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Void formation is a critical reliability concern for solder joints in electronic packaging. The control of microstructures and the quantity of impurities in Cu electroplated films significantly affect void formation at the joint interface, but studies investigating these factors are rare. In this study, three Cu films (denoted as A, B, and C) are fabricated using an electroplating process. The Cu A film has a faceted grain texture embedded with twin boundaries, while Cu B and C films have similar columnar textures. After thermal aging at 200 °C for 1000 h, the SAC 305 (Sn-3.0Ag-0.5Cu) solder joints with Cu A and B films exhibit robust interfacial structures without voids. However, microstructural collapse is observed in the solder joint of SAC 305/Cu C, where many crevices are formed parallel to the interface. Based on the microanalysis, the concentration of impurities is higher in Cu C than in Cu A and B. Moreover, discrete voids rather than continuous crevices are present in the SAC305/Cu C system when the impurity concentration in Cu C is reduced. The findings demonstrate that impurity control in Cu electroplated film is critical for the control of void/crevice formation in electronic solder joints.

A better replacement of electrocatalytic platinum on counter electrodes of dye-sensitized solar cells (DSSCs) has received increasing attention to achieve a balance between efficient charge transfer and cost-effectiveness. Using an electrochemical polymerization method, a polymeric layer of poly(2H,2′H,4H,4′H-3,3′-spirobi[thieno[3,4-b][1,4]dioxepine]), called poly(spiroBiProDOT), was fabricated on a fluorine-doped tin oxide (FTO) counter electrode. For comparison, poly(3,4-ethylenedioxythiophene), called PEDOT, a polymer layer and Pt were also deposited on the FTO counter electrode. Photovoltaic characterizations of the fabricated solar cells based on poly(spiroBiProDOT), PEDOT, and Pt counter electrodes were performed, and maximum power conversion efficiencies of 7.9%, 6.8%, and 8.31% were achieved, respectively. Poly(spiroBiProDOT) exhibits a stronger competitiveness to replace Pt in comparison with PEDOT. The competitiveness mainly comes from the better charge transfer in poly(spiroBiProDOT) due to its ordered thiophene moiety connected by a spiro linkage, which can increase the photocurrent density, and therefore, the cell efficiency. Electron density calculation, microstructural characterization, and impedance analysis were performed to rationalize the better efficiency of poly(spiroBiProDOT).

Due to its superior chemical stability, mechanical strength, light weight, and flexibility, polyimide (PI) has been widely used as a polymeric substrate of flexible printed circuit boards such as flexible copper clad laminates (FCCLs). The development of an adhesiveless dual-layer structure is imperative for the application of FCCLs in globalized 5G consumer electronics. In this work, autocatalytic metallization on a silane-grafted PI film was developed to fabricate a high-quality Cu/PI substrate. PI was functionalized by amine-terminated organosilanes to load polyvinylpyrrolidone-capped Pd nanoclusters (PVP-nPd) as a catalyst. The effects of organosilanes with different numbers of amine functional groups on the adsorption of the PVP-nPd catalyst and the subsequent metallization of Cu were systematically investigated. Comprehensive surface characterizations were carried out on the PI films before and after silanization. The organosilane bearing three amine groups was found to outperform its counterpart with one amine group, exhibiting a fourfold increase in catalyst adsorption, which also improved the metallization efficiency.

Silicon (Si) on-chip metallization was carried out through surface functionalization and electroless deposition of copper (Cu). Surface functionalization of Si was performed by grafting an amine (N...

Surface metallization of polymer substrate and film adhesion are crucial to the development of flexible electronics. This study demonstrates the co-silanization engineering on the polyimide (PI) film by mutual intercropping of two organosilane molecules to improve their grafting orientability and enhance the adsorbability toward the PI substrate and loaded metal atoms. The mutual intercropping-inspired co-silanization engineering is implemented by using 3-[(trimethylsilyl)ethynyl]pyridine (TEP) as a supporting organosilane to spatially confine the grafting orientation of the supported aminosilane, 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (ETAS), leading to the formation of a well-oriented organosilane composite nanolayer as adhesion promotion layer for flexible conductors. The flexible Cu conductor electrolessly deposited on the PI film by co-silanization shows improved adhesion strength (0.9 kgf/cm) compared to those based on mono-silanization (0.51 kgf/cm) and sputtered Ta/Cu (0.4 kgf/cm). Superior deformability (bendability) was also achieved for the co-silanized Cu/PI sample by retaining good electrical property after bending cycle up to 1000.

For pursuing a more comprehensive mechanism of void formation at the Sn/Cu interface, different grain size Cu samples with and without twinned boundaries are electrodeposited for the Sn/Cu joint an...

Controlling the orientation of the dye molecules adsorbed on the TiO2 surface needs extensive attention for improving the photovoltaic parameters of dye-sensitized solar cells (DSSCs). The suppression of the charge recombination and self-aggregation of dye molecules on the TiO2 surface also plays a vital role in the improvement of cell efficiency. In this report, based on the bi-anchored structure containing N-alkyl-attached 1,8-naphthalamide derivative as the donor system and spiroBiproDOT as the π-spacer, an organic dimeric dye (D-Dye) was designed and synthesized by Suzuki coupling, followed by Knoevenagel condensation. The maximum power conversion efficiency of 7.1% with a Voc and Jsc of 0.70 V and 14.6 mA cm−2, respectively, was achieved for the DSSC employing D-Dye. A monomeric dye (M-Dye) was also synthesized and the resultant cell efficiency of 4.85% was achieved with Voc and Jsc of 0.67 V and 9.93 mA cm−2, respectively, which was 33% lower than that of its dimeric analogue (D-Dye). The photo-physical experiment was carried out for both organic dyes to understand their light absorption characteristics. The incident photon-to-current conversion efficiency (IPCE) and electrochemical impedance measurements were also obtained to rationalize the better photovoltaic performance of DSSCs employing the dimeric D-Dye, which was due to the effective suppression of the charge recombination and self-aggregation of dye molecules. The co-adsorption of D-Dye (0.4 mM) with N-719 (0.4 mM) in the ratio of 10 : 1 v/v (D-Dye:N-719) further enhanced the cell efficiency to 8.34% (Voc of 0.77 V and Jsc of 14.9 mA cm−2).

