Time-Lapse Imagery and Quantitative Analysis of Microstructural Evolution of SAC305 BGA Joints During Extreme High Temperature Aging

2020 ◽  
Author(s):  
KM Rafidh Hassan ◽  
Mohammad S. Alam ◽  
Jing Wu ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Mechanical Properties ◽  
Aging Time ◽  
Microstructural Evolution ◽  
Solder Joints ◽  
Time Lapse ◽  
Lead Free ◽  
Aging Effects ◽  
Extreme High Temperature ◽  
Lead Free Solders ◽  
Temperature Aging

Abstract Solder joints provide mechanical support, electrical and thermal interconnection between packaging levels in microelectronics assembly systems. Proper functioning of these interconnections and the reliability of the electronic packages depend largely on the mechanical properties of the solder joints. Lead free solders are common as interconnects in electronic packaging due to their relatively high melting point, attractive mechanical properties, thermal cycling reliability, and environment friendly chemical properties. However, environmental conditions, such as, operating temperature, aging temperature, and aging time significantly affect these properties due to the microstructural evolution of the solder that occurs during aging. Moreover, 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 T = 125–200 °C. Mechanical properties as well as microstructural study of lead free solders at elevated temperatures are limited in literature. Previous investigations on the microstructural evolution mainly emphasized on aging at temperatures up to 125 °C. In addition, those studies were limited on investigating the coarsening of Ag3Sn IMC particles within the beta-Sn matrix. In this work, the microstructural evolutions of SAC305 (96.5Sn-3.0Ag-0.5Cu) BGA joints were investigated for different aging conditions utilizing Scanning Electron Microscopy (SEM). In particular, our approach has been to monitor aging induced microstructural changes occurring within fixed regions in selected lead free solder joints and to create time-lapse imagery of the microstructure evolution. Aging was performed at T = 125, 150, and 175 °C for several durations up to 20 days, and the topography of the microstructure of a fixed region was captured using the SEM system. This process generated several images of the microstructure as the aging progressed. We have also explored the Mechanical behavior, and aging effects of SAC305 solder joints at the extreme high testing temperature of T = 150 °C using the method of nanoindentation. To study the aging effects, solder joints were preconditioned for 0, 1, 5, 10, and 30 days at T = 125 °C in a box oven. Nanoindentation testing was then performed on the aged specimens at a test temperature of T = 150 °C to extract the elastic modulus, hardness, and creep performance of the aged material. As expected, the analysis of the evolving SAC305 BGA microstructure showed a significant amount of diffusion of silver and copper in the beta-tin matrix during aging. In addition, a very remarkable growth of copper-tin layer at solder joint and copper pad interface in the PCB side has been visualized and measured with aging time and temperature. The Quantitative analysis of the evolving microstructure showed that the particles coalesced during aging leading to a decrease in the number of particles. This caused an increase in the average diameter of the particles, which helped us to build a model to guide the growth of IMC particles at extreme high temperature aging. Nanoindentation test results also showed a huge degradation in mechanical properties with aging time increment.

Nanoindentation Characterization of Lead-free Solders and Intermetallic Compounds under Thermal Aging

2010 ◽  
Vol 2010 (1) ◽  
pp. 000314-000318
Author(s):  
Tong Jiang ◽  
Fubin Song ◽  
Chaoran Yang ◽  
S. W. Ricky Lee
Keyword(s):  
Mechanical Properties ◽  
Thermal Aging ◽  
Solder Joints ◽  
Lead Free ◽  
Small Range ◽  
Lead Free Solder ◽  
Solder Alloys ◽  
Aging Test ◽  
Free Solder ◽  
Lead Free Solders

The enforcement of environmental legislation is pushing electronic products to take lead-free solder alloys as the substitute of traditional lead-tin solder alloys. Applications of such alloys require a better understanding of their mechanical behaviors. The mechanical properties of the lead-free solders and IMC layers are affected by the thermal aging. The lead-free solder joints on the pads subject to thermal aging test lead to IMC growth and cause corresponding reliability concerns. In this paper, the mechanical properties of the lead-free solders and IMCs were characterized by nanoindentation. Both the Sn-rich phase and Ag3Sn + β-Sn phase in the lead-free solder joint exhibit strain rate depended and aging soften effect. When lead-free solder joints were subject to thermal aging, Young's modulus of the (Cu, Ni)6Sn5 IMC and Cu6Sn5 IMC changed in very small range. While the hardness value decreased with the increasing of the thermal aging time.

