Aging-informed behavior of Sn3.8Ag0.7Cu solder alloys (original) (raw)
Related papers
Constitutive and Aging Behavior of Sn3.0Ag0.5Cu Solder Alloy
IEEE Transactions on Electronics Packaging Manufacturing, 2000
We describe double-lap shear experiments on Sn3.0Ag0.5Cu solder alloy, from which fits to Anand's viscoplastic constitutive model, power-law creep model, and to time-hardening primary-secondary creep model are derived. Results of monotonic tests for strain rates ranging from 4.02E-6 to 2.40E-3 1 , and creep response at stress levels ranging from 19.5 to 45.6 MPa are reported. Both types of tests were conducted at temperatures of 25 C, 75 C, and 125 C. Following an earlier study where Anand model and time hardening creep parameters for Sn3.8Ag0.7Cu and Sn1.0Ag0.5Cu solder alloys were reported, here we report power law model parameters so as to enable a comparison between all three alloys. Primary creep in Sn3.0Ag0.5Cu solder alloy is shown to be significant and are considered in addition to secondary creep and monotonic behavior. Aging influence on behavior is also shown to be significant. On the basis of experimental data, the following four aspects are discussed: 1) difference between testing on bulk versus joint specimen; 2) consistency between the creep and monotonic behaviors; 3) comparison against behaviors of Sn1.0Ag0.5Cu and Sn3.8Ag0.7Cu alloys as well as aganist Sn40Pb, 62Sn36Pb2Ag and 96.5Sn3.5Ag alloys; and 4) comparison of Sn3.0Ag0.5Cu and Sn3.8Ag0.7Cu relative to their aging response.
Constitutive Behavior of Sn3.8Ag0.7Cu and Sn1.0Ag0.5Cu Alloys at Creep and Low Strain Rate Regimes
IEEE Transactions on Components and Packaging Technologies, 2008
Constitutive models for SnAgCu solder alloys are of great interest at the present. Commonly, constitutive models that have been successfully used in the past for Sn-Pb solders are used to describe the behavior of SnAgCu solder alloys. Two issues in the modeling of lead-free solders demand careful attention: 1) Lead-free solders show significantly different creep strain evolution with time, stress and temperature, and the assumption of evolution to steady state creep nearly instantaneously may not be valid in SnAgCu alloys and 2) Models derived from bulk sample test data may not be reliable when predicting deformation behavior at the solder interconnection level for lead-free solders due to the differences in the inherent microstructures at these different scales. In addition, the building of valid constitutive models from test data derived from tests on solder joints must de-convolute the effects of joint geometry and its influence on stress heterogeneity. Such issues have often received insufficient attention in prior constitutive modeling efforts. In this study all of the above issues are addressed in developing constitutive models of Sn3.8Ag0.7Cu and Sn1.0Ag0.5Cu solder alloys, which represent the extremes of Ag composition that have been mooted at the present time. The results of monotonic testing are reported for strain rates ranging from 4.02E-6 to 2.40E-3 s 1. The creep behavior at stress levels ranging from 7.8 to 52 MPa is also described. Both types of tests were performed at temperatures of 25 C, 75 C and 125 C. The popular Anand model and the classical time-hardening creep model are fit to the data, and the experimentally obtained model parameters are reported. The test data are compared against other reported data in the literature and conclusions are drawn on the plausible sources of error in the data reported in the prior literature. Index Terms-Anand model, lead-free solders, primary creep, time-hardening creep model. I. INTRODUCTION T HERE exist several constitutive models in varying degrees of sophistication and ranges of applicability for describing the behavior of solder alloys. Broadly speaking however, constitutive models for solder alloys can be classified into Manuscript
Journal of Electronic Materials, 2015
Vickers hardness, Charpy impact and tensile properties of 16MND5 steel, a bainitic forging steel that is used for nuclear power reactor pressure vessel, were investigated before and after varied thermal aging durations at 350 o C up to 3,000 h. After thermal aging for 500 h, the steel exhibits a remarkable increase in the ductile-to-brittle transition temperature (DBTT), a slight increase in the hardness, and slight degradations in the yield stress, ultimate tensile strength and elongation at room temperature. These facts indicate thermal aging induced embrittlement of the steel, which are further evidenced by the intergranular cleavage cracks on fracture surfaces in impact tests and a wheel-spokes like fracture morphology in tensile tests. As thermal aging duration is further extended, the embrittlement seems saturated as manifested by consistent DBTTs and fracture morphologies. Based on the metallographic observations and Rietveld refinements of neutron diffraction patterns under different aging conditions, the possible mechanisms of the thermal aging induced embrittlement are discussed.