Locknut is a critical component used in the precision machinery and its stable service performance over a long period of time in a variety of different environments presents a crucial challenge. In this study, a flank-locking precision locknut was pretreated in an immersion corrosion of 5 wt% NaCl solution to simulate the possible corrosion effects. The tightening and loosening of the locknut after 0-, 1-, 2- and 4-h corrosion treatments, respectively, was tested according to the ISO 2320 Standard. An in-house test setup with horizontal configuration was employed in measuring the torque–axial force characteristics under loading–unloading cycles. It was found that the corrosion of the locknut accelerated after 1-h immersion. The corroded specimens after 2- and 4-h treatment demonstrated more variance in measured tightening and loosening torques than their less corroded counterparts. However, after five loading–unloading cycles, the variance in measured torque decreased and the associated torque constants became more stable. Moreover, the torque constants were ∼10% higher for the 2- and 4-h corrosion-treated locknuts than their pristine counterpart. The surface morphology after corrosion and friction wear was closely related to the measured testing results.

The effect of multiple reflowing processes on interfacial reactions and mechanical properties of the Sn-9.0 wt.%Zn (SZ)/Ag and Sn-3.0 wt.%Ag-0.5 wt.%Cu (SAC)/Ag couples was investigated in this study. The SZ/Ag and SAC/Ag couples were reflowed at 240°C for 10 min in one up to five times. After reflowing, all couples were quenched in icy water and air-cooling conditions. The experimental results revealed that the AgZn3, Ag5Zn8, and AgZn phases were formed in the SZ/Ag couple. The thin AgZn3 layer was observed when the SZ/Ag couple was quenched in icy water. When the number of reflows was increased, a rod-shaped Zn phase gradually became a fine needle-shaped Zn phase. Only the Ag3Sn phase was formed in the SAC/Ag couple. The growth mechanism of the intermetallic compound was diffusion-controlled in both reaction couples. A brittle fracture was observed in the SZ/Ag solder joint. The fracture surface showed the ductile and slightly brittle failure in the SAC/Ag solder joint.

Introduction of an ultrathin compact layer in dye-sensitized solar cells (DSSCs) can improve the cell efficiency under standard one sun illumination (> 100,000 lx). Herein, an ultrathin Nb2O5 layer is deposited on the TiO2-coated photoanode using a facial dip-coating method and its effects on the cell efficiency under a low level of light intensity (300–6000 lx) is studied. The results show that the ultrathin Nb2O5 layer helps the DSSCs to improve their power conversion efficiency (PCE) through different ways under standard one sun and low power illuminations. Under strong one sun illumination, the PCE of DSSC is improved by improving the short-circuit current density (JSC) which can be attributed to an increment of the surface area of photoanode for more dye adsorption and the blocking effect of Nb2O5. Under low power illumination, the introduction of Nb2O5 blocking layer improves the fill factor by effectively suppressing the charge recombination on the photoanode.

The use of organic additives is crucial for Cu electrodeposition. However, specific impure species originating from the additives are incorporated in the Cu electroplated layer, causing serious reliability problems such as void formation at the solder/Cu joints. In this study, three Cu substrates were electroplated using various additive formulas. The use of organic additives results in an incorporation of a higher level of impurity in the Cu-electroplated layers and also affects the atomic deposition behavior of Cu which alters the grain microstructures. By using a specific additive formula, the grain growth of Cu evolves into a slender structure with a high density of twins. Thermal aging experiments of the Sn/Cu joints show that the void formation is successfully suppressed at the joint using a slender-grained Cu substrate, and that the suppression effect is attributed to the high microstructural stability of the twinning structure.

The existence of voids in the solder joints has been a serious reliability problem in microelectronics. A comprehensive understanding of the formation mechanism of voids is the cornerstone to solve the problem. This study reports an unusual phenomenon of voiding in the Sn/Cu solder joints and the most unique finding is that the voids were formed at the solder side (the Sn/Cu6Sn5 interface) rather than at the Cu side (the Cu3Sn/Cu interface) due to Kirkendall effect. Cross-sectional and topographic examination of the Sn/Cu interface using a scanning electron microscopy clearly positioned the voids on the surface of the Cu6Sn5 grains and their grain boundaries (triple junctions). Gas chromatograph (GC)/flame ionization detector (FID) microanalysis was performed to rationally correlate the outgassing of the Cu electroplated substrate and the void formation at the Sn/Cu6Sn5 interface.

