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In this paper, the effects of moisture sensitivity during preconditioning (30 °C/60% RH, 192 hours) tests and material property changes after reliability stressing on flip chip chip-scale package (FCCSP) were comprehensively investigated by various experimental data as well as theoretical explanation. Since the integrity of FCCSP is dependent on the mechanical integrity of underfill and PCB used in package assembly process, deep insight was given on the material properties in order to understand degradation mechanism induced by the combined stresses of preconditioning test and environmental stresses in a sequence. As a result of DOE (Design of Experiment) for 2 different PCB, failures were found only in J PCB because of a large CTE change before and after moisture absorption. After moisture absorption, large CTE change from 27.78 to 32.04 of J PCB could aggravate the thermal mismatch between a PCB and an underfill, it caused shear displacement by more than 2,309 ppm in the interface. According to the DOE for underfill, we verified that higher modulus underfill could improve the reliability of flip chip packages. Based on our works, we recommend the optimized value for underfill modulus is from 8 GPa to 12 GPa. We explained logically two different failure mechanisms of delamination. One is induced by CTE mismatch of PCB, and the other is by underfill modulus by means of electron microscope. Finally, as to reliability concerns of moisture resistance arisen from the absence of the photo-sensitive polyimide (PSPI) passivation layer, we demonstrated that potential risk is minimal if FCCSP is assembled with an appropriate underfill as well as PCB.

Axial compression test was conducted to investigate the effect of confinement on plain concrete cylinders by wrapping polyethylene naphthalate fiber reinforced polymer (PEN FRP) with large rupture strain (LRS) capacity. To draw comparison on the confinement effect by PEN FRP wrapping, the confining effect by basalt FRP (BFRP) wrapping was also investigated. A total of 25 tests was completed. Test variables were two different FRP composites (PEN FRP, BFRP) and number of FRP layers (1, 2, 3 layers of PEN FRP and 2, 4, 6 layers of BFRP) in the main confinement tests (21 tests). In the additional confinement tests, the test variable was overlap length of PEN FRP (four tests). Confinement by BFRP and LRS PEN FRP was both effective as demonstrated by continuously ascending stress–strain relationship of the confined concrete. The PEN FRP wrapped concrete deformed more both axially and laterally to develop strength equivalent to that of the BFRP wrapped concrete. A simplified procedure for rational modelling of stress–strain relationship of the confined concrete was suggested. The suggested procedure is applicable for both BFRP and PEN FRP confined circular concretes on condition that basic confinement test data specific to the FRP composite are provided.

A decellularized extracellular matrix (dECM) is an excellent biomaterial in regenerative medicine, due to its biomimetic nature in targeting tissues and organs. In this study, we prepared cell-derived ECMs (CDM) derived from four different cell sources, characterized them individually, and found that intrinsic properties of each CDM were substantially different in terms of the fibrous matrix, total protein, and biochemical factors. Based on such information, we selected two ECM candidates, the human lung fibroblast derived matrix (hFDM) and the umbilical cord-blood mesenchymal stem cell derived matrix (UMDM) for the study of ECM-macrophage interactions in vitro and in vivo. In fact, UMDM was the richer in both total protein and angiogenic-related cytokines than any other CDM. When THP-1 cell-derived macrophages (M0) were seeded onto the UMDM or the hFDM, it showed a mixed cell morphology of macrophage phenotype and the macrophages (M0) preconditioned on UMDM presented more diverse cytokine release profiles. The treatment of conditioned medium obtained from CDM-seeded macrophages showed that UMDM could yield significantly advanced wound closure in 24 h via the human dermal fibroblast scratch model. To investigate the role of ECM on macrophage polarization in vivo, we prepared an ECM hydrogel, a mixture of each CDM and Pluronic F127/hyaluronan, and applied them onto a full-thickness mouse skin wound model for 2 weeks. The therapeutic efficacy as assessed via histology and immunofluorescence staining (α-SMA and CD206) revealed that the UMDM-treated group showed more effective wound healing compared to the other groups, as proven via the thinner epidermal layer, significant recovery of skin appendage, better neovascularization, and higher recruitment of myofibroblasts and larger number of macrophages (M2) at 7 days. The difference between UMDM and hFDM was marginal. Taken together, among the CDMs, UMDM and hFDM are promising resources of ECM, showing a great potential for wound healing. Although the mechanism is not fully understood, bioactive innate factors in UMDM may contribute individually and/or collectively to advance wound healing.

