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Based on the characteristics of octopus arm suction cup shape and distribution, a laser cylindrical texture with dimensions of R = 500 μm, W = 200 μm, and H = 50 μm was designed on the surface of G20CrMo substrate material using laser surface processing technology. The grooves of texture were filled with SnAgCu and comparative tests were respectively conducted under dry friction and grease lubrication conditions with a loading force of 10 N, reciprocating frequency of 1 Hz, and stroke of 8 mm. A comprehensive characterization and parameter analysis of wear scars were performed using various material surface analysis instruments. The experimental results showed that the cylindrical textured surface filled with SnAgCu reduced the friction coefficient by 22.9% compared to G20CrMo substrate surface under the dry friction condition. In addition, under the grease lubrication condition, although the cylindrical textured unfilled surface resulted in a higher friction coefficient, the friction coefficient and wear loss of cylindrical textured surface filled with SnAgCu were respectively reduced by 18.6% and 60% compared to those of G20CrMo substrate surface. [ABSTRACT FROM AUTHOR]

Based on the principles of micro-alloying and composite, the graphene reinforced Sn2.5Ag0.7Cu0.1Ce composite solder was designed. Ni nanoparticle-modified reduced graphene oxide (Ni-rGO) was prepared by thermal decomposition method, and the powder-melting method was proposed for the first time to prepare Ni-rGO reinforced Sn2.5Ag0.7Cu0.1Ce composite solder. The microstructure, wettability, electrical resistivity, and mechanical properties of the composite solder were systematically studied. Results indicated that the Ni nanoparticles uniformly adhered to the rGO with a size of 26.3 nm. The effective incorporation of Ni-rGO into the solder matrix was achieved. The result broke the technical difficulty that graphene cannot be effectively added to low melting point metals. With the addition of Ni-rGO, the grain size gradually decreased, and the eutectic structures increased. Deep etching results revealed that columnar β-Sn was stacked from layered β-Sn, the addition of 0.05 wt% Ni-rGO led to an increase in sheet-like Ag3Sn within the eutectics. Additionally, Ni-rGO was found at the grain boundaries of composite solder, serving as nucleation sites for Ag3Sn and Cu6Sn5. At an addition of 0.05 wt%, the tensile strength reaches a maximum of 58.1 MPa, with elongation of 33.8%, surpassing the strength of commercial Sn3.0Ag0.5Cu solder. Therefore, the high-strength and tough composite solder was obtained. This study offered a new approach for the development of low-melting-point composite materials.

Friction and wear behaviors of Ti alloys are vital to their applications in aerospace components and ocean devices. The spherical SnAgCu–Al2O3 (S–SA) are synthesized via spark plasma sintering (SPS) to prepare the Ti–S–SA for achieving excellent lubrication. On a ball‐on‐flat tribometer, Ti–S–SA exhibits the best friction and wear performance among the samples prepared by SPS. Approximately 12.0 wt% of Al2O3 is coated with 15.0 wt% SnAgCu to form a SnAgCu‐enriched film, resulting in the reduction of binding ability of the Al2O3 with the surface material. The rotation of Al2O3 particles improved as SnAgCu deformed under a low load. Subsequently, the friction resistance reduces, and a low material loss is observed from the friction surface; these phenomena facilitate excellent tribological behavior. Under coordinating functions of 12.0 wt% Al2O3 and 15.0 wt% SnAgCu, Ti–S–SA shows a friction coefficient of 0.20 and the wear rate of ≈3.39 × 10−4 mm3 N−1 m−1. [ABSTRACT FROM AUTHOR]

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Abstract A broad range of electronics applications involve the long-term exposure to combinations of thermal excursions and vibration with constantly varying amplitudes, and the ultimate life is very often limited by fatigue of the solder joints. The assessment of this is usually based on a combination of simplified accelerated tests and the assumption of simple acceleration factor expressions or models. Neither of the latter can, however, even account for observed effects of accelerated test parameters. To make matters worse common constitutive relations may be strongly misleading. Also, current damage accumulation rules cannot account for major interactions between thermal cycling and vibration or even just for ongoing variations in vibration amplitudes or thermal cycling parameters, respectively. Even if we are 'just' aiming to decide between alternative material, design, or process parameters, or to compare a new product to a previous (supposedly similar) one, we should be concerned with the relative performance in service and not just in accelerated tests. The main objective of the present work is to combine two recent mechanistic models into a more comprehensive one that includes interactions between effects of thermal cycling and vibration with varying amplitudes. Important parameters in the resulting model still remain to be determined but a detailed understanding of the underlying mechanisms and the consequences of their interactions for realistic Tin-Silver-Copper (SnAgCu) joints allows for the prevention of surprises, the definition of appropriate test protocols, and the proper interpretation of results. This includes the identification of 'worst case' real life scenarios to test for, as well as justification for the use of shear testing in thermal cycling when event detection is not an option. Extension of the model to new alloys is briefly discussed as well. [ABSTRACT FROM AUTHOR]