An organosulfide, 3‑(2‑benzthiazolylthio)‑1‑propanesulfonsaure (ZPS), is used as an accelerator and formulated with a suppressor (polyethylene glycol, PEG) and chloride ions (Cl−) in the copper plating solution containing electrolytes (Cu sulfate and sulfuric acid) to prepare the Cu films. Microstructural characterization using focus ion beam (FIB), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) reveals that an increase of the ZPS concentration accelerates the grain growth of the electroplated Cu films. Impurity examination based on time-of-flight secondary ion mass spectrometer (TOF-SIMS) shows that such microstructural evolution effectively suppresses the impurity incorporation in the electroplated Cu films. The suppression effect on impurity incorporation by using a high level of ZPS concentration plays an important role in retaining the microstructural stability and integrity of the electroplated Cu solder joints subjected to thermal aging.

The mechanical performance of electroplated Cu plays a crucial role in next-generation Cu-to-Cu direct bonding for the three-dimension integrated circuit (3D IC). This work reports direct-current electroplated (111)-preferred and nanotwin-doped nanocrystalline Cu, of which strength is at the forefront performance compared with all reported electroplated Cu materials. Tension and compression tests are performed to present the ultrahigh ultimate strength of 977 MPa and 1158 MPa, respectively. The microstructure of nanoscale Cu grains with an average grain size around 61 nm greatly contributes to the ultrahigh strength as described by the grain refinement effect. A gap between the obtained yield strength and the Hall–Petch relationship indicates the presence of extra strengthening mechanisms. X-ray diffraction and transmission electron microscopy analysis identify the highly (111) oriented texture and sporadic twins with optimum thicknesses, which can effectively impede intragranular dislocation movements, thus further advance the strength. Via filling capability and high throughput are also demonstrated in the patterned wafer plating. The combination of ultrahigh tensile/compressive strength, (111) preferred texture, superfilling capability and high throughput satisfies the critical requirement of Cu interconnects plating technology towards the industrial manufacturing in advanced 3D IC packaging application.

Background Cu-Cu direct bonding is a promising technology to construct a temperature resistant bonding structure for emerging power devices and vehicle electronics. The main challenge is the ease oxidation of Cu and slow solid-state atomic diffusion at the bonding surface. Methods In this study, nanocrystalline Cu is constructed on the bonding surfaces using electrodeposition and direct bonding is carried out in a formic acid atmosphere. Microstructural and strength analyses are performed to investigate the bonding performance of the Cu-Cu joints. Significant findings The bonding strength analysis indicates that a well-bonded Cu-Cu joint with a high shear strength of 71 MPa can be achieved by direct bonding of two Cu surfaces with a nanocrystalline structure (average grain size = 78 nm). Microstructural analysis shows that significant grain growth accompanying formation of twins at the bonding interface contribute to high bonding strength, which is attributed to enhanced atomic diffusion on the nanocrystalline Cu surfaces.

Cost-effective copper (Cu) electroplating is the primary technique used to fabricate wires/interconnects in microelectronics. Grain microstructure and impurity incorporation in electroplated Cu plays an important role in its mechanical, electrical, and thermal properties. In this study, a specific plating formula with a basic electrolyte and a suppressor, polyethylene glycol (PEG) and chloride ion (Cl−), is used to fabricate the Cu layers. An adjustment of plating current density dramatically alters the grain microstructure and impurity incorporation in the electroplated Cu. Scanning electron microscopy (SEM) and coincidence site lattice (CSL) analyses show that the Cu deposit plated at a low current density (

The solid/liquid reaction couple technique was employed to investigate the interfacial reactions between Cu-xZn (x = 0 wt.%, 5 wt.%, 15 wt.%, 30 wt.%, 40 wt.%) alloys and lead-free solders Sn, Sn-3.0Ag-0.5Cu (SAC, in wt.%), and Sn-9Zn (SZ, in wt.%) alloys at 240°C, 270°C, and 300°C for 0.5 h to 100 h. (Cu,Zn)6Sn5 and (Cu,Zn)3Sn phases were formed in the Sn/Cu-xZn (x = 5 wt.%, 15 wt.%, 30 wt.%) reaction couples, but with increasing reaction temperature and time, (Cu,Sn)Zn phase was formed, replacing (Cu,Zn)3Sn phase. Metastable T phase and (Cu,Sn)Zn phase were formed in the Sn/Cu-40Zn reaction couple at 300°C. (Cu,Zn)6Sn5 and (Cu,Zn)3Sn phases formed in the SAC/Cu-xZn (x = 5 wt.%, 15 wt.%) reaction couples. Furthermore, (Cu,Zn)6Sn5 and (Cu,Zn)Sn phases were observed when the SAC solders reacted with Cu-30Zn and Cu-40Zn alloys. T phase and (Cu,Sn)Zn phase were formed in the SAC/Cu-40Zn reaction couple reacted at 300°C for 100 h. (Cu,Sn)Zn5 and (Cu,Sn)5Zn8 phases were formed in the SZ/Cu-Zn reaction couples at 240°C. However, with increasing reaction time and temperature, only (Cu,Sn)5Zn8 phase was detected. Therefore, it can be concluded that the intermetallic compound (IMC) formation was sensitive to both the reaction temperature and the Zn content in the Cu-Zn alloy.

The use of functional additives in the electroplating process results in an impurity incorporation in the Cu plated layer. A high level of impurity residual has been recognized as a severe reliability problem to the Sn/Cu joints because voids are prone to form at the Sn/Cu interface in the thermal aging process. This study focuses on the effect of aging temperature on the formation and distribution of voids. Two electroplated Cu substrates and one rolled Cu foil were joined Sn balls to prepare the Sn/Cu joints for thermal aging in the range of 100–200 °C. The microstructural examination results indicated that the additive formula of polyethylene glycol (PEG) and Cl− resulted in massive void formation at the Sn/Cu interface, and the distribution of voids showed a strong dependence on the aging temperature. The strong temperature dependence of void distribution led to an unusual evolution of microstructure and shear strength in the Sn/Cu joints.