BACKGROUND: Macrophages, with many different phenotypes play a major role during wound healing process, secreting the cytokines crucial to angiogenesis, cell recruitment and ECM remodeling. Therefore, macrophage-derived cytokines may be attractive therapeutic resource for wound healing. METHODS: To obtain a conditioned media (CM) from macrophages, human monocyte THP-1 cells were seeded on TCP or human fibroblast-derived matrix (hFDM) and they were differentiated into M1 or M2 phenotype using distinct protocols. A combination of different substrates and macrophage phenotypes produced M1- and M2-CM or M1-hFDM- and M2-hFDM-CM, respectively. Proteome microarray determines the cytokine contents in those CMs. CMs-treated human dermal fibroblast (hDFB) was analyzed using collagen synthesis and wound scratch assay. Concentrated form of the CM (CCM), obtained by high-speed centrifugation, was administered to a murine full-thickness wound model using alginate patch, where alginate patch was incubated in the M2-CCM overnight at 4 °C before transplantation. On 14 day post-treatment, examination was carried out through H&E and Herovici staining. Keratinocyte and M2 macrophages were also evaluated via immunofluorescence staining. RESULTS: Cytokine analysis of CMs found CCL1, CCL5, and G-CSF, where CCL5 is more dominant. We found increased collagen synthesis and faster wound closure in hDFB treated with M2-CM. Full-thickness wounds treated by M2-hFDM-CCM containing alginate patch showed early wound closure, larger blood vessels, increased mature collagen deposition, enhanced keratinocyte maturation and more M2-macrophage population. CONCLUSION: Our study demonstrated therapeutic potential of the CM derived from M2 macrophages, where the cytokines in the CM may have played an active role for enhanced wound healing.

Cell-derived matrix (CDM) has proven its therapeutic potential and been utilized as a promising resource in tissue regeneration. In this study, we prepared a human fibroblast-derived matrix (FDM) by decellularization of in vitro cultured cells and transformed the FDM into a nano-sized suspended formulation (sFDM) using ultrasonication. The sFDM was then homogeneously mixed with Pluronic F127 and hyaluronic acid (HA), to effectively administer sFDM into target sites. Both sFDM and sFDM containing hydrogel (PH/sFDM) were characterized via immunofluorescence, sol–gel transition, rheological analysis, and biochemical factors array. We found that PH/sFDM hydrogel has biocompatible, mechanically stable, injectable properties and can be easily administered into the external and internal target regions. sFDM itself holds diverse bioactive molecules. Interestingly, sFDM-containing serum-free media helped maintain the metabolic activity of endothelial cells significantly better than those in serum-free condition. PH/sFDM also promoted vascular endothelial growth factor (VEGF) secretion from monocytes in vitro. Moreover, when we evaluated therapeutic effects of PH/sFDM via the murine full-thickness skin wound model, regenerative potential of PH/sFDM was supported by epidermal thickness, significantly more neovessel formation, and enhanced mature collagen deposition. The hindlimb ischemia model also found some therapeutic improvements, as assessed by accelerated blood reperfusion and substantially diminished necrosis and fibrosis in the gastrocnemius and tibialis muscles. Together, based on sFDM holding a strong therapeutic potential, our engineered hydrogel (PH/sFDM) should be a promising candidate in tissue engineering and regenerative medicine.

The effectiveness of seismic retrofitting using three different fibers—carbon fiber (CF), glass fiber (GF), polyethylene terephthalate (PET) fiber—and a fiber combination of aramid fiber (AF) and PET fiber (called hybrid fiber reinforced polymer (HF)) wrapped on reinforced concrete (RC) circular columns was experimentally evaluated. A total of 11 RC circular columns were tested: three control columns and eight retrofitted columns in three different test groups. The purpose of fiber wrapping was flexural strength improvement as well as enhancement of rotational capacity in the plastic hinge region. Mechanical properties of CF, GF, AF, and PET were first defined; that is, CF, GF, and AF exhibited linear stress–strain behavior with limited ultimate strain capacity typically less than 3%, while ductile PET exhibited as much as 15% strain and non-linear stress–strain behavior with a very low elastic modulus. In the RC column tests, all three different fibers and the AF + PET fiber combination were effective in enhancing the strength and ductility but resulted in different structural behaviors and failure modes depending on the fiber type and the fiber amount used. The column sections were then analytically studied by section analysis using the behavior of confined concrete, the non-linear relationship of fiber-reinforced polymer (FRP), and the actual material properties of reinforcement. The analytical and experimental results revealed that ductile PET is beneficial, as it demonstrates more ductile behavior with a degree of strength enhancement similar to that of CF and GF.

Results of an experimental study aimed to evaluate tensile performance, lap-splice length of carbon fabric-reinforced cementitious matrix system (C-FRCM), and performance of concretes confined by C-FRCM are presented. Green high-strength mortar was used in this study which actively utilized recycled fine aggregate and fine waste glass powder to partially substitute cementitious binder. Test plans were developed in due consideration of prefabricated C-FRCM for strengthening concrete columns: 14 tensile tests, 12 lap-splice tests, and 6 uniaxial compression tests of plain concrete specimens confined by C-FRCM were performed. Test variable for the tensile test was number of fabric layers (one or two layers). Nominal strength of the C-FRCM with two fabric layers was 11.0 MPa while it was 7.4 MPa with one fabric layer in tension. Full strength of the carbon fabric was developed in all tensile tests while the C-FRCM with two fabric layers (with axial fiber amount = 0.59% by vol.) showed pseudo-ductile behavior. From the lap-splice tests in direct tension, an increased lap-splice length was required for the double fabrics over that for the single fabrics. The required splice length was about 170 mm for the single fabrics and it was about 310 mm for the double fabrics. Plain concrete cylinders and prismatic specimens were laterally confined by C-FRCM and subjected to uniaxial compression. All test results showed strain-softening behavior. Compressive strength increased by 10–41% while ductility also increased by 6–45% indicating applicability of the prefabricated type C-FRCM in the future.

