Because failures in lead-free solder joints occur at locations other than the most highly shear-strained regions, reliability prediction is challenging. To gain physical understanding of this phenomenon, physically based understanding of how elastic and plastic deformation anisotropy affect microstructural evolution during thermomechanical cycling is necessary. Upon solidification, SAC305 (Sn-3.0Ag-0.5Cu) solder joints are usually single or tricrystals. The evolution of microstructures and properties is characterized statistically using optical and orientation imaging microscopy. In situ synchrotron x-ray measurements during thermal cycling are used to examine how crystal orientation and thermal cycling history change strain history. Extensive characterization of a low-stress plastic ball grid array (PBGA) package design at different stages of cycling history is compared with preliminary experiments using higher-stress package designs. With time and thermal history, microstructural evolution occurs mostly from continuous recrystallization and particle coarsening that is unique to each joint, because of the specific interaction between local thermal and displacement boundary conditions and the strong anisotropic elastic, plastic, expansion, and diffusional properties of Sn crystals. The rate of development of recrystallized microstructures is a strong function of strain and aging. Cracks form at recrystallized (random) boundaries, and then percolate through recrystallized regions. Complications arising from electromigration and corrosion are also considered.

The role of elastic and plastic anisotropy of Sn in recrystallization and damage evolution during thermal cycling in SAC305 solder joints

In this paper, thermal cycling tests and finite-element analysis (FEA) for a plastic ball grid array package with Sn-3.8Ag-0.7Cu lead-free solder joints have been performed. The solder joint fatigue lives were predicted and compared by using different 2-D and 3-D FEA models. The effects of solder constitutive models and fatigue life models on solder fatigue life prediction have been investigated. In order to obtain fatigue parameters, new averaging volumes were proposed for the solder fatigue life prediction. Different reference temperatures were simulated to investigate its effect on the solder fatigue life prediction. The effect of intermetallic compound thickness on solder joint fatigue life prediction was also investigated.

Fatigue Reliability Analysis of Sn–Ag–Cu Solder Joints Subject to Thermal Cycling

Method for measuring nanoscale local strain in a dual phase steel using digital image correlation with nanodot patterns

High temperature reliability of lead-free solder joints in a flip chip assembly

This paper presents the characterization of the mechanical properties of three lead-free solder alloys 95.5Sn-4.0Ag-0.5Cu (SAC405), 96.5Sn-3.0Ag-0.5Cu (SAC305), and 98.5Sn-1.0Ag-0.5Cu (SAC105) at the solder joint scale. Several actual ChipArray® ball grid array (CABGA) packages were cross-sectioned, polished, and used as test vehicles. Compressive tests were performed using a nanocharacterization system over the temperature range of 25°C to 105°C. Images of the cross-sectioned solder joints were recorded by microscope during the tests. The recorded images were then processed by using a digital image correlation (DIC) program to calculate the displacement and strain fields on the solder joints. Finite-element method (FEM) modeling was used to extract the Poisson’s ratio, Young’s modulus, and coefficient of thermal expansion (CTE) of the solder alloys over the temperature range. The methodology developed in this paper enables characterization of the mechanical properties of the actual solder joints at low strain range with high accuracy.

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Characterizing the Mechanical Properties of Actual SAC105, SAC305, and SAC405 Solder Joints by Digital Image Correlation

http://ws.binghamton.edu/park/publications/2011-1_Da_Yu_High-cycle_fatigue.pdf

High-cycle fatigue life prediction for Pb-free BGA under random vibration loading

http://ws.binghamton.edu/park/publications/2010-3_Tung_Nguyen_Glue_Reliability.pdf

Effect of glue on reliability of flip chip BGA packages under thermal cycling

http://ws.binghamton.edu/park/publications/2011-3_Tung_Nguyen_SAC.pdf

Characterization of elasto-plastic behavior of actual SAC solder joints for drop test modeling

Thermo-mechanical behavior of solder joints, especially the solder bumps located at the chip corners where most failures usually occur was investigated. Digital Image Correlation (DIC) technique with optical microscope was adopted to quantify the deformation behavior and strains of a solder bump of flip-chip package subjected to thermal loading. A flip-chip specimen was cross-sectioned after manual polishing process followed by wet etching method in order to generate natural speckle patterns with high enough contrast on the measuring surface for employing DIC technique. The sample was placed in a miniature heating chamber and subjected to in-situ thermal loading from 25 °C to 100°C. During the heating, sequential microscopic images of the cross-sectioned surface of a solder bump were acquired, and the deformation behavior and strain distributions were successfully measured with submicron accuracy by applying DIC technique on the captured images. The computed full-field displacement fields clearly depicted both normal and shear deformation of the solder bump under the thermal loading. In addition, from the strain fields, it was observed that strains were mostly concentrated on the bottom portion of solder bump near the pad connected to substrate. In order to assess the thermo-mechanical strains of the flip-chip interconnections more quantitatively, the average strains of solder joints at different locations were also measured and compared to one another. By doing so, the strain trends of solder bumps were effectively analyzed with respect to the distance to neutral point (DNP). Finally, finite element analysis was conducted by simulating the thermal loading applied in the experiments, and comparison between the simulation and experimental results of displacements and strains was made. The comparison results exhibited satisfactory agreement, which ensured the validity of the experimental data and methodology. This study can further expedite the studies of electronic-package reliability through fatigue and crack failure analysis of the solder joints due to thermal cyclic loading.© 2009 ASME

Tung T. Nguyen

Papers

High-cycle fatigue life prediction for Pb-free BGA under random vibration loading

Characterizing the Mechanical Properties of Actual SAC105, SAC305, and SAC405 Solder Joints by Digital Image Correlation

Effect of glue on reliability of flip chip BGA packages under thermal cycling

Characterization of elasto-plastic behavior of actual SAC solder joints for drop test modeling

Deformation and Strain Measurement of Flip-Chip Solder Bump Under In-Situ Thermal Loading