SnPb Solder Research Articles

전단펀치-크리프 시험에 의한 리플로우 시간별 Pb-free 솔더 합금 접합부에 대한 고온 크리프 물성 평가

In this study, shear punch-creep (SP-Creep) at Sn-4Ag/Cu pad the joint was tested by using environment-friendly Pb-free solder alloy Sn-4Ag of electronic components. Pb eutectic alloy (Sn-37Pb) joints limited to environmental issues with reflow time (10sec, 30sec, 100sec, 300sec) according to two types of solder alloy joints are compared and evaluated by creep strain rate, rupture time and IMC (Intermetallic Compound) behavior. As the results, reflow time increases with increasing thickness of IMC can be seen at overall 100sec later in case of two solder joints on the IMC thickness of Sn-4Ag solder joints thicker than Sn-37Pb solder joints. In addition, when considering creep evaluation factors, lead-free solder alloy Sn-4Ag has excellent creep resistance more than Pb eutectic alloy. For this reason, the two solder joints, such as in the IMC (Cu6Sn5) was formed. However, the creep resistance of Sn-4Ag solder joints was largely increased in the precipitation strengthening effect of dispersed Ag3Sn with interface more than Sn-37Pb solder joints.

Thermal Cycling Reliability of Alternative Low-Silver Tin-based Solders

Sn-3.0Ag-0.5Cu (SAC305) alloy is the most widely used solder in electronic assemblies. However, issues associated with cost and drop/shock durability have resulted in a continued search for alternative solder alloys. One approach to improve the drop/shock reliability has been to reduce the silver content in Sn-Ag-Cu alloys. Another approach is doping Sn-Ag-Cu solder with additional elements. Moreover, conflicting results have been reported in literature on the effects of aging on Sn-Ag-Cu alloys. In 2008, International Electronics Manufacturing Initiative (iNEMI) started the “Characterization of Pb-Free Alloy Alternatives” project to provide a comprehensive study of fifteen tin-based solder interconnect compositions benchmarked against the eutectic tin-lead solder. For this study, temperature cycle durability was the primary focus and solders were selected to study the effect of varying silver content, microalloy additions, and aging. This paper reports the preliminary findings from one of the test conditions conducted under the iNEMI project. The cycles to failure for a temperature cycling test condition from −15°C to 125°C, with dwell times of 60 minutes at both extremes are presented. The test assembly consisted of sixteen 192 I/O BGAs and sixteen 84 I/O BGAs soldered on to LG451HR laminate. Preliminary findings revealed that the reduction of silver resulted in a reduction in cycles to failure. In all cases, the fifteen tin-based solders were more durable than the eutectic SnPb solder. Aging did not affect the cycles to failure in SAC105 solder; however, the cycles to failure decreased with aging in SAC305 solder. In addition, aging resulted in a wider distribution of cycles to failure in 192 I/O BGAs.

Interfacial Reaction of Sn-Ag-Cu Lead-Free Solder Alloy on Cu: A Review

This paper reviews the function and importance of Sn-Ag-Cu solder alloys in electronics industry and the interfacial reaction of Sn-Ag-Cu/Cu solder joint at various solder forms and solder reflow conditions. The Sn-Ag-Cu solder alloys are examined in bulk and in thin film. It then examines the effect of soldering conditions to the formation of intermetallic compounds such as Cu substrate selection, structural phases, morphology evolution, the growth kinetics, temperature and time is also discussed. Sn-Ag-Cu lead-free solder alloys are the most promising candidate for the replacement of Sn-Pb solders in modern microelectronic technology. Sn-Ag-Cu solders could possibly be considered and adapted in miniaturization technologies. Therefore, this paper should be of great interest to a large selection of electronics interconnect materials, reliability, processes, and assembly community.

Effects of Solvents in the Polyethylene Glycol Series on the Bonding of Copper Joints Using Ag2O Paste

The effects of reducing solvents on the bonding process using silver oxide paste in a copper joint were investigated. Three solvent types were tested: diethylene glycol (DEG), triethylene glycol (TEG), and polyethylene glycol (PEG). The strength of the joints was assessed by fracturing, which occurred at the interface of the copper oxide layer and the copper substrate in DEG and TEG samples and at the bonded interface in the PEG sample. Analysis of the samples revealed that, in the DEG and TEG samples, the copper substrate was oxidized during the bonding process, which compromised the shear strength of the joints. In contrast, the PEG sample exhibited nonuniform sintering of the silver layer while retaining good shear strength. It was found that the combination of DEG and PEG produced optimum shear strength in the copper joint, as PEG suppressed the growth of copper oxide and DEG promoted the formation of a dense sintered silver layer. The bonding strength achieved was higher than that of the gold-to-gold joint made using standard Pb-5Sn solder.