Evolution of Lead Free Solder Material Behavior Under Elevated Temperature Aging

2007 ◽  
Author(s):  
Hongtao Ma ◽  
Jeffrey C. Suhling ◽  
Yifei Zhang ◽  
Pradeep Lall ◽  
Michael J. Bozack
Keyword(s):  
Elevated Temperature ◽  
Room Temperature ◽  
Solder Joints ◽  
Material Behavior ◽  
Lead Free ◽  
Lead Free Solder ◽  
Room Temperature Aging ◽  
Free Solder ◽  
Lead Free Solders ◽  
Temperature Aging

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 °C) were unexpectedly large and universally detrimental to reliability. Such effects for lead free solder materials are much more dramatic at the higher aging temperatures (e.g. 100–150 °C) typical of the harsh 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. In the current work, we have explored the effects of elevated temperature isothermal aging on the mechanical behavior and reliability of lead free solders. The effects of aging on mechanical behavior have been examined by performing stress-strain and creep tests on SAC405 and SAC305 samples that were aged for various durations (0–6 months) at several elevated temperatures (80, 100, 125, and 150 °C). Analogous tests were performed with 63Sn-37Pb eutectic solder samples for comparison purposes. Variations of the temperature dependent mechanical properties (elastic modulus, yield stress, ultimate strength, creep compliance, etc.) were observed and modeled as a function of aging time and temperature. In this paper, we have concentrated our efforts on presenting the results for samples aged at 125 °C. In addition, the new elevated temperature aging data were correlated with our room temperature results from last year’s investigation. The results obtained in this work have demonstrated the significant effects of elevated temperature exposure on solder joints. As expected, the mechanical properties evolved at a higher rate and experienced larger changes during elevated temperature aging (compared to room temperature aging). After approximately 200 hours of aging, the lead free solder joint material properties were observed to degrade at a nearly constant rate. We have developed a mathematical model to predict the variation of the properties with aging time and aging temperature. Our data for the evolution of the creep response of solders with elevated temperature aging show that the creep behavior of lead free and tin-lead solders experience a “crossover point” where lead free solders begin to creep at higher rates than standard 63Sn-37Pb solder for the same stress level. Such an effect is not observed for solder joints aged at room temperature, where SAC alloys always creep at lower rates than Sn-Pb solder.

Effects of Thermal Cycling on the Mechanical and Microstructural Evolution of SAC305 Lead-Free Solder

2019 ◽  
Author(s):  
S. M. Kamrul Hasan ◽  
Abdullah Fahim ◽  
Jeffrey C. Suhling ◽  
Sa’d Hamasha ◽  
Pradeep Lall
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
High Temperature ◽  
Thermal Cycling ◽  
Microstructural Evolution ◽  
Lead Free ◽  
Lead Free Solder ◽  
Temperature Extreme ◽  
Aging Effects ◽  
Free Solder

