Effect of nano-Al2O3 reinforcement on the microstructure and reliability of Sn–3.0Ag–0.5Cu solder joints

Nanoparticle reinforced lead-free solder has previously been studied by several investigators, but few studies have evaluated its reliability. In this study, resistor chip (RC) micro joints were soldered using nano-Al₂O₃ particle reinforced Sn–Ag–Cu solder paste. The microstructure and reliability of RC micro joints having different nano-Al₂O₃ contents (0, 0.25, 0.5 and 1.0 wt%) were investigated in detail. More than 40 solder joints for each condition were made and examined in order to achieve reliable data. The results indicated that nano-Al₂O₃ particles refined the β-Sn grain size and enlarged the eutectic area of the micro solder joints. Those nanoparticles also reduced the IMC thickness of the Ni-solder and Cu-solder interfaces. Those effects can be attributed to the poor-wetting behavior of nano-Al₂O₃ particles. The nano-Al₂O₃ reinforcement mainly enhanced the reliability of the micro solder joints, but did not affect the strength of as-soldered joints obviously. The improvement of reliability was proportional to the nano-Al₂O₃ content. The microstructure and fracture analysis indicated that the reinforcement and stability of Ni-IMC and Cu-IMC interfaces accounted for better reliability.     

Effect of Ag doping on the electrical properties of thermally deposited CdS–La2O3 TFTs

This paper describes a new approach for repairing memories. Repair is implemented by deletion of either rows and/or columns on which faulty cells lie. These devices are commonly referred to as redundant memories, because redundant columns and rows are added. A new repair technique and an algorithm are proposed. The algorithm is based on a fault-counting technique and on a reduced-covering approach. The innovative feature is that reduced covering permits an heuristic, but efficient, criterion to be included in the selection of the rows and/or columns to be deleted. This retains independence of the repair process on the distribution of faulty cells in memory, while allowing a good repairability/ unrepairability detection. The main benefits that result by using the proposed repair algorithm are a reduction in execution time to determine the repair-solution for the device under test and its suitability for implementation in a defect analysis system. Illustrative examples and theoretical results are provided to substantiate the validity of the proposed repair technique     

Sn addition on the tensile properties of high temperature Zn–4Al–3Mg solder alloys

The Zn–4Al–3Mg based solder alloy is a promising candidate to replace the conventional Pb–5Sn alloy in high-temperature electronic packaging. In this study, the tensile properties of Zn–4Al–3Mg–xSn alloys (x = 0, 6.8 and 13.2 wt.%) at high temperatures (e.g., 100 °C, and 200 °C) were investigated. It was found that the uniaxial tensile strength (UTS) of Zn–4Al–3Mg–xSn solder alloys all decrease monotonously with the increment of temperature. The elongation ratio at 100 °C is superior to that at room temperature whereas follows a significant drop at 200 °C. The microstructure observations show that a typical brittle fracture of Zn–4Al–3Mg alloy occurs at room temperature and 200 °C under normal tension, whereas a ductile fracture is found at 100 °C. The 6.8 wt.% Sn addition in Zn–4Al–3Mg alloy causes a dramatic decrease of yield strength, and a slight deterioration of the ductility.     

Effect of solder resist dissolution on the joint reliability of ENIG surface and Sn–Ag–Cu solder

The electroless nickel immersion gold (ENIG) process results in surface defects, such as pinholes and black pads, which weaken the solder joint and eventually degrade the reliability of the PCB. Contamination of the plating solutions, including dissolution of the solder resist (SR), can be a cause of the pinholes and black pads. This study examined the effects of SR dissolution on the solder joint reliability and electroless Ni plating properties. Electroless Ni plating was performed by adding 1 to 10 ppm hardener (melamine) to the fresh Ni solution. Many black pads were observed in the 7 and 10 ppm hardener-added surfaces. In addition, the content of P was highest when 7 and 10 ppm hardener was added. The ball shear tests were carried out to confirm the joint reliability between the ENIG surface with hardener-added and the Sn-3.0Ag-0.5Cu solder (SAC 305). The ball shear strength decreased with increasing dissolution of the hardener. In particular, the shear strength was the lowest at 7 and 10 ppm hardener addition. In addition, the failure mode of the solder joint was changed from ductile to brittle mode with increasing hardener addition. That is, as the hardener additive increases, intermetallic compound (IMC) phases were changed from (Cu,Ni)₆Sn₅ to (Cu,Ni)₃Sn₄ and Cu₆Sn₅ (brittle structure).     