Welding Technology of Gold Alloy

Conducting ring is an electric transmission device to achieve current, video, data signal and power transmission between two relatively slewing mechanism, so it has been widely used in all kinds of precision turntable and inertial navigation equipment. The slip ring and brush wire of conducting ring are connected to other equipment by copper wire or copper transfer metal plates. Currently, Eutectic 63Sn-37Pb solder and electric iron manual welding are often used. But for gold alloy, when SnPb solder is used, gold element will dissolve in solder because Au dissolves in Sn easily, and brittleness intermetallic was produced at the interface during cooling, which embrittled the joint. This paper analyzed the solderability of gold alloy and copper, summed up the research status of soldering technology of gold alloy and copper in China and abroad. It pointed out that it is necessary and urgent to develop soldering technology of gold alloy with copper.

Effect of Mold Surface Roughness on the Interfacial Heat Transfer Coefficient During Solidification of Solder Alloys

Solder joints are strongly dependent on how well the solder alloy can wet the substrate. One of the parameters which can be used to characterize the wettability of solder alloys on a substrate is the heat transfer coefficient at the interface alloy/substrate, hi. This study focus on the effect of the surface roughness of the substrate on the interfacial heat transfer coefficient during solidification of solder alloys. A comparative study is carried out with two lead-free solders alternatives and the traditional Sn-Pb solder (Sn 0.7wt%Cu, Sn 3.5 wt%Ag and Sn 38wt%Pb, respectively). These alloys were directionally solidified using a solidification apparatus having a water cooled bottom made of low carbon steel with two different surface finishing: machined and polished. The experimental thermal data collected by thermocouples positioned along the casting length were used as input information into an Inverse Heat Transfer Code implemented in this work in order to determine the hi variation in time. A power–law function given by (where a and m are constants which depend on the alloy composition, substrate and melt superheat and t is the time) which is based on both theoretical and experimental analyses is proposed. The transient hi profile has a typical drastic reduction from a high initial value due to the development of an air gap, followed by a recovery to an essentially constant value. The literature generally reports a decrease in hi with increasing surface roughness. However, in the present work an opposite behavior has been detected, which is explained based on contact interactions between alloy and substrate that are subjected to thermal contraction and thermal expansion during the soldering process, respectively.

Effect of indium addition on the microstructural formation and soldered interfaces of Sn-2.5Bi-1Zn-0.3Ag lead-free solder

The microstructural formation and properties of Sn-2.5Bi−xIn-1Zn-0.3Ag (in wt%) alloys and the evolution of soldered interfaces on a Cu substrate were investigated. Apart from the relatively low melting point (about 195°C), which is close to that of conventional eutectic Sn-Pb solder, the investigated solder presents superior wettability, solderability, and ductility. The refined equiaxial grains enhance the mechanical properties, and the embedded bulk intermetallic compounds (IMCs) (Cu6Sn5 and Cu5Zn8) and granular Bi particles improve the joint reliability. The addition of In reduces the solubility of Zn in the β-Sn matrix and strongly influences the separation and growth behaviors of the IMCs. The soldered interface of Sn-2.5Bi-xIn-1Zn-0.3Ag/Cu consists of Cu-Zn and Cu-Sn IMC layers.

Electrorecrystallization of Metal Alloy

This work first reports the behavior of electrorecrystallization of metal alloy, solder in this study. The electrorecrystallization is the recrystallization of metal alloy induced by electrical current stressing without the need of prior treatment. The synchrotron radiation X-ray diffraction (XRD) in situ analysis shows that the crystal facets of the Pb matrix of 95Pb5Sn solder alloy gradually diminish during electrical current stressing. The XRD analysis incorporating with in situ synchrotron extended X-ray absorption for fine structure (EXAFS) reveals complete dissolution, giving rise to supersaturation, of the Sn-rich secondary phase upon current stressing. The supersaturation behavior was explained through the crystal relaxation of the Pb matrix induced by current stressing. The recrystallization gives rise to Sn nanorod. High resolution TEM analysis of the nanorod reveals the semi-coherent/incoherent interfaces and provides explanation for the formation of the Sn nanorod.

