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1.
Temperature-induced solder joint fatigue is a main reliability concern for aerospace and military industries whose electronic equipment used in the field is required to remain functional under harsh loadings. Due to the RoHS directive which eventually will prevent lead from being utilized in electronic systems, there is a need for a better understanding of lead-free thermomechanical behavior when subjected to temperature variations. As solder joints mechanical properties are dependent of their microstructural characteristics, developing accurate solder joint fatigue models means to correctly capture the microstructural changes that undergo the solder alloy during thermal cycling. This study reports the Sn3.0Ag0.5Cu (SAC305) solder joints microstructural evolution during damaging temperature cycles. Electron BackScatter Diffraction (EBSD) analysis was conducted to assess the SAC305 microstructure corresponding to a specific damage level. Investigated microstructural features included the β-Sn grain size and crystallographic orientation, as well as the grain boundary misorientation and Ag3Sn intermetallic compound (IMC) size. As-reflowed and damaged components were also mechanically characterized using nanoindentation technique. The microstructural analysis of SAC305 solder joints prior to thermal cycling showed a highly textured microstructure characteristic of hexa-cyclic twinning with two β-Sn morphologies consisting of preferentially orientated macrograins known as Kara's beach ball, along with smaller interlaced grains. The main observation is that recrystallization systematically occurred in SAC305 solder joints during thermal cycling, creating a high population of misoriented grain boundaries leading to intergranular crack initiation and propagation in the high strain regions. The recrystallization process is accompanied with a progressive loss of crystallographic texture and twinning structure. Ag3Sn IMCs coalescence is another strong indicator of SAC305 solder damage since the bigger and more spaced the IMCs are the less dislocation pinning can prevent recrystallization from occurring. 相似文献
2.
J. Zhao Y. Mutoh Y. Miyashita T. Ogawa A. J. McEvily 《Journal of Electronic Materials》2001,30(4):415-421
Fatigue crack growth behavior of two typical solders 63Sn-37Pb and 95Pb-5Sn has been investigated under room temperature (20°C)
and frequency of 10 Hz. Fatigue crack growth behavior of the 63Sn-37Pb specimen tested at stress ratios up to 0.5 and the
95Pb-5Sn specimen tested at stress ratios up to 0.7 were dominantly cyclic dependent. Intergranular crack growth was observed
for the 63Sn-37Pb specimen tested at stress ratio of 0.7, which indicates that a crack grows under influence of creep. The
difference of effect of stress ratio on crack growth behavior between two solders may results from the difference of homologous
temperature. Fatigue crack growth mechanisms for solder materials are summarized as follows: A crack propagates in a transgranular
manner at low homologous temperature and low stress ratio, while it propagates along eutectic grain boundaries at high homologous
temperature and high stress ratio under influence of creep. At the intermediate homologous temperatures, a crack propagates
in a transgranular manner with some region of intergranular fracture. 相似文献
3.
Due to the high homologous temperature and fast cooling rates, the microstructures of SnAgCu (SAC) solders are in a meta-stable state in most applications, which is the cause of significant microstructural evolution and continuous variation in the mechanical behavior of the joints during service. The link between microstructures evolution and deformation behavior of Sn-4.0Ag-0.5Cu solder during isothermal ageing is investigated. The evolution of the microstructures in SAC solders are visualized at different scales in 3D by using a combination of synchrotron x-ray and focused ion beam/scanning electron microscopy tomography techniques at different states of ageing. The results show that, although the grain structure, morphology of dendrites, and overall volume fraction of intermetallics remain almost constant during ageing, considerable coarsening occurs in the Ag3Sn and Cu6Sn5 phases to lower the interfacial energy. The change in the morphometrics of sub-micron intermetallics is quantified by 3D statistical analyses and the kinetic of coarsening is discussed. The mechanical behavior of SAC solders is experimentally measured and shows a continuous reduction in the yield resistance of solder during ageing. For comparison, the mechanical properties and grain structure of β-tin are evaluated at different annealing conditions. Finally, the strengthening effect due to the intermetallics at different ageing states is evaluated by comparing the deformation behaviors of SAC solder and β-tin with similar grain size and composition. The relationship between the morphology and the strengthening effect due to intermetallics particles is discussed and the causes for the strength degradation in SAC solder during ageing are identified. 相似文献
4.