Effect of small Sn–3.5Ag–0.5Cu additions on the structure and properties of Sn–9Zn solder in ball grid array packages

Sn–9Zn with various additions of Sn–3.5Ag–0.5Cu powder was prepared by mechanically dispersing different weight percentages (1, 3, 5 and 7) of Sn–Ag–Cu powder into Sn–9Zn solder paste. In the Sn–Zn solder, scallop-shaped AuZn₃ intermetallic compound was found at the interfaces. On the other hand, in the Sn–3.5Ag–0.5Cu content solders, an additional ε-AgZn₃ intermetallic compound layer was found to be well adhered on the top surface of the AuZn₃ layer and the ε-AgZn₃ layer thickness increased with the number of reflow cycles. In addition, fine spherical-shaped ε-AgZn₃ intermetallic compound particles as well as an acicular-shaped Zn-rich phase was clearly observed in the β-Sn matrix. On increasing the Sn–Ag–Cu content, the shear load was increased from 1.80 to 2.03 kg after one reflow cycle. In the Sn–3.5Ag–0.5Cu content solders, the fracture surfaces exhibited typical ductile behavior with very rough dimpled surfaces while the fracture surface in the Sn–Zn solder gave fractures with a brittle appearance. In the fracture surface of the Sn–3.5Ag–0.5Cu content solders, some dimples were clearly observed associated with the formation of spherical-shaped ε-AgZn₃ intermetallic compound particles.     

Microstructure and morphology of interfacial intermetallic compound CoSn3 in Sn–Pb/Co–P solder joints

A systematical microscopic analysis on structure, morphology, and growth of CoSn₃ intermetallic compound (IMC) that formed at the interface between Sn–Pb alloy and Co–P films was carried out using scanning electron microscopy with back-scattered electron imaging and high-resolution transmission electron microscopy with energy dispersive spectrometry. CoSn₃ IMC with two kinds of morphology was found out after Sn–Pb alloy reacted with Co–P films with different microstructures. One kind of CoSn₃ with stacking fault was distributed densely on nanocrystalline and amorphous Co–P films, and the other kind of CoSn₃ without stacking fault existed sparsely on the Co–P film with nanocrystalline/amorphous mixed structure. The stacking fault was caused by the fast growth of CoSn₃ for the cases of Co-7 at.% P and Co-23 at.% P. Co-12 at.% P film with a nanocrystalline/amorphous mixed microstructure had the best diffusion-barrier property among Co–P films with different compositions, because the diffusion of Sn into Co–P was the least. Our study shed light on diffusion-barrier performance of Co-based metallization.     

Effects of Al doping on properties of xAl–3%In–TiO2 photocatalyst prepared by a sol–gel method

A sol–gel method was used to prepare Al–In co-doped TiO₂ photocatalyst. The materials were characterized by XRD, FT–IR, XPS, and N₂ adsorption–desorption measurements. Photocatalytic degradation of methyl orange on the materials was investigated. The diffraction peaks of all the samples are in accordance to the diffraction peaks of anatase phase TiO₂. The addition of Al and In can lead to crystallite size shrinking of anatase TiO₂ in xAl–3%In–TiO₂. The incorporation of Al³⁺ ions into TiO₂ crystal are in the way of substituting Ti⁴⁺ ions in anatase lattice. 0.5%Al–3%In–TiO₂ has the maximum specific surface area of 108.9 m²/g and the smallest average pore size of 7.0 nm. The aluminum doped xAl–3%In–TiO₂ materials have larger adsorption capacity than that of 3%In–TiO₂. Total decoloration efficiency increases gradually with increasing Al content up to 0.5%, while 0.5%Al–3%In–TiO₂ has the maximal decoloration efficiency. 0.5%Al–3%In–TiO₂ also shows much improved activity as compared to 3%In–TiO₂ in each reuse cycle.     