Electronic products are subjected to high G-levels daring mechanical shock and vibration. Failure-modes include solder-joint failures, pad cratering, chip-cracking, copper ti ace fracture, and underfill fillet failures. The second-level interconnects may be experience high strain rates and accrue damage during repetitive exposure to mechanical shock. Industry migration to lead-free solders has resulted in proliferation of a wide variety of solder alloy compositions. One of the popular tin-silver-copper alloys is Sn3Ag0.5Cu. The high strain rate properties of lead-free solder alloys are scarce. Typical material tests systems are not well suited for measurement of high strain rates typical of mechanical shock. Previously, high strain rates techniques such as the split Hopkinson ptessute bat (SI IPS) can be used for strain rates of 1000s-1. However, measurement of materials at strain rates of 1-100s-1 which are typical of mechanical shock is difficult to add) ess. In this paper, a new test-technique developed by the authors has been presented for measurement of material constitutive behavior. The instrument enables attaining strain rates in the neighborhood of 1-100s-1'. High-speed cameras operating at 300,000 fps have been used in conjunction with digital image correlation (DlC)for the measurement of full-field strain during the test. Constancy of crosshead velocity has been demonstrated during the test from the unloaded state to the specimen failure. Solder alloy constitutive behavior has been measured for SAC305 solder. Constitutive model has been fit to the mateiial data. Samples have been tested at various time under thermal aging at 25°C and 125°C. I he constitutive model has been embedded into an explicit finite element framework for the purpose of life-prediction of lead-free interconnects. Test assemblies has been fabricated and tested under Joint Electron Device Engineering Council (JEDEC) JESD22-BI11 specified condition for mechanical shock. Model predictions have been correlated with experimental data. [ABSTRACT FROM AUTHOR]

The microstructure, mechanical response, and failure behavior of lead-free solder joints in electronic assemblies are constantly evolving when exposed to isothermal aging and/or thermal cycling environments. A direct and deleterious effect on packaging reliability has been observed during elevated temperature isothermal aging for fine-pitch ball grid array (BGA) packages with Sn-1.0Ag-0.5Cu (SAC105), Sn-3.0Ag-0.5Cu (SAC305), and Sn-37Pb solder ball interconnects. Package sizes range from 19 mm with 0.8-mm pitch BGAs to 5 mm with 0.4-mm pitch BGAs with three different board finishes (ImSn, ImAg, and SnPb) previously studied. This paper presents the latest results from an on-going investigation on the aging temperatures were 25^\circC, 55^\circC, 85^\circC, and 125^\circC, applied for a period of 12 months. Subsequently, the specimens were thermally cycled from -40^\circC to 125^\circC with 15 min dwell times at the high temperature. Weibull analysis of failures versus cycle number show a \sim57\% reduction in package lifetimes when aged at 125^\circC compared to no aging for 19 mm BGAs, for MLFs the degradation is even worse, more than 58% reduction in experiment result. In contrast, the reliability performance of Sn-37Pb is much more stable over long time up to 12 months and temperature. We also study the evolution during isothermal aging, which is one of the major failure modes of solder joints due to its high homologous temperature. The degradation is observed for both SAC alloys on all tested package sizes and board finishes. For the 19 mm SAC105 case, e.g., there was a 53% (57%) reduction of characteristic lifetime at 125^\circC for 6 months (12 months) compared to room temperature aging. The trends are in the expected directions; namely, the reliability is reduced when using higher aging temperatures, smaller solder balls, and SAC105. The dominant failure mode can be associated with the growth of Cu6Sn5 intermetallic compounds during the aging, particularly on the pad side. [ABSTRACT FROM AUTHOR]

A direct and deleterious effect on packaging reliability has been observed during elevated temperature isothermal aging for fine-pitch ball grid array (BGA) packages with Sn-1.0Ag-0.5Cu (SAC105), Sn-3.0Ag-0.5Cu (SAC305), and Sn-37Pb solder ball interconnects. Package sizes ranging from 19 mm with 0.8-mm-pitch BGAs to 5 mm with 0.4-mm-pitch μ BGAs with three different board finishes (ImSn, ImAg, and SnPb) were evaluated. The aging temperatures were 25°C, 55°C, 85°C, and 125°C, applied for a period of 6 mo. Subsequently, the specimens were thermally cycled from -40°C to 125°C with 15-min dwell times at the high temperature. Weibull analysis of failures versus cycle number show a ~ 50% reduction in package lifetimes when aged at 125°C compared to the same at room temperature, with less dramatic but measurable reductions in lifetime at 85°C and even 55°C. In contrast, the reliability performance of Sn-37Pb is much more stable over time and temperature. The degradation was observed for both SAC alloys on all tested package sizes and board finishes. For the 19-mm SAC105 case, for example, there was a 53% (32%) reduction of characteristic lifetime at 125°C (85°C) compared to room temperature aging. The trends were in the expected directions; namely, the reliability was reduced when using higher aging temperatures, smaller solder balls, and SAC105. The dominant failure mode can be associated with the growth of Cu6Sn5 intermetallic compounds during the aging, particularly on the pad side. [ABSTRACT FROM AUTHOR]

Sn-Ag-based solders are susceptible to appreciable microstructural coarsening due to the combined effect of thermal and mechanical stimuli during service and storage. This results in evolution of the creep properties of the solder over time, necessitating the development of a thermo-mechanical history-dependent creep model for accurate prediction of the long-term reliability of microelectronic solder joints. In this paper, the coarsening behavior of Ag3Sn and Cu6Sn5 precipitates in ball grid array-sized joints of Sn-3.8Ag-0.7Cu solder attached to Ni bond-pads with four different thermo-mechanical histories is reported. Because of the substantial numerical superiority of Ag3Sn over Cu6Sn5, it was inferred that the evolution of mechanical properties during aging is controlled largely by the coarsening of Ag3Sn. An effective diffusion length (\barx) for Ag diffusion in Sn was defined, and it is shown to adequately describe the thermo-mechanical history dependence of Ag3Sn particle size. The shear creep behavior of these joints was experimentally characterized, and the entire creep data were fitted to a unified model combining exponential primary creep and power-law steady state creep. The parameter \barx was then incorporated into the creep equation to produce a unified creep model, which can adapt to thermo-mechanical history-dependent microstructural coarsening in the solder. Predictions using this creep law show very good agreement with experimental creep data for several different test and microstructural conditions. [ABSTRACT FROM PUBLISHER]

