Jing-Chie Lin

Effects of surfactant treatment of silver powder on the rheology of its thick-film paste

Abstract The effects of surfactant treatment and surface area of silver powder on the screen printability of the conducting silver pastes were investigated in the present study. The silver powders treated with both caprylic acid and triethanolamine (lots S10T2, S8T2 and S7T3) were observed to be more appropriate for thick-film paste as compared to the powders treated with a single surfactant (lots C and A) or none (lot O). The pastes prepared from lots S10T2, S8T2 and S7T3 exhibited a pseudoplastic flow and also demonstrated good screenability. The surface area (SA), rather than the tap density (TD), was observed to play a dominant role in determining the paste rheology for powders treated with the same surfactants. The pastes prepared from powders having a greater SA (5–10 × 103 m2 kg−1) demonstrated better printability than those having a smaller SA (

On the resistance of silver migration in Ag-Pd conductive thick films under humid environment and applied d.c. field

Abstract Silver migration occurring in pure silver conductive thick films was minimized by using Ag-Pd alloys. The in situ microscopic observation, under humid environment and an applied d.c. field, showed that the out-growth of silver dendrites from the cathode decreases with increasing (5–20%) amount of Pd in the Ag-Pd specimens, and ceases completely at 30% Pd. The enhancement of silver migration resistance with increasing Pd concentration in Ag-Pd conductors was evident by the measurements of the short circuit current between a couple of thick-film electrodes in distilled water at 5 V. Through the study of anodic potentiodynamic polarization in 0.01 M NaOH and the examination of the surface films on the thick films by X-ray diffraction and surface analyses (Auger and ESCA), it was found that the anodic formation of PdO blocks the silver dissolution, and minimizes the occurrence of silver migration.

Effects of Sip size and volume fraction on properties of Al/Sip composites

Abstract Al–12 wt.% Si alloy matrix composites reinforced with high volume fraction of Si p were fabricated by squeeze infiltration. The effects of the compacting pressure on the volume fraction of Si p in preforms, and the influences of Si p size and volume fraction on the properties of Al/Si p composites were examined through this study. Si particles were compacted at different pressure of 40–130 MPa followed by sintered at 1000 °C for 7 h to obtain preforms containing 60–70 volume fraction (vol.%) of Si p . The sintered preforms were then infiltrated with Al–12 wt.% Si alloy at 750 °C under a 75 MPa squeeze infiltration pressure. It was found that lower coefficient of thermal expansion (CTE) and smaller density may be obtained with higher Si p volume fraction, yet increasing Si p volume fraction leads to higher amount of porosities in the composites and thus lowers the thermal conductivity (TC) and flexural strength. Besides, with the same Si p volume fraction, coarse Si particles result in higher CTE and TC, while finer Si particles may lower CTE and enhance the flexural strength of the composites effectively. From the results obtained in this study, it is expected that the high volume fraction Si p reinforced Al/Si p composites posses good potential in electronic packaging applications.

Interfacial Reactions Between Metal and Gallium Arsenide

The phase formation sequence for GaAs/metal ternary diffusion couples is discussed. The diffusion path concept is introduced and is used with the phase diagram to understand interfacial reactions between GaAs and metal. The correlation between growth kinetics and interface morphology is discussed. Studies of bulk and thin film couples in two systems, GaAs/Pd and GaAs/Pt, are given to illustrate these concepts.

Solid–liquid interdiffusion bonding between In-coated silver thick films

Abstract Solid–liquid interdiffusion (SLID) bonding between two pieces of In-coated silver thick films was investigated. The silver thick film was prepared by screen-printing of silver paste on an aluminum oxide substrate. Indium was coated in thickness ranging from 3 to 12 μm onto the silver thick films using thermal deposition (in vacuum). Two pieces of the In-coated thick films were placed in intimate contact (with a compressive stress of 0.04 MPa) and heated (at 180–250 °C) for various durations (600–3600 s) to undergo SLID bonding. Measurement of the bonding strength indicated that the SLID bond in 3-μm-In-coated thick-film couples is stronger than that in 8-μm-In-coated couples. X-Ray diffraction, scanning electron microscopy and electron probe microanalysis were used to analyze the bond. The stronger bond comprises a central zone of γ-Ag 2 In sandwiched by two Ag films; the weaker bond comprises a central zone of AgIn 2 sandwiched by two layers of γ-Ag 2 In. In the latter case, diffusion of excess indium from the coat into the interface between the silver film and alumina substrates is responsible for bond weakening. The development of microstructures in the SLID process for both strong and weak bonds is proposed.

