Table of contents

Interfacial joining (bonding) is a widely accepted welding process and one of the environmentally benign technologies used in industrial production. As the bonding temperature is lower than the melting point of the parent materials, melting of the latter is kept to a minimum. The process can be based on diffusion bonding, pressure welding, friction welding, ultrasonic bonding, or brazing-soldering, all of which offer many advantages over fusion welding. In addition, surface technologies such as surface modification, spraying, coating, plating, and thin-film formation are necessary for advanced manufacturing, fabrication, and electronics packaging. Together, interfacial joining and surface technology (IJST) will continue to be used in various industrial fields because IJST is a very significant form of environmentally conscious materials processing.

The international symposium of IJST 2013 was held at Icho Kaikan, Osaka University, Japan from 27–29 November, 2013. A total of 138 participants came from around the world to attend 56 oral presentations and 36 posters presented at the symposium, and to discuss the latest research and developments on interfacial joining and surface technologies. This symposium was also held to commemorate the 30th anniversary of the Technical Commission on Interfacial Joining of the Japan Welding Society.

On behalf of the chair of the symposium, it is my great pleasure to present this volume of IOP Conference Series: Materials Science and Engineering (MSE). Among the presentations, 43 papers are published here, and I believe all of the papers have provided the welding community with much useful information. I would like to thank the authors for their enthusiastic and excellent contributions. Finally, I would like to thank all members of the committees, secretariats, participants, and everyone who contributed to this symposium through their support and invaluable effort for the success of IJST 2013.

Yasuo Takahashi Chair of IJST 2013

Details of the committees are available in the PDF

All papers published in this volume of IOP Conference Series: Materials Science and Engineering have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

The interfacial contact and extension of two joining surfaces are numerically studied using a finite element method. The joining surface is assumed to have two-dimensional triangular asperities. Surface-asperity-induced voids are formed at the initial contact. The interfacial extension of the initial contact area is very different from that of void surface area. The initial void surface area shrank once before full contact was attained. The large asperity angle facilitates interfacial extension and void-surface shrinkage, resulting in the formation of numerous metallic bonds. The pressure-welding-induced interfacial extension and metallic bond formation are largely influenced by the asperity angle, whose effects are experimentally confirmed.

Solid-state bonding between two superplastic steels-ultra-high carbon steel (UHCS) and a structure steel (commonly referred to as 40Cr in china; yet contains only 1 mass% Cr)- was investigated. Industry-grade pure iron sheet was used as an interlayer and the bonding was carried out at the superplastic deformation temperature T = 750 °C . For a pre-pressing stress of P = 56.6 MPa, the initial strain rate was 1.5 × 10⁻⁴s⁻¹, and for a bonding time of t = 10min, the joint tensile strength reached up to 702 MPa a value 35% higher than what could be obtained without an interlayer. The bonding strength reached the tensile strength of 40Cr base metal through the same thermal-stress cycling. Based on the results, it was concluded that the weldability of 1.6 mass%C-UHCS / 40Cr steel was improved by using a pure iron interlayer.

Interfacial contact mechanisms and the superplastic behaviour of fine-grained high carbon steel during solid-state bonding were investigated. According to the results, typical superplastic deformation occurred at the bonding interface under conditions of superplasticity- causing temperature (T = 1003~1053K), bonding pressure (P = 34~44.3MPa), and bonding area ratio (S = 30~50%). The stress exponent, n, was about 2.25 while the activation energy, Q, was about 189 kJmol⁻¹ both indicating and confirming superplastic solid-state bonding. Predominant bonding mechanism controlled by superplastic deformation was experimentally identified.

The interfacial deformation and friction behavior between an Al ribbon and an electric pad (or substrate) during ultrasonic bonding is analyzed, based on numerical simulation and experimental results. The friction heating is estimated by the friction slip work at the bonding interface between the ribbon and pad. The temperature rise of the bonding interface is calculated by the numerical simulation and compared with the experimental results. It is suggested that the electric pad reduces the temperature rise, as compared to the bonding process without a pad. The shear stress at the bonding interface increases as the bonding progresses. The frictional slip due to adhesion increases stress and heats the bond interface.