Abstract: Nanoparticles were prepared with a consumable-electrode direct current arc (CDCA) technique. The results showed that the calorimetric melting onset temperature of the nanoparticles of SnAgCu solder alloy could be as low as 179°C, equivalent to that of the traditionally used SnPb eutectic alloy (183°C). Moreover, the homogenous melting model (HMM) and Gibbs–Thomson equation were employed to theoretically estimate the size-dependent melting temperature of the as-prepared nanoparticles. The structure and morphology of the nanoparticles were analyzed with a high-resolution transmission electron microscopy (HRTEM). The CDCA technique showed promising prospect in manufacturing large amounts of nanoparticles with controlled shape, small size, narrow particle size distribution and nearly oxide-free composition. This undoubtedly puts forward a novel feasible approach to manufacture high quality lead-free solders for electronic products. [Copyright &y& Elsevier]

Despite being expensive and time consuming, board-level drop testing has been widely used to assess the drop or impact resistance of the solder joints in handheld microelectronic devices, such as cellphones and personal digital assistants (PDAs). In this study, a new test method, which is much simpler and quicker, is proposed. The method involves evaluating the elastic strain energy and relating it to the impact resistance of the solder joint by considering the Young’s modulus of the bulk solder and the fracture stress of the solder joint during a ball pull test at high strain rates. The results show that solder joints can be ranked in order of descending elastic strain energy as follows: Sn-37Pb, Sn-1Ag-0.5Cu, Sn-3Ag-0.5Cu, and Sn-4Ag-0.5Cu. This order is consistent with the actual drop performances of the samples. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, effect of adding small amount of Er on the microstructure, physical and mechanical properties of Sn3.8Ag0.7Cu solder has been investigated. The purpose is to understand if the heavy rare earth Er has similar effect as light rare earth Ce or La on improving properties of SnAgCu lead-free solder. The results indicated that adding small amount of Er can evidently improve the wettability, mechanical strength and creep rupture life of the Sn3.8Ag0.7Cu solder alloy. It is pointed out that proper Er content in the Sn3.8Ag0.7Cu solder alloy should be in a range of 0.05–0.25wt%. Moreover, the size of intermetallic compounds (IMC) was measured quantitatively for the Sn3.8Ag0.7Cu solder alloys with various Er contents. It is felt that the increase in mechanical strength may be related to the refining of IMCs of the solder due to the addition of small amount of Er. [Copyright &y& Elsevier]

The global transition to lead-free (Pb-free) electronics has led component and equipment manufacturers to transform their tin-lead (SnPb) processes to Pb-free. At the same time, Pb-free legislation has granted exemptions for some products whose applications require high long-term reliability. However, due to a reduction in the availability of SnPb components, compatibility concerns can arise if Pb-free components have to be utilized in a SnPb assembly. This compatibility situation of attaching a Pb-free component in a SnPb assembly is generally termed "backward compatibility." This paper presents the results of microstructural analysis of mixed solder joints which are formed by attaching Pb-free solder balls (SnAgCu) of a ball-grid-array component using SnPb paste. The experiment evaluates the Pb phase coarsening in bulk solder microstructure and the study of intermetallic compounds formed at the interface between the solder and the copper pad. [ABSTRACT FROM PUBLISHER]

Abstract: The recrystallization behaviour of tin in various SnAgCu solder joints, chip-scale packages (CSPs), 0402 resistors and single-overlap shear specimens was studied. The objective of the study was to determine the effect of solder composition (hypoeutectic, eutectic and hypereutectic SnAgCu), the surface finish of printed circuit board (PCB) and the type of the solder joints on the recrystallization of tin during thermomechanical fatigue and isothermal creep. The results show that after reflow the solder joints consist only of a few tin grains. During thermomechanical fatigue recrystallization nucleates at the locations where the strain is concentrated, i.e. in the neck region of CSP, in the solder between the 0402 resistor and PCB and in the vicinity of voids. The recrystallized grains facilitate the occurrence of intergranular fracture. The results indicate that solder joints with hypoeutectic composition have a tendency to recrystallize more readily than joints with eutectic or hypereutectic composition. [Copyright &y& Elsevier]

In solder ball grid array (BGA) technology, solder joint reliability is one of the critical issues in microelectronics manufacturing industries. In this reliability aging study, Sn3.5AgO.7Cu solder joints were subjected to accelerated temperature cycling (ATC) test in TBGA assembly. Fatigue fracture occurred, very close to the solder/intermetallic compound (IMC) interface, at the TBGA component side due to the larger coefficient of thermal expansion (CTE) mismatch compared to the PCB side. During reflow, needle-type and scallop-type morphologies of (Cu,Ni)6Sn5 IMCs were formed at the TBGA component and PCB interfaces. In the process of thermal cycling, a layer of (Ni,Cu)3Sn4 IMC grew beneath the (Cu,Ni)6Sn5 IMC due to the out diffusion of Ni from the under bump metallization (UBM). After extended thermal cycling aging, Ni-Sn-P IMC was found between the (Ni,Cu)3Sn4 IMC and the In3P layer at the printed circuit board (PCB) interface. Grain ripening and spalling of (Cu,Ni)6Sn5 IMC grains into the solder joint was also observed in the process of thermal cycling. The spalling phenomena of (Cu,Ni)6Sn5 IMCs was caused by interface structure change and cyclic shear stresses and strains incurred during temperature cycling. [ABSTRACT FROM PUBLISHER]