Analysis of the Electronic Assembly Repair Process for Lead-Free Parts Under Combined Loading Conditions

The conversion from tin-lead (SnPb) to lead-free electronics has created concern amongst engineers about the reliability of electronic assemblies and the ramifications that reliability changes may have on the life-cycle cost and availability of critical systems that use lead-free electronics. In this paper, the impact of lead-free solder on the repair of electronic assemblies subject to combined thermal and vibration loading is studied. The cost, repair time, and availability of boards are quantified using a previously developed repair simulator for a test board developed and tested by the Joint Council on Aging Aircraft & Joint Council on Pollution Prevention that includes ceramic leadless chip carrier, thin small outline package, and plastic ball grid array packaged parts using SnPb and lead-free solders. This paper describes the process of calibrating a physics-of-failure reliability simulator using experimental highly accelerated life testing test results for a specific board assembly and using the calibrated model to generate failure distributions corresponding to combined thermal and vibration loading over an actual product life cycle for use in the repair simulator. The results of the repair simulation indicate that longer dwell times appear to cause more damage than larger Δ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> ; under combined loading conditions, SnPb appears to be more reliable than tin-silver-copper (for the board and parts considered in this paper) and as a result, repair cost is lower; and the number of failures and repair times track repair costs (depending on the capacity of repair process).

Size and constraint effects on interfacial fracture behavior of microscale solder interconnects

The fracture behavior of solder joints has long been an important issue in the reliability evaluation of electronic components and packages. In this study, experimental and finite element methods were used to characterize the interfacial fracture behavior of “Cu-wire/solder/Cu-wire” sandwich-structured microscale Sn–3.0Ag–0.5Cu solder joints with different diameters (100–575μm) and thicknesses (35–325μm) under quasi-static micro-tension loading, with systematic comparison to Sn–37Pb solder joints. Dynamic stress intensity factors for the microcracks in Cu, Sn–3.0Ag–0.5Cu, and Sn–37Pb under pulse tensile loading and high speed propagation were calculated. The numerical simulation results showed that the interface stress intensity factors KII and KI for the crack set at the solder/IMC interface increased with increasing the thickness of the joints from 35μm to ∼125μm, and thereafter decreased and then became stable. With increasing the diameter of the joints, basically KI increases while KII decreases. Under the quasi-static micro-tension loading, the crack driving forces in Sn–3.0Ag–0.5Cu solder joints are lower than that in Sn–37Pb joints, and this means that fracture is less likely to occur in Sn–3.0Ag–0.5Cu solder joints than in Sn-joints. The rapid expansion of a high hydrostatic pressure region may enhance the mechanical performance of interconnects when the diameter-to-thickness ratios of the joints are very large. As the diameter of the solder joints increases, the evolution of the energy release distribution results in a change of the fracture position and mechanism in the interconnects. Compared to Sn–37Pb solder, the Sn–3.0Ag–0.5Cu lead-free solder shows a lower resistance to rapid crack propagation under constant tensile loading.

A Comparative Study of Soldering Temperatures and Materials on the Reliability of Photovoltaic Modules

To find out the important factors which decisively affect the soldering quality of photovoltaic modules, solar cells were soldered under different conditions (different temperatures, PbSn vs. SnAgCu solder, manual vs. semi-automatic). Experimental results show that the soldering quality of PbSn under 350°C in the semi-automatic soldering process was quite stable while the soldering quality of lead-free solder was generally unacceptable in the manual or semi-automatic process under different temperatures. This result indicates that the soldering process with lead-free solder still needs to be further improved. It was also found that most cracks were formed on the interface between the solder and the silver paste and then expanded outwards.

Impact of Isothermal Aging on the Long-Term Reliability of Fine-Pitch Ball Grid Array Packages With Different Sn-Ag-Cu Solder Joints

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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> 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 Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> intermetallic compounds during the aging, particularly on the pad side.

