites looked like clew with only Zn doping, it was mainly Sn with little Zn. Different from the above, dendritic microstructures of SAC solder without doping entirely looked like branches, contents were mainly Cu and Sn. From the points of corrosion and whisker growth, Zn, In dopings in SAC solders may be not benefit to micro/nanoelectronic packaging, though other mechanical or soldering characteristics can be improved with their dopings.

Effects of addition of copper particles of different size to Sn-3.5Ag solder

In this study, copper particles with different sizes 20–30 nm, 3 and 10 μm were incorporated into Sn-3.5Ag solder paste to form Sn–Ag–Cu composite solder. The Cu particles were added at 0.7 and 3% by paste mixing for 30 min. The composite solder samples were prepared on copper substrate at 240°C for 60 s. Differential scanning calorimetry was conducted to measure the melting point of the composite solder. The wetting angle and microstructure of the composite solder were studied using optical microscope and scanning electron microscope. Micro hardness was measured using a 10 gf load. It was reported that the lowest melting point was obtained at 216.3°C when Cu nanoparticles was added at 3% to Sn-3.5Ag. The microstructure of Sn-3.5Ag solder structure was dendritic in nature. With the addition of Cu nanoparticles, the microstructures were modified with more refined Sn structures. The existence of sunflower morphology of un-melted copper was observed when Cu microparticles were added.

A Replaceable Lead-Free Solder for Sn-37Pb

In this paper, a new kind of Sn-Bi lead-free solder was fabricated via rapid solidification method by adding a series of microelements which can optimize the properties of Sn-Bi solder. When the solder was manufactured by Single Roller Melt Spinning Process, the faster the cooling rate is, the better the effect of restraining Bi segregation is. When the melt spinning rate was up to 1000 rpm, it had the best result. The effects of microelements on the melting characteristics, microstructure and properties of the new solder were also systemically studied. The results show that when the added content of Ag is 0.7%, Cu 0.3%, Ge 0.1%, In 0.5% and Sb 0.5%, the microstructure of the solder is fine, the extent of Bi segregation obviously decreases and the mechanical property is similar to that of Sn-37Pb solder. The melting point of the new solder is close to that of the Sn-37Pb solder. The mechanical and soldering properties are also similar to that of it.

Addition of cobalt nanoparticles into Sn‐3.8Ag‐0.7Cu lead‐free solder by paste mixing

PurposeThe purpose of this paper is to investigate the effects of addition Co nanoparticles on the characteristic properties of Sn‐3.8Ag‐0.7Cu solder.Design/methodology/approachCobalt (Co) nanoparticles were added to Sn‐Ag‐Cu solders by thoroughly blending various weight percentages (0‐2.0 wt%) of Co nanoparticles with near eutectic SAC387 solder paste. Blending was done mechanically for 30 min to ensure a homogeneous mixture. The paste mixture was then reflowed on a hot plate at 250°C for 45 s. The melting points of nanocomposite solder were determined by differential scanning calorimetry. Spreading rate of nanocomposite was calculated following the JIS Z3198‐3 standard. The wetting angle was measured after cross‐sectional metallographic preparation.FindingsNo significant change in melting point of the solder was observed as a result of Co nanoparticle addition. The wetting angles of the solder increased with the addition of nanoparticles, while the spreading rate decreased. Although the wetting angle increased, the values were still within the acceptable range. Scanning micrograph observations revealed that the as‐solidified microstructure of the composite solder was altered by the addition of Co nanoparticles. Microhardness of the solders slightly increased upon Co nanoparticles addition to SAC387.Originality/valueThe paper demonstrates that a simple process like paste mixing can be used to incorporate nanoparticles into solder.

Effect of rare earth Ce on the microstructure, physical properties and thermal stability of a new lead-free solder

In this paper, in order to develop a low silver content lead-free solder with good overall properties, a newly designed solder alloys of Sn-0.3Ag-0.7Cu-20Bi-xCe type, with addition of varying amounts of rare earth Ce (0.05 mass%, 0.1 mass% and 0.2 mass%) were studied. The melting temperature of Sn-0.3Ag- 0.7Cu can be decreased substantially through addition of 20 mass% Bi; while the segregation of Bi element in the microstructure of the as-cast alloys can be relieved by micro-alloying with trace amount of rare earth Ce. Besides, aging treatments (160?C held for 6 h) of these solder alloys imply that appropriate amount of Ce addition can not only depress the diffusion induced aggregation of Bi in the microstructure but promote the homogenization during annealing. Compared with Bi-free Sn-0.3Ag-0.7Cu solder, Sn-0.3Ag-0.7Cu- 20Bi exhibits better wettability. More excitingly, the wetting property of Sn-0.3Ag-0.7Cu-20Bi can be further improved by doping little amounts of Ce, especially 0.5 mass%, in which case the spreading area of the solder can be increased to the largest extent. On the whole, the present study reveals that Sn-0.3Ag-0.7Cu- 20Bi-xCe (x=0.05-0.1) is a promising lead-free solder candidate considering the microstructure, melting temperature and wetting properties.