The present study reveals the stress distribution in the substrate during ultrasonic bonding. The deformations of the Si substrate, Al ribbon, and Al pad were numerically analyzed using a finite element method. Experimental observation of the interface using a highspeed video camera was also conducted to determine the actual interfacial slip amplitude. This amplitude becomes smaller than that of tool-tip with bonding time. It was suggested from the numerical simulations that frictional adhesion enhanced the friction force, resulting in an increase in the equivalent stress in the ribbon and pad. As a result, very large stresses occur in the substrate during ultrasonic bonding. These stresses evolve with the progress of ultrasonic bonding, i.e., frictional adhesion.

Ultrasonic welding of pure aluminum sheets is performed using two weld tools, one with a knurled surface and one with a cylindrical surface. Relative motion behaviors of each weld tool, with respect to the working materials, during ultrasonic welding tests are analyzed using the digital correlation method. Weld microstructure development is investigated on the basis of transitional weld stages in the context of relative motion behaviors. The dominant relative motion is between the two work materials at the beginning of the weld but changes to be the motion between the weld tool and the work material it is in contact with as weld time increases. Thermo-mechanical effects of the relative motion of the weld tool and the work materials, on the development of weld microstructure, are discussed.

Thermosonic bonding of aluminum on polyphenylene sulfide was carried out in order to examine the effect of surface roughening of aluminum on the joint strength. Repeated chemical treatment of aluminum by immersion in aqueous sodium hydroxide and hydrochloric acid solutions increased its surface roughness (Ra ~25 μm) and surface area (~445% increase). Consequently, the bonding strength (~1.8N in average) was enhanced through anchoring effects.

A new joining method for dissimilar metal sheets was developed where a rotated consumable rod of Al alloy is pressed onto an Al alloy sheet at the part overlapped with a mild steel sheet. The metal flow in the joining region is increased by the through-hole in the Al sheet and consumable Al rod. The rod creates the joint interface and pads out of the thinly joined parts through pressing. This produces a higher joint strength than that of conventional friction stir spot welding. Measurements of the joint interface showed the presence of a 5-10 nm thick amorphous layer consisting of Al and Mg oxides.

The effect of weld line shape on material flow during the friction stir welding of aluminum and steel was investigated. The material flow velocity was evaluated with simulated experiments using plasticine as the simulant material. The validity of the simulated experiments was verified by the marker material experiments on aluminum. The circumferential velocity of material around the probe increased with the depth from the weld surface. The effect is significant in cases where the advancing side is located on the outside of curve and those with higher curvature. Thus, there is an influence of weld line shape on material flow.

The tensile shear strength and cross tension strength of friction stir spot welded joints were evaluated in the cases of lap joints of 270 N/mm² grade and 980 N/mm² grade cold rolled steel sheets with respect to the stir zone area, hardness distribution, and interface condition between the sheets. The results suggested that both the tensile shear strength and cross tension strength were based on the stir zone area and its hardness in both grades of steel. The "hook" shape of the interface also affected the joint strength. However, the joining that occurred across the interfaces had a significant influence on the value of the joint strength in the case of the 270 N/mm² grade steel.

Metal (silver or copper) ions were doped into borosilicate glass using an electric field- assisted ion exchange method. The optical transmittance of the metal doped glass was measured to determine why the doped glass exhibited an excellent laser micro-machinability. The doped metal ions were found to have enhanced the optical absorption of the glass, especially in the ultraviolet range. This in turn facilitated the efficient absorption of incident laser irradiation, and hence improved laser machinability of the glass. The metal doped glass also exhibited some absorption in the visible range, leading to a slight yellow-brown coloration. Transmission electron microscope (TEM) observations indicated that the metal ions had penetrated the glass and therein formed nanometer-sized (~6 nm) fine particles. In an attempt to control the optical characteristics in the ultraviolet-visible range, metal doped glass was heat-treated following the ion exchange doping step. In the case of silver-doped glass with heat treatment at 723 K, silver nanoparticles aggregated locally yielding an inhomogeneous structure. The heat-treated samples had a high optical absorption in the ultraviolet range.

