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

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

A non-ordinary state-based peridynamics modeling of fractures in quasi-brittle materials

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

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.

/pdf/characterizing-the-mechanical-properties-of-actual-sac105-4twiz9b6xs.pdf

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

http://ws2.binghamton.edu/park/publications/2010-1_Da_Yu_Free_Drop_Test.pdf

Dynamic responses of PCB under product level free drop impact

In this work, free drop impact responses of printed circuit boards (PCBs) mounted in cellular phones has been investigated to assess their dynamic responses and investigate the effects of fastening methods. The digital image correction (DIC) method was used in order to measure a full-field deformation of PCBs during drop from a certain height. Three different fastening techniques which have point or edge contact between the PCBs and the casings were considered. Along with the drop impact experiments, the impact response analysis using ANSYS/LS-DYNA has been performed. To validate the numerical model, the impact response has been compared with the experimental one extracted from the DIC of the PCB. The deformations of the numerical model are well matched with the experimental ones. The effects of assembly method are investigated to assess reliability of PCBs.

Influence of fastening methods on the dynamic response and reliability assessment of PCBS in cellular phones under free drop

This work develops an assessment methodology based on experiments and finite element analysis (FEA) to determine the solder joint fatigue life of electronic components under random vibration loading. Specially designed PCB with Ball Grid Array (BGA) packages attached was mounted to the Electro dynamic shaker and was applied to different random vibration excitations at the supports. Meanwhile, an event detector monitored the resistance of the daisy chained circuits and recorded the failure time of the electronic components. In addition accelerometers and dynamic signal analyzer were utilized to record the time history data of both the shaker input and the PCB's response, and to obtain the transmissibility function of the test vehicles. This finite element based fatigue life prediction approach consists of two steps: The first step aims at characterizing fatigue properties of the solder joint by generating its own S-N (stress-life) curve. A sinusoidal vibration over a limited frequency band centered at the test vehicle's 1st natural frequency was applied and the time to failure was recorded. The resulting stress was obtained from the FE model through harmonic analysis in ANSYS. Spectrum analysis specified for random vibration, as the second step, was performed numerically in ANSYS to obtain the response Power Spectral Density (PSD) of the critical solder ball. The volume averaged Von Mises stress PSD was calculated out of the FEA results and then was transformed into time history data through inverse Fourier transform. Rainflow cycle counting was used to estimate cumulative damage of the critical solder joint. The calculated fatigue life based on the Rainflow cycle counting results, the S-N curve, and the modified Miner's rule agreed with actual testing results.

Da Yu

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

Dynamic responses of PCB under product level free drop impact

Influence of fastening methods on the dynamic response and reliability assessment of PCBS in cellular phones under free drop

Finite element based fatigue life prediction for electronic components under random vibration loading