Visualization of Microstructural Evolution in Lead Free Solders during Isothermal Aging Using Time-Lapse Imagery

2017 ◽  
Author(s):  
Nianjun Fu ◽  
Sudan Ahmed ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Microstructural Evolution ◽  
Isothermal Aging ◽  
Time Lapse ◽  
Lead Free ◽  
Lead Free Solders

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.

scholarly journals Comparison between SAC405 Lead-Free Solders and EN(P)EPIG and EN(B)EPIG Surface Finishes

2015 ◽  
Vol 773-774 ◽  
pp. 232-236 ◽  
Author(s):  
Osman Saliza Azlina ◽  
Ali Ourdjini ◽  
Mohd Halim Irwan Ibrahim
Keyword(s):  
Isothermal Aging ◽  
Optical Microscope ◽  
Hazardous Substances ◽  
Lead Free ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
Reflow Soldering ◽  
Soldering Process ◽  
Surface Finishes ◽  
Lead Free Solders

In electronics industries, most of them had to shifted their solder materials from leaded solders into lead-free solders due to the environmental concerns and follow the legislation of Restriction of use Hazardous Substances (RoHS). Thus, Sn-Ag-Cu solder is one of the choices that can replace the leaded solder and also offer better properties. This study investigates the comparison between Sn-4.0Ag-0.5Cu (SAC405) and EN(P)EPIG and EN(B)EPIG surface finishes. Reliability of solder joint has been assessed by performing solid state isothermal aging at 150oC for 250 up to 2000 hours. After reflow soldering process, (Cu,Ni)6Sn5intermetallic compound (IMC) is dominated at near centre of solder meanwhile (Ni,Cu)3Sn4IMC is dominated at near outside of solder ball.Moreover, aging time resulted in an increase in thickness and changed the morphology into more spherical, dense and large grain size. Analysis by optical microscope revealed that the IMC thickness of EN(B)EPIG produced thicker IMC compared to EN(P)EPIG surface finish during reflow as well as isothermal aging.

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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