Abstract Lead free electronic assemblies are often subjected to thermal cycling during qualification testing or during actual use. The dwell periods at the high temperature extreme during thermal cycling cause thermal aging phenomena in the solder material, including microstructural evolution and material property degradation. In addition, lead free solders can also experience aging effects during the ramp periods between the low and high temperature extremes of the cycling. In this study, the mechanical behavior evolution occurring in SAC305 lead free solder subjected to various thermal cycling exposures has been investigated. 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 from −40 C to +125 C under a stress-free condition (no load). Several thermal cycling profiles were examined including: (1) 90 minute cycles with 15 minutes ramps and 30 minutes dwells, (2) air-to-air thermal shock exposures with 30 minutes dwells and near instantaneous ramps, (3) 30 minute cycles with 15 minutes ramps and no dwells (saw tooth profile), (4) 150 minute cycles with 45 minutes ramps and 30 minutes dwells, and (5) no cycling (simple aging at the high temperature extreme). For each profile, 10–15 samples were cycled for various durations of cycling (e.g. 48, 96, and 240 cycles), which were equivalent to various aging times at the high temperature extreme of T = 125 C. After cycling, the stress-strain curves and mechanical properties including effective elastic modulus and Ultimate Tensile Strength (UTS) of all the cycled samples were measured. For each cycling profile, the evolutions of the mechanical properties were characterized as a function of the cycling duration, as well as the net aging time at the high temperature extreme. Comparison of the results of various thermal cycling profiles showed that the detrimental effects of aging are accelerated in a thermal cycling environment. Furthermore, microstructure evolution during thermal cycling has also been investigated to validate the observed mechanical properties degradation. The test results revealed that the mechanical properties degradation of SAC305 are higher in thermal cycling compared to simple equivalent aging. For example, the elastic modulus and UTS of SAC305 reduced by 41%, and 38%, respectively after 5 days aging whereas these properties reduced by 69%, and 51%, respectively after 5 days equivalent aging using thermal cycling profile #4 (240 cycles).

Formation and Mechanical Properties of Intermetallic Compounds in Sn-Cu High-Temperature Lead-Free Solder Joints

2010 ◽  
Vol 654-656 ◽  
pp. 2450-2454 ◽  
Author(s):  
De Kui Mu ◽  
Hideaki Tsukamoto ◽  
Han Huang ◽  
Kazuhiro Nogita
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Intermetallic Compounds ◽  
Solder Joints ◽  
Nickel Content ◽  
Lead Free ◽  
Lead Free Solder ◽  
Nickel Addition ◽  
Free Solder ◽  
Lead Free Solders

High-temperature lead-free solders are important materials for electrical and electronic devices due to increasing legislative requirements that aim at reducing the use of traditional lead-based solders. For the successful use of lead-free solders, a comprehensive understanding of the formation and mechanical properties of Intermetallic Compounds (IMCs) that form in the vicinity of the solder-substrate interface is essential. In this work, the effect of nickel addition on the formation and mechanical properties of Cu6Sn5 IMCs in Sn-Cu high-temperature lead-free solder joints was investigated using Scanning Electron Microscopy (SEM) and nanoindentation. It was found that the nickel addition increased the elastic modulus and hardness of the (Cu, Ni)6Sn5. The relationship between the nickel content and the mechanical properties of the IMCs was also established.

scholarly journals Effect of Co-Addition of Ag and Cu on Mechanical Properties of Sn–5Sb Lead-Free Solder

2021 ◽  
Author(s):  
Biao Yuan ◽  
Zhimin Liang ◽  
Zongyuan Yang ◽  
Fei Shen ◽  
Da Xu ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Young’S Modulus ◽  
Room Temperature ◽  
Solder Joints ◽  
Young's Modulus ◽  
Lead Free ◽  
Unloading Rate ◽  
Free Solder ◽  
Co Addition ◽  
Lead Free Solders

AbstractSn–Sb lead-free solders are considered to substitute the tin–lead solders due to their great mechanical properties. At room temperature, the mechanical properties of Ni/Au/Sn–5Sb/Au/Ni and Ni/Au/Sn–5Sb–0.3Ag–0.05Cu/Au/Ni linear solder joints were investigated by nanoindentation experiments at different loads. The results showed that the Sn–Sb intermetallic compound (IMC) was distributed in the β-Sn matrix in Ni/Au/Sn–5Sb/Au/Ni solder joints. Co-addition of Cu and Ag resulted in the formation of the rod-shaped Cu6Sn5 and the fine granular Ag3Sn IMCs. At the same load and loading/unloading rate, the indentation depth and residual indentation morphologies of Ni/Au/Sn–5Sb–0.3Ag–0.05Cu/Au/Ni solder joints were smaller than those of Ni/Au/Sn–5Sb/Au/Ni solder joints. The hardness of the two kinds of solder joints decreased with the increase in load, while the Young’s modulus was independent of load. In addition, compared to the Ni/Au/Sn–5Sb/Au/Ni solder joints, the hardness, Young’s modulus and stress exponents of Ni/Au/Sn–5Sb–0.3Ag–0.05Cu/Au/Ni solder joints achieved an improvement due to the co-addition of Ag and Cu.