Effect of Ag doping on structure andcritical temperature of Bi2Sr2CaCu2O8+δ superconductors

The effects of Ag substitution for Bi, Sr and Cu on the c-axis lattice parameter and critical temperature (T_c) were determined for the Bi_2−xSr_2−yCaCu_2−zO_8+δ (BSCCO-2212) superconducting phase. Two distinct regimes of behavior were observed: fast cooling represented the regime where the uptake of excess oxygen was the controlling factor and slow cooling represented the regime where the cation content was the controlling factor on the structure and properties. Samples showed higher T_c values and longer c-axes with increased cooling rate. A linear increase in T_c with increase in c-axis length was observed for the faster-cooled samples. For the slow-cooled samples, increased c-axis length was observed when Ag was substituted for Bi and Sr, whereas substituting Ag for Cu caused no change in c-axis length. In addition, any deviation from the ideal 2212 stoichiometry was shown to reduce the T_c values of samples that were slowly cooled and fully oxygenated. Preliminary results obtained by high-resolution transmission electron microscopy coupled with electron energy loss spectroscopy indicated that relatively small amounts of Ag (≈1 at.%) can occupy Bi sites and a larger amount (≈10 at.%) of Ag can substitute for Cu.     

Geometry effect on mechanical performance and fracture behavior of micro-scale ball grid array structure Cu/Sn–3.0Ag–0.5Cu/Cu solder joints

Solder joint integrity has long been recognized as a key issue affecting the reliability of integrated circuit packages. In this study, both experimental and finite element simulation methods were used to characterize the mechanical performance and fracture behavior of micro-scale ball grid array (BGA) structure Cu/Sn–3.0Ag–0.5Cu/Cu solder joints with different standoff heights (h, varying from 500 to 100 μm) and constant pad diameter (d, d = 480 μm) and contact angle under shear loading. With decreasing h (or the ratio of h/d), results show that the stiffness of BGA solder joints clearly increases with decreasing coefficient of stress state and torque. The stress triaxiality reflects the mechanical constraint effect on the mechanical strength of the solder joints and it is dependent on the loading mode and increases dramatically with decreasing h under tensile loading, while the change of h has very limited influence on the stress triaxiality under shear loading. Moreover, when h is decreased, the concentration of stress and plastic strain energy along the interface of solder and pad decreases, and the fracture location of BGA solder joints changes from near the interface to the middle of the solder. Both geometry and microstructure greatly affect the shear behavior of joints, the average shear strength shows a parabolic trend with decreasing standoff height. Furthermore, the brittle fracture of BGA solder joints after long-time isothermal aging was investigated. Results obtained show that, under the same shear force, the stress intensity factors, K_I and K_II, and the strain energy release rate, G_I, at the Sn–3.0Ag–0.5Cu/Cu₆Sn₅ interface and in the Cu₆Sn₅ layer obviously decrease with decreasing h, hence brittle fracture is more prone to occur in the joint with a large standoff height.     

Effect of Cu–Al substitution on the structural and magnetic properties of Co ferrites

In this work copper aluminum substituted cobalt nanocrystalline spinel ferrites having general formula Co_1−xCu_xFe_2−x Al_xO₄, with 0.0≤x≤0.8 have been synthesized by using a co-precipitation method. The Cu–Al substituted samples were annealed at 600 °C and characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM). XRD analysis confirmed a single phase spinel structure and the crystalline size calculated using Scherrer׳s formula found to be in the range of 14−24 nm. This crystalline size is small enough to achieve the suitable signal to noise ratio in the high density recording media. The FTIR spectra reveal two prominent frequency bands in the wave number range 350–600 cm⁻¹, which confirm the cubic spinel structure and completion of chemical reaction. Magnetic studies reveal that the coercivity (H_c) attains a maximum value of 1142 Oe at 14 nm. The increasing trend of magnetic parameters (coercivity and retentivity) is consistent with crystallinity. The role played by the Cu–Al ions in improving the structural and magnetic properties are analyzed and understood. The optimized magnetic parameters suggest that the material with composition Co_0.6Cu_0.4Fe_1.6Al_0.4O₄ may have a potential application for high density recording media. Our simple, economic and environmental friendly preparation method may contribute towards the controlled growth of high quality ferrite nanopowder, potential candidates for recording.     