Study on melt properties, microstructure, tensile properties of low Ag content Sn–Ag–Zn Lead-free solders

Sn–Ag solders have been regarded as the most promising solders to replace Sn–Pb solders in the future, but the reliability and cost issues limit its use. Therefore a low-Ag content Sn–Ag–Cu solder, SAC105 was researched, which still has some problems. Sn–Ag–Zn solders are obviously superior in many aspects in comparison to Sn–Ag–Cu solders, but the low-Ag Sn–Ag–Zn solders were rarely studied. In this paper, properties of Sn–xAg–yZn (x=1, 1.5, 2, 3; y=1, 1.5, 2, 2.5, 3, 4) solders, including melt properties, microstructure, and tensile properties were investigated. It was found that reduction of Ag content in Sn–Ag–Zn solders leads to the same problems as in Sn–Ag–Cu solders in melt properties and tensile properties. Although Sn–xAg–1Zn solders have higher strength, the elongation is lower. Results show that melt properties and tensile properties can be improved by the optimization of Zn content, but excessive Zn additon could lead to worse properties as well. Sn–2Ag–2.5Zn and Sn–1.5Ag–2Zn solders were found to have optimized properties. In addition, relations between melt properties and microstructure, as well as microstructure and tensile properties, were discussed.

Texture evolution and its effects on growth of intermetallic compounds formed at eutectic Sn37Pb/Cu interface during solid-state aging

The growth orientation of Cu6Sn5 intermetallic compounds (IMCs) formed at the eutectic Sn37Pb/polycrystalline Cu interface during solid-state aging was investigated. The results indicate that the interfacial Cu6Sn5 grains exhibit textured growth under solid-state conditions, and their preferred orientations are affected by the initial joint preparation conditions. Cu6Sn5 grains in the [0001] direction normal to the interface are stable in solid and molten Sn37Pb solder at 200°C, but are rapidly consumed at 280°C. This effect leads to the formation of different textures in the Cu6Sn5 layer during the solid-state aging treatment of joints formed at 200 and 280°C. In addition, the influence of texture evolution on the growth of interfacial IMCs was evaluated. The results indicate that Sn diffusion is faster along the [0001] direction of the Cu6Sn5 crystal than along an angle of 25–45° to the [0001] direction; therefore, more IMCs are generated at the interface of the joints formed at 200°C than at those formed at 280°C under the same solid-state reaction conditions.

Effect of electromigration induced joule heating and strain on microstructural recrystallization in eutectic SnPb flip chip solder joints

A refinement of the lamellar microstructure was observed in eutectic SnPb solder joints in electromigration. Electromigration has both atomic flux and electron flow. The latter generated joule heating and the former caused strain. The formation of nanoscale lamellar microstructure spent a large amount of interfacial energy, and we proposed that the driving force comes from the strain induced by electromigration under a high current density. Kinetically, refinement of the lamellar microstructure required fast atomic diffusion at a high homologous temperature. The joule heating mainly from the on-chip Al interconnect lines tremendously increased the temperature of solder bumps and enabled fast atomic diffusion. The strain induced by electromigration, when combined with a high homologous temperature, could lead to recrystallization in the sample to form the nanoscale lamellae.

Multiscale microstructural characterization of Sn-rich alloys by three dimensional (3D) X-ray synchrotron tomography and focused ion beam (FIB) tomography

Abstract Sn-rich (Pb-free) alloys serve as electrical and mechanical interconnects in electronic packaging. It is critical to quantify the microstructures of Sn-rich alloys to obtain a fundamental understanding of their properties. In this work, the intermetallic precipitates in Sn–3.5Ag and Sn–0.7Cu, and globular lamellae in Sn–37Pb solder joints were visualized and quantified using 3D X-ray synchrotron tomography and focused ion beam (FIB) tomography. 3D reconstructions were analyzed to extract statistics on particle size and spatial distribution. In the Sn–Pb alloy the interconnectivity of Sn-rich and Pb-rich constituents was quantified. It will be shown that multiscale characterization using 3D X-ray and FIB tomography enabled the characterization of the complex morphology, distribution, and statistics of precipitates and contiguous phases over a range of length scales.