In the current research, trace rare earth (RE) element Y was incorporated into a promising lead-free solder, Sn3.8Ag0.7Cu, in an effort to improve the comprehensive properties of Sn3.8Ag0.7Cu solder. The range of Y content in Sn3.8Ag0.7Cu solder alloys varied from 0 wt.% to 1.0 wt.%. As an illustration of the advantage of Y doping, the melting temperature, wettability, mechanical properties, and microstructures of Sn3.8Ag0.7CuY solder were studied. Trace Y additions had little influence on the melting behavior, but the solder showed better wettability and mechanical properties, as well as finer microstructures, than found in Y-free Sn3.8Ag0.7Cu solder. The Sn3.8Ag0.7- Cu0.15Y solder alloy exhibited the best comprehensive properties compared to other solders with different Y content. Furthermore, interfacial and microstructural studies were conducted on Sn3.8Ag0.7Cu0.15Y solder alloys, and notable changes in microstructure were found compared to the Y-free alloy. The thickness of an intermetallic compound layer (IML) was decreased during soldering, and the growth of the IML was suppressed during aging. At the same time, the growth of intermetallic compounds (IMCs) inside the solder was reduced. In particular, some bigger IMC plates were replaced by fine, granular IMCs. [ABSTRACT FROM AUTHOR]

Abstract: Optical microscopy was used to discern the different grain orientations and grain boundaries on the polished cross-sections of near-eutectic lead-free board-level SnAgCu (SAC) solder interconnects. Strain distributions with submicron accuracy of the deformations on the cross-sections of the solder interconnects were measured when the package was subjected to thermal loading from room temperature to 100°C. The results were correlated with the locations of different grains, grain boundaries and larger primary intermetallics. It revealed anisotropic nature of deformations in different grains of the SAC solder, which is similar to the thermomechanical behavior of pure Sn. The strain distribution in a solder interconnect varied significantly in different grain orientations. The primary intermetallics (Ag3Sn plates) also behaved very differently from the surrounding Sn matrix under the thermal loading. The demonstrated strain localization along the grain boundaries and bigger primary intermetallics provides a clue for the path of fatigue crack growth that leads to a failure because of anisotropic thermomechanical response of SAC solder during thermal cycling. [Copyright &y& Elsevier]

The effect of different reflow profiles on the reliability of lead-free (LF) Sn-3.0 Ag-0.5 Cu (wt.%) (SAC 305) ball grid array (BGA) devices assembled with a SnPb eutectic paste was investigated. The memory modules in a back-to-back configuration were reflowed on standard graphic cards finished with immersion silver (IAg) or hot air solder leveling (HASL) coatings. The reflow peak temperatures ranged from 209 degC to 227 degC, while the time above liquidus (TAL) varied from 45 to 80 s. Depending on the reflow conditions, the solder interconnects displayed varied degrees of SnPb and LF solders intermixing. It was established that in order to receive a homogeneous solder alloy, the reflow peak temperature had to be in the 218 degC-222 degC range. The reliability of solder interconnects of memory modules was assessed by subjecting the cards to 1500 cycles of accelerated thermal-cycling with a profile from 0 degC to 100 degC. It was found that the control SnPb/SnPb assemblies displayed superior reliability to that of the mixed assemblies. Regardless of the degree of homogeneity of the BGA balls, the predominant failure mode of the mixed solder joints was interfacial cracking through a Pb-rich phase near the intermetallic layer. In contrast, only partial cracks propagating diagonally through the bulk solder were present on the control boards. It was concluded that a combination of state of stress and segregation of the Pb-rich phase at the interface was responsible for the shortened thermal-mechanical fatigue life of the mixed solder interconnects [ABSTRACT FROM PUBLISHER]

Environmental and health concerns, due to the leaching of lead from landfills into ground water, have necessitated legislation that restricts the use of lead in electronics. The transition from the eutectic tin-lead composition used in electronic solders to lead-free solder is imminent. Understanding the impact of this transition on lead-free wave soldering is crucial because a large segment of printed circuit boards (PCBs) used in electronic home appliances are wave soldered. The usage of volatile organic compound (VOC)-free flux chemistry is expected to gather momentum in conjunction with lead-free wave soldering because of process requirements and environmental considerations. A thorough review of published literature indicated that there is limited information available on the application of water-soluble VOC-free flux chemistries for lead-free wave soldering. Consequently, the objectives of this research were to select a preferred VOC-free water-soluble flux chemistry, understand the process window of wave soldering using a 96.5Sn/3.0Ag/0.5Cu lead-free alloy, and study the impact of the lead-free wave soldering process on different surface finishes. Many of the earlier process recommendations were based on a solder pot temperature of 260 degC and higher. However, the packaging of through hole components may not withstand the higher pot temperature and longer contact time. Hence, assembly at a lower solder pot temperature and shorter contact time are highly desired. Consequently, experiments were conducted to verify the feasibility of reducing the solder pot temperature (250 degC) and the contact time (2 s). Three VOC-free fluxes, from three different vendors, were evaluated and the best flux chosen was used to establish the process window. It was demonstrated through this study that it is possible to wave solder, using a lead-free solder with low silver content, different surface finishes with a wide process window. The effect of lead-free process temperatures - - on the cleaning of the VOC-free water-soluble flux residues was evaluated. Residues were washed and cleaned using the existing equipment sets without any change in the process parameters. The process developed based on the initial set of experiments has been validated by the successful assembly of a number of lead-free prototype assemblies [ABSTRACT FROM PUBLISHER]