Creep-Fatigue Life Assessment for Sn-3.0Ag-0.5Cu Solder
Journal of Solid Mechanics and Materials Engineering, 2009
This paper describes the creep-fatigue life assessment of Sn-3.0Ag-0.5Cu solder under pull-push loading using fast-fast, fast-slow, slow-fast and strain-hold strain waveforms. Strain controlled creep-fatigue tests were carried out using solid bar specimen, and the effect of strain waveform on the creep-fatigue life was discussed. Creep-fatigue damage was evaluated by the linear damage rule, the frequency modified fatigue life, the ductility exhaustion model, the strain range partitioning method and the grain boundary sliding model. The strain range partitioning method and the grain boundary sliding model only predicted the creep-fatigue lives within a small scatter.
Creep behavior of the ternary 95.5Sn-3.9Ag-0.6Cu solder—Part I: As-cast condition
Journal of Electronic Materials, 2004
Compression creep tests were performed on the 95.5Sn-3.9Ag-0.6Cu (wt.%) solder. The specimens were aged prior to testing at 125°C, 24 h or 150°C, 24 h. Applied stresses were 2-40 MPa. Test temperatures were Ϫ25°C to 160°C. The 125°C, 24-h aging treatment caused the formation of coarsened Ag 3 Sn particle boundaries within the larger ternary-eutectic regions. The 150°C, 24-h aging treatment resulted in contiguous Ag 3 Sn boundaries in the ternary-eutectic regions as well as a general coarsening of Ag 3 Sn particles. The 125°C, 24-h aging treatment had only a small effect on the strain-time curves vis-à-vis the as-cast condition. Negative creep was observed at 75°C for time periods Ͼ10 5 sec and stresses of 3-10 MPa. The creep kinetics exhibited a sinh term (stress) exponent, p, of 5.3 Ϯ 0.6 and an apparent-activation energy, ∆H, of 49 Ϯ 5 kJ/mol when data from all test temperatures were included. A good data correlation was observed over the [Ϫ25-125°C] temperature regime. Steady-state creep kinetics exhibited a greater variability in the [125-160°C] regime because of the simultaneous coarsening of Ag 3 Sn particles. The aging treatment of 150°C for 24 h resulted in a more consistent stress dependence and better reproducibility of the creep curves. Negative creep was observed in samples aged at 150°C for 24 h when tested at Ϫ25°C, 25°C, and 75°C. The values of p and ∆H were 4.9 Ϯ 0.3 kJ/mol and 6 Ϯ 5 kJ/mol, respectively. Only a slight improvement in the data correlation was observed when the analysis examined separated [Ϫ25-75°C] and [75-166°C] temperature regimes. Creep testing did not cause observable deformation in any of the sample microstructures.
2007
The need for predicting fatigue life in solder joints is well appreciated at the present time. Currently, however, there are very few experimentally validated material parameters for popular SnAgCu alloys. Furthermore, the validity of Coffin-Manson life models, being empirical, also needs to be explored for these alloys which creep in a manner significantly different from SnPb solder alloys. In this paper, we present a modeling approach inspired by cohesive zone theory of modern fracture mechanics and Weibull distributions of material failure. The approach relies on the accurate estimation of inelastic strains at the crack tip estimated through finite element analysis, which are then used to make decisions on crack propagation. Like most popular cohesive zone models, the modeling approach presented here requires the estimation of two parameters. Unlike most cohesive zone models however, no special elements are needed in the finite element model and estimation of the parameters is more straightforward. We demonstrate the applicability of the modeling approach via the simulation of fatigue crack growth in Sn3.8Ag0.7Cu solder joints subjected to anisotropic thermal cycling. Anisotropic thermal cycling conditions were created experimentally using a simulated power cycling testing device and fatigue crack fronts were tracked at different life cycles using traditional dye-and-pry methods. The experiments were repeated for varying temperature profiles. Experimental results were coupled with numerical analysis to obtain fracture parameters for Sn3.8Ag0.7Cu. The model and the parameters were then validated by verifying their predictive ability against a variety of temperature profiles. In a separate study, the authors have developed a time hardening creep model for describing the behavior of Sn3.8Ag0.7Cu. The time hardening model accounts for primary and secondary creep and does not restrict itself to the assumption of steady state creep. The need for accurate estimation of - inelastic strains in the finite element model is thus met using a valid constitutive model to describe solder creep behavior. The ability of the model to predict three dimensional crack fronts for a variety of fatigue loading environments, with sufficient accuracy, is a key result of this work.