Sn-Ag-Cu-X 무연솔더로 솔더링 된 접합부의 진동파괴 거동

Environmental and health concerns over the lead have led to investigation of the alternative Pb-free solders to replace commonly used Pb-Sn solders in microelectronic packaging application. The leading candidates for lead-free solder alloys are presently the near eutectic Sn-Ag-Cu alloys. Therefore, extensive studies on reliability related with the composition have been reported. However, the insufficient drop property of the near eutectic Sn-Ag-Cu alloys has demanded solder compositions of low Ag content. In addition, the solder interconnections in automobile applications like a smart box require significantly improved vibration resistance. Therefore, this study investigated the effect of alloying elements (Ag, Bi, In) on the vibration fatigue strength. The vibration fatigue was conducted in 10~1000Hz frequency and 20Grms. The interface of the as-soldered cross section close to the Cu pad indicated the intermetallic compound () regardless of solder composition. The type and thickness of IMC was not significantly changed after the vibration test. It indicates that no thermal activities occurred significantly during vibration. Furthermore, as a function of alloying composition, the vibration crack path was investigated with a focus on the IMCs. Vibration crack was initiated from the fillet surface of the heel for QFP parts and from the plating layer of chip parts. Regardless of the solder composition, the crack during a vibration test was propagated as same as that during a thermal fatigue test.

Effect of silicon addition on mechanical and electrical properties of Sn–Zn based alloys rapidly quenched from melt

Abstract In the present study, the effect of Si additions (0.1–0.5 wt.%) on mechanical and electrical properties of Sn–12Zn–3Bi based alloys was studied and analyzed. The investigation indicates that the mechanical properties of quaternary alloy Sn–12Zn–3Bi–0.5Si are higher than that of binary Sn–12Zn and ternary Sn–12Zn–3Bi melt spun-alloys. The addition of silicon to the Sn–12Zn–3Bi ternary system improves the electrical resistivity of the alloy and lowers the melting temperature. The Sn–12Zn–3Bi–0.3Si alloy has a melting point around 195 °C. Electrical resistivity of Sn–Zn–Bi–Si solder alloys, 9–14 μΩ cm, is much lower than that of Sn–37Pb solder. Test results indicate that adding small amount of Si can evidently improve the solderibility, mechanical, creep resistance, melting point and electrical properties of the binary Sn–12Zn and ternary Sn–12Zn–3Bi alloys. The change in mechanical and electrical properties is discussed based on the microstructural observations.

Creep–Fatigue Crack Growth Behavior of Pb-Containing and Pb-Free Solders at Room and Elevated Temperatures

Fatigue crack growth tests of lead-containing (Sn-37Pb) and lead-free (Sn-3.0Ag-0.5Cu) solders were conducted at frequencies ranging from 0.1 Hz to 10 Hz at stress ratio of 0.1, at room temperature and at 70°C. The J-integral range (ΔJ) and the modified J-integral (C *) were used in assessing the cycle-dependent and time-dependent crack growth behavior for both solders. The experimental results showed that the crack growth behavior of both solders at the lower frequency and higher temperature was predominantly time dependent, whereas the crack growth behavior of both solders at the higher frequency and lower temperature was predominantly cycle dependent, with the transition in fatigue crack growth behavior from cycle dependent to time dependent expressed as f + 6500exp(1/T) = 6520. In both the cycle-dependent and time-dependent regions, the crack growth resistance of the lead-free solder was higher than that of lead-containing solder. Fracture surface observations showed that, as the frequency decreased and/or the temperature increased, the fracture path changed from transgranular to intergranular for Sn-37Pb solder, and from transgranular to mixed transgranular–intergranular for Sn-3.0Ag-0.5Cu solder.

Characterization of Sn-3.5Ag-1.0Cu Lead-Free Solder Prepared via Powder Metallurgy Method

The toxicity in the Sn-Pb solder has promoted the development of Pb-free solder in the electronics industries. Among the Pb-solders, the Sn-3.5Ag-1.0Cu solder is considered a potential replacement and being studied by many researchers. In the present study, the characteristics of Sn-3.5Ag-1.0Cu lead-free solder were studied. The raw materials were tin, silver and copper powders in micron size. The solder was prepared using powder metallurgy route which includes blending, compacting and sintering. Four blending times and two compacting pressures were used to investigate for optimum condition. The melting temperature of the samples were studied using differential scanning calorimeter (DSC) and the presence of Sn Ag, Cu were confirmed using x-ray diffraction analysis (XRD). Finally the effect of variables on the hardness of the solders is reported.