Cu-Zr based alloys have been used as metallic glass alloys owing to their high glass forming ability (GFA). Ni is added into these alloys to enhance their mechanical property and improve GFA. These Cu-Ni-Zr ternary alloys have a high potential to be used as metallic glass alloys. Herein, we investigated and assessed thermodynamically the phase equilibria of the Cu-Ni-Zr ternary system at 800 °C using the calculation of phase diagram (CALPHAD) method based on the experimental data. Thirty-three alloys were prepared using the arc melting method. At 800 °C, the isothermal section of the Cu-Ni-Zr ternary system composed of 15 single-phase regions, 20 two-phase regions, and 8 three-phase regions; no ternary intermetallic compounds were found. In addition, a continuous solid solution was formed by the Cu10Zr7 and Ni10 Zr7 phases at 800 °C. Furthermore, the thermodynamic parameters were optimized using the phase equilibrium data. The calculated isothermal section and metallic glass region prediction of the Cu-Ni-Zr ternary system were reasonable and satisfactory compared with the literature data.

Traditional fluorogens with aggregation-induced emission (AIEgens) generally exhibit strong luminescence with monotonous wavelengths in the aggregated state, whereas apparent solvatochromic emission intensities and wavelengths (shift) are observed in molecules with twisted intramolecular charge transfer (TICT) characteristic molecules. Herein, we develop a platform to construct strong luminescent nanoparticles with tunable emission colors based on a TICT-AIEgen, 3,6-divinylaryl-substituted carbazole (C12P). Also based on the same molecule, through different nanoparticle fabrication approaches, fluorescent nanoparticles with different emission colors were obtained. A detailed analysis reveals that AIE and TICT characteristics play different roles in nanoparticle emission, with AIE primarily controlling the emission intensity while TICT is more involved in manipulating the emission wavelengths. Applications of the as-prepared nanoparticles in cell imaging were preliminarily demonstrated.

Development of emerging technologies such as artificial intelligence, big data, and smart vehicles brings increasing demands on high-performance integrated circuits (ICs). To achieve this goal, ultra-miniaturization of Cu interconnects as well as diffusion barrier layer to increase the integration density is imperative. In this study, we demonstrate that an ultrathin organosiloxane nanolayer exhibits excellent barrier efficacy against the active diffusion of Cu towards Si. The organosiloxane nanolayer is constructed on the SiO2 surface using dehydration to covalently tether the hydrolyzed organosilane molecules. The amine termini of organosilanes are used to adsorb catalytic Pd nanocluster to accomplish the Cu metallization on Si. Rapid thermal annealing is performed with respect to the Si/SiO2/organosiloxane/Cu junctions to evaluate the efficacy of diffusion barrier. Based on microstructural and crystallographic examinations, the organosiloxane nanolayer with a shorter alkyl chain performs better with a higher breakdown temperature of 923 K at which the Cu diffusion and the Cu silicide formation at the junctions occur. The grafting conformations of organosilane molecules with various alkyl chain lengths on the SiO2 surface are constructed based on energy minimization calculations to rationalize the diffusion barrier efficacy.

Intensification of light harvesting is an imperative strategy to improve the photovoltaic performance of dye-sensitized solar cells (DSSCs). The typical way is to employ a light scattering layer on top of the photoanode to augment the photon scattering of incident light for light harvesting of dye sensitizers. In this study, we have designed a new light scattering layer consisting of micro-sized sericite flakes and TiO2 nanoparticles, and material optimization is performed by using two sizes of TiO2 nanoparticles (P25-TiO2 of 20-30 nm and B-TiO2 of 30-100 nm) as the matrix to dope sericite flakes. This hybrid scattering layer gives rise to an enhancement of power conversion efficiency of DSSC under 1 sun and low-intensity illuminations. Maximum cell efficiencies of 8.667 % and 8.963 % are recorded for the DSSCs employing P25-TiO2/5 wt% sericite and B-TiO2/25 wt% sericite scattering layer, respectively, at 1 sun illumination, which outperforms that employing pure TiO2 scattering layer (8.2 %). Maximum cell efficiencies of 22.936 % and 23.121 % are optimized at 6,000 lux following the same TiO2/sericite hybrid systems. Such addition of sericite in the scattering layer indeed enhances the light harvesting performance and offers a new pathway to prepare more efficient light scattering layer.

Epoxy with low viscosity and good fluidity before curing has been widely applied in the packaging of electronic and electrical devices. Nevertheless, its low flexibility and toughness renders the requirement of property improvement before it can be widely acceptable in dynamic loading applications. This study investigates the possible use of 2-hydroxyethyl methacrylate (HEMA) toughening agent and nano-powders, such as alumina, silicon dioxide, and carbon black, to form epoxy composites for dynamic property improvement. Considering the different combinations of the nano-powders and HEMA toughener, the Taguchi method with an L9 orthogonal array was adopted for composition optimization. The dynamic storage modulus and loss tangent of the prepared specimen were measured by employing a dynamic mechanical analyzer. With polynomial regression, the curve-fitted relationships of the glass transition temperature and storage modulus with respect to the design factors were obtained. It was found that although the raise in the weight fraction of nano-powders was beneficial in increasing the rigidity of the epoxy composite, an optimal amount of HEMA toughener existed for its best damping improvement.