Interfacial reactions of Sn–58Bi and Sn–0.7Cu lead-free solders with Alloy 42 substrate

Eutectic Sn–58 wt%Bi (SB) and Sn–0.7 wt%Cu (SC) lead-free solders reacting with Alloy 42 substrates were investigated at 240, 270, 300, and 330 °C for various reaction times. The FeSn₂ phase was the only phase formed at the solder/Alloy 42 interface for all couples. However, this FeSn₂ phase had two different microstructures. The intermetallic compound (IMC) morphology near the solder/Alloy 42 interface was dense with a tiny microstructure after reflowing at 240 °C. Massive spalling FeSn₂ phases with large and platy grain were observed in the solder matrix. When the reflow temperature was increased the IMC morphology assumed bulk or cylindrical shape with no spalling IMCs observed at the solder/Alloy 42 interface. The IMC thickness increased with increasing reaction temperature and time. Both SB/Alloy 42 and SC/Alloy 42 couples presented a diffusion controlled growth mechanism in. The activation energies for SB/Alloy 42 and SC/Alloy 42 couples were 86.2 and 103.4 kJ/mol, respectively.     

Impact of Ni concentration on the intermetallic compound formation and brittle fracture strength of Sn–Cu–Ni (SCN) lead-free solder joints

Cu₆Sn₅ and Cu₃Sn are common intermetallic compounds (IMCs) found in Sn–Ag–Cu (SAC) lead-free solder joints with OSP pad finish. People typically attributed the brittle failure to excessive growth of IMCs at the interface between the solder joint and the copper pad. However, the respective role of Cu₆Sn₅ and Cu₃Sn played in the interfacial fracture still remains unclear. In the present study, various amounts of Ni were doped in the Sn–Cu based solder. The different effects of Ni concentration on the growth rate of (Cu, Ni)₆Sn₅/Cu₆Sn₅ and Cu₃Sn were characterized and compared. The results of characterization were used to evaluate different growth rates of (Cu, Ni)₆Sn₅ and Cu₃Sn under thermal aging. The thicknesses of (Cu, Ni)₆Sn₅/Cu₆Sn₅ and Cu₃Sn after different thermal aging periods were measured. High speed ball pull/shear tests were also performed. The correlation between interfacial fracture strength and IMC layer thicknesses was established.     

Effect of Chromium Doping on the Thermoelectric Properties of Bi2Te3: Cr x Bi2Te3 and Cr x Bi2−x Te3

The thermoelectric (TE) properties of Bi₂Te₃ compounds intercalated and substituted with Cr, namely Cr _x Bi₂Te₃ and Cr _x Bi_2?x Te₃, respectively, have been investigated to study the influence of chromium on the TE properties of Bi₂Te₃. The Seebeck coefficients were found to be positive for all the samples in the temperature range between 300 K and 550 K. Although no effective enhancement of the Seebeck coefficient was observed, doping with Cr by means of either substitution or intercalation clearly not only improved the electrical conductivity but also lowered the thermal conductivity of Bi₂Te₃. As a result of the improvement, the figure of merit ZT is increased up to 0.8 and 0.65 at 300 K for 1% intercalated and 1% substituted Bi₂Te₃, respectively.     

Effect of the Phase Composition and Local Crystal Structure on the Transport Properties of the ZrO2–Y2O3 and ZrO2–Gd2O3 Solid Solutions

Russian Microelectronics - The results of investigating the crystal structure, ionic conductivity, and local structure of the (ZrO2)1 –x(Gd2O3)x and (ZrO2)1 –x(Y2O3)x (x = 0.04, 0.08,...     

Investigation of optical and electronic properties in Al–Sn co-doped ZnO thin films

Al-Sn co-doped ZnO thin films were deposited onto quartz substrates by sol-gel processing. The surface morphology and electrical and optical properties were investigated at different annealing temperatures. The surface morphology showed a closely packed arrangement of crystallites in all the doped films. As prepared co-doped films show a preferred orientation along an (0 0 2) plane. This preferred orientation was enhanced by increasing the annealing temperature to between 400 °C and 500 °C, but there was a shift to the (1 0 1) plane when the annealing temperature rose above 500 °C. These samples show, on average, 91.2% optical transmittance in the visible range. In this study, the optical band gap of all the doped films was broadened compared with pure ZnO, regardless of the different annealing temperature. The carrier concentration and carrier mobility of the thin films were also investigated.     