A Ag nanoparticles-based technology for joining semiconductor materials through sintering has been developed. Currently, a paste consisting of Ag nanoparticles is used for die bonding in the electronics industry. A binder-free Ag nanojoining material has been developed for fabricating electronic devices. In this study, we investigated the joining ability of this binder-free tape-type Ag nanojoining material with respect to Si chips. A paste-type Ag nanojoining material that contained an organic binder was also investigated for comparison. The microstructures of the Si-joining material interfaces were observed using a focused ion beam system. The cleaved surfaces of the joints were observed using scanning electron microscopy. High-quality joints that contained only a few pores could be formed between a Au thin film electroplated on the Si chip and the tape-type material after sintering, owing to the simplicity of the joining process and the binder-free nature of the joining material.

The brazing of C/C composites and Inconel-600 Ni-based heat resistant alloy was conducted using Fe-Ni-Cr-P-Si brazing filler alloy with inserting various thickness of Nb foil as stress relief interlayer. SEM observation of cross section of brazing interface revealed that Nb foil was resolved into the brazing filler layer on C/C composites side. Nb diffused to the surface of C/C composites and acted as the active metal element to enhance the wettability of molten metal on graphite matrix of C/C composites during the brazing process. The variation in shear strength values of the brazed joint with Nb layer thickness suggested that the Nb layer should be remained at least 100 μm.

Many kinds of stainless steel have been used in the engineering field. So it is necessary to investigate the effect of SUS chemical compositions on the brazing ability of filler metal. In this study, SUS315J containing Cr, Ni, Si, Cu, and Mo was employed as a base metal. Excellent spreading ability of the molten nickel-based brazing filler on SUS315J was obtained as compared with that on SUS316. Copper and silicon influenced the significant spreading ability of the filler.

It is difficult to join dissimilar metals when an intermetallic compound is formed at the joining interface. Spot brazing can be accomplished in a short time by resistance heating. Therefore, it is said that the formation of a intermetallic compound can be prevented. In this study, aluminum and copper were joined by spot brazing with a cover plate. The cover plate was used to supply heat to base metals and prevent heat dissipation from the base metals. The ability to braze Al and Cu was investigated by observation and analysis. Pure aluminum (A1050) plate and oxygen-free copper (C1020) plate were used as base metals. Cu-Ni-Sn-P brazing filler was used as the brazing filler metal. SPCC was employed as cover plate. Brazing was done with a micro spot welder under an argon gas atmosphere. Brazing ability was estimated by tensile shear strength and cross sectional microstructure observation. Al and Cu can be joined by spot brazing with Cu-Ni-Sn-P brazing filler and cover plate.

The brazing of copper to stainless steel (SUS304 JIS) was performed using a low- silver-content brazing filler metal, Ag-50Cu, under an Ar gas atmosphere with a conventional furnace, owing to the potential economic benefits of using low-silver-content filler metals. The brazeability of the low-silver-content brazing filler metal to copper and SUS304 was investigated. A good joint was obtained, and a drastic dissolution reaction occurred at the copper side. Molten BAg8 penetrated along the crystal grain boundary of the copper base metal when BAg8 was used as the filler metal. This was caused by the dissolution of Ni from the stainless steel into the molten filler metal. Ag-50Cu, which was investigated in this work, can be used instead of BAg8 filler metal.

Wetting and spreading of molten brazing filler material are important factors that influence the brazing ability of a joint to be brazed. Several investigations into the wetting ability of a brazing filler alloy and its surface tension in molten state, in addition to effects of brazing time and temperature on the contact angle, have been carried out. In general, dissimilar-metals brazing technology and high-performance brazed joint are necessities for the manufacturing field in the near future. Therefore, to address this requirement, more such studies on wetting and spreading of filler material are required for a deeper understanding. Generally, surface roughness and surface conditions affect spreading of molten brazing filler material during brazing. Wetting by and interfacial reactions of the molten brazing filler material with the metallic substrate, especially, affect strongly the spreading of the filler material. In this study, the effects of surface roughness and surface conditions on the spreading of molten brazing filler metallic alloys were investigated. Ag-(40-x)Cu-xIn and Ag- (40-x)Cu-xSn (x=5, 10, 15, 20, 25) alloys were used as brazing filler materials. A mild-steel square plate (S45C (JIS); side: 30 mm; thickness: 3mm) was employed as the substrate. A few surfaces with varying roughness were prepared using emery paper. Brazing filler material and metallic base plate were first washed with acetone, and then a flux was applied to them. The filler, 50 mg, was placed on the center of the metallic base with the flux. A spreading test was performed under Ar gas using an electrically heated furnace, after which, the original spreading area, defined as the sessile drop area, and the apparent spreading area, produced by the capillary grooves, were both evaluated. It was observed that the spreading area decreased with increasing In and Sn content.