Titanium (Ti) is a promising choice as the photoelectrode substrate of dye-sensitized solar cells (DSSCs) due to its high compatibility and stability. To enhance the efficacy of Ti more than a substrate, structural modification of Ti via anodization is performed to construct a TiO2 nanotube structure on the surface. Optimization of the TiO2 nanotube structure as a function of anodization potential is carried out in conjunction with the photovoltaic characterization of DSSCs using commercial N719 dye and synthesized organic D-Dye as the sensitizer. The highly oriented TiO2 nanotube structure not only increases the interactive contact area in between the Ti substrate and active semiconductor layer composed of TiO2 nanoparticles but also serves as a fast pathway for charge transfer and an additional channel to carry sensitizers, thereby greatly improving the cell efficiency. Maximum efficiency of 7.67% (Jsc of 16.06 mA/cm2, Voc of 0.693 V, and FF of 0.689) is achieved for the cell constructed by anodized Ti photoelectrode using N719 dye under 1 sun illumination. Incorporation of D-Dye further enhances the cell efficiency to 7.93% (Jsc of 16.65 mA/cm2, Voc of 0.701 V, and FF of 0.68) and this is attributed to the spatial effect of D-Dye molecules which have a long wingspan capable of suppressing the molecular aggregation. Under low light illuminations, maximum efficiency of 15.31% and 18.06% are reached for the cells constructed by anodized Ti photoelectrode using D-Dye under 3000 and 6000 lx illumination, respectively.

Bismuth-telluride (Bi2Te3)-based compounds are common thermoelectric materials used for low-temperature applications, and nickel (Ni) is usually deposited on the Bi2Te3 substrates as a diffusion barrier. Deposition of Ni on the p-type (Sb-doped) and n-type (Se-doped) Bi2Te3 substrates using electroplating and interfacial reactions between Sn and Ni-coated Bi2Te3 substrates are investigated. Electrodeposition of Ni on different Bi2Te3 substrates is characterized based on cyclic voltammetry and Tafel measurements. Microstructural characterizations of the Ni deposition and the Sn/Ni/Bi2Te3 interfacial reactions are performed using scanning electron microscopy. A faster growth rate is observed for the Ni deposition on the n-type Bi2Te3 substrate which is attributed to a lower activation energy of reduction due to a higher density of free electrons in the n-type Bi2Te3 material. The common Ni3Sn4 phase is formed at the Sn/Ni interfaces on both the p-type and n-type Bi2Te3 substrates, while the NiTe phase is formed at a faster rate at the interface between Ni and n-type Bi2Te3 substrates.

Ni is the most commonly used barrier in thermoelectric solder joints, and its role is to avoid excessive reaction between the bismuth telluride (Bi 2 Te 3 ) element and the Sn-based solder. This study, for the first time, demonstrates a strong effect of the Bi 2 Te 3 substrate on the electrodeposition of Ni layer, consequently affecting the interfacial reaction with the Sn-4 wt.% Ag-0.5 wt% Cu (SAC405) solder. Two types of Bi 2 Te 3 substrates, prepared using zone-melting and ball-milling/hot-pressing methods, exhibit different crystal structures, and this structural difference significantly affects the microstructures of the Ni diffusion barrier electroplated on the Bi 2 Te 3 substrates and the growth of their intermetallic compound (IMC) at the SAC405/Ni/Bi 2 Te 3 solder joints. The Ni layer electroplated on a zone-melted Bi 2 Te 3 substrate (anisotropic crystal structure) has a small grain size and a high grain-boundary density, and one IMC, (Cu,Ni) 6 Sn 5 , is formed at the interface between SAC405 and Ni after joining. The other (Ni,Cu) 3 Sn 4 phase is formed at the (Cu,Ni) 6 Sn 5 /Ni interface after thermal aging and grows at a progressively faster rate with increasing aging time. In contrast, the Ni layer electroplated on a ball-milled/hot-pressed Bi 2 Te 3 substrate (isotropic crystal structure) has a large grain size and a low grain-boundary density, and only the (Cu,Ni) 6 Sn 5 phase is formed at the SAC405/Ni interface, with a very sluggish growth rate after joining and thermal aging. Since the IMCs are electrically resistive and mechanically brittle, the latter solder joint with a large-grained Ni layer on a ball-milled/hot-pressed Bi 2 Te 3 substrate appears to have better reliability.

Effect of Ni grain size on the formation and growth kinetics of intermetallic compounds at the Sn/Ni interface is studied. For a coarse-grained Ni foil, only the Ni 3 Sn 4 phase is formed with a thickness of 28 μm after aging at 200 °C for 1000 h. For a Ni electroplated layer with a fine-grained microstructure, the Ni 3 Sn 4 phase grows at a very sluggish rate and its thickness is only 5 μm in the same reaction condition. The suppression effect on the Ni 3 Sn 4 growth is attributable to the diffusion barrier effect of a thin Ni 3 Sn 2 phase formed on the Ni electroplated layer.

In this paper, we first incorporated Al(NO 3 ) 3 ·9H 2 O as the Al source into ZnO nanorods (NRs) lattice via the hydrothermal method to modify nature properties of ZnO NRs for the fabrication of perovskite solar cells (PSCs). The X-ray diffraction (XRD) pattern of Al-doped ZnO NRs exhibits higher 2θ values and stronger intensity of (002) plane. Larger optical band gap and higher electrical conductivity of Al-doped ZnO NRs are also observed relative to non-doped ZnO ones. The steady-state photoluminescence shows effective charge extraction and collection at the interface between Al-doped ZnO NRs and perovskite layer. The optimized PSC based on Al-doped ZnO NRs showed an open-circuit voltage of 0.84 V, a short-circuit current density of 21.93 mA/cm 2 , a fill factor of 57%, and a power conversion efficiency of 10.45% that was 23% higher than the non-doped ZnO ones.