Enhanced formaldehyde-sensing properties of mixed Fe2O3–In2O3 nanotubes

Pure In₂O₃ and mixed Fe₂O₃–In₂O₃ nanotubes were prepared by simple electrospinning and subsequent calcination. The as-prepared nanotubes were characterized by scanning electron microscopy, powder X-ray diffraction, and energy-dispersive X-ray spectrometry. Gas sensors were fabricated to investigate the gas-sensing properties of In₂O₃ and Fe₂O₃–In₂O₃ nanotubes. Compared to pure In₂O₃, Fe₂O₃–In₂O₃ nanotubes exhibited better gas-sensing properties for formaldehyde at 250 °C. The response of the Fe₂O₃–In₂O₃ nanotube gas sensor to 100 ppm formaldehyde was approximately 33, which is approximately double the response of the pure In₂O₃ nanotube gas sensor. In both cases the response time was ~5 s and the recovery time was ~25 s.     

Effect of annealing on the microstructure and bonding interface properties of Ag–2Pd alloy wire

This study investigated the mechanical and electrical properties of Ag–2Pd wire after thermal annealing. The thermal stability of the tested wire was examined by separately imposing static annealing at 275 °C, 325 °C and 375 °C in a vacuum environment. It was found that annealing the Ag–2Pd wire at 275 °C promoted the formation of a fully annealed structure with equiaxed grains. Annealing Ag–2Pd wire had a shorter heat affect zone (HAZ) length than those of conventional wire, and offered outstanding mechanical properties. A long-term electrical test found Ag₃(Pd)Al and Ag₂(Pd)Al compounds between the Ag–Pd ball and Al pad. These results confirmed the high-reliability properties of annealed Ag–2Pd wires for the wire bonding process.     

Effect of Fe doping on structural and magnetic properties of La2/3Ca1/3Mn1−yFeyO3 (y=0–0.03) thin films

We have characterized the magnetic and structural properties of pure and ⁵⁷Fe-doped La_2/3Ca_1/3MnO₃ thin films and targets, substituted with 1% and 3% of ⁵⁷Fe on the Mn site. The films were prepared via high O₂-pressure (500 mTorr) by DC magnetron sputtering on (1 0 0) SrTiO₃ and (1 0 0) LaAlO₃ single-crystal substrates. Mössbauer spectra measured at room temperature confirm the presence of Fe³⁺ with octahedral coordination, thus indicating that Fe is incorporated into the structure by substituting Mn. Structural analysis by X-ray diffraction (XRD) shows that the films are single phase and c-axis oriented and that the Fe doping gives rise to a relaxation of the epitaxial strain. Interestingly, the Curie temperature and the magnetoresistance (MR) show a non-monotonic behavior with Fe doping. This indicates that initially the strain relaxation induced by the Fe doping is more important than the reduction of ferromagnetic coupling due to the Fe incorporation.     

Effects of H2O Pretreatment on the Capacitance–Voltage Characteristics of Atomic-Layer-Deposited Al2O3 on Ga-Face GaN Metal–Oxide–Semiconductor Capacitors

Atomic layer deposition (ALD) of Al₂O₃ on Ga-face GaN is studied with respect to the effects of growth saturation, precursor injection sequence, and H₂O pretreatment. A metal–oxide–semiconductor capacitor (MOSCAP) structure is fabricated to measure the capacitance–voltage (C–V) characteristics. The origin of C–V hysteresis is explained by a model considering the different trapping behaviors of interface states and oxide border traps. The interface state density (D _it) is extracted as a function of band bending using an ultraviolet (UV)-assisted method. It is found that H₂O pretreatment followed by saturated ALD growth produces the best interface quality, with a reduced D _it compared with growth without H₂O pretreatment.     

Effect of annealing and electrochemical properties of sol–gel dip coated nanocrystalline V2O5 thin films

Nanocrystalline vanadium pentoxide (V₂O₅) thin films were deposited on glass substrates by a simple and cost effective sol–gel dip coating method. The effect of annealing on microstructure and optical properties of V₂O₅ thin films were investigated. Formation of nanorods with the average diameter of 500–750 nm after annealing is observed by scanning electron microscopy. X-ray diffractometry indicates that an orthorhombic structured thin film is transformed to β-V₂O₅ nanorods by subsequent annealing at 500 °C. It was also confirmed that the growth of nanorods strongly correlates with annealing conditions; nanorod formation can be explained by surface diffusion phenomenon. The electrochemical performance of the V₂O₅ nanorods was investigated by cyclic voltammetry.