Anisotropic conductive film (ACF) is commonly used as underfill for flip chip assembly. The prese... more Anisotropic conductive film (ACF) is commonly used as underfill for flip chip assembly. The present study focuses on elastic recovery and stress distribution along the interfaces of particle-pads and underfill-pads associated with heat or a mechanical loading. In the same manner as the experimental process for ACF assemblies, ACF interconnection is simulated using FEM. Firstly, the properties of the nickel were determined by fitting FEM to the experimental results. After that, the nickel properties are used for ACF interconnection analysis. We found that delamination may also occur at a three-joint interface of a particle, a pad and an underfill at the lowest temperature during a heat cycle.
American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP, Nov 1, 1995
The characteristic of thermal stresses near the apex in dissimilar materials under a uniform temp... more The characteristic of thermal stresses near the apex in dissimilar materials under a uniform temperature change is theoretically and numerically investigated. The materials are composed of two isotropic homogeneous wedges with arbitrary angles. The dominant factor of thermal stresses near the apex is represented by Kr{sup p{minus}1}, where p{minus}1 is the order of the stress singularity and K indicates the intensity of the stress field. For the bonded structures of Cu/Si{sub 3}N{sub 4}, the relationship between the wedge angle {var_phi}{sub 1} of material 1 and the total angle {var_phi}{sub 1} + {var_phi}{sub 2} of the bonded wedge, in which K becomes zero, is clarified theoretically. Also, it is shown that the distribution of the intensity K for each root p is divided into two forms. Finally, a relation between the distribution of the thermal stresses near apex and characteristic length of the bonded structure is examined by FEM.
ABSTRACT Portable electronics devices such as mobile phone and portable music player become compa... more ABSTRACT Portable electronics devices such as mobile phone and portable music player become compact and improve their performance. High-density packaging technology such as CSP (Chip Size Package) and Stacked-CSP is used for improving the performance of devices. CSP has a bonded structure composed of materials with different properties. A mismatch of material properties may cause stress singularity, which lead to the failure of bonding part in structures.In the present study, a strain singular field near inter-face edge in three-dimensional joints is investigated using digital image correlation method. A specimen which silicon chip was embedded in resin is used in experiment and tensile load is applied to the specimen. Photograph of specimen surface is taken before and after loadings by laser microscope. Displacement on the surface was evaluated by the digital image correlation method (DICM) using data of surface pattern on the specimen, which the cross correlation coefficients for surface pattern are maximized. Strain on surface of specimen is calculated by using the moving least square method. On the other hand, 3D element free Galerkin method is applied to compute the displacement and strain distribution in a three-dimensional model of the specimen. In the element free Galerkin method, the physical values, i.e., displacement, strain and stress, can be obtained by using the displacement data at node. In this research, strain distribution near the edge of interface is computed based on the element free Galerkin method. Finally, the strain distribution obtained by the digital image correlation method and the moving least square method is compared with that obtained by the element free Galerkin method. The intensity of strain singularity is determined numerically and experimentally.
In the present paper, singular stress fields at the vertex on the interface in three-dimensional ... more In the present paper, singular stress fields at the vertex on the interface in three-dimensional bonded joints are analyzed using BEM. The order of stress singularity is determined solving an eigen equation based on FEM formulation and the stress distribution is expressed using the result of the eigen-value analysis. A simple relationship between the thickness of layer and a value of stress is introduced. Then, stress distributions for various thicknesses of layer are unified using the relationship, and the unified intensity of stress singularity is determined.
A new formulation for an adhesive force between a substrate and an indenter is presented. The bou... more A new formulation for an adhesive force between a substrate and an indenter is presented. The boundary condition taking into account surface stresses is used for the present analysis. The surface stress is originated from surface energy. A paraboloidal indenter is pressed to the substrate, and then adhesion occurs between both surfaces. Surface energy and surface stress will vary at the adhesion surface, and then the surfaces deform in a concave way. An attractive force occurs to keep the contact of two adhesion surfaces. In the present paper, an effect of surface stress on the adhesive force will be clarified.
A new model for analyzing indentation plasticity, proposed by Tanaka, Koguchi, and Mura, is discu... more A new model for analyzing indentation plasticity, proposed by Tanaka, Koguchi, and Mura, is discussed in relation to the plasticity in ceramics. The model is based on the punching of prismatic dislocation loops to accommodate the volume of plastic penetration at the indentation. The theory predicts that the hardness/Young’s s constant irrespective of the yield strength. The predicted profiles at the unloaded state in Si3N4 and ZrO2 ceramics were closely coincident with the indentation profiles showing the amount of spring back-up to 30–40% as revealed by the topographic analysis on scanning electron microscope (SEM) photographs of these materials.