Surface metallization of polyimide (PI) is the key process for the preparation of flexible printed circuit boards (FPCBs). To meet the miniaturization demand, the ultrathinness of FPCB by the removal of the intermediate adhesive layer is imperative. The common adhesiveless process relies on the surface activation of hydrophobic PI through alkaline hydrolysis to generate the hydrophilic carboxylate anion sites for the metallic deposition. However, the alkaline hydrolysis process involves the imide ring cleavage caused by the attack of a strong nucleophile (OH

Autocatalytic metallization of polyimide (PI) is accomplished through surface composite engineering as a facile approach to fabricate flexible printed circuit boards. The surface composite engineering of PI involves the generation of active sites by plasma activation, attachment of amine-terminated organosilanes through covalent bonding with the active sites, adsorption of a palladium catalyst by a complex reaction with the amine groups, and electroless deposition of copper through autocatalytic metallization. Three aminosilanes with various numbers of amine units are employed to silanize the PI surface and to create amine functionalities, successfully achieving a high coverage of copper deposition. The standard 90° peeling test further identifies that the aminosilane with one amine unit outperforms the others with two and three amine units in the adhesion performance of the copper layer, with the highest peel strength reaching 0.8 kgf/cm. A systematic study is performed to experimentally and theoretically explore the grafting conformation of the three aminosilane/PI composite systems at the atomic level, and the correlation with the peel strength performance is also investigated.

A Sn/Bi bilayer was deposited on a hot air solder leveling (HASL)-treated metal-core printed circuit board (MCPCB) using electroplating as a low-temperature die-bonding material for light-emitting diode (LED). The eutectic feature of the Sn/Bi contact enabled the die-bonding process to accomplish through a liquid/solid reaction at 185 °C with a proper compression force. A high-temperature die-bonding structure composed of a Bi layer sandwiched by two intermetallic compounds (IMCs) formed after thermocompression. Employment of the Sn/Bi bilayer for low-temperature die-bonding prevented the LEDs from thermal stress problems, and the resulting high-temperature IMC/Bi/IMC die-bonding structure was capable of withstanding multiple bonding reactions and high temperature/current operation environment. Durability tests including mechanical, thermal, and optical performance were systematically performed and compared with other commercially available die-bonding materials (Ag paste and solder alloys).

The Fe-42 wt.% Ni alloy, also known as a 42 invar alloy (Alloy 42), is used as a lead-frame material because its thermal expansion coefficient is much closer to Si substrate than Cu or Ni substrates. In order to enhance the wettability between the substrate and solder, the Sn layer was commonly electroplated onto the Alloy 42 surface. A clear understanding of the phase equilibria of the Fe-Ni-Sn ternary system is necessary to ensure solder-joint reliability between Sn and Fe-Ni alloys. To determine the isothermal section of the Fe-Ni-Sn ternary system at 270°C, 26 Fe-Ni-Sn alloys with different compositions were prepared. The experimental results confirmed the presence of the Fe3Ni and FeNi phases at 270°C. Meanwhile, it observed that the isothermal section of the Fe-Ni-Sn ternary system was composed of 11 single-phase regions, 19 two-phase regions and nine tie-triangles. Moreover, no ternary compounds were found in the Fe-Ni-Sn system at 270°C.

Sn–Bi alloys form some of the common types of Pb-free solders. Au is used as one of the under bump metallization layers due to advantages such as corrosion resistance and anti-oxidation properties. Phase equilibria information plays a vital role in the development of materials technology and serves as an important tool to understand interfacial reactions at heterointerfaces. In this study, the phase equilibria in the Au–Bi–Sn ternary system were experimentally investigated at temperatures of 80, 125, and 150 °C. The results indicated that a ternary phase with a composition of Au45 – 48-Bi36 – 38-Sn14–19 (at.%) was found in the Au–Bi–Sn ternary system at these three temperatures.

Front-side metallization of a Si wafer was carried out using electroless deposition of nickel-phosphorus (Ni-P) catalyzed by polyvinylpyrrolidone-capped palladium nanoclusters (PVP-nPd). A 3-[2-(2-Aminoethylamino)ethylamino] propyl-trimethoxysilane (ETAS) layer was covalently bonded on the Si surface as bridge linker to the Pd cores of PVP-nPd clusters for improving adhesion between the Ni-P layer and the Si surface. To investigate the effects of an interfacial ETAS layer on the Ni silicide formation at the Ni-P/Si contact, the Ni-P-coated Si samples were thermally annealed via rapid thermal annealing (RTA) from 500°C to 900°C for 2 min. To compare with the ETAS sample, the sputtered Ni layer on Si and electroless Ni-P layer on ion-Pd-catalyzed Si (both are standard processes) were also investigated. The microstructural characterizations for the Ni-P or Ni layer deposited on the Si wafer were performed using x-ray diffractometer, scanning electron microscopy, and transmission electron microscopy. Our results showed that the ETAS layer acted as a barrier to slow the atomic diffusion of Ni toward the Si side. Although the formation of Ni silicides required a higher annealing temperature, the adhesion strength and contact resistivity measurements of annealed Ni-P/Si contacts showed satisfactory results, which were essential to the device performance and reliability during thermal annealing.