This study aims to develop a new brazing process employing plasma MIG. Because the energy density of the plasma produced by the plasma electrode is low, the base metal can be heated extensively without melting of the base metal, consequently improving the wettability of bead. This paper discussed the dissimilar metal joining of aluminum to steel by plasma MIG brazing process. Fracture occurred at the HAZ in the aluminum plate at 80 MPa.

Laser brazing with Ti as an active element in silver-copper alloy braze metal has been carried out for binder-less cubic boron nitride and tungsten carbide, using silver-copper- titanium braze alloys with titanium content that varied between 0.28 mass% and 1.68 mass%. Observations of the interface using electron probe microanalysis and scanning acoustic microscopy show that efficient interface adhesion between binder-less cubic boron nitride and the silver-copper-titanium braze alloy was achieved for the braze with a titanium content of 0. 28 mass%.

The morphology and growth of interfacial intermetallic compound (IMC) between Sn-3.0Ag-0.5Cu solder alloy and Cu substrate metal of solder joint is reported. The IMC morphology and IMC thickness layer were observed at three different porosities of porous Cu interlayer. The results revealed that during soldering process, Cu₆Sn₅ compound with scallop like morphology was formed at the interface of both the solder alloy and Cu substrate and at solder alloy and porous Cu interlayer. By adding porous Cu interlayer at the solder joint, the IMC thickness increased with increasing soldering temperature and the number of pores in porous Cu interlayer. The effect of porosity on increasing the IMC layer was also due to the slower cooling rate during solidification of molten solder.

Corrosion of stainless steel in a flow soldering bath by a lead-free solder was investigated using a cone-plate-type rotational viscometer. The rotational torque of the stainless-steel cone in contact with a molten solder was measured at various shear rates. The delicate measured torque was related to the change of the viscosity of the solder owing to dissolution of materials originating from the cone. The estimated viscosity coefficient was ten times greater than the values which have been reported. The result was attributed to the tin content of the solder combined with oxygen from the passive state oxide film on the cone surface. The increase of the viscosity of the silver-containing solder was much greater than in case of pure Sn.

The interface bonding between lamellae dominates the properties and performance of plasma-sprayed ceramic coatings. In this study, the interlamellar interface bonding and its effect on the splat microstructure were examined using TEM analysis of the microstructure of a plasma-sprayed Al₂O₃ coating. The obtained results revealed that the intersplat interface microstructure depends significantly on the intersplat bonding. An amorphous phase was observed in the interface region in which the bonding was formed, while the γ-Al₂O₃ phase was observed at the interface where no bonding was formed. In addition, it was found that the interface bonding significantly influenced the interface microstructure of the coating. After heat treatment, the phase of the bonding between adjacent splats was transformed from amorphous to γ-Al₂O₃. In the interface region in which the amorphous phase recrystallization occurred, nanosized pores evolved owing to the volume shrinkage accompanying the transformation of alumina from the amorphous to the γ-Al₂O₃ phase.

Cold spray is a new process for bonding copper and aluminum. In this paper, the interfacial states of cold-sprayed copper on aluminum substrate were evaluated and compared with those resulting from hot extruding. No critical intermetallic layers were observed at the cold-sprayed interfaces and good electrical and mechanical properties were achieved. The effect of annealing on the characteristics of cold-sprayed bonding material was also examined. By annealing at appropriate temperature, a continuous layer of an intermetallic compound was formed and the electrical conductivity and bending strength were improved. This indicates that a good bonding state is obtained by using cold-spray technology in combination with subsequent thermal processing.

The effects of coating thickness and interfacial roughness on the interfacial fracture toughness of tungsten carbide-cobalt (WC-Co) coatings were evaluated using a ring compression test. WC-Co powder was sprayed on steel (JIS:SS400) rings by a high-velocity air- fuel method in coatings with various thicknesses and values of interfacial roughness. The ring compression test was carried out, and the cracking and delamination behavior of the coatings was observed using charge-coupled-device cameras. The results showed that cracking perpendicular to the loading direction occurred in the coatings during the ring compression test, and the cracking strength obtained from the ring compression test decreased slightly with increasing coating thickness, but was independent of the interfacial roughness. Upon further increase of the compression load, the coatings delaminated from the substrate. The interfacial fracture toughness calculated from the delamination of the coatings during the ring compression test decreased with increasing coating thickness and increased with increasing interfacial roughness.