Abstract: The gold/lead-free solder system, or Au/SnAgCu is a potential flip chip interconnect solutions for fine-pitch applications. This paper studies the interfacial microstructures and initial isothermal solid–liquid interdiffusion kinetics during the first 3 s of bonding at 230–290 °C. As revealed by Scanning Electron Microscopy (SEM), different morphologies of AuSn, AuSn2 and AuSn4 are observed under different bonding conditions. The initial Au–Sn solid/liquid interdiffusion kinetics is discussed with respect to its microstructures. The rate of Au consumption is used as a measure of the rate of intermetallic compound (IMC) formation. The fitted power law relationship reveals kinetically that Au consumption follows the Arrhenius relationship with a time exponent of 0.5. Isothermal aging at temperatures between 125 °C and 165 °C gives rise to activation energies and the rate of Au consumption in solid–liquid interdiffusion to be two orders of magnitude faster than solid interdiffusion. [Copyright &y& Elsevier]

Abstract: Mechanical and microstructural properties of SnAgCu solder joints with hypoeutectic, eutectic and hypereutectic compositions were studied. Eutectic SnPb joints were used as the reference. Reflowed lap shear specimens made of FR-4 glass epoxy printed circuit boards with OSP and NiAu surface finishes were used in the tests. Mechanical properties and microstructural features of the joints were examined in the as-reflowed condition and after isothermal aging at 85°C for 1000h. Both the composition and PCB surface finish had a notable effect on the mechanical behaviour of the SnAgCu solder joints. The shear strength value of SnAgCu solder joints was mainly dependent on the size and distribution of Ag3Sn dispersions. The coarseness of the dispersions depends strongly on the amount of Ag in the solder alloy, the cooling rate after the reflow and the aging history of the solder joints. [Copyright &y& Elsevier]

Nanosized Cu6Sn5 dispersoids were incorporated into Sn and Ag powders and milled together to form Sn-3Ag-0.5Cu composite solders by a mechanical alloying process. The aim of this study was to investigate the interfacial reaction between SnAgCu composite solder and electroless Ni-P/Cu UBM after heating for 15 min. at 240°C. The growth of the IMCs formed at the composite solder/EN interface was retarded as compared to the commercial Sn3Ag0.5Cu solder joints. With the aid of the elemental distribution by x-ray color mapping in electron probe microanalysis (EPMA), it was revealed that the SnAgCu composite solder exhibited a refined structure. It is proposed that the Cu6Sn5 additives were pinned on the grain boundary of Sn after heat treatment, which thus retarded the movement of Cu toward the solder/EN interface to form interfacial compounds. In addition, wetting is an essential prerequisite for soldering to ensure good bonding between solder and substrate. It was demonstrated that the contact angles of composite solder paste was <25°, and good wettability was thus assured. [ABSTRACT FROM AUTHOR]

Electroless Ni-P under bump metallization (UBM) has been widely used in electronic interconnections due to the good diffusion barrier between Cu and solder. In this study, the mechanical alloying (MA) process was applied to produce the SnAgCu lead-free solder pastes. Solder joints after annealing at 240°C for 15 min were employed to investigate the evolution of interfacial reaction between electroless Ni-P/Cu UBM and SnAgCu solder with various Cu concentrations ranging from 0.2 to 1.0 wt.%. After detailed quantitative analysis with an electron probe microanalyzer, the effect of Cu content on the formation of intermetallic compounds (IMCs) at SnAgCu solder/electroless Ni-P interface was evaluated. When the Cu concentration in the solder was 0.2 wt.%, only one (Ni, Cu)3Sn4 layer was observed at the solder/electroless Ni-P interface. As the Cu content increased to 0.5 wt.%, (Cu, Ni)6Sn5 formed along with (Ni, Cu)3Sn4. However, only one (Cu, Ni)6Sn5 layer was revealed, if the Cu content was up to 1 wt.%. With the aid of microstructure evolution, quantitative analysis, and elemental distribution by x-ray color mapping, the presence of the Ni-Sn-P phase and P-rich layer was evidenced. [ABSTRACT FROM AUTHOR]

Taking the most promising substitute of the Sn-3.8Ag-0.7Cu solder as the research base, investigations were made to explore the effect of rare earths (REs) on the creep performance of the Sn-3.8Ag-0.7Cu solder joints. The SnAgCu-0.1RE solder with the longest creep-rupture life was selected for subsequent research. Creep strain tests were conducted on Sn-3.SAg-0.7Cu and SnAgCu-0.1RE solder joints in the intermediate temperature range from 298 K to 398 K, corresponding to the homologous temperatures η = 0.606, 0.687, 0.748, and 0.809 and η = 0.602, 0.683, 0.743, and 0.804, respectively, to acquire the relevant creep parameters, such as stress exponent and activation energy, which characterize the creep mechanisms. The final creep constitutive equations for Sn-3.8Ag-0.7Cu and SnAgCu-0.1RE solder joints were established, demonstrating the dependence of steady-state creep rate on stress and temperature. By correcting the apparent creep-activation energy of Sn-3.8Ag-0.7Cu and SnAgCu-0.1RE solder joints from the experiments, the true creep-activation energy is obtained. Results indicated that at low stress, the true creep-activation energy of Sn-3.8Ag-0.7Cu and SnAgCu-0.1RE solder joints is close to the lattice self-diffusion activation energy, so the steady-state creep rates of these two solder joints are both dominated by the rate of lattice self-diffusion. While at high stress, the true creep-activation energy of Sn-3.8Ag-0.7Cu and SnAgCu-0.1RE solder joints is close to the dislocation-pipe diffusion activation energy, so the steady-state creep rates are dominated by the rate of dislocation-pipe diffusion. At low stress, the best-fit stress exponents n of Sn-3.8Ag-0.7Cu and SnAgCu-0.1RE solder joints are 6.9 and 8.2, respectively, and the true creep-activation energy of them both is close to that of lattice self-diffusion. At high stress, it equals 11.6 and 14.6 for Sn-3.8Ag-0.7Cu and SnAgCu-0.1RE solder joints, respectively, and the true creep-activation... [ABSTRACT FROM AUTHOR]

