Analysis of Sn-Bi Solders: X-ray Micro Computed Tomography Imaging and Microstructure Characterization in Relation to Properties and Liquid Phase Healing Potential

This work provides an analysis of X-ray micro computed tomography data of Sn-xBi solders with x = 20, 30, 35, 47, 58 wt.% Bi. The eutectic thickness, fraction of eutectic and primary phase are analyzed. Furthermore, the 3D data is evaluated by means of morphology parameters, such as, shape complexity, flatness, elongation and mean intercept length tensor. The investigated alloys are categorized in three groups based on their morphology, which are described as “complex dominant”, “complex- equiaxed” and “mixed”. The mechanical behavior of Sn-Bi alloys in the semi-solid configuration and the correlation with microstructural parameters are discussed. A varying degree of geometric anisotropy of the investigated alloys is found through the mean intercept length tensor. Representative volume element models for finite element simulations (RVE-FEM) are created from tomography data of each alloy to analyze a correlation of geometric and elastic anisotropy. The simulations reveal an elastic isotropic behavior due to the small difference of elastic constants of primary and eutectic phase. A discussion of properties in the semi-solid state and liquid phase healing is provided.

Characterizing the conductivity of ICA joints by the mean intercept length of Ag flakes

Purpose – The purpose of this paper is to present a novel and alternative method for the characterization of isotropic conductive adhesive (ICA) joints’ conductivity by the calculation of the mean intercept length of conductive flakes in the cured joint. ICAs are widely used in the field of hybrid electronics or special printed circuit board applications, such as temperature sensitive or flexible circuits. The main quality parameters of the ICA joints are the conductivity and the mechanical strength. Design/methodology/approach – For the experiments, one-component Ag-filled thermoset ICA paste was used on FR4 printed circuit test board to join zero-ohm resistors. Six different curing temperatures were applied: 120, 150, 175, 210, 230 and 250°C. The conductivity of the joints was measured in situ during the curing process. Micrographs were taken from the cross-sectioned joints, and the mean intercept length was calculated on them after image processing steps. Findings – Results of the measured conductivity and the mean intercept length were compared, and acceptable correlation was found for what can be used for characterizing the conductibility of ICA joints. Research limitations/implications – Investigating and characterizing the conductivity of ICA joints by an image processing method. Originality/value – The main advantage of this method compared to the electrical measurements is that the conductivity characterization is possible on any kind of component. Therefore, this method can be used in any appliances not only in test circuits.

Grain Size Analysis Using Automated-EBSP

This work discusses using the automated Electron BackScatter Pattern (EBSP) technique of electron diffraction in the Scanning Electron Microscope (SEM) for measuring grain size in polycrystalline materials. A quantitative analysis of 2-D grain size from a standard metallographic section can be made in less than one hour using an automated-EBSP system on a traditional SEM and dedicated analysis software. Thus, the automated EBSP technique provides a useful and cost-effective way to determine grain size. A common measure used to describe grain size is mean intercept length (MIL) and the present discussion will be limited to determining MIL using EBSP.Grain size analysis using optical microscopy is strongly influenced by sample preparation, which involves etching of the polished section to reveal boundaries. Boundaries that are to be avoided in determining MIL, such as sub-grain boundaries and twin boundaries, may be revealed and mistaken for random high angle boundaries.

A Global Relationship Between Trabecular Bone Morphology and Homogenized Elastic Properties

An alternative concept of the relationship between morphological and elastic properties of trabecular bone is presented and applied to human tissue from several anatomical locations using a digital approach. The three-dimensional morphology of trabecular bone was assessed with a microcomputed tomography system and the method of directed secants as well as the star volume procedure were used to compute mean intercept length (MIL) and average bone length (ABL) of 4 mm cubic specimens. Assuming isotropic elastic properties for the trabecular tissue, the general elastic tensors of the bone specimens were determined using the homogenization method and the closest orthotropic tensors were calculated with an optimization algorithm. The assumption of orthotropy for trabecular bone was found to improve with specimen size and hold within 6.1 percent for a 4 mm cube size. A strong global relationship (r2 = 0.95) was obtained between fabric and the orthotropic elastic tensor with a minimal set of five constants. Mean intercept length and average bone length provided an equivalent power of prediction. These results support the hypothesis that the elastic properties of human trabecular bone from an arbitrary anatomical location can be estimated from an approximation of the anisotropic morphology and a prior knowledge of tissue properties.