Skin injuries are frequently encountered in daily life, but deep wounds often poorly self-heal and do not recover completely. In this study, we propose a novel skin patch that combines antibiotic, cell-derived extracellular matrix (ECM) and biocompatible polyvinyl alcohol (PVA) hydrogel. Methods: Decellularized human lung fibroblast-derived matrix (hFDM) was prepared on tissue culture plate (TCP) and PVA solution was then poured onto it. After a freeze-thaw process, PVA was peeled off from TCP along with hFDM tightly anchored to PVA. Subsequently, ciprofloxacin (Cipro)-incorporated PVA/hFDM (PVA/Cipro/hFDM) was fabricated via diffusion-based drug loading. Results: In vitro analyses of PVA/Cipro/hFDM show little cytotoxicity of ciprofloxacin, stability of hFDM, rich fibronectin in hFDM, and good cell attachment, respectively. In addition, hFDM proved to be beneficial in promoting cell migration of dermal fibroblasts and human umbilical vein endothelial cells (HUVECs) using transwell inserts. The antibacterial drug Cipro was very effective in suppressing colony growth of gram-negative and -positive bacteria as identified via an inhibition zone assay. For animal study, infected wound models in BALB/c mice were prepared and four test groups (control, PVA, PVA/Cipro, PVA/Cipro/hFDM) were administered separately and their effect on wound healing was examined for up to 21 days. The results support that Cipro successfully reduced bacterial infection and thus encouraged faster wound closure. Further analysis using histology and immunofluorescence revealed that the most advanced skin regeneration was achieved with PVA/Cipro/hFDM, as assessed via re-epithelialization, collagen texture and distribution in the epidermis, and skin adnexa (i.e., glands and hair follicles) regeneration in the dermis. Conclusion: This work demonstrates that our skin patch successfully consolidates the regenerative potential of ECM and the antibacterial activity of Cipro for advanced wound healing.

Decellularized extracellular matrix (ECM)-based scaffold has been a very useful resource for effective tissue regeneration. In this study, we report a novel ECM patch that physically combines human fibroblast-derived matrix (hFDM) and poly(vinyl alcohol) (PVA) hydrogel. hFDM was obtained after decellularization of in vitro cultured human fibroblasts. We investigated the basic characteristics of hFDM alone using immunofluorescence (fibronectin, collagen type I) and angiogenesis-related factor analysis. Successful incorporation of hFDM with PVA produced an hFDM/PVA patch, which showed excellent cytocompatibility with human mesenchymal stem cells (hMSCs), as assessed via cell adhesion, viability, and proliferation. Moreover, in vitro scratch assay using human dermal fibroblasts showed a significant improvement of cell migration when treated with the paracrine factors originated from the hMSC-incorporated hFDM. To evaluate the therapeutic effect on wound healing, hMSCs were seeded on the hFDM/PVA patch and they were then transplanted into a mouse full-thickness wound model. Among four experimental groups (control, PVA, hFDM/PVA, hMSC/hFDM/PVA), we found that hMSC/hFDM/PVA patch accelerated the wound closure with time. More notably, histology and immunofluorescence demonstrated that compared to the other interventions tested, hMSC/hFDM/PVA patch could lead to significantly advanced tissue regeneration, as confirmed via nearly normal epidermis thickness, skin adnexa regeneration (hair follicle), mature collagen deposition, and neovascularization. Additionally, cell tracking of prelabeled hMSCs suggests the in vivo retention of transplanted cells in the wound region after the transplantation of hMSC/hFDM/PVA patch. Taken together, our engineered ECM patch supports a strong regenerative potential toward advanced wound healing.

Decellularized extracellular matrix (ECM)-based scaffold has been a very useful resource for effective tissue regeneration. In this study, we report a novel ECM patch that physically combines human fibroblast-derived matrix (hFDM) and polyvinyl alcohol (PVA) hydrogel. hFDM was obtained after decellularization of in vitro cultured human fibroblasts. We investigated the basic characteristics of hFDM itself using immunofluorescence (fibronectin, collagen type Ⅰ) and angiogenesis related factors analysis. Successful incorporation of hFDM with PVA produced an hFDM/PVA patch, which showed an excellent cytocompatibility with human mesenchymal stem cells (hMSCs), as assessed via cell adhesion, viability, and proliferation. Moreover, in vitro scratch assay using human dermal fibroblasts showed a significant improvement of cell migration when treated with the paracrine factors orignated from the hMSCs-incorporated hFDM. To evaluate therapeutic effect on wound healing, hMSCs were seeded on the hFDM/PVA patch and they were then transplanted into mouse full-thickness wound model. Among four experimental groups (control, PVA, hFDM/PVA, hMSC/hFDM/PVA), we found that hMSC/hFDM/PVA patch accelerated the wound closure with time. More notably, histology and immunofluorescence demonstrated that compared to normal skin tissue, hMSC/hFDM/PVA patch could lead to significantly advanced tissue regeneration, as confirmed via nearly normal epidermis thickness, skin adnexa regeneration (hair follicle), mature collagen deposition, and neovascularization. Additionally, cell tracking of pre-labelled hMSCs suggegsts the in vivo retention of transplanted cells in the wound region after transplantation of hMSC/hFDM/PVA patch. Taken together, our engineered ECM patch demonstrates a strong regeneration potential toward advanced wound healing.