Evaluating Creep Deformation in Controlled Microstructures of Sn-3Ag-0.5Cu Solder
Journal of Electronic Materials, 2018
The reliability of solder joints is affected significantly by thermomechanical properties such as creep and thermal fatigue. In this work, the creep of directionally solidified (DS) Sn-3Ag-0.5Cu wt.% (SAC305) dog-bone samples (gauge dimension: 10 9 2 9 1.5 mm) with a controlled <110> or <100> fibre texture is investigated under constant load testing (stress level: $ 30 MPa) at a range of temperatures from 20°C to 200°C. Tensile testing is performed and the secondary creep strain rate and the localised strain gradient are studied by two-dimensional optical digital image correlation (2-D DIC). The dominating creep mechanisms and their temperature dependence are explored at the microstructural scale using electron backscatter diffraction (EBSD), which enables the understanding of the microstructural heterogeneity of creep mechanisms at different strain levels, temperatures and strain rates. Formation of subgrains and the development of recrystallization are observed with increasing strain levels. Differences in the deformation of b-Sn in dendrites and in the eutectic regions containing Ag 3 Sn and Cu 6 Sn 5 are studied and related to changes in local deformation mechanisms.
The influence of aging on the stress-strain and creep behavior of sac solder alloys
2010
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. In our prior work on aging effects, we have demonstrated that the observed material behavior variations of Sn-Ag-Cu (SAC) lead free solders during room temperature aging (25 o C) and elevated temperature aging (125 o C) were unexpectedly large and universally detrimental to reliability. Such effects for lead free solder materials are especially important for the harsh applications environments present in high performance computing and in automotive, aerospace, and defense applications. However, there has been little work in the literature, and the work that has been done has concentrated on the degradation of solder ball shear strength (e.g. Dage Shear Tester). Current finite element models for solder joint reliability during thermal cycling accelerated life testing are based on traditional solder constitutive and failure models that do not evolve with material aging. Thus, there will be significant errors in the calculations with the new lead free SAC alloys that illustrate dramatic aging phenomena.
Materials Science and Engineering: A, 2003
Understanding and quantification of creep behavior of lead-free solder joints are essential for lifetime prediction of electronic systems. This is especially true for circuits with surface mount and chip components that are subjected to severe environments and higher temperatures. Creep deformation behavior of Sn Á/4Ag Á/0.5Cu, Sn Á/3.5Ag Á/0.5Ni and Sn Á/2Ag Á/1Cu Á/1Ni solder alloys was determined at room temperature (25 8C) and at elevated temperature (85 8C) using miniature single shear lap joint specimens that are comparable in size to actual solder joints used in electronic packaging. Various creep parameters such as global creep strain, secondary creep rates as well as the strain for the onset of tertiary creep in the solder joint were determined. The effects of Cu and Ni alloy additions on the creep properties of eutectic Sn Á/3.5Ag solder joints were studied by comparing with the creep deformation behavior of eutectic Sn Á/3.5Ag solder joints that were used as the baseline. General findings in this study revealed that the creep resistance of Sn Á/4Ag Á/0.5Cu solder joints is comparable to but slightly higher than that of eutectic Sn Á/3.5Ag solder joints at both room and elevated testing temperatures, particularly at lower stresses. The Sn Á/3.5Ag Á/0.5Ni solder joints have comparable creep resistance to Sn Á/4Ag Á/0.5Cu and eutectic Sn Á/3.5Ag solder joints at 85 8C, but much better creep resistance at room temperature. The Sn Á/2Ag Á/1Cu Á/1Ni solder joints were two orders of magnitude less creep resistant than solder joints made with other solder materials at 85 8C. However, the shear strains for the onset of tertiary creep in Sn Á/2Ag Á/1Cu Á/1Ni solder joints were found to be the highest at 85 8C. Microstructural analysis showed significant creep deformation along Sn grain boundaries. #
Deformation behavior of solder alloys under variable strain rate shearing & creep conditions
The rate-dependent deformation behavior of Sn3.8Ag0.7Cu Pb-free alloy and Sn-Pb eutectic alloy under constant and variable shearing strain rates and creep conditions was studied systematically with thin-walled specimens using a biaxial servo-controlled tension-torsion material testing system. The shearing tests were conducted at strain rates between 10-6 /sec to 10-1 /sec. Variable strain rate tests were also conducted for sudden strain rates change and stress relaxation to study the post-yielding flow stress dependency on stress. Shearing creep tests were carried at room temperatures under a variety of stress level. It is believed that such a fundamental study of deformation behavior of solder alloys under complex stress conditions is important to understand effects of soldering processes and microstructures on solder interconnect reliability, and also to implement sophisticated 3-D time-dependent nonlinear FEM analyses on electronic packages and assemblies.