Evolution of Lead Free Solder Material Behavior During Isothermal Aging

2006 ◽  
Author(s):  
Hongtao Ma ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall ◽  
Michael J. Bozack
Keyword(s):  
Isothermal Aging ◽  
Room Temperature ◽  
Material Behavior ◽  
Lead Free ◽  
Aging Effects ◽  
Uniaxial Test ◽  
Room Temperature Aging ◽  
Free Solder ◽  
Lead Free Solders ◽  
Temperature Aging

Solder materials demonstrate evolving microstructure and mechanical behavior that changes significantly with environmental exposures such as isothermal aging and thermal cycling. These aging effects are greatly exacerbated at higher temperatures typical of thermal cycling qualification tests for harsh environment electronic packaging. In the current study, mechanical measurements of thermal aging effects and material behavior evolution of lead free solders have been performed. Extreme care has been taken so that the fabricated solder uniaxial test specimens accurately reflect the solder materials present in actual lead free solder joints. A novel specimen preparation procedure has been developed where the solder uniaxial test specimens are formed in high precision rectangular cross-section glass tubes using a vacuum suction process. The tubes are then sent through a SMT reflow to re-melt the solder in the tubes and subject them to any desired temperature profile (i.e. same as actual solder joints). Using specimens fabricated with the developed procedure, isothermal aging effects and viscoplastic material behavior evolution have been characterized for 95.5Sn4.0Ag-0.5Cu (SAC405) and 96.5Sn-3.0Ag-0.5Cu (SAC305) lead free solders, which are commonly used as the solder ball alloy in lead free BGAs and other components. Analogous tests were performed with 63Sn-37Pb eutectic solder samples for comparison purposes. In our total experimental program, samples have been solidified with both reflowed and water quenching temperature profiles, and isothermal aging has been performed at room temperature (25 °C) and elevated temperatures (100 °C, 125 °C and 150 °C). In this paper, we have concentrated on reporting the results of the room temperature aging experiments. Variations of the temperature dependent mechanical properties (elastic modulus, yield stress, ultimate strength, creep compliance, etc.) were observed and modeled as a function of room temperature aging time. Microstructural changes during. room temperature aging have also been recorded for the solder alloys and correlated with the observed mechanical behavior changes.

Creep and Microstructural Evolution in Lead-Free Microelectronic Solder Joints

2003 ◽  
Author(s):  
I. Dutta ◽  
C. Park ◽  
S. Choi
Keyword(s):  
Microstructural Evolution ◽  
Life Prediction ◽  
Solder Joints ◽  
Creep Testing ◽  
Lead Free ◽  
Creep Model ◽  
Second Phase ◽  
Impression Creep ◽  
Microstructural Coarsening ◽  
Lead Free Solders

Microelectronic solder joints are typically exposed to aggressive thermo-mechanical cycling (TMC) conditions, resulting in significant strain-enhanced microstructural coarsening during service. This microstructural evolution produces continuously evolving mechanical properties during extended use. Since solder joint life is dictated largely by the creep strain range, it is necessary to develop microstructurally adaptive creep models for solders to enable accurate prediction of joint life. In this paper, we present (1) a new closed-form creep model incorporating microstructural coarsening in lead-free solders, which can be easily incorporated into life-prediction models; and (2) a methodology for impression creep testing of Sn-3.5Ag solders which can potentially enable creep testing of individual flip chip or BGA balls in a package. The proposed creep model incorporates the effects of both static and strain-enhanced coarsening of second phase intermetallic particles which are present in lead-free solders, and shows that as a joint undergoes TMC, the creep rate increases continuously, adversely impacting life. This inference is supported by the impression creep experiments, which are shown to capture the essential features of creep in Sn-Ag alloys, in accordance with the available literature. It is also shown that the creep resistance of a given alloy composition is strongly dependent on the microstructure, making it important that creep data used for joint life prediction be based on testing of actual joints or very tightly controlled microstructures.

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