Extracellular matrix (ECM) is crucial to many aspects of vascular morphogenesis and maintenance of vasculature function. Currently the recapitulation of angiogenic ECM microenvironment is still challenging, due mainly to its diverse components and complex organization. Here we investigate the angiogenic potential of human lung fibroblast-derived matrix (hFDM) in creating a three-dimensional (3D) vascular construct. hFDM was obtained via decellularization of in vitro cultured human lung fibroblasts and analyzed via immunofluorescence staining and ELISA, which detect multiple ECM macromolecules and angiogenic growth factors (GFs). Human umbilical vein endothelial cells (HUVECs) morphology was more elongated and better proliferative on hFDM than on gelatin-coated substrate. To prepare 3D construct, hFDM is collected, quantitatively analyzed, and incorporated in collagen hydrogel (Col) with HUVECs. Capillary-like structure (CLS) formation at 7 day was significantly better with the groups containing higher doses of hFDM compared to the Col group (control). Moreover, the group (Col/hFDM/GFs) with both hFDM and angiogenic GFs (VEGF, bFGF, SDF-1) showed the synergistic activity on CLS formation and found much larger capillary lumen diameters with time. Further analysis of hFDM via angiogenesis antibody array kit reveals abundant biochemical cues, such as angiogenesis-related cytokines, GFs, and proteolytic enzymes. Significantly up-regulated expression of VE-cadherin and ECM-specific integrin subunits was also noticed in Col/hFDM/GFs. In addition, transplantation of Col/hFMD/GFs with HUVECs in skin wound model presents more effective re-epithelialization, many regenerated hair follicles, better transplanted cells viability, and advanced neovascularization. We believe that current system is a very promising platform for 3D vasculature construction in vitro and for cell delivery toward therapeutic applications in vivo . Statement of Significance Functional 3D vasculature construction in vitro is still challenging due to the difficulty of recapitulating the complex angiogenic extracellular matrix (ECM) environment. Herein, we present a simple and practical method to create an angiogenic 3D environment via incorporation of human lung fibroblast-derived matrix (hFDM) into collagen hydrogel. We found that hFDM offers a significantly improved angiogenic microenvironment for HUVECs on 2D substrates and in 3D construct. A synergistic effect of hFDM and angiogenic growth factors has been well confirmed in 3D condition. The prevascularized 3D collagen constructs also facilitate skin wound healing. We believe that current system should be a convenient and powerful platform in engineering 3D vasculature in vitro , and in delivering cells for therapeutic purposes in vivo .

Epoxy molding compounds (EMC) are commonly applied to mitigate the thermo-mechanical reliability issue associated with the chip-to-package interaction (CPI) of LK/ULK applied flip chip packages. To understand the effect of EMC viscoelastic properties on the stress level induced on the bump, under bump and chip edge interconnects, a series of numerical simulations and reliability test using CPI test vehicles (TV) are carried out using 28/14/10nm process. The results showed that the higher storage modulus leads to lower stress level at the near bump and under bump interconnect layers, and enhanced CPI reliability. An improved approach based on phase lag (tan δ) value and stress relaxation is proposed to evaluate the performance of EMC materials. Our CPI TV thermo-mechanical test results shows good agreement to our newly proposed guide line. Additionally, we show that high modulus induced EMC/SR delamination can be effectively eliminated by increasing SR thickness.

In this study, a new precast concrete (PC) beam-column joint of moment resisting frame applicable for moderate seismic regions is proposed. A semi PC beam-column connection with U-shaped strands is developed in an attempt to improve workability and provide effective stress transfer mechanism at the joint. The structural system consists of PC beams with U-shaped strands, PC columns, PC slabs, and topping concrete. A series of three interior and three exterior semi PC joint specimens was tested to investigate the structural behavior of the system subjected to the lateral cyclic load. Key test variables are the number of strands placed in the PC beam and the presence or absence of the transverse reinforcements at the connection. The experiment and performance evaluation of the system were conducted in accordance with ACI T1.1–01 (2001). According to the test results, the proposed structural system with transverse reinforcements at the joint is sufficient to use in moderate seismic regions.

The use of carbon fibers (CF) and glass fibers (GF) were combined to strengthen concrete flexural members. In this study, data of tensile tests of 94 hybrid carbon-glass FRP sheets and 47 carbon and GF rovings or sheets were thoroughly investigated in terms of tensile behavior. Based on comparisons between the rule of mixtures and test data, positive hybrid effects were identified for various (GF/CF) ratios. Unlike the rule of mixtures, the hybrid sheets with relatively low (GF/CF) ratios also produced pseudo-ductility. From the calibrated results obtained from experiments, a new analytical model for the stress-strain relationship of hybrid FRP sheets was proposed. Finally, the hybrid effects were verified by structural tests of concrete members strengthened with hybrid FRP sheets and either carbon or glass FRP sheets.