Anisotropic conductive film (ACF) is commonly used as underfill for flip chip assembly. The prese... more Anisotropic conductive film (ACF) is commonly used as underfill for flip chip assembly. The present study focuses on elastic recovery and stress distribution along the interfaces of particle-pads and underfill-pads associated with heat or a mechanical loading. In the same manner as the experimental process for ACF assemblies, ACF interconnection is simulated using FEM. Firstly, the properties of the nickel were determined by fitting FEM to the experimental results. After that, the nickel properties are used for ACF interconnection analysis. We found that delamination may also occur at a three-joint interface of a particle, a pad and an underfill at the lowest temperature during a heat cycle.
American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP, Nov 1, 1995
The characteristic of thermal stresses near the apex in dissimilar materials under a uniform temp... more The characteristic of thermal stresses near the apex in dissimilar materials under a uniform temperature change is theoretically and numerically investigated. The materials are composed of two isotropic homogeneous wedges with arbitrary angles. The dominant factor of thermal stresses near the apex is represented by Kr{sup p{minus}1}, where p{minus}1 is the order of the stress singularity and K indicates the intensity of the stress field. For the bonded structures of Cu/Si{sub 3}N{sub 4}, the relationship between the wedge angle {var_phi}{sub 1} of material 1 and the total angle {var_phi}{sub 1} + {var_phi}{sub 2} of the bonded wedge, in which K becomes zero, is clarified theoretically. Also, it is shown that the distribution of the intensity K for each root p is divided into two forms. Finally, a relation between the distribution of the thermal stresses near apex and characteristic length of the bonded structure is examined by FEM.
ABSTRACT Portable electronics devices such as mobile phone and portable music player become compa... more ABSTRACT Portable electronics devices such as mobile phone and portable music player become compact and improve their performance. High-density packaging technology such as CSP (Chip Size Package) and Stacked-CSP is used for improving the performance of devices. CSP has a bonded structure composed of materials with different properties. A mismatch of material properties may cause stress singularity, which lead to the failure of bonding part in structures.In the present study, a strain singular field near inter-face edge in three-dimensional joints is investigated using digital image correlation method. A specimen which silicon chip was embedded in resin is used in experiment and tensile load is applied to the specimen. Photograph of specimen surface is taken before and after loadings by laser microscope. Displacement on the surface was evaluated by the digital image correlation method (DICM) using data of surface pattern on the specimen, which the cross correlation coefficients for surface pattern are maximized. Strain on surface of specimen is calculated by using the moving least square method. On the other hand, 3D element free Galerkin method is applied to compute the displacement and strain distribution in a three-dimensional model of the specimen. In the element free Galerkin method, the physical values, i.e., displacement, strain and stress, can be obtained by using the displacement data at node. In this research, strain distribution near the edge of interface is computed based on the element free Galerkin method. Finally, the strain distribution obtained by the digital image correlation method and the moving least square method is compared with that obtained by the element free Galerkin method. The intensity of strain singularity is determined numerically and experimentally.
In the present paper, singular stress fields at the vertex on the interface in three-dimensional ... more In the present paper, singular stress fields at the vertex on the interface in three-dimensional bonded joints are analyzed using BEM. The order of stress singularity is determined solving an eigen equation based on FEM formulation and the stress distribution is expressed using the result of the eigen-value analysis. A simple relationship between the thickness of layer and a value of stress is introduced. Then, stress distributions for various thicknesses of layer are unified using the relationship, and the unified intensity of stress singularity is determined.
A new formulation for an adhesive force between a substrate and an indenter is presented. The bou... more A new formulation for an adhesive force between a substrate and an indenter is presented. The boundary condition taking into account surface stresses is used for the present analysis. The surface stress is originated from surface energy. A paraboloidal indenter is pressed to the substrate, and then adhesion occurs between both surfaces. Surface energy and surface stress will vary at the adhesion surface, and then the surfaces deform in a concave way. An attractive force occurs to keep the contact of two adhesion surfaces. In the present paper, an effect of surface stress on the adhesive force will be clarified.
A new model for analyzing indentation plasticity, proposed by Tanaka, Koguchi, and Mura, is discu... more A new model for analyzing indentation plasticity, proposed by Tanaka, Koguchi, and Mura, is discussed in relation to the plasticity in ceramics. The model is based on the punching of prismatic dislocation loops to accommodate the volume of plastic penetration at the indentation. The theory predicts that the hardness/Young’s s constant irrespective of the yield strength. The predicted profiles at the unloaded state in Si3N4 and ZrO2 ceramics were closely coincident with the indentation profiles showing the amount of spring back-up to 30–40% as revealed by the topographic analysis on scanning electron microscope (SEM) photographs of these materials.
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Papers by Hideo Koguchi