In Situ Optical Creep Observation of Joint-Scale Tin–Silver–Copper Solder Shear Samples

The viscoplastic behavior of as-fabricated, undamaged, microscale Sn-3.0 Ag-0.5Cu (SAC305) Pb-free solder is investigated and compared with that of eutectic Sn-37Pb solder and near-eutectic Sn-3.8Ag-0.7Cu (SAC387) solder from prior studies. Creep measurements of microscale SAC305 solder shear specimens show significant piece-to-piece variability under identical loading. Orientation imaging microscopy reveals that these specimens contain only a few, highly anisotropic Sn grains across the entire joint. For the studied loads, the coarse-grained Sn microstructure has a more significant impact on the scatter in primary creep compared to that in the secondary creep. The observed lack of statistical homogeneity (microstructure) and joint-dependent mechanical behavior of microscale SAC305 joints are consistent with those observed for functional microelectronics interconnects. Compared with SAC305 joints, microscale Sn-37Pb shear specimens exhibit more homogenous behavior and microstructure with a large number of small Sn (and Pb) grains. Creep damage in the Pb-free joint is predominantly concentrated at highly misoriented Sn grain boundaries. The coarse-grained Sn microstructure recrystallizes into new grains with high misorientation angles under creep loading. In spite of the observed joint-dependent behavior, as-fabricated SAC305 is significantly more creep resistant than Sn-37Pb solder and slightly less creep resistant than neareutectic SAC387 solder. Average model constants for primary and secondary creep of SAC305 are presented. Since the viscoplastic measurements are averaged over a wide range of grain configurations, the creep model constants represent the effective continuum behavior in an average sense. The average secondary creep behavior suggests that the dominant creep mechanism is dislocation climb assisted by dislocation pipe diffusion.

Section: Objectives Of the Studymentioning

confidence: 99%

Section: Materials Measurementsmentioning

confidence: 99%

Section: Materials Measurementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Viscoplastic Creep Response and Microstructure of As-Fabricated Microscale Sn-3.0Ag-0.5Cu Solder Interconnects

Cuddalorepatta

Williams

Dasgupta

2010

“…Several previous studies have examined the creep behaviour of Sn-Ag-Cu, Sn-Ag and Sn-Cu solders in both bulk [8][9][10][11][12][13][14][15][16][17] and joint form, 13,14,[18][19][20][21][22][23][24][25][26][27][28][29] where variations in stress exponent (n) and activation energy (Q) values are reported with different proposed mechanisms. The disagreements may be justified by differences in testing methods, temperature ranges and sample preparation methods.…”

Section: Introductionmentioning

confidence: 99%

Evaluating Creep Deformation in Controlled Microstructures of Sn-3Ag-0.5Cu Solder

Gourlay

Britton

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.

Uniaxial Ratchetting Behavior of Solder Alloys and Its Simulation by an Elasto-Plastic-Creep Constitutive Model

Sasaki

Ohguchi

2011

Ratchetting deformation occurring at solder joints in electronic packaging is a concern for electronic devices. Therefore, ratchetting deformation due to thermal cycling at solder joints should be simulated by structural analysis employing tools such as the finite-element method (FEM). However, simulation of ratchetting deformation is difficult, and little modeling to simulate ratchetting deformation accurately has been reported. This work experimentally examines uniaxial ratchetting deformation of Pb-free and Pb-containing solder alloys to elucidate the effect of rate on uniaxial ratchetting. An elastoplastic-creep constitutive model is developed to simulate uniaxial ratchetting deformation. The constitutive model incorporates a method to determine the material constants simply from a small number of pure tensile tests and subsequent stress relaxation tests. Uniaxial ratchetting deformation of solder alloys was successfully simulated using this constitutive model and simple method for material constant determination.