We have recently developed a thermodynamic database for micro-soldering alloys, alloy database for micro-solders (ADAMIS). ADAMIS which consists of the elements Ag, Bi, Cu, In, Pb, Sb, Sn, and Zn has been constructed by the calculation of phase diagrams (CALPHAD) method. The thermodynamic parameters for describing the Gibbs energy of the liquid and solid phases have been evaluated by optimizing the experimental data on phase boundaries and thermo-chemical properties. In this paper, the phase equilibria and the related thermodynamic properties pertaining to the Sn-Ag-X (X=Bi, In, Cu, and Zn) alloys are examined using ADAMIS. Typical examples of the isothermal and vertical section phase diagrams, liquidus surface, etc. for these promising lead-free solders are presented. In addition, ADAMIS is also applied to calculate the nonequilibrium solidification process using the Scheil model. [ABSTRACT FROM PUBLISHER]

In this paper, we report development of a new process for lead-free solder bumping with no flux residues, using stencil printing and hydrogen radicals, which can lessen both the environmental load and the manufacturing cost of solder bumping. In this process the reduction of the hydrogen radicals, instead of the flux, will eliminate the surface oxides of the stencil printed lead-free solder paste. Sn-3.0Ag-0.5Cu lead-free solder paste, which contains no residue flux was printed on an 8-in wafer. Hydrogen plasma was radiated for a minute during the reflow process, and the printed paste formed a bump. Reflow experiments without hydrogen radicals treatment were also carried out for comparison, where no successful reflow could be observed. [ABSTRACT FROM PUBLISHER]

Pb-free solder is one of the biggest issues in today's electronic packaging industry. This paper introduces a newly developed Sn/3.5Ag alloy plating process for wafer level bumping. The effects of Under Bump Metallization (UBM) on the process, interfacial reaction, and mechanical strength have been investigated. Four different types of sputtering-based UBM layers-TiW/Cu/electroplated Cu, Cr/CrCu/Cu, NiV/Cu, and TiW/NiV-were fabricated with eutectic Pb/63Sn and Sn/3.5Ag solder. The result shows that the Sn/Ag solder gains Cu or Ni from UBM's and becomes Sn/Ag/Cu or Sn/Ag/Ni during reflow process. Sn/Ag solder has higher reactivity with Cu and Ni than Pb/63Sn. The Intermetallic Compound (IMC) spalling from the interface between UBM/solder has been observed on Cr/CrCu/Cu and TiW/NiV UBM's. However, the IMC spalling phenomena did not decrease the bump shear strength with a bump size of 110 μm, whereas a size of 60 μm brought a decrease in shear value and failure mode change. [ABSTRACT FROM PUBLISHER]

The microstructure, joint strength and failure mechanisms of SnPbAg, SnAg and SnAgCu solders on Cu/Ni/Au BGA pad metallization were investigated after multiple reflows or high temperature aging. In the SnPbAg system, a two-layer structure, i.e., Ni3Sn4 and (Au, Ni)Sn4, was formed at the solder-substrate metallization interface after aging at 125, 150, and 175°C. However, such structure was not present in the two Pb-free solder systems. Only a layer of Ni3Sn4 intermetallic compound in the SnAg system and a layer of Cu-Sn-Ni-Au intermetallic compound in the SnAgCu system were found at respective interfaces, even after the two solder systems had been heat treated for 1000 h at the afore-mentioned temperatures. The formation of the (Au, Ni)Sn4 ternary compound in the SnPbAg system was due to re-settlement of Au at the interface which led to brittle failure in this system during ball shear testing. In contrast, SnAg and SnAgCu systems failed exclusively inside the solder ball during shear testing after aging at 150°C for up to 1000 h. The two Pb-free solder systems showed good resistance to thermal aging with the solder ball shear strength being maintained at 1.60 to 1.70 kgf. The SnPbAg system degraded in mechanical performance with aging time and had strength as low as 1.20 kgf after aging at 150°C for 1000 h. The growth rates of intermetallic compound layers at 125, 150, and 175°C aging temperatures and the activation energy for the formation of different intermetallic compound layers were also determined in this investigation. [ABSTRACT FROM PUBLISHER]

For a successful transition to Pb-free manufacturing in electronics assembly, it is critical to understand the behavior of Pb-free solders (in bulk and paste form) and their interaction with the Pb-free printed wiring board (PWB) finishes. This paper presents the results obtained from solder paste spread tests and wetting balance experiments with several Pb-free solder alloys and Pb-free PWB finishes. The solder alloys studied were Sn3.4Ag4.8Bi, Sn4.0Ag0.5Cu, Sn3.5Ag and Sn0.7Cu. Eutectic Sn37Pb was used as a reference. The PWB surface finishes were Sn, NiAu, Ag and OSP. Wetting balance experiments were conducted in air while the spread tests were performed in air and nitrogen to understand the effect of reflow atmosphere on the spreading. Surface analysis techniques such as Nomarski phase contrast microscopy, Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to characterize the as-received PWB finishes. Sequential electrochemical reduction analysis (SERA) was also performed on the as-received PWB test coupons and on the Sn test coupons after multiple reflow cycles. The effect of multiple reflow cycles on the wetting performance, spreading and the surface composition of the PWB finishes was studied. [ABSTRACT FROM PUBLISHER]