Grain-boundary character and grain growth in bulk tin and bulk lead-free solder alloys 总被引:1,自引:0,他引:1
A. U. Telang T. R. Bieler J. P. Lucas K. N. Subramanian L. P. Lehman Y. Xing E. J. Cotts 《Journal of Electronic Materials》2004,33(12):1412-1423
Grain-boundary deformation is the primary failure mode observed in solder joints. Understanding the effects of alloy composition
variations and cooling rates on microstructural stability and deformation processes will allow development of improved joints.
The effects of these variables on grain-boundary character were investigated in a pure-tin ingot and a reflowed sample; ingots
of Sn-3.5wt.%Ag and Sn-3.8wt.%Ag-0.7wt.%Cu; and solder balls with 1.63-wt.% or 3-wt.%Ag. The microstructure was characterized
using orientation imaging microscopy (OIM). After aging (150°C for 200 h), the fine-grained polycrystalline microstructure
in both pure-tin specimens grew considerably, revealing preferred misorientations and ledge formation at grain boundaries.
Aging of the alloy ingots showed only slight grain growth caused by precipitate pinning. The solder balls showed similar phenomena.
The role of alloying elements, cooling rate, and the anisotropy of the coefficient of thermal expansion (CTE) in tin on microstructural
evolution, grain-boundary character, and properties of solder joints are discussed. 相似文献
5.
Liang Zhang Cheng-wen He Yong-huan Guo Ji-guang Han Yong-wei Zhang Xu-yan Wang 《Microelectronics Reliability》2012,52(3):559-578
Lead free solder alloys for electronic assembly is being driven by environmental and health concerns regarding toxicity of lead and, more importantly, by the perceived economic advantage of marketing “green” products. Of the currently available lead free solders, SnAg has the greatest potential. In this solder, the Ag3Sn compound is distributed in a eutectic network throughout the β-Sn matrix and these results represent mechanical strength. In order to further improve the microstructures and properties of SnAg-based alloys, alloying elements such as rare earth, Zn, In, P, Cu, Ni and particles such as ZrO2, POSS are selected to meet the requirement of high reliability of high-density electronics devices. For SnAg solder bearing rare earth (Ce and La), the creep-rupture life of solder joints can be remarkably increased up to four times more than that of the original SnAg solder joints at room temperature, meanwhile, rare earths can dramatically reduce the thickness of IMCs layer at solder/pad interfaces and also refine the microstructure of the alloy which results in the enhancement of mechanical properties of the SnAg solder. Moreover, the addition of ZrO2 nanoparticles significantly refined the size of Ag3Sn due to the adsorption effect of the ZrO2 nanoparticles. This paper summarizes the effects of alloying elements and particles on the wettability, mechanical properties, creep behavior, microstructures, etc. of SnAg-based lead free solder alloys. 相似文献
6.
J.W. Ronnie Teo Z.F. Wang X.Q. Shi G.Y. Li S. Yuan 《Journal of Electronic Materials》2007,36(12):1635-1642
The effects of bonding temperature and applied load on the mechanical integrity of 80Au-20Sn solder joints and the optical
performance of laser diodes (LDs) are presented. Insufficient solder wetting at 280°C and poor joint integrity at an applied
load below 0.196 MPa resulted in solder failure during die shear test. As the bonding temperature and applied load increased,
the joint integrity and the optical performance improved. Shear testing further showed fracture in the LD due to the high
mechanical strength of 80Au-20Sn solder and good adhesion properties of the solder joint. Microstructure studies showed good
metallurgical stability with little interfacial intermetallic compound (IMC) formed. However, beyond an applied load of 0.523 MPa,
the LD performances degraded due to modification of the bandgap energy in the active region. From our experimentation, a bonding
window with good bonding integrity and high optical performance was, nevertheless, achieved. 相似文献
7.