Glass fibre-reinforced polymer (GFRP) bars can be used to avoid steel reinforcement corrosion in bridge decks, which usually have no transverse reinforcement. In this study, 35 flexural tests of beams and slabs were carried out to experimentally determine the bond strength of spliced GFRP bars with no transverse reinforcement. The test variables included splice length, cover thickness, and bar spacing. The splice lengths were relatively large to test realistic splice lengths used in the field (longer than 30 d b in most tests). In addition, four beams with conventional steel rebar splices were also tested to compare their bond strengths with those of the GFRP bars. Test results showed that the bond strengths of the specimens with GFRP bars were lower than those of the steel rebars. Although the average bond strength of the GFRP bars decreased with increasing splice length and decreasing cover thickness/bar spacing, the bond strength of the long splice increased when c / d b ⩾ 2.5, in which c denotes the smaller of the minimum concrete cover and 1/2 of the bar clear spacing. Two equations for predicting the average bond strength of GFRP bars in unconfined concrete are proposed based on the regression analysis of the 33 test results from the beams and slabs that failed by concrete splitting.

In this study, we investigated the effect of the current density on the interfacial reaction and mechanical reliability of an electroless Ni/immersion Au (ENIG) substrate with Sn-3.5Ag solder. We first evaluated the interfacial reactions of the solder joint under aging for up to 800h and current stressing with current densities of 3x10^2A/cm^2 and 5x10^3A/cm^2. Also, we successfully revealed the correlation between the interfacial reaction behavior and mechanical reliability under current stressing. With increasing aging time, the thickness of the Ni"3Sn"4 layer increased. At both low and high current densities, the thickness of the Ni"3Sn"4 layer increased up to 400h and decreased thereafter at the cathode, while that of the IMC increased up to 800h at the anode. After the die shear test, the ductile fracture was observed in the as-reflowed joint without current stressing. The fracture mode changed from ductile fracture to brittle fracture when thermal aging and current flow were simultaneously applied. The combination of the current stressing and isothermal aging at high temperature significantly deteriorated the mechanical reliability of the solder joint.

Compared to conventional Sn-Pb solder, ternary Pb free solder alloys are particular susceptible to brittle fracture through the formation of intermetallic compound layers. However, the conventional...

As silicon semiconductor technologies need to achieve smaller dimensions, the development of System-onChip (SOC) devices with a large variety of functional blocks becomes very difficult to realize. A 3-D stacked package is a promising alternative to improve the performance and density of devices beyond traditional package scaling limits. However, there are many issues related to process integration, thermal management, and reliability of 3-D stacked packages. In this study, the printed circuit board (PCB), silicon carrier and silicon chip are integrated with the ultrasonic bonding method. Die shear tests on the joints were carried out with increasing bonding time and input power to optimize the bonding conditions. The integrated chips were successfully bonded with and without non-conductive film (NCF) using ultrasonic energy. The measured electrical resistance of multi-chip package bonded with NCF was lower than that of multi-chip package bonded without NCF. Thermal cycle and high temperature storage test...

The effect of displacement rate and intermetallic compound (IMC) growth on the shear strength of electroplated Sn-2.5Ag (in wt.%) flip chip solder with Cu under-bump metallization (UBM) were investigated after multiple reflows. Cu"6Sn"5 IMC was formed at the interface after one reflow. After five reflows, two different IMC layers, consisting of a scallop-shaped Cu"6Sn"5 phase and a planar Cu"3Sn phase, and their thicknesses increased with increasing reflow number up to 10. The shear strengths peaked after four reflows, and then decreased with increasing reflow number. Increasing displacement rate increased the shear force. The tendency toward brittle fracture characteristics was intensified with increasing displacement rate and reflow number.

The objective of this study was to propose a development length equation for GFRP bars. A total of 104 modified pullout tests were completed while the test variables were embedment length (15, 30, ), net cover thickness (), top-cast bar effect, different GFRP bar types (K2KR, K3KR and AsUS), and bar diameters (10, 13, 16 mm). Average bond stresses were determined based on modified pullout test results. Two variable linear regression analysis was performed of the average bond stresses. Utilizing 5% fractile concept, a conservative development length design equation was derived. The design equation derived in this study was compared to the ACI 440 committee equation. The cross-comparison revealed that the current equation resulted in shorter development lengths than those determined by the ACI 440 equation when the net cover thickness was large (greater than ). On the other hand, when the net cover thickness was small (equal to or less than ), the development lengths required by the current equation were larger than those by the ACI equation. The bond stresses were significantly influenced by the cover thicknesses. The current equation results in development lengths that are more economical when the cover thickness is large, and more conservative lengths when the cover thickness is small than the ACI 440 committee equation.

The failure of expansion joints for bridges generally occurs in non-shrinkage mortar another problem is the release of anchors in expansion joints due to the impact and vibration that occurs when cars are driving over a bridge. In this study, to overcome the failure of expansion joints that is related to the failure of non-shrinkage mortar, an elastomeric mortar has been developed. The elastomeric mortar has a highly developed pull-out capacity compared with that of non-shrinkage mortar. Moreover, an anchor system that can be changed easily and prevent the fracture of expansion joints has been developed.

The objective of this study was to propose a development length equation for bottom and top GFRP bars. Including the bottom and top GRPP bars, a total of 104 modified pullout tests were completed. The test variables were embedment length (15, 30, 45db), net cover thickness (0.5~2.0db), different GFRP bar types, and bar diameters (10, 13, 16mm). The average bond stresses were determined based on the modified pullout test results. Two variable linear regression analyses were performed on the results of the average bond stresses. Utilizing the 5% fractile concept, a conservative development length design equation was derived. The design equation of the development length for bottom and top GFRP bars was proposed and the design equation derived in this study was compared to the ACI 440.1R-06 committee equation.