The constitutive behaviour of Sn96.5Ag3.5, Sn95.5Ag4Cu0.5 and Sn63Pb37 solder was investigated on ultra small flip chip solder joints (V=1×10−12 m3). In order to run experiments on these small specimens, a micro shear tester has been designed. The tester is optimised to achieve high precision. It is able to record force displacement hysteresis with a resolution of better than 1 mN and 20 nm for force and displacement measurements, respectively. It was found that the creep behaviour of the lead-free solders exhibit a very high dependence on stress (Sn96.5Ag3.5: n=11; Sn95.5Ag4Cu0.5: n=18), while the eutectic SnPb showed a low stress dependence of n=2. [Copyright &y& Elsevier]

Lead-free solder reflow process has presented challenges to no-flow underfill material and assembly. The currently available no-flow underfill materials are mainly designed for eutectic Sn-Pb solders. This paper presents the assembly of lead-free bumped flip-chip with developed no-flow underfill materials. Epoxy resin/HMPA/metal AcAc/Flux G system is developed as no-flow underfills for Sn/Ag/Cu alloy bumped flip-chips. The solder wetting test is conducted to demonstrate the fluxing capability of the underfills for lead-free solders. A 100% solder joint yield has been achieved using Sn/Ag/Cu bumped flip-chips in a no-flow process. A scanning acoustic microscope is used to observe the underfill voiding. The out-gassing of HMPA at high curing temperatures causes severe voiding inside the package. A differential scanning calorimeter (DSC) used to study the curing degree of the underfill after reflow with or without post-cure. The post-curing profiles indicate that the out-gassing of HMPA would destroy the stoichiometric balance between the epoxy and hardener, and result in a need for high temperature post-cure. The material properties of the underfills are characterized and the influence of underfill out-gassing on the assembly and material properties is investigated. The impact of lead-free reflow on the material design and process conditions of no-flow underfill is discussed. [ABSTRACT FROM PUBLISHER]

Sn-Ag-Cu (SAC) is now recognized as the standard lead free solder alloy for packaging interconnect in the electronics industry. This paper analyzes the performance of both SAC and eutectic Sn-Pb solder alloys on Kulicke & Soffa's (K&S') Ultra CSP® wafer level package (WLP) at a thermal cycling (TC) test. The Ultra CSP standard Al/Ni-V/Cu under bump metallurgy (UBM) system was used to analyze if this UBM system with SAC solder would produce acceptable reliability in the TC test. In this study, two TC tests were performed. In the first test, two parts were removed from the TC chamber about every 200 cycles to investigate the characteristics of deformation and crack growth in the SAC and eutectic Sn-Pb Ultra CSP solder joints during TC testing. These TC test results showed that both the SAC and eutectic Sn-Pb Ultra CSPs exhibited normal solder joint fatigue failures during the testing. The SAC Ultra CSP had an equal or 18% higher Weibull life than the eutectic Sn-Pb one. Based on these results it was concluded that the SAC Ultra CSP with the Al/Ni-V/Cu UBM system produces acceptable solder joint reliability in a TC test. The results also revealed that the deformation and crack growth characteristics of the SAC and eutectic Sn-Pb Ultra CSP solder joints were significantly different. The eutectic Sn-Pb solder joints showed significant inelastic shear deformation during the TC testing while the SAC solder joints did not display significant inelastic deformation even at the high temperature regime of the TC test. [ABSTRACT FROM PUBLISHER]

First, the light intensity (luminance) distributions reflected from quad flat package (QFP) gull wing lead solder fillets were calculated by a simple geometrical model, using a modified diffusion equation. The dependence of the microscope angle θ (= incident angle of light) on the highlight distribution from specular surfaces was obtained. Luminance distributions from top to toe fillets were experimentally observed, using Sn-Pb eutectic solder and two kinds of Pb-free solder (Sn-Ag-Cu and Sn-Zn-Bi systems) and the characteristics were compared with the simulation results. As the Sn-Pb solder fillet has a specular (or smooth) surface, it is not so difficult to identify the profiles of Sn-Pb fillets by changing θ. On the other hand, the luminance distributions for Pb-free solder were strongly affected by the surface roughness. However, it is not impossible to extract the characteristics of the fillet profile if wetting properties of Pb-free solder are taken into consideration. It was found for Pb-free solder that the fillet formation characteristics extraction becomes easy if elements of Bi and In are doped because the wetting properties were improved. In addition, some problems with characteristics extraction of fillet formation for Pb free solder are discussed from the viewpoint of an external feature inspection system [ABSTRACT FROM PUBLISHER]

This paper examines the assembly process for flip chip die with SnAgCu solder bumps and the results of liquid-to-liquid thermal shock testing. The SnAgCu alloy required a thicker dip layer of flux to achieve good wetting compared to the SnPb eutectic alloy. A liquid spray flux yielded more consistent solder wetting with the SnAgCu alloy. With both fluxes, a nitrogen reflow atmosphere was necessary with the SnAgCu alloy. A peak reflow temperature of 246°C was used for the assembly of the SnAgCu thermal shock test vehicles. A lower peak temperature of 235°C did not yield sufficient solder wetting. Liquid-to-liquid thermal shock testing was performed from -40°C to +125°C. The SnPb alloy performed slightly better than the SnAgCu and the dip flux was better that the spray flux. The degree of delamination with the SnAgCu alloy was significantly higher than with the SnPb alloy. Cracks in the underfill between adjacent solder balls were observed. The SnPb alloy extruded into these cracks more readily than the SnAgCu and created electrical shorts [ABSTRACT FROM PUBLISHER]