The changes in microstructure and microhardness of Sn-0.5Ag, Sn-1.0Ag, and Sn-0.7Cu Pb-free solders were investigated during high temperature aging at 200 °C. As-solidified microstructures, revealed by cross-polarized light microscopy, consist of relatively large Sn grains in both Sn-Ag and Sn-Cu solders. Upon aging at 200 °C, 2 h, Sn grains become smaller compared to the as-solidified ones. In addition, the microhardness of Sn-Ag solders increases after 200 °C, 2 h aging, while that of Sn-Cu solder decreases. Detailed observation of the coarsening and redistribution of intermetallic particles in each system further explains this response of mechanical properties during high temperature aging. To investigate the effect of aging temperature, solders were aged at a lower temperature, 150 °C for up to 1000 h and compared with aging at 200 °C. The microstructural changes during the high temperature aging were characterized in terms of Sn grain size, crystal orientation, and IMC growth kinetics, and were further correlated with the changes of their mechanical properties. 相似文献
8.
Cerium (Ce)-containing Sn-3.9Ag-0.7Cu alloy exhibits desirable attributes of microstructural refinement, increased ductility, and mechanical shock performance, while possessing better oxidation resistance than other rare-earth-containing solders. In addition to the beneficial mechanical properties, it is imperative to study the reliability performance of novel solder alloys in the form of electromigration experiments, in comparison with Sn-3.9Ag-0.7Cu. In this study, electromigration tests were conducted on solder joints at elevated temperature with a constant current using a V-groove testing methodology. The microstructural change of solder joints during electromigration was investigated by scanning electron microscopy, and the void growth was monitored utilizing the three-dimensional (3D) x-ray microtomography imaging technique. The current density inside the solder matrix was determined by 3D microstructure-based finite-element modeling. Finally, the product of diffusivity and effective charge number of solder joints during electromigration was calculated from both marker displacement and 3D void growth. It was found that electromigration-induced Cu diffusion in Sn-3.9Ag-0.7Cu-0.5Ce alloy was greatly accelerated, and void formation at the cathode side was retarded as a result of finer microstructure and existence of CeSn3 intermetallic particles. 相似文献
9.
Effect of SiC Nanoparticle Additions on Microstructure and Microhardness of Sn-Ag-Cu Solder Alloy 总被引:1,自引:0,他引:1
In this work, lead-free composite solders were produced by mechanically mixing nominal 20 nm moissanite SiC particles with
Sn-3.8Ag-0.7Cu solder paste. The effects of the amount of SiC addition on the melting behavior, microstructure, and microhardness
of as-solidified composite solders were systematically investigated. In comparison with solder without the addition of SiC
nanoparticles, the subgrain of β-Sn, the intermetallic compounds (IMCs) average grain size and distance decreased significantly
in the composite solder matrix. This was possibly ascribed to the strong adsorption effect and high surface free energy of
the SiC nanoparticles. Our results showed that 0.05 wt.% addition of SiC nanoparticles could improve the microhardness by
44% compared with the noncomposite and that the average grain size and distance changed from 0.5 μm to 0.2 μm and from 0.6 μm to 0.32 μm, respectively. The refined IMCs, acting as a strengthening phase in the solder matrix, enhanced the microhardness of the
composite solders, in good agreement with the prediction of the classic theory of dispersion strengthening. 相似文献
10.
Numerical prediction of mechanical properties of Pb-Sn solder alloys containing antimony, bismuth and or silver ternary trace elements 总被引:1,自引:0,他引:1
Solder joint interconnects are mechanical means of structural support for bridging the various electronic components and providing
electrical contacts and a thermal path for heat dissipation. The functionality of the electronic device often relies on the
structural integrity of the solder. The dimensional stability of solder joints is numerically predicted based on their mechanical
properties. Algorithms to model the kinetics of dissolution and subsequent growth of intermetallic from the complete knowledge
of a single history of time-temperature-reflow profile, by considering equivalent isothermal time intervals, have been developed.