In order to join metals to graphite or ceramics by soldering or brazing, a new surface modification method using induction heating was developed for graphite and ceramics. Such source metals as Cu, Ni, Cr, etc. were induction-heated in vacuum atmosphere and making deposited films on the deposition substrate, or the target substrate; graphite, AlN, Si₃N₄. The applicability of this method was investigated and the deposited layer was analysed by SEM observation, Auger electron spectrum analysis, X-ray diffractometry, and EPMA. By comparison of ambient vacuum pressure during deposition and the saturated vaopr pressure of source metals, this method was considered to utilize the sublimation phenomenon.

The aim of this study was to develop thin film capacitors with superior properties that could provide an alternative to materials currently used in conventional multi-layer ceramic capacitors fabricated by sintering. To this end, an artificial dielectric super lattice technique, incorporating pulsed laser deposition, was applied to improving the dielectric properties of thin film capacitors. This method permits the A-site atoms of a perovskite ABO₃ structure to be selected layer by layer at a nanoscopic scale; consequently, multi-layer BaTiO₃- SrTiO₃ thin films were produced on Pt(111)/Ti/SiO₂/Si(100) and SrTiO₃(111) substrates. Hetero-epitaxial grain growth was observed between BaTiO₃ and SrTiO₃, with the lattice mismatch between them introducing a compressive residual strain at the interface. The dielectric properties of these multi-layer thin-film capacitors were found to be superior to those of conventional solid-solution thin films once the thickness of the layers and the ratio of the two oxides were optimized.

The effect of strain and deformation route on the recrystallization behavior of aluminum sheets has been investigated using well lubricated cold rolling and continuous equal channel angular extrusion. Three different deformation routes in plane strain corresponding to (1) simple shear, (2) compression, and (3) the combination of simple shear and compression were performed on 1100 aluminum sheet. Fixed amounts of the equivalent strain of 1.28 and 1.06 were accumulated in each route. In case of the combined deformation route, the ratio of shear strain to the total equivalent strain was varied. The recrystallized grain size was finer if the combined deformation route was employed instead of the monotonic route under the same amount of equivalent strain at either strain level. The density of high angle grain boundaries that act as nucleation sites for recrystallization was higher in materials deformed by the combined route. The orientation imaging micrographs revealed that the change in deformation route is effective for introducing a larger number of new high angle grain boundaries with relatively low misorientation angle.

The objective of this investigation was to obtain an improved understanding of magnetic pulse welding processes and the mechanisms of electromagnetic forces applied to a one-turn flat coil. Results of simple numerical investigation and experiments show that the electromagnetic forces on the middle part of the coil can be canceled out by loading the welded workpieces on both sides of the coil and can prevent coil deformation and improve its lifetime.

The melting points of 3d transition metal elements show an unusual local minimal peak at manganese across Period 4 in the periodic table. The chemical bonding properties of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel and copper are investigated by the DV-Xα cluster method. The melting points are found to correlate with the bond overlap populations. The chemical bonding nature therefore appears to be the primary factor governing the melting points.

The density distribution of point-contact current is theoretically investigated. Finite current is introduced to a semi-infinite body from the outside. The following assumptions are made: the contact area is circular, magnetic effects are ignored, the contact area is equipotential, the potential equals zero at an infinite distance from the contact area, and the electric permittivity and resistivity are constant. The density distribution of point-contact current for a non-steady state is obtained in an integral form and the derivation process is discussed. The results show that the current density distribution for the non-steady state agrees with that for the steady state. Further, the results suggest that the analytical solution of the density distribution of point-contact current for the steady state is applicable to thermal analysis as well.

This paper reports a method to improve mechanical properties retaining the electrical properties of Ni-based ohmic contact material for n-type 4H-SiC. Ni/Ti bilayered films varying only in the thickness of the Ti layer were deposited on SiC substrates and annealed at 1273 K for a very short time in vacuum. The interfacial structures were analyzed by X-ray diffraction. The electrical and mechanical properties were measured by DC conduction test and constant-load scratch test, respectively. An appropriate thickness of the Ti layer on Ni improves the mechanical properties retaining the electrical properties by forming TiC instead of the free carbon.