Flat plate systems are commonly designed as a gravity-force-resisting system (GFRS) along with stiffer lateral-force-resisting systems (LFRS) such as shear walls, and moment resisting frames; however, deformation compatibility between the GFRS and LFRS results in positive moments (producing tension at the slab bottom) at the slab-column connections in flat plate systems. Continuous slab-bottom reinforcement (integrity reinforcement) passing through the column is required to prevent progressive collapse; however, for posttensioned flat plate (PT-flat plate) systems, there have been arguments among engineers on applying continuous slab-bottom reinforcement since ACI 318 and 352 provisions do not clearly specify the requirement on the slab-bottom reinforcement for PT flat plates. The purpose of this study is to investigate the effects of continuous slab-bottom reinforcement passing through the column core on the hysteretic behavior of the PT slab-column connections. Test results for six, 3/5 scaled specimens for interior PT flat plate connections subjected to constant gravity loads and quasistatic reversed cyclic lateral loads are presented and indicate that the slab-bottom reinforcement conforming to ACI-ASCE 352R.1 is not required to prevent collapse, but does significantly improves the hysteretic energy absorption capacity.

The traditional ball shear test is not suitable for evaluating joint reliability under drop loading, since the applied test speeds, usually lower than 5 mm/s, are well below the impact velocity applied to the solder joint in a drop test. The present study expands recently reported research by investigating the effect of thermal aging on the joint strength and fracture mode of Sn-3.0Ag-0.5Cu ball grid arrays during high-speed shear testing, with a shear height of 50 μm and a shear speed ranging from 0.01 m/s to 3 m/s. The test specimens were aged at 393 K for 1000 h. After reflow, a (Ni,Cu)3Sn4 intermetallic compound (IMC) layer was observed at the solder/Ni-P interface and the thickness of the IMC layer was increased through the aging process. The shear strength increased with increasing shear speed. The fracture surface of the solder joints showed three different fracture modes according to the shear speed and aging time. The fracture mode changed from ductile fracture to brittle fracture with increasing shear speed.

This study investigated the microstructural evolution and evaluated the thermo-mechanical reliability of a Sn-3.0Ag-0.5Cu (in wt.%) flip chip package during a thermal shock test. The reliability of the flip chip bonded packages was evaluated by means of the thermal shock in the temperature range of 233 K to 398 K. After 250 thermal shock cycles, cracks finally occurred at the corner solder bump joint on the chip side interfacial regions. In that, the crack initiated at the solder region near the intermetallic compound (IMC) layers. For the interpretation of the failure mechanism of the package, finite element analyses were conducted. From the finite element analysis or computational simulation result, the distribution of the plastic work in the corner solder bump was found to be most considerable. This means that the corner solder bump has the highest potential for first crack initiation and growth, because the thermo-mechanical failure of the solder joints is mainly caused by the accumulation of the plastic work. This matched well with the experimental results.

The failure behaviors of flip chip solder joints under various loading conditions of the high-speed shear test (H-SST) were investigated with an experimental and non-linear 3-dimensional finite element modeling study. The solder composition used in this study was Sn -3.0 Ag -0.5 Cu ( in wt .%). The shear forces were far greater by H-SST than by low-speed shear test (L-SST). The shear force further increased with increasing shear speed, mainly due to the high strain-rate sensitivity of the solder alloy. Brittle interfacial fractures were more easily achieved by H-SST, especially at the higher shear speed. This was discussed in terms of the relationship between the strain-rate and work-hardening effect and the resulting stress concentration at the interfacial regions

Glass fiber reinforced polymer (GFRP) bars are sometimes used when corrosion of conventional reinforcing steel bar is of concern. In this study, a total of 36 beams and one-way slabs reinforced using GFRP bars were tested in flexure. Four different GFRP bars of 13 mm diameter were used in the test program. In most test specimens, the GFRP bars were lap spliced at center. All beams and slabs were tested under 4-point loads so that the spliced region be subject to constant moment. Test vari- ables were splice lengths, cover thicknesses, and bar spacings. No stirrups were used in the spliced region so that the tests result in conservative bond strengths. Average bond stresses that develop between GFRP bars and concrete were determined through non- linear analysis of the cross-sections. An average bond stress prediction equation was derived utilizing two-variable linear regres- sion. A splice length equation based on 5% fractile concept was then developed. As a result of this study, a rational equation with which design splice lengths of the GFRP bars can be determined, was proposed.

The electromigration of conventional Sn-37Pb and Pb-free Sn-3.0Ag-0.5Cu (in wt.%) solder bumps was investigated with a high current density of 2.5 × 104 A/cm2 at 423 K using flip-chip specimens comprised of an upper Si chip and a lower bismaleimide triazine (BT) substrate. Electromigration failure of the Sn-37Pb and Sn-3.0Ag-0.5Cu solder bumps occurred with complete consumption of electroless Ni immersion Au (ENIG) underbump metallization (UBM) and void formation at the cathode side of the solder bump. Finite element analysis and computational simulations indicated high current crowding of electrons in the patterned Cu on the Si chip side, whereas the solder bumps and Cu line of the BT substrate had a relatively low density of flowing electrons. These findings were confirmed by the experimental results. The electromigration reliability of the Sn-3.0Ag-0.5Cu solder joint was superior to that of Sn-37Pb.