The information for dissolution is derived during the heating cycle of reflow and for the growth process from cooling curve
of reflow profile. A simple and quick analysis tool to derive tensile stress-strain maps as a function of the reflow temperature
of solder and strain rate has been developed by numerical program. The tensile properties are used in modeling thermal strain,
thermal fatigue and to predict the overall fatigue life of solder joints. The numerical analysis of the tensile properties
as affected by their composition and rate of testing, has been compiled in this paper. A numerical model using constitutive
equation has been developed to evaluate the interfacial fatigue crack growth rate. The model can assess the effect of cooling
rate, which depends on the level of strain energy release rate. Increasing cooling rate from normalizing to water-quenching,
enhanced the fatigue resistance to interfacial crack growth by up to 50% at low strain energy release rate. The increased
cooling rates enhanced the fatigue crack growth resistance by surface roughening at the interface of solder joint. This paper
highlights salient features of process modeling. Interfacial intermetallic microstructure is affected by cooling rate and
thereby affects the mechanical properties. 相似文献
11.
Youngseok Kim Shijo Nagao Tohru Sugahara Katsuaki Suganuma Minoru Ueshima Hans-Juergen Albrecht Klaus Wilke Joerg Strogies 《Journal of Electronic Materials》2014,43(12):4428-4434
The trends of miniaturization, multi-functionality, and high performance in advanced electronic devices require higher densities of I/O gates and reduced area of soldering of interconnections. This increases the electric current density flowing through the interconnections, increasing the risk of interconnection failure caused by electromigration (EM). Accelerated directional atomic diffusion in solder materials under high current induces substantial growth of intermetallic compounds (IMCs) at the anode, and also void and crack formation at the cathode. In the work discussed in this paper, addition of SiC nanoparticles to Sn-Ag-Bi-In (SABI) lead-free solder refined its microstructure and improved its EM reliability under high current stress. Electron backscattering diffraction analysis revealed that the added SiC nanoparticles refined solder grain size after typical reflow. Under current stress, SABI joints with added nano-SiC had lifetimes almost twice as long as those without. Comparison of results from high-temperature aging revealed direct current affected evolution of the microstructure. Observations of IMC growth indicated that diffusion of Cu in the SiC composite solder may not have been reduced. During current flow, however, only narrow voids were formed in solder containing SiC, thus preventing the current crowding caused by bulky voids in the solder without SiC. 相似文献
12.
The addition of Cu nanoparticles into the solder pastes by mechanical mixing method creates a positive effect on the microstructure refinement of the LED solder joints. The grain size of β-Sn and Cu6Sn5 decrease obviously due to the increasing concentration of the nanoparticles in the solder pastes. However, the addition of nanoparticles facilitates the formation of voids in the solder joints, especially when the concentration of nanoparticles is higher than 0.5 wt% in the solder pastes. Both the microstructure refinement and void percentage affect the shear strength of the solder joints. Since the increase of the void percentage is limited when the concentration of nanoparticles increases from 0 to 0.5 wt%, the microstructure refinement shows a dominant effect on the shear performance and thus improves the shear strength of the solder joints from 49.8 to 55 MPa. Further addition of nanoparticles in the solder pastes leads to a sharp increase of the void percentage. Consequently, the shear strength of the solder joints decreases from 55 to 48.8 MPa when the concentration of doped particles increases from 0.5 to 1 wt% in the solder pastes. 相似文献
13.
Improved mechanical properties in new,Pb-free solder alloys 总被引:7,自引:0,他引:7
The mechanical properties of solders benefit from uniform dispersion of fine precipitates and small effective grain sizes.