In this study, we investigated the nucleation and growth of TE₃SiC₂ by an interfacial reaction between a SiC substrate and a Ti/Al bilayered film at various temperatures. The specimens were prepared by depositing Ti/Al on a 4H-SiC substrate and subsequently annealing the substrate in a vacuum. The interfacial structures were analyzed by X-ray diffraction analysis and transmission electron microscopy. Ti₃SiC₂ nucleated even when annealed at a low temperature of 973 K. The Ti₃SiC₂ grains formed at 973 K were isolated and nonepitaxial with respect to the SiC substrate. By increasing the annealing temperature to 1273 K, the Ti₃SiC₂ grains became epitaxial with the SiC substrate, spreading preferentially on it, and coalesced with each other, forming a layer without grain boundaries.

The present paper describes the influence of surface orientation of n-type GaN on the electrical properties and the interfacial reaction between GaN and Ti during annealing. Although the contact formed on (0001) Ga-face of GaN performs the highest electrical conductance in the as-deposited state, the conductance deteriorates significantly by annealing even at a low temperature of 773 K. A considerable amount of Ti-Ga intermetallic compounds is formed at the deteriorated interfaces, to which the deterioration is attributed.

In the present study, after the formation of Ti₃SiC₂ on p-type GaN by depositing Ti- Si-C ternary film with a composition stoichiometrically close to Ti₃SiC₂ and subsequent annealing at temperatures of 973 K and 1073 K (lower than the annealing temperature for a contact between p-type SiC and Ti₃SiC₂), the resulting contact properties were analysed by X- ray diffraction, a direct-current conduction test, and a Hall-effect measurement test. The X-ray diffraction results reveal that the Ti₃SiC₂ phase is successfully formed after the annealing. The direct-current conduction test shows that ohmic-like contacts are achieved after the formation of Ti₃SiC₂. However, the Hall-effect measurement test reveals that the dominant carrier type of the specimens is inverted from p-type to n-type even after the annealing at 973 K. The N vacancy formation during the annealing is likely the cause of this change. The contact properties of the annealed specimens are discussed because it is difficult to achieve ohmic contact formation between n-type GaN and Ti₃SiC₂.

The purpose of this study has been to develop a low cost bonding technique for thermoelectric Mg₂Si/Si-Ge modules that provides reliable bonding. Aluminum was chosen as an alternative material to conventional silver alloy braze because of its cost advantage and bondability. The shear strength of an aluminum joint between a Mg₂Si element and nickel electrode was 19 MPa. The generation capacity of a prototype Mg₂Si/Si-Ge twin couple module was about 20% higher than that of a conventional Si-Ge/Si-Ge twin couple module at 923 K (ΔT = 620 K).

A 2 × 4 phased array antenna module has been developed for 60-GHz-band short- range high-speed wireless communication terminals. To realize the required vertical distance between the antenna elements, the module is made of five sheets of multi-layered organic substrates vertically stacked with Cu balls, and the 1 x 4 dipole array antenna is placed on both the top and bottom organic substrates. To reduce the mutual coupling between the element antennas, a monolithic microwave integrated circuit (MMIC) is flip-chip mounted on the feed line of each element antenna. The Au-stud bump flip-chip mounting technique helps achieve a lower return loss in the transition section at the MMIC than the Au-wire bonded. The placement accuracy of each antenna element in the vertical direction, 60-GHz signal vertical interconnection between the substrates with Cu balls, and flip-chip mounting of the MMIC are confirmed by 3-D computed tomography (CT) scans.

An incrementally coupled "mechanical-ultrasonic" finite element model, in which both the ultrasound vibration and the bonding force are considered simultaneously, is used to model the thermosonic Cu wire-bonding process on Cu/low-k structures and to study the influence of the passivation layer on the stress condition in the Cu/low-k layer. Results show that the passivation layer acts as a stress buffer layer during the wirebonding process. The introduction of a passivation layer alleviates some of the impact effect from the free air ball (FAB). Increasing the passivation thickness can lead to significant stress alleviation. However, as the elastic modulus of passivation increases, the alleviation effect increases notably at first and then decreases.