The surface morphology, electrical property, solderability and interfacial reaction with Sn–3.5 wt.%Ag solder of two electroless nickel–boron (EN–B) deposits (Ni–1 wt.%B and Ni–3 wt.%B) were investigated. The B content of the EN–B layer decreased with increasing pH value. The crystallinity and solderability of the EN–B plating layer decreased with increasing B content, while the electrical resistivity increased. Reaction layers of Ni 3 Sn 4 and Ni 3 B were formed at the interfaces between the Sn–3.5Ag solder and the two EN–B deposit layers. The thickness of the interfacial Ni 3 Sn 4 intermetallic compound (IMC) layer decreased with increasing B content, i.e., decreasing Ni content. These study results confirmed that the interfacial reaction between solder and the EN–B layer is significantly affected by the B content of the EN–B layer.

In this study, new moment-resisting precast concrete beam-column joint is proposed for moderate seismic regions. The new joint includes the connection reinforcing bars, penetrated the joint and lap-spliced with the bottom bars of precast U-beam. To evaluate the performance for non-contact lapped splice, experimental and analytical work were conducted, for major variables of the length of lap and the diameter of connection reinforcing bars(D19, D22, and D25). Results of experimental and analytical works show that these variables have much influence on flexural strength and ductility, and deformation of lapped joint. Using nonlinear finite element method, analytic research was performed for investigating crack and fracture patterns, load-deflection curve, comparison of internal force, evaluation of ductility, stains of reinforcement bar.

The effects of multiple reflows on the microstructural variation and joint strength of the flip chip solder joints were investigated. Conventional Sn–37Pb and a representative Pb-free Sn–3.0Ag–0.5Cu were used, and a popular low cost under bump metallurgy (UBM) of immersion Au/electroless Ni–P plating was employed. In case of Sn–37Pb, only Ni 3 Sn 4 intermetallic compound layer was formed during multiple reflows. In case of Sn–3.0Ag–0.5Cu, (Cu,Ni) 6 Sn 5 intermetallic compound layer was observed after a single reflow, while (Ni,Cu) 3 Sn 4 layer was additionally settled at the interface between the (Cu,Ni) 6 Sn 5 layer and Ni–P UBM. The thicknesses of the intermetallic compound layers increased and coarsened. The shear force of the both joints slightly decreased during the multiple reflows. The decrease of the joint strength was caused by different softening phenomena between the two cases, and that is discussed in the main text.

최근 전자 제품에 대한 가치 및 평가 기준이 변화하고 있다. 소비자들의 선택의 기준에 있어서 제품의 가격과 성능뿐만 아니라, 고장 없이 오랫동안 사용할 수 있는 제품, 즉 신뢰성이 높은 제품에 대한 선호도가 증가하고 있다. 이러한 제품 개발을 위해서는 제품 설계 단계부터 다양한 신뢰성 평가 및 피드백 과정들을 수행해야 한다. 하지만 과도한 신뢰성 평가는 금전적인 낭비를 초래하며, 제품 출시를 지연시켜 회사의 경쟁력을 약화시키는 주요 원인으로 작용할 수 있다. 따라서 합리적인 신뢰성 평가 방법의 고완 및 효율적인 평가가 이루어져야 함은 자명하다. 또한, 단순한 신뢰성 평가보다는 실질적인 환경에 가까운 복합 시험 평가에 대한 관심이 증가하고 있다. 한정된 제품 크기 내에서 다양한 기능을 수행할 수 있는 멀티미디어기기 및 디지털 컨버전스 제품에 대한 관심과 수요가 증가하고 있다

Use of both carbon fiber (CF) and glass fiber (GF) at the same time to strengthen existing flexural members was exploited. Using a proper volumetric GF / CF ratio, the CF can rupture first followed by subsequent rupture of GF at higher stress and strain showing a pseudo-ductile behavior. A theoretical study indicated that the ratio is 4.62 : 1 and higher where the pseudoductile effect can be shown. Flexural tests of plain concrete beams strengthened using fibers were first carried out. Hybrid FRP sheet using 8.8 : 1 ratio was then fabricated and the sheet was used to strengthen reinforced concrete beams. The RC beams strengthened using 1-ply and 2-ply hybrid sheets both revealed increased strength over a non-strengthened beam and ductile flexural behavior. A comparable beam strengthened using CF also showed increased strength but with limited ductility.

Failure behaviors of ball grid array (BGA) solder ball joints under various loading conditions of high-speed shear test were investigated with an experimental and non-linear 3-dimensional finite element modeling work. A representative Pb-free solder alloy, Sn-3.0Ag-0.5Cu, was employed in this study. Far greater shear forces were measured by high-speed shear test than by low-speed shear test. The shear force further increased with shear speed mainly due to the high strain-rate sensitivity of the solder alloy. Brittle interfacial fractures can be more easily achieved by high-speed shear test, especially in higher shear speed. This was discussed with the relationship between the strain-rate and work-hardening effect and resulting stress concentration at interfacial regions. Shear force decreased with shear height, and it could be found that excessively high shear heights unfavorably affected the test results leading to unexpectedly high standard deviation values or shear tip sliding from the solder ball surface.