Ethyl cellulose (EC) was added to a titania (TiO2) paste from 2 wt.% to 18 wt.% as a binder/dispersant, and its effects on the photovoltaic performance of dye-sensitized solar cells (DSSCs) were investigated. The TiO2 mesoporous film constructed on the photoanode exhibited a dense and network structure composed of well-interconnected TiO2 nanoparticles when using a proper amount of EC (10 wt.%). Excessive and deficient addition of EC resulted in aggregation of TiO2 nanoparticles and formation of pores, respectively, in the TiO2 film. The power conversion efficiency (PCE) of DSSC showed a strong dependence on the EC content and the highest PCE of 7.53% with the highest short-circuit current density (J SC) of 12.7 mA/cm2 was achieved when the content of EC was 10 wt.%. The incident photon-to-current conversion efficiency (IPCE) results indicated that the TiO2 mesoporous film fabricated using a proper EC addition was beneficial for electron generation (also confirmed by dye desorption experiments) and electron transport, and, therefore, improved the photovoltaic performance of DSSCs.

Microstructural evolution of the Cu/solder/Cu pillar-type bonding structures with a reduced solder volume subjected to thermal aging at 423 K to 473 K(150 °C to 200 °C) was investigated. In a bonding structure employing a Ni single layer as the diffusion barrier, solder was consumed with formation of the Ni3Sn4 phase at the bonding interfaces due to an usual Sn/Ni interfacial reaction. However, an unusual Sn/Cu reaction occurred with formation of the Cu6Sn5 (and Cu3Sn) phase on the periphery of the Cu pillar due to out-diffusion of Sn toward the pillar periphery. Consumption of solder was accelerated by the above two reactions which led to the formation of a continuous gap in the bonding structure. Employment of a thicker Ni layer plus a Cu cap layer as the diffusion barrier in the bonding structure effectively blocked out-diffusion of Sn toward the periphery of the Cu pillar and therefore retarded the gap formation. The retardation effect was attributed to an increment of diffusion distance on the pillar periphery due to an effective diffusion barrier composed by Ni and thicker Cu-Sn (Cu6Sn5 + Cu3Sn) phase layers. Detailed phase identification and microstructural evolution in the bonding structures were also investigated using scanning electron microscopy and transmission electron microscopy.

The Sn/p-Bi2Te3/Sn sandwich-type sample was current stressed with a density of 150 A/cm2 to investigate the effects of current stressing on the p-Bi2Te3/Sn interfacial reactions. Asymmetrical heating phenomenon was observed at the anodic Sn/p-Bi2Te3 (50 °C) and cathodic p-Bi2Te3/Sn (120 °C) interfaces due to the Peltier effect. Besides the Peltier effect, the electromigration effect also influenced the growth of the SnTe phase and therefore polarity growth behavior was observed at the two interfaces. The growth of the SnTe phase at the cathodic p-Bi2Te3/Sn interface was accelerated because Peltier and electromigration effects drove more Sn atoms (dominant diffusion species) for the phase growth. By measuring the electromigration-induced atomic flux of Sn, the product of diffusivity and effective charge number (D × z*) was calculated to be 6.3 × 10−9 cm2 s−1 at 120 °C.

Electrodeposition of Cu receives considerable attention due to its wide application in microelectronic products. Sn-rich alloys are commonly used to join the electroplated Cu to form solder joints, while their interactions give rise to undesired Kirkendall voids. Suppression of voids is imperative to ensure reliable solder joints with mechanical robustness. In this study, twinned Cu with various crystal orientations are constructed using electroplating and their efficacy on void suppression are investigated. Four Cu electroplated films (Cu A, B, C, and D) with numerous twin boundaries and different (111) and (110) ratios are joined with Sn-rich solder (SAC305) and thermally aged at 200 °C. The voiding propensity is in an order of Cu D > Cu C > Cu B > Cu A, inversely corresponding to their (111) ratios (Cu A > Cu B > Cu C > Cu D). Particularly, a void-free solder joint constructed by the electroplated Cu A film with plenty of twinned bamboo structures is observed. The findings demonstrate that Σ3 twin boundary in the bamboo structure with 〈111〉-preferred orientation has much higher efficiency at suppressing the Kirkendall effect than that in 〈110〉-preferred Cu films.

Dye-sensitized solar cells (DSSCs) based on different configurations under various light intensity are characterized, where commercial N719 dye and synthesized D-Dye are used as photo-sensitizer. Regardless of cell configuration, organic D-Dye serves as an efficient photo-sensitizer, giving rise to high cell efficiency comparable with N719. The highest efficiency of 20.98% (Voc of 0.6 V, Jsc of 0.62 mA/cm2, FF of 0.71) is achieved as the front-illuminated rigid DSSC is constructed by applying 8 μm TiO2 layer under 6000 LUX illumination. At the same condition the efficiency of 19.69% (Voc of 0.63 V, Jsc of 0.57 mA/cm2, FF of 0.74) is recorded for N719. Higher efficiency for D-Dye is attributed to high response of its absorption spectrum to the emission spectrum of indoor T5 irradiance. Charge transfer resistance is measured to be 53.1 Ω for D-Dye in conjunction with 8 μm TiO2 which is higher than thicker TiO2 (10 μm and 12 μm) at 0.75 V applied bias under dark condition, indicating that reduction of TiO2 thickness facilitates charge transfer by suppressing charge recombination under low illuminations. A systematic study of the efficiency as a function of key factors like TiO2 thickness, electrode type, and light intensity is explored.

