Improved predictions of lead free solder joint reliability that include aging effects (original) (raw)
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The Anand Parameters for SAC Solders after Extreme Aging
The mechanical behavior of lead free solder materials is often represented using the Anand viscoplastic constitutive model. This nine parameter model is built into popular commercial finite element codes, and is widely used in the electronic packaging industry. Reliability prediction results are often highly sensitive to the specified Anand parameters, and there are great variations in the available literature values for common solder alloys. In this work, we have explored the range of Anand parameters possible for four common SAC (SnAg -Cu) alloys by testing samples with a wide range of microstructures. The lead free solder materials tested include 98.5Sn1.0Ag0.5Cu (SAC105), 97.5Sn2.0Ag0.5Cu (SAC205), 96.5Sn3.0Ag0.5Cu (SAC305), 95.5Sn4.0Ag0.5Cu (SAC405). These SACN05 solders have various Ag contents from N = 1.0 to 4.0%, and all contain 0.5% Cu. For each lead free solder alloy, four different cooling profiles and resultant microstructures have been investigated that yielded vastly different mechanical behaviors. These included water quenched (WQ), reflowed (RF), reflowed + 6 months of aging at 100 o C, and reflowed + 12 months of aging at 100 o C. The nine Anand parameters were determined for each unique solder alloy and microstructure from a set of stress strain tests performed at three different strain rates and five different temperatures (15 sets of conditions). After deriving the Anand parameters for each alloy and microstructure, the stress-strain curves have been calculated for various temperatures and strain rates, and excellent agreement was found between the predicted results and experimental stress-strain curves. The large range of microstructures examined has allowed us to explore the extreme values of the material properties and Anand parameters possible for a given SACN05 alloy. The WQ microstructures are extremely fine, and yield high mechanical properties at the upper limits possible for the solder alloys. The RF + 6 months of aging and RF + 12 months of aging microstructures are highly coarsened, and yield similar and highly degraded mechanical properties. After such a long durations of aging, any further changes in the microstructure, mechanical response, and mechanical properties will be rather small. Thus, the results for these " extreme aging " cases can be regarded as approaching the highest level of mechanical behavior degradation possible for a lead free solder material. Such limiting values found for a severely aged SAC alloy can be used by designers as a conservative set of constitutive parameters in finite element simulations.
The effects of SAC alloy composition on aging resistance and reliability
Proceedings - Electronic Components and Technology Conference, 2009
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.
The effects of aging temperature on SAC solder joint material behavior and reliability
Proceedings - Electronic Components and Technology Conference, 2008
The effects of aging on mechanical behavior of lead free solders have been examined by performing creep tests on four different SAC alloys (SAC105, SAC205, SAC305, SAC405) that were aged for various durations (0-4 months) at room temperature (25degC), and several elevated temperatures (75, 100, and 125 degC). Analogous tests were performed with 63Sn-37Pb eutectic solder samples for comparison purposes. Variations of the creep properties were observed and modeled as a function of aging time and aging temperature. In addition, the chosen selection of SAC alloys has allowed us to explore the effects of silver content on aging behavior.
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.
Analysis and Modeling of Aged SAC-Bi Solder Joints Subjected to Varying Stress Cycling Conditions
Materials
Solder joints are subjected to varied stress cycle circumstances in the electronic packaging service life but are also influenced by aging. There has been limited investigation into the influence of aging and varying cycles on SnAgCu-Bi (SAC-Bi) solder joint fatigue. Cyclic fatigue tests were performed on solder joints of several alloys, including SnAgCu (SAC305), SnAgCu-Bi (SAC-Q), and SnCu-Bi (SAC-R). Individual solder joints were cycled under varying stress levels, alternating between mild and harsh stress levels. At least seven samples were prepared for each alloy by alternating between 25 mild stress (MS) cycles and three harsh stress (HS) cycles until the solder joint broke off. The impact of aging on Bi-doped solder joints fatigue under varied amplitude stress was examined and predicted for 10 and 1000 h under 125 °C. Because of the “Step-up” phenomenon of inelastic work, a new fatigue model was developed based on the common damage accumulation (CDA) model. The experimental r...
Comparing and Benchmarking Fatigue Behaviours of Various SAC Solders under Thermo-Mechanical Loading
2020 IEEE 8th Electronics System-Integration Technology Conference (ESTC), 2020
While the fatigue behaviours (including fatigue life predictions) of lead-free solder joints have been extensively researched in the last 15 years, these are not adequately compared and benchmarked for different lead-free solders that are being used. As more and more fatigue properties of lead-free solders are becoming available, it is also critical to know how fatigue behaviours differ under different mathematical models. This paper addresses the challenges and presents a comparative study of fatigue behaviours of various mainstream lead-free SnAg -Cu (SAC) solders and benchmarked those with lead-based eutectic solder. Creep-induced fatigue and fatigue life of leadbased eutectic Sn63Pb37 and four lead-free SAC solder alloys: SAC305, SAC387, SAC396 and SAC405 are analysed through simulation studies. The Anand model is used to simulate the inelastic deformation behaviour of the solder joints under accelerated thermal cycling (ATC). It unifies the creep and rateindependent plastic behaviour and it is used to predict the complex stress-strain relationship of solders under different temperatures and strain rates, which are required in the prediction of fatigue life using the fatigue life models such as Engelmaier, Coffin-Mason and Solomon as the basis of our comparison. The ATC was carried out using temperature range from − ℃ ℃. The fatigue damage propagation is determined with finite element (FE) simulation, which allows virtual prototyping in the design process of electronics devices. The simulation was carried out on a BGA (36 balls, × matrix) mounted onto Cu padded substrate. Results are analysed for plastic strain, Von mises stress, strain energy density, and stress-strain hysteresis loop. The simulation results show that the fatigue behaviours of lead-based eutectic Sn63Pb37 solder is comparable to those of lead-free SAC solders. Among the four SAC solders, SAC387 consistently produced higher plastic strain, strain energy and stress than the other solders. The fatigue life's estimation of the solder joint was investigated using Engelmaier, Coffin-Manson, and Solomon models. Results obtained show that SAC405 has the highest fatigue life (25.7, 21.1 and 19.2 years) followed by SAC396 (18.7, 20.3 and 17.9 years) and SAC305 (15.2, 13.6 and 16.2 years) solder alloys respectively. Predicting the fatigue life of these solder joints averts problems in electronics design for reliability and quality, which if not taken care of, may result in lost revenue. Predictive fatigue analysis can also considerably reduce premature failure, and modern analysis technique such as one used in this research is progressively helping to provide comprehensive product life expectancy data.
