Accelerated thermal fatigue of lead-free solder joints as a function of reflow cooling rate (original) (raw)
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Thermal cycling reliability of lead-free chip resistor solder joints
Soldering & Surface Mount Technology, 2004
The solder joint reliability of ceramic chip resistors assembled to laminate substrates has been a long time concern for systems exposed to hush environments such as those found in automotive and aerospace applications. This is due to a combination of the extreme t e m p e r a m excursions experienced by the assemblies along with the large coefficient of thermal expansion mismatches between the alumina bodies of the chip resistors and the glass-epoxy composites of the printed circuit boards (PCBs). These reliability challenges are exacerbated for components with larger physical size (distance to neutral point) such as the 2512 resistors used in situations where higher voltages and/or currents lead to power dissipations up to 1 Wan. In this work the thermal cycling reliability of several 2512 chip resistor lead free solder joint configurations has been investigated. In an initial study, a comparison has been made between the solder joint reliabilities obtained with components fabricated with both tin-lead and pure tin solder terminations. In the main portion of the reliability testing, two temperature ranges (-40 to 125 "C and -40 to 150 "C) and five different solder alloys have been examined. The investigated solders include the normal eutectic SnAgCu (SAC) alloy recommended by earlier studies (95.5Sn-3.8Ag-O.7Cu), and three variations of the lead free ternary SAC alloy that include small quaternary additions of bismuth and indium to enhance fatigue resistance. For each configuration, thermal cycling failure data has been gathered and analysed using two-parameter Weibull models to rank the relative material performances. The obtained lead free results have been compared lo data for standard 63Sn-37Pb joints. In addition, a second set of thermally cycled samples was used for microscopy studies to examine crack propagation, changes in the microstructure of the solders, and intermetallic growth at the solder to PCB pad interfaces.
Reliability of Lead-Free Solder Joints Under a Wide Range of Thermal Cycling Conditions
2011
In this paper, we report a comprehensive set of accelerated thermal cycling (ATC) tests that were performed on test vehicles with different package types, sizes, pitches, and solder joint alloy metallurgies using four different thermal cycling profiles: 0 to 100, -40 to 125, -55 to 125, and -60 to 150°C. Samples from the tests were analyzed for their failure modes, and failure rates were calculated by using Weibull statistics. The characterized life for each test condition was determined and analyzed. The impact of solder alloy metallurgies, package types, sizes, and pitches on acceleration factors of the ATC tests to fatigue life was also analyzed and discussed. The quantified discrepancies among several acceleration factors from different studies compared to the experimental data presented in this paper are illustrated. The results provide valuable guidance on the effects of package types, size, pitches, and solder joints alloy metallurgies on various ATC test conditions. In addition, failure analysis was performed at different stages of the tests for each thermal cycling condition. Dramatic failure mode shifts at extreme ATC conditions were observed. The significance and the long-term impact of the failure modes and failure mechanism shift between various ATC test conditions to the life prediction of lead-free solders are extensively discussed.
Thermal cycling reliability of lead free solders for automotive applications
2004
The solder joint reliability of ceramic chip resistors assembled to laminate substrates has been a long time concern for systems exposed to hush environments such as those found in automotive and aerospace applications. This is due to a combination of the extreme t e m p e r a m excursions experienced by the assemblies along with the large coefficient of thermal expansion mismatches between the alumina bodies of the chip resistors and the glass-epoxy composites of the printed circuit boards (PCBs). These reliability challenges are exacerbated for components with larger physical size (distance to neutral point) such as the 2512 resistors used in situations where higher voltages and/or currents lead to power dissipations up to 1 Wan. In this work the thermal cycling reliability of several 2512 chip resistor lead free solder joint configurations has been investigated. In an initial study, a comparison has been made between the solder joint reliabilities obtained with components fabricated with both tin-lead and pure tin solder terminations. In the main portion of the reliability testing, two temperature ranges (-40 to 125 "C and -40 to 150 "C) and five different solder alloys have been examined. The investigated solders include the normal eutectic SnAgCu (SAC) alloy recommended by earlier studies (95.5Sn-3.8Ag-O.7Cu), and three variations of the lead free ternary SAC alloy that include small quaternary additions of bismuth and indium to enhance fatigue resistance. For each configuration, thermal cycling failure data has been gathered and analysed using two-parameter Weibull models to rank the relative material performances. The obtained lead free results have been compared lo data for standard 63Sn-37Pb joints. In addition, a second set of thermally cycled samples was used for microscopy studies to examine crack propagation, changes in the microstructure of the solders, and intermetallic growth at the solder to PCB pad interfaces.