Compared with conventional reflow soldering using a furnace, laser reflow soldering brings advantages such as localized heating, rapid rise and fall in temperature, non-contact soldering and the fact that it is an easily automated process. In this study, to elucidate the characteristics of laser reflow soldering, we investigated the microstructures of a Sn-Ag-Cu solder bump and a Sn-Bi solder bump on a Cu pad after reflow and aging. In the as-soldered condition, we found obvious microstructural refinement and a thin intermetallic compound (IMC) layer at the interface for both the Sn-Ag-Cu solder bump and the Sn-Bi solder bump using laser reflow soldering. Also, during isothermal aging, the total thickness of the IMC layer increased, and a distinct second layer was observed at the interface between the Cu pad and the first layer, regardless of the soldering method. In particular, the growth of the IMC layer was faster in the case of the laser reflow soldering than in the case of the conventional reflow soldering.

Anatase (A-) TiO₂ is a photocatalytic material that can decompose air-pollutants, acetaldehyde, bacteria, and so on. In this study, three kinds of powder (A-TiO₂ without HAp, TiO₂ + 10mass%HAp, and TiO₂+30mass%HAp, where HAp is hydroxyapatite and PBS is polybutylene succinate) were plasma sprayed on biodegradable PBS substrates. HAp powder was mixed with A-TiO₂ powder by spray granulation in order to facilitate adsorption of acetaldehyde and bacteria. The crystal structure was almost completely maintained during the plasma spray process. HAp enhanced the decomposition of acetaldehyde and bacteria by promoting adsorption. A 10mass% HAp content was the most effective for decomposing acetaldehyde when plasma preheating of the PBS was not carried out before the plasma spraying. The plasma preheating of PBS increased the yield rate of the spray process and facilitated the decomposition of acetaldehyde by A-TiO₂ coatings without HAp. HAp addition improved photocatalytic sterilization when plasma preheating of the PBS was performed.

For heat removal from systems such as electronic equipment, satellite thermal control systems, and nuclear reactors, reduction of thermal contact resistance (TCR) is the most crucial issue to be addressed. Several studies have attempted to propose evaluation equations for predicting TCR for flat rough surfaces. However, as is well known, there are still wide discrepancies among measured results, even for similar materials. In this study, based on the conventional unit cell model for flat surfaces with roughness and the newly proposed contact surface model for wavy surfaces with roughness, thermal contact resistance under a low contact pressure of 0.I-I.0 MPa is investigated theoretically and experimentally. Comparison of the measured and calculated results shows that the measured temperature drop at the interface (that is, the thermal contact resistance) between flat surfaces with roughness lies between the values evaluated by the unit cell model for the cases with and without the heat flow constriction. Furthermore, when the rough surface has waviness, the introduction of macroscopic constriction resistance is shown to be important for evaluating the temperature drop at the interface.

A multi-beam structure using Ti-Ni wire to grip rough surfaces and control detachment was manufactured. The grip-and-release mechanism of the structure was investigated. The experimental results were analyzed with a model assuming beam theory and using a fracture criterion at the adhered interface. The fracture criterion of the adhesion interface is suggested to depend on the shear stress.

Contact between a silica glass lens and silicone rubber is experimentally investigated by simultaneously measuring displacement, force and contact radius. The relationship between these three parameters is derived using elastic theory. The discrepancy between the theoretical relationship and the experimental results is observed to increase as the deformation of the silicone rubber increases. Under smaller deformation conditions, the elastic theory shows good agreement with the experimental results, although infinite stress on the edge of the contact area is predicted in the theory, and time dependence and adhesion hysteresis are observed in all experiments. It is suggested that time dependence and adhesion hysteresis in contact are not induced by the deformation of the bulk of the silicone rubber, but are induced by surface effects. The result suggests that the applicability limit of the elastic theory must be carefully considered in the JKR analysis of point contact for polymers.

An analysis on a tapered elastic beam whose side surface partially adhered to a rigid surface was carried out to study the effect of the beam shape on the gripping force. Considering the total energy of the system, the relation between the gripping force and the displacement was obtained analytically in closed form. The analytical result is significant because it provides an intuitive picture of the gripping force. Although, an individually tapered beam can generate less gripping force for flat or slightly wavy surfaces, compared to a rectangular beam, the analysis result suggests that the tapered beam has more ability to absorb surface waviness. This result can be applied to a multi-beam structure.