Flexible copper clad laminate (FCCL) is the key base material for versatile applications such as mobile devices, wearable electronics, and point-of-care biosensors. Development of adhesiveless FCCL is urgent to achieve a thinner, lighter, and thermally stable substrate for advanced high-frequency (5G) applications. In this study, a co-silanization method is proposed to functionalize the polyimide (PI) surface for efficient metal immobilization and adhesion enhancement. The co-silanization treatment features the establishment of a barricade-like network structure by the assistant organosilane, trimethoxyphenylsilane (TMPS), to generate spatial confinement effect (SCE) to effectively control the positioning and grafting orientation of the functional organosilane, 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (ETAS), on the PI film. Benefitting from the effective positioning and grafting, the two types of organosilanes form a composite well-organized molecular nanolayer which is in possession of strong tethering ability for metal attachment and immobilization. Compared to the mono-silanization system with ETAS only (0.652 kgf/cm), the co-silanization treatment (ETAS + TMPS) remarkably enhances the peel strength of the deposited metal layer on PI by 53% (~1 kgf/cm).

Out of several d-block elements, such as tungsten, zinc, cobalt, nickel, platinum, aluminum, and copper, titanium (Ti) has received more attention as a photoanode in dye-sensitized solar cells due to its high mechanical strength, flexibility, and good corrosion resistance towards common electrolytes. Charge transfer and electron injection efficiency can be modified by using anodizing oxidation technology (AOT) and applying different voltages on a Ti sheet, which modifies the thickness, color and surface structure of the Ti sheet. In this study, the variation in solar power efficiency was investigated by manufacturing solar devices with Ti sheets modified by AOT treatment followed by H2O2 etching. The investigated results show that the improved efficiency of the solar cell could be attributed to the robust and nanoporous structure of the surface layer on the Ti sheet, which was created by sequential AOT treatment and peroxide etching. Further studies have been performed to increase the efficiency of solar cells using N719 dye and changing the concentration of electrolyte under different light illumination. The maximum power conversion efficiency of 5.27% (JSC of 9.501 mA/cm2, VOC of 0.750 V with 0.741 FF) was observed using modified Ti foil and 0.00625 M iodine by applying a 60 V potential difference under 1 sun illumination.

This study develops a simple and efficient method to metallize polyimide (PI) using an electro-less Ni-P film and a silane compound coupling agent and then finishing with a Cu electroplated layer. The adhesive strength of the metallized layers on PI is an important measure for newly-developed techniques. The focus is on the adhesive medium such as the silane compound agent. This study uses an additive formula to deposit the Cu electroplated layer, which is important to the adhesive performance. Although different additive formulas can be used to deposit a uniform Cu layer on the electroless Ni-P film, focus ion beam (FIB) analysis shows that the grain microstructures of the Cu electroplated layers are different. A fracture analysis using a 90-degree peeling test shows that the fracture paths are also different in the metallized PI samples, so there are different peeling strengths.

Titanium (Ti) is a common anode substrates for dye-sensitized solar cells (DSSCs), which is flexible, has good resistance to corrosion, and electrical conductivity. However, Ti is not transparent and the resultant DSSC requires rear illumination. In order to improve the photovoltaic performance, anodizing oxide technology (AOT) is used to modify the Ti substrate [1-3]. The color of Ti surface then changes from silver to purple because a reflective Ti oxide layer forms on the substrate surface. The surface Ti oxide layer acts as a blocking layer, which goes better charge recombination for the anode [3]. The power conversion efficiency of the DSSC increases from 2.61 to 3.65 % after the AOT treatment. The improvement in the efficiency is attributed to an improvement in the short-circuit current density.

Titanium (Ti) has high potential in many practical applications such as biomedicine, architecture, aviation, and energy. In this study, we demonstrate an innovative application of dye-sensitized solar cells (DSSCs) based on Ti photoanodes that can be integrated into the roof engineering of large-scale architectures. A chromatic Ti foil produced by anodizing oxidation (coloring) technology is an attractive roof material for large-scale architecture, showing a colorful appearance due to the formation of a reflective TiO2 thin layer on both surfaces of Ti. The DSSC is fabricated on the backside of the chromatic Ti foil using the Ti foil as the working electrode, and this roof-DSSC hybrid configuration can be designed as an energy harvesting device for indoor artificial lighting. Our results show that the facet-textured TiO2 layer on the chromatic Ti foil not only improves the optical reflectance for better light utilization but also effectively suppresses the charge recombination for better electron collection. The power conversion efficiency of the roof-DSSC hybrid system is improved by 30-40% with a main contribution from an improvement of short-circuit current density under standard 1 sun and dim-light (600-1000 lx) illumination.

In this study, a post-annealing-free, adhesive nickel/phosphorous (Ni/P) layer was deposited on a 3-[2-(2-aminoethylamino)ethylamino] propyl-trimethoxysilane-modified (ETAS-modified) silicon (Si) surface through an electroless deposition process catalyzed by a novel polyvinylpyrrolidone-capped palladium nanocluster (PVP-nPd). ETAS was covalently bonded on the Si surface, whereas the amino groups on ETAS bridged with the palladium core in the PVP-nPd clusters. Because of the mentioned two effects, the deposited Ni/P layer showed superior adhesion on the Si wafer without the requirement of conventional annealing treatment. Compared with the Ni/P films deposited on bare and ETAS-modified Si surfaces by using commercial Sn/Pd colloids, the adhesion of the Ni/P film catalyzed by PVP-nPd on the ETAS-modified Si wafer improved 4- and 2-fold, respectively. Keywords: Electroless, Palladium nanoclusters, Self-assembling monolayer, Adhesion