There is tremendous interest at present with Pb-free solder assembly in the surface mount assembly industry in response to recent Japanese and European initiatives and proposed governmental restrictions regarding Pb usage and disposal. Many different solder alloys have been proposed as potential Pb-free solder replacements and the most promising of these fall into the general alloy families of tin-silver (Sn-Ag), tin-silver-copper (Sn-Ag-Cu) and tin-silver-bismuth (Sn-Ag-Bi). Published melting point data on some of these alloys indicates that they should be capable of reduced reflow temperatures relative to the commonly available Sn-3.5Ag alloy, which melts at 221°C. Differential scanning calorimetry (DSC) and reflow visualization was used to characterize the melting and wetting of the Pb-free alloys and generate the practical reflow temperature requirements. This was compared to the DSC data to gain insight on the meaning of the DSC melting data for surface mount applications. The results show that, in general, the wetting performance of the Sn-Ag-Bi alloys are more similar to Sn-Ag and Sn-Ag-Cu than would be predicted by the major onset melting temperature data as measured by the DSC [ABSTRACT FROM PUBLISHER]

Solder paste is primarily used as a bonding medium for surface mount assemblies (SMA) in the electronics industry, and is typically deposited using the stencil printing process. Stencil printing is a very important and critical stage in the reflow soldering of surface mount devices, and a high proportion of all SMA defects are related to this process. This is likely to continue with the drive toward the introduction of lead-free solder pastes. Work is continuing on the metallurgical properties of these lead-free solders, including solder joint strength and material compatibility. However, the initial challenge for the new Pb-free formulations is in achieving repeatable solder deposit from print to print and from pad to pad. To meet this challenge, new flux formulations are being developed. For a smooth transition to Pb-free soldering formulations, a proper understanding of the solder paste printing performance is necessary. The key parameters that affect solder paste printing have been identified and are the subject of numerous studies. In lead-free solder paste, the replacement of lead with other elements (including Bi, Cu) changes the density of this dense suspension. In this paper, we investigate the effects of printer parameters, i.e. squeegee speed and pressure (defined as the process window) on the printing performance of a variety of lead-free solder pastes. A three-level design of experiment on these factors was used. Comparisons are presented with lead-rich solder pastes. The metal content of the lead-free solders had a significant effect on the process window [ABSTRACT FROM PUBLISHER]

The evolution of intermetallics at and near SnAgCu/Cu and SnAgCu/Ni interfaces was examined, and compared to the behavior, near PbSn/metal and Sn/metal interfaces. Two different solder compositions were considered, Sn93.6Ag4.7Cu1.7 and Sn95.5Ag3.5Cu1.0 (Sn91.8Ag5.1 Cu3.1 and Sn94.35Ag3.8Cu1.85 in atomic percent). In both cases, phase formation and growth at interfaces with Cu were very similar to those commonly observed for eutectic SnPb solder. However, the evolution of intermetallics at SnAgCu/Ni interfaces proved much more complex. The presence of the Cu in the solder dramatically altered the phase selectivity at the solder/Ni interface and affected the growth kinetics of intermetallics. As long as sufficient Cu was available, it would combine with Ni and Sn to form (Cu,Ni)6)Sn5 which grew instead of the Ni3Sn4 usually observed in PbSn/Ni and Sn/Ni diffusion couples. This growing phase would, however, eventually consume essentially all of the available Cu in the solder. Because the mechanical properties of Sn-Ag-Cu alloys, depend upon the Cu content, this consumption can be expected to alter the mechanical properties of these Pb-free solderjoints. After depletion of the Cu from the solder, further annealing then gradually transformed the (Cu,Ni)6Sn5 phase into a (Ni,Cu)3Sn4 phase. [ABSTRACT FROM AUTHOR]

New under bump metallization (UBM) is required for future microelectronics to minimize reliability concerns with solder interconnects. In this study, electroless FeP film was prepared as UBM. Solderability of electroless NiP, electrodeposite Fe and electroless FeP films with eutectic SnAgCu solder was investigated by static wetting tests and wetting balance measurements. Results revealed that the solderability of NiP film has almost no change with thermal aged for the film in air atmosphere increasing. The contact angles for FeP and Fe films with SnAgCu solder increased and the maximum wetting force decreased with heating time increasing from 0 h, 48 h, 89 h–160 h at 180 °C. But the solderability of FeP film was found to be better than those of NiP and Fe whether the films in base or thermal aged at 180 °C for 89 h. Even after thermal aged in air atmosphere at 180 °C for 160 h, the FeP also performed the smallest contace angle compared with the NiP and the Fe. Oxide layer on the surface of FeP was much easier to be removed by rosin mildly activated flux during reflow process because loose structure. It was proved to be the key for the highly solderability of electroless FeP. Image 1 • Solderability of electroless NiP has almost no change with oxide time increasing from 0 hour to 160 hours at 180 oC in air. • Solderability of electroless FeP and electrodeposite Fe films reduced with the oxide time increasing. • Solderability of FeP was found to be better than those of NiP and Fe whether in base or oxidation at 180 oC for 160 h. • Difference of oxide layer was proved to be the key for highly solderability of electroless FeP. [ABSTRACT FROM AUTHOR]

The article proposes a generalized high cycle fatigue evaluation methodology for solder joints based on a local stress finite element method (FEM) and compares with experimental results. A method to predict the damage initiation of surface mount technology (SMT) solder joints is accomplished in this article by making use of generic coupon level SAC387 solder specimens. High cycle fatigue (HCF) experiments conducted on generic solder specimens are followed by means of FKM guidelines, which are translated to microelectronic elements for the first time. The FEM predicted lifetime values of solder joints agree with the experimental results performed on SMT components. In addition, the overall results show that the predicted values act as a threshold damage line from which the solder joint failure regimes can be differentiated. The results also show the differences in the predicted damage line and failure line for SMT solder joints. • Generic coupon level solder specimen to predict the damage line of an SMT solder joint. • Simplistic SN method based on the FKM guidelines used first time in microelectronics. • Predicted damage line and failure line are different depending on the component type. [ABSTRACT FROM AUTHOR]