Metallurgical methods of attaining such a beneficial microstructure have been investigated in two new, near-eutectic, Pb-free
solder alloys systems—Sn-Zn-In (m.p. ∼188°C) and Sn-Ag-Zn (m.p.∼217°C). It has been found that small alloying additions of
Ag dramatically improve the mechanical properties of the ternary Sn-8Zn-5In alloy. The improvement is attributed to the elimination
of the coarse and nonuniform distribution of plate-like dendrites and refining the effective grain size in the solidified
microstructure. Also, small amounts of Cu dramatically improve the ductility in the ternary Sn-3.5Ag-lZn alloy. The quaternary
Sn-3.5Ag-lZn-0.5Cu has better mechanical properties than the binary Sn-3.5Ag alloy because it has a uniform fine dispersion
of precipitates and a small effective grain size. The combination of high mechanical strength and high ductility is likely
to yield improved fatigue resistance properties in the interconnection of electronic components. 相似文献
14.
M. S. Yeh 《Journal of Electronic Materials》2002,31(9):953-956
The Sn-20In-2.8Ag solder alloy is a potential lead-free solder for replacing the traditional Sn-Pb solders. In this study,
the mechanical properties of the bulk material are reported by tensile test at various strain rates and temperatures. The
Sn-20In-2.8Ag solder possessed a solidus and liquidus between 170.8°C and 195.5°C. The ultimate tensile strength (UTS) and
elongation were 59.3 MPa and 50.2% at a strain rate of 10−3 s−1 at room temperature. Moreover, the UTS of this alloy decreased, but its elongation increased, with increasing testing temperature.
Stress exponents of Sn-20In-2.8Ag alloy varied from 6.5 at room temperature to 4 at 100°C, and the activation energy for creep
was 51.0 kJ/mol at the higher temperature range from 50°C to 100°C. The typical intergranular creep fracture mode was observed
in Sn-20In-2.8Ag solder during tensile creep deformation. 相似文献
15.
Weimin Xiao Yaowu Shi Yongping Lei Zhidong Xia Fu Guo 《Journal of Electronic Materials》2006,35(5):1095-1103
Lead-free solders with excellent material properties and low cost are essential for the electronics industry. It has been
proved that mechanical properties of SnAgCu alloys can be remarkably improved with a minute addition of rare earth (RE) elements.
For comparison and optimization, three valuable solder candidates, Sn3.8Ag0.7Cu0.05RE, Sn3Ag0.5Cu0.05RE, and Sn2.9Ag1.2Cu0.05RE,
were chosen due to the excellent properties of their own SnAgCu basic alloys. Wetting properties, melting temperature, bulk
tensile properties, and joint tensile and shear properties were investigated. In addition, the microstructures of solder joints
were observed and the effects of microstructure on mechanical properties were analyzed. Experimental results indicated that
the tensile and shear strengths of solder joints were decreased from Sn3.8Ag0.7Cu0.05RE, Sn2.9Ag1.2Cu0.05RE, to Sn3Ag0.5Cu0.05RE,
in order. Such difference in mechanical properties could be attributed to the influence of slightly coarse or strong Cu6Sn5 scallops in the reaction layer as well as superior eutectic network and large volume percentage of large primary intermetallic
compounds (IMCs) inside the solder joints. It is also suggested that the size and volume percentage of large primary IMCs
inside the solder be controlled. In addition, serration morphology was observed at the edge of large primary and eutectic
IMCs in the three solder joints, which could be related to the content of Ag, Cu, and RE. The serration morphology was proved
to be beneficial to mechanical properties theoretically. Furthermore, the three alloys investigated possessed similar wetting
properties, melting temperatures, and bulk tensile properties. 相似文献
16.