This study was focused on the formation and reliability evaluation of solder joints with different diameters and pitches for flip chip applications. We investigated the interfacial reaction and shear strength between two different solders (Sn-37Pb and Sn-3.0Ag-0.5Cu, in wt.%) and ENIG (Electroless Nickel Immersion Gold) UBM (Under Bump Metallurgy) during multiple reflow. Firstly, we formed the flip chip solder bumps on the Ti/Cu/ENIG metallized Si wafer using a stencil printing method. After reflow, the average solder bump diameters were about 130, 160 and 190@mm, respectively. After multiple reflows, Ni"3Sn"4 intermetallic compound (IMC) layer formed at the Sn-37Pb solder/ENIG UBM interface. On the other hand, in the case of Sn-3.0Ag-0.5Cu solder, (Cu,Ni)"6Sn"5 and (Ni,Cu)"3Sn"4 IMCs were formed at the interface. The shear force of the Pb-free Sn-3.0Ag-0.5Cu flip chip solder bump was higher than that of the conventional Sn-37Pb flip chip solder bump.

This study focused on the feasibility of using Ni flip chip bumps with a Sn-2.5Ag (wt.%) solder encapsulation. The interfacial reaction and die shear property of the Ni flip chip bump with a Sn-Ag solder cap bonded on the electroplated Cu/Sn-Ag substrate were investigated with increasing bonding time. After bonding for 1s (Cu"xNi"1"-"x)"6Sn"5 and Cu"6Sn"5 intermetallic compound (IMC) layers were formed at the upper and lower interfaces, respectively, with the former IMC being the predominant phase during bonding. The transformation of the solder cap into the (Cu"xNi"1"-"x)"6Sn"5 IMC depleted the solder after bonding for 30s, and then the Ni concentration in the IMC gradually decreased with increasing bonding time. The shear property peaked after 30s, and then decreased with increasing bonding time. The fractures occurred at the solder/Cu"6Sn"5 interface and inside the (Cu"x Ni"1"-"x)"6Sn"5 IMC after bonding for 1s and 30s, respectively, after which the fracture location shifted toward the (Ni"xCu"1"-"x)"3Sn"4/(Cu"x Ni"1"-"x)"6Sn"5 interface with increasing bonding time.

We fabricated a Ni metal mask using the electroforming process, in combination with photolithography, and evaluated the effects of adding wetting agents to the electrolyte on the microstructure and mechanical properties. Photo masking, exposure, and development procedures were used to produce additive patterns on the stainless steel substrate. Subsequently, a textured Ni metal mask (30 μm thickness and 100 μm hole size) was formed on the substrate using the electroforming process. We found that the microstructure and mechanical properties varied considerably with the different combinations of the wetting agents added, i.e., the addition of SF-1, SF-2, or both SF-1 and SF-2. The addition of both wetting agents significantly reduced the grain size, resulting in an improved Vickers’s hardness (638 HV) and a reduced surface roughness (11.39 nm). Moreover, the friction coefficient of the Ni mask was reduced to 0.66. The wear resistance of the Ni mask was comparable to that of a commercial stainless steel mask due to the improved hardness and reduced friction coefficient.

The applicability of headed bars in exterior beam-column joints under reversed cyclic loading was investigated. A total of ten pullout tests were first performed to examine pullout behavior of headed bars subjected to monotonic and cyclic loading with test variables such as connection type between head and bar stem (weld or no weld), loading methods (monotonic or cyclic loading), and head shape (small or large circular head and square head). Two full-scale beam-column joint tests were then performed to compare the structural behavior of exterior beam-column joints constructed using two different reinforcement details: i.e. standard hooks and headed bars. Both joints were designed following the recommendations of ACI-ASCE Committee 352 for Type 2 performance: i.e. the connection is required to dissipate energy through reversals of deformation into inelastic range. The pullout test results revealed that welded head to the stem did not necessarily result in increased pullout strength when compared to non-welded head. Relatively large circular head resulted in higher peak load than smaller circular and square head. Both beam-column joints with conventional hooks and headed bars behaved similarly in terms of crack development, hysteresis curves, and peak strengths. The joint using the headed bars showed better overall structural performance in terms of ductility, deformation capacity, and energy dissipation. These experimental results demonstrate that the headed bars using relatively small head can be properly designed far use in external beam-column joint.

The development length equations of the GFRP rebars are suggested based on the pullout tests performed in this study. A total of 48 pullout and modified pullout tests were completed. Test variables included embedment length (L=10, 15, 20, and ), vertical and horizontal installation of the rebars, height of the rebars (H=100 and 300 mm), and cover thickness . D13 GFRP rebars domestically developed were used in the experimental program. The average of the bond strength of all vertically installed GFRP rebars was 6.39 MPa with a 5% fractile of 4.63 MPa. A basic development length equation was derived that resulted in an equation equivalent to the one proposed in the ACI 440.1R-03. Careful reevaluation of the bond strength using the modified pullout test indicated that a modification of the design equation was necessary so that the basic development length increases by 11%. The top bar effect of the horizontally installed rebars as well as the effect of the cover thickness were determined and included in the set of suggested equations. Since the current equations were derived from testing rebars embedded in relatively low strength concrete , they result in conservative development lengths when applied to bars embedded in higher strength concretes.