Effect of RE on Microstructure and Interfacial Reactions of SnAgCu Solder

Effect of rare earth content on microstructure and interfacial reactions of low Ag content SnAgCu solder is researched by adopting the X-ray diffraction, JSM-5610LV scanning electronic microscope, energy spectrum analysis and JEM2100 ultrahigh resolution electron microscopy. The results show that proper quantities of rare earth (0.1%) can refine the eutectic microstructure of the solder alloy; and petal-like rare earth compound can be found in the solder alloy while the rare earth addition is 0.5%. The growing rate of the interfacial intermetallic compound can be reduced during the soldering with adding 0.1% rare earth in the Sn2.5Ag0.7Cu solder alloy.

Properties and microstructure of Sn-9Zn lead-free solder alloy bearing Pr

In the present work, effects of trace amount of Pr on the microstructure, wettability and mechanical properties of Sn-9Zn solder were studied. The range of Pr content in Sn-9Zn solder alloys varied from 0.01 to 0.25 wt%. Test results indicate that adding appropriate amount of Pr can evidently improve the wettability and mechanical properties of the Sn-9Zn solder alloy. The Sn-9Zn-0.08Pr solder shows the best comprehensive properties compared to other solders with different Pr content. At the same time, notable changes in microstructure were found compared with the Pr-free alloy. The needle-like Zn-rich phase in the Sn-9Zn solder was refined and became more uniform. Moreover, the thickness of the IMC layer at Sn-9Zn/Cu substrate was remarkably depressed with Pr addition.

The study of mechanical properties of Sn–Ag–Cu lead-free solders with different Ag contents and Ni doping under different strain rates and temperatures

In this paper, the tensile tests were conducted at 25 °C to investigate the effect of Ag content and Ni doping on the microstructures and mechanical properties of Sn–3.0Ag–0.5Cu, Sn–2.0Ag–0.5Cu, Sn–1.0Ag–0.5Cu, Sn–1.0Ag–0.5Cu–0.05Ni and Sn–1.0Ag–0.5Cu–0.02Ni solders. The effect of strain rate on mechanical properties was investigated for each solder using stain rates of 10 −5 s −1, 10 −4 s −1, 10 −3 s −1, 10 −2 s −1 and 10 −1 s −1. In addition, the effect of temperature on mechanical properties was investigated for Sn–1.0Ag–0.5Cu–0.02Ni solder by conducting tests at −35 °C, 25 °C, 75 °C and 125 °C. Test results show that the elastic modulus, yield stress and ultimate tensile strength increase with increasing strain rate and Ag content, but they decrease with increasing temperature. The elastic modulus, yield stress and ultimate tensile strength are lower and the elongation is larger for Sn–1.0Ag–0.5Cu–0.05Ni solder compared with Sn–1.0Ag–0.5Cu–0.02Ni solder. The strain rate and Ag content dependent mechanical property models have been developed for Sn–Ag–Cu solders for the first time. In addition, the temperature and rate-dependent mechanical property models have also been developed for Sn–1.0Ag–0.5Cu–0.02Ni solder. The microstructures of solders were also analyzed. The Ag content affects Ag 3Sn intermetallic compound dispersion and Sn dendrite size. The microstructures of solder have fine Sn dendrites and more dispersed IMC particles for the high Ag content solder, which makes the solder exhibit high strength and yield stress.

The Microstructural Aspect of the Ductile-to-Brittle Transition of Tin-Based Lead-Free Solders

Abstract This work focuses on specific aspects of the ductile-to-brittle transition in the fracture behavior of tin-based lead-free solders. This transition is essentially associated with the crystal structure of β-Sn, which is the main constituent of these solders. Moreover, the transition is affected by many factors, including the ambient temperature, the applied strain rate, the mechanical constraint, and certain solder microstructural features such as the shape, size, and spatial distribution of intermetallic particles. Since the mechanical constraint in the solder is related with the specimen dimensions, this work compares the fracture behavior of two different sizes of specimens made of tin-based solders: Rectangular beams and solder joints. Both types of specimens were tested in impact, while the produced fracture surfaces were studied using scanning electron microscopy. The detailed fractography analysis allowed the correlation of the overall solder fracture behavior with certain features in the solder microstructure. This study used also the additional insight into the embrittlement mechanism of tin-based solders to explain previous results from the thermal cycling of eutectic tin-lead solder joints.

The Correlation between the Liquid Structure and the Solidification Microstructure of Sn-Cu Lead-Free Solders

The liquid structure of two lead-free solder molten alloys, Sn-0.5Cu and Sn-1.8Cu (wt.%), have been investigated using X-ray diffraction method. The main peak for liquid structure of Sn-0.5Cu is similar to that of pure Sn. A pre-peak has been found in the low Q part on the structure factor S(Q) of Sn-1.8Cu tested under 320°C and the pre-peak decreases its intensity with increasing temperature, but it disappeared finally when the testing temperature reached 350°C. The microstructure of the solder matrix as well as interfacial reaction between liquid solders and Cu substrate was also studied. The structural unit size corresponding to the pre-peak almost equals to magnitude of crystal planar distance of Cu6Sn5 phase. The appearance of a pre-peak may be due to existence of clusters with Cu6Sn5-phase-like structure in the melt. Quantity and size of clusters increases with decreasing temperature but their structural unit size remains constant. Cu6Sn5 phases develop from incorporating and growing of the clusters during solidification, thus result in the correlation between liquid structure and solid microstructure.