Industry migration to leadfree solders has resulted in a proliferation of a wide variety of solder alloy compositions. The most popular amongst these are the Sn–Ag–Cu family of alloys like SAC105 and SAC305. Electronics subjected to shock and vibration may experience strain rates of 1–100/s. Electronic product may often be exposed to high temperature during storage, operation and handling in addition to high strain rate transient dynamic loads during drop-impact, shock and vibration. Properties of leadfree solder alloys at high strain rates at low and high temperatures experienced by the solder joint during typical mechanical shock events are scarce. Previous studies have showed the effect of high strain rates and thermal aging on the mechanical properties of leadfree alloys including elastic modulus and the ultimate tensile strength. The ANAND viscoplastic constitutive model has been widely used to describe the inelastic deformation behavior of solders in electronic components. In this study, SAC105 and SAC305 leadfree alloys have been tested at strain rates of 10, 35, 50 and 75/s at various operating temperatures of 50 °C, 75 °C, 100 °C and 125 °C. Full-field strain in the specimen have been measured using high speed imaging at frame rates up to 75,000 fps in combination with digital image correlation. The cross-head velocity has been measured prior-to, during, and after deformation to ensure the constancy of cross-head velocity. Stress–strain curves have been plotted over a wide range of strain rates and temperatures. Experimental data for the pristine specimen has been fit to the ANAND's viscoplastic model. 相似文献
17.
18.
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 Sn3.8Ag0.7Cu0.15Y 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. 相似文献
19.
This study investigates the microstructural evolution and kinetics of intermetallic (IMC) formation in Sn-3.5Ag-0.7Cu lead-free solder joints with different percentages of Sb element, namely, Sn-3.5Ag-0.7Cu-xSb (x=0, 0.2, 0.5, 0.8, 1.0, 1.5, and 2.0). To investigate the elemental interdiffusion and growth kinetics of IMC formation, isothermal aging test is performed at temperatures of 100/spl deg/C, 150/spl deg/C, and 190/spl deg/C, respectively. Scanning electron microscope (SEM) is used to measure the thickness of intermetallic layer and observe the microstructural evolution of solder joint. The IMC phases are identified by EDX and XRD. Results show that some of the antimony powders are dissolved in the /spl beta/-Sn matrix (Sn-rich phase), some of them participate in the formation of Ag/sub 3/(Sn,Sb) and the rest dissolves in the Cu/sub 6/Sn/sub 5/ IMC layer. There is a significant drop in IMC thickness when Sb is added to 0.8 wt%. Over this amount the thickness of the IMC increases slightly again. The activation energy and growth rate of the IMC formation are determined. Results reveal that adding antimony in Sn-3.5Ag-0.7Cu solder system can increase the activation energy, and thus reduce the atomic diffusion rate, so as to inhibit the excessive growth of the IMC. The solder joint containing 0.8 wt% antimony has the highest activation energy. SEM images reveal that the number of small particles precipitating in the solder matrix increases with the increase in Sb composition. Based on the observation of the microstructural evolution of the solder joints, a grain boundary pinning mechanism for inhibition of the IMC growth due to Sb addition is proposed. 相似文献
20.
Nano-sized, nonreacting, noncoarsening oxide dispersoids have been incorporated into solder alloys to create a new, improved
solder structure with an ultrafine grain size of ∼200–500 nm. The new solders exhibit significantly enhanced creep resistance
combined with increased strength. The well-known thermal instability problem with ultrafine-grained structure appears to have
been overcome in these solder alloys and the microstructure was seen to be quite stable upon high temperature exposure (e.g.
120°C). This is attributed to the presence of very fine dispersoid particles which impede grain boundary sliding and dislocation
movement. The dispersions are seen to have a profound effect on the mechanical deformation characteristics of the solders
with respect to creep. As much as three orders of magnitude reduction in the steady state creep rate has been achieved. The
new solders also exhibit improved ductility under high strain rate deformation and improved strength (4–5 times higher tensile
strength) at low strain rates. It is demonstrated that with a dispersion of TiO2 particles, the Pb-Sn eutectic solder with a melting point of 183°C can be made more creep-resistant than the 80Au-20Sn eutectic
solder with a much higher melting point of 278°C. The new creep-resistant solders can be useful for optical and optoelectronic
packaging in which dimensional stability of the assembled structure is essential. 相似文献