Thermal Fatigue-Life Prediction of Lead-Free Solder Joints
Electronic and Photonic Packaging, Electrical Systems Design and Photonics, and Nanotechnology, 2004
Reliability of lead-free solder joints is investigated. Emphasis is placed on the design for reliability (DFR) of lead-free solder joints. In particular, the thermal-fatigue life of the lead-free solder joints of a plastic ball grid array (PBGA) package assembly is predicted and discussed.
Thermomechanical damage accumulation during power cycling of lead-free surface mount solder joints
2008
It is well known that in surface mount technology (SMT), thermal strains in electronic assemblies are induced in the solder joints by the mismatch between the coefficients of thermal expansion (CTE) of the components, substrate and solder, both during their processing and in service. Therefore, thermo-mechanical damage is likely to occur in the solder and the principle reliability hazard in SMT assemblies is the resulting fatigue cracking of the solder fillet, caused by cyclic thermal stresses. These stresses may be caused by both cyclic variations in power dissipation within equipment and by external environmental temperature changes. Most work reported to date has focused on the effects of environmental temperature changes, although for many types of equipment power cycling may result in significant stresses. The present paper describes the experimental determination of the actual temperature distribution in a chip resistor assembly when it is powered. The paper also discusses the significance of such experimentally determined non-uniform temperature distributions in electronic assemblies to fatigue damage accumulation due to both power cycling and to cyclic variations in the ambient temperature whilst the chip resistor is powered. This fatigue damage accumulation study is carried out using finite element analysis.
Thermal Fatigue Evaluation of Pb-Free Solder Joints: Results, Lessons Learned, and Future Trends
JOM, 2015
Thermal fatigue is a major source of failure of solder joints in surface mount electronic components and it is critically important in high reliability applications such as telecommunication, military, and aeronautics. The electronic packaging industry has seen an increase in the number of Pb-free solder alloy choices beyond the common near-eutectic SnAg -Cu alloys first established as replacements for eutectic SnPb. This paper discusses the results from Pb-free solder joint reliability programs sponsored by two industry consortia. The characteristic life in accelerated thermal cycling is reported for 12 different Pb-free solder alloys and a SnPb control in 9 different accelerated thermal cycling test profiles in terms of the effects of component type, accelerated thermal cycling profile and dwell time. Microstructural analysis on assembled and failed samples was performed to investigate the effect of initial microstructure and its evolution during accelerated thermal cycling test. A significant finding from the study is that the beneficial effect of Ag on accelerated thermal cycling reliability (measured by characteristic lifetime) diminishes as the severity of the accelerated thermal cycling, defined by greater DT, higher peak temperature, and longer dwell time increases. The results also indicate that all the Pb-free solders are more reliable in accelerated thermal cycling than the SnPb alloy they have replaced. Suggestions are made for future work, particularly with respect to the continued evolution of alloy development for emerging application requirements and the value of using advanced analytical methods to provide a better understanding of the effect of microstructure and its evolution on accelerated thermal cycling performance.