Volume 1: Advanced Packaging; Emerging Technologies; Modeling and Simulation; Multi-Physics Based Reliability; MEMS and NEMS; Materials and Processes, 2013
SnAgCu (SAC) solders undergo continuous microstructural coarsening during both storage and service. In this study, we use cross-sectioning and image processing techniques to periodically quantify the effect of isothermal aging quantitatively on phase coarsening and evolution, in SAC305 (Sn3.0Ag0.5Cu) solder. SAC305 alloy is aged for (24-1000) hours at 100C (~ 0.7-0.8T melt ). The characteristic parameters monitored during isothermal aging include size, volume fraction, and inter-particle spacing of both nanoscale Ag 3 Sn intermetallic compounds (IMCs) and micronscale Cu 6 Sn 5 IMCs, as well as the volume fraction of pure tin dendrites in SAC305 solder.
2018 IEEE 68th Electronic Components and Technology Conference (ECTC), 2018
Despite being widely investigated for the last two decades, solder joints thermomechanical durability assessment remains a major concern for industries wishing to switch from lead-based (SnPb) to lead-free electronics. Amongst the variety of lead-free solder compositions, 96.5Sn-3.0Ag-0.5Cu (SAC305) solder alloy has become the preferred substitute to classic SnPb solders. However, unlike SnPb assemblies, the return on experience is limited and the microstructure is very different for SAC305 solder joints. The use of SAC305 solder paste requires to understand the mechanical and fatigue behaviors of the soldered interconnects. This paper presents the experimentation based on strain gages measurements, allowing the determination of the shear stress-strain response of SAC305 solder joints subjected to different thermal cycling conditions. The area of the experimental shear strain-stress hysteresis loops gives the values of the strain energy density corresponding to each thermomechanical loading. The finite element modeling of the test assembly showed a good correlation between experimental and numerical strain energy densities. The experimental shear strain-stress curves also provide the necessary data to derive SAC305 solder joints constitutive laws.
Lead free solders are renowned as interconnects in electronic packaging due to their relatively high melting point, attractive mechanical properties, thermal cycling reliability, and environment friendly chemical properties. The mechanical behavior of lead free solders is highly dependent on the operating temperature. Previous investigations on mechanical characterization of lead free solders have mainly emphasized stress-strain and creep testing at temperatures up to 125 °C. However, electronic devices, sometimes, experience harsh environment applications including well drilling, geothermal energy, automotive power electronics, and aerospace engines where solders are exposed to very high temperatures from 125-200 °C. Mechanical properties of lead free solders at elevated temperatures are limited. In this work, we have investigated the mechanical behavior of several SAC and SAC+X lead free solder alloys including SAC305 (96.5Sn-3.0Ag-0.5Cu) and SAC_Q at extreme high temperatures up to 200 °C. Stress-strain tests were performed on as reflowed alloys at four elevated temperatures (T = 125, 150, 175, and 200 °C). In addition, changes of the mechanical behavior of these alloys due to long-term aging have been studied. Extreme care has been taken during specimen preparation so that the fabricated solder uniaxial test specimens accurately reflect the solder material microstructures present in actual lead free solder joints High temperature tensile properties of the solders including initial modulus, yield stress, and ultimate tensile strength have been compared. As expected, our results show substantial degradations of the mechanical properties of lead-free solders at higher temperatures and with aging. The degradations are even more significant when the samples are stored in a high temperature environment for a particular span of time. Furthermore, Comparison of the results for different solders has shown that the addition of dopants (e.g. Bi, Ni, and Sb) in the traditional SAC alloys improve their high temperature properties significantly.
2011 IEEE 61st Electronic Components and Technology Conference (ECTC), 2011
Solder joints in electronic assemblies are typically subjected to thermal cycling, either in actual application or in accelerated life testing used for qualification. Mismatches in the thermal expansion coefficients of the assembly materials leads to the solder joints being subjected to cyclic (positive/negative) mechanical strains and stresses. This cyclic loading leads to thermomechanical fatigue damage that involves damage accumulation, crack initiation, crack propagation, and failure. While the effects of aging on solder constitutive behavior (stress-strain and creep) have been examined in some detail, there have been no prior studies on the effects of aging on solder failure and fatigue behavior.