IEEE 70th Electronic Components and Technology Conference (ECTC), 2020
In electronic packages, solder joints are frequently exposed to thermal cycling environment where temperature variations occur from very low to high temperature. These exposures can occur in real life applications as well as in accelerated thermal cycling tests used for the characterization of thermal-mechanical fatigue behavior. Due to temperature variations and CTE mismatches of the assembly materials, cyclic temperature leads to damage accumulation due to shear fatigue and material property evolves in the solder joints. In addition, the thermal cycling dwell periods at the high temperature extremes will cause thermal aging phenomena in the solder material. This leads to microstructural evolution and material property degradation. Further aging effects can occur during the ramp periods between the low and high temperature extremes of the cycling. While changes in solder materials during aging have been examined in detail in prior studies, there have been limited studies examining material evolution occurring during thermal cycling. In a previous study of the authors, mechanical behavior evolutions of SAC305 lead-free solder material under several different thermal cycling profiles have been reported. The results demonstrated severe degradations in the mechanical properties, especially for thermal cycles with the long ramp and dwell periods. In our other recent work, evolution of the mechanical behavior of real solder joints has been investigated. In the current investigation, these prior studies have been extended. In particular, the mechanical behavior evolutions in both bulk SAC305 solder samples and SAC305 solder joints have been investigated under the same slow thermal cycling profile, and then the results were compared. In the first part of this study, miniature bulk solder uniaxial test specimens were prepared by reflowing solder in rectangular cross-section glass tubes with a controlled temperature profile. After reflow solidification, the samples were placed into the environmental chamber and thermally cycled between-40 C to +125 o C under a stress-free condition (no load). The thermal cycle consisted of 150 minutes cycles with 45 minutes ramps and 30 minutes dwells. The test specimens were separated into groups that were subjected to various durations of cycling (e.g. 0, 10, 50, 100, 250 cycles, etc.). After the environmental exposures, stress-strain curves of the cycled uniaxial samples were recorded, and then the mechanical properties were measured including the effective elastic modulus (E), yield stress (YS), ultimate tensile strength (UTS). The evolutions of the mechanical properties were characterized as a function of number of applied thermal cycles. In the second part of this study, the evolution of the mechanical behavior in thermally cycled BGA solder joints was studied using nanoindentation. PBGA solder joint strip specimens were first prepared by cross sectioning BGA assemblies followed by surface polishing to facilitate nanoindentation testing. Single grain solder joints were tested since they had large regions of solder material with equivalent mechanical behavior, which could then be indented several times after various durations of cycling. After preparation, the solder joint strip samples were thermally cycled using the same thermal cycling profile as the bulk samples. At various points in the cycling, the package was taken out from the chamber, and nanoindentation was performed to obtain the modulus and hardness. This allowed for investigation of the evolution of the mechanical properties of the SAC305 solder joints with the duration of thermal cycling. The results for the thermally cycled bulk samples showed that the detrimental effects of aging are accelerated in a thermal cycling environment. Similar degradations were found in the BGA solder joints subjected to thermal cycling. The degradation for both bulk samples and solder joints showed exponential variation with number of cycles. However, the degradation rates were higher in the bulk solder samples relative to those in the real solder joints. For example, the effective elastic modulus and yield stress reduced by 69% and 43%, respectively, for the bulk samples; whereas for the real solder joints, these values both reduced by 26%.
Recent Lead-Free Solders Research Projects Thermal Fatigue Behavior of Sn-rich Pb-free Solders
2000
During device operation thermal fatigue damage occurs in solder joints due to the coefficient of thermal expansion mismatch between the different materials in the package. This damage accumulates and eventually leads to failure. In order to fully characterize the reliability of these lead-free solder alternatives, a fundamental understanding of the relationship between microstructure and fatigue behavior must be developed.
The Influence of Elevated Temperature Aging on Reliability of Lead Free Solder Joints
2007 Proceedings 57th Electronic Components and Technology Conference, 2007
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 (Ma, et al., ECTC 2006), we demonstrated that the observed material behavior variations of SAC405 and SAC305 lead free solders during room temperature aging (25 1-4244-0985-3/07/$25.00 ©2007 IEEE