Effect of surface properties of silver powder on the sintering of its thick-film conductor

Abstract The effect of the surface properties of silver powder on the sintering of its thick film has been investigated in this study. The variations in the sintering structure have been observed to depend upon the kind of surfactant treatment of the powders and their surface area (SA). Silver powders treated with both caprylic acid and triethanolamine show a better densification in both dried prints as well as fired films as compared with those treated with single surfactant or none. For the powders treated with both surfactants, the surface area primarily determines the densification of fired films. Powders with SA greater than 7 × 10 3 m 2 kg −1 have thus been observed to be appropriate for thick-film applications, even at firing temperatures (450 °C) considerably lower than usual (800 °C). Structural evolution during firing has been studied by inspecting the morphology (as shown by scanning electron microscope) and sheet resistivity of the films.

Fabrication of micrometer Ni columns by continuous and intermittent microanode guided electroplating

Micrometer nickel columns were fabricated by a novel process called microanode guided electroplating (MAGE). In the MAGE process, a microanode of platinum (125 µm in diameter) was controlled to move in either continuous or intermittent mode to guide the progress of Ni-electroplating. The microfabrication was guided from the location of a copper substrate that is initially in contact with the microanode to develop a micrometer column and its appearance was determined by the motion mode (i.e., continuous or intermittent) of the microanode. The intermittent MAGE was superior to the continuous one for fabricating micrometer nickel columns with fine surface morphology and uniform diameter. Different models are proposed and they are simulated by the commercial software ANSYS 8.0 to understand the quantitative distribution in the process of MAGE.

Surface and transverse morphology of micrometer nickel columns fabricated by localized electrochemical deposition

Micrometer nickel columns were fabricated locally on a copper substrate in a Watts bath by microanode guided electroplating which is commonly known as localized electrochemical deposition (LECD). A microanode of platinum (125 ?m in diameter) served to move up intermittently, thus guiding the growth of Ni deposit from the substrate. The separation between the microanode and top of the microcolumn was initially set at 10 ?m before setting out the electroplating. The electroplating current and local potential near the local region after the LECD were monitored and examined in this work. Surface and transverse morphology of the microcolumns were examined through a scanning electron microscope. LECD performed at biases less than 3.56 ? 0.01 V led to columns with smooth surfaces and circular internal transverse fully compacted, whereas when performed at biases higher than 3.56 ? 0.01 V it led to columns with a rough surface and distorted circular internal transverse with porosity in the center. The higher the bias, the worse the surface smoothness. The less circular the transverse, the less compactness in the transverse center. A compromise between the estimated supplying rate and the consumption rate of the nickel ions in the local region after the LECD is discussed to understand the dependence of the morphologies on the biases.

Processing and properties of high volume fraction aluminium/silicon composites

Abstract High volume fraction Al/Sip composites are attractive for electronic packaging applications owing to their low density and coefficient of thermal expansion (CTE), together with their good thermal conductivity (TC) and flexural strength. In this study, the effects of sintering temperature, particle (Sip) size, and volume fraction (vol.-%) on the properties of Al/Sip composites produced by hot pressing were investigated. Pure Al powders were mixed with 75-85 vol.-%Sip with average particle sizes of 42 and 15 μm were hot pressed at 500°C and 620°C for 20 min. The results indicate that composites sintered in the liquid phase show higher relative density, TC, and flexural strength than those sintered in the solid phase. However, the CTEs were lower when sintered in the liquid phase than in the solid phase. As the volume fraction of Sip was increased, lower values of CTE, TC, and flexural strength were obtained. For a given volume fraction of Sip, finer Si particles result in a lower CTE and an improvement in the flexural strength of the composites.

Influence of sodium halides (NaF, NaCl, NaBr, NaI) on the photocatalytic performance of hydrothermally synthesized hematite photoanodes.

It has been suggested that a high concentration of Fe(3+) in solution, a low pH, and noncomplexing ions of high ionic strength are all essential for developing a high-quality hematite array. Our curiosity was piqued regarding the role of the electrolyte ions in the hydrothermal synthesis of hematite photoanodes. In this study, we prepared hematite photoanodes hydrothermally from precursor solutions of 0.1 M FeCl3 at pH 1.55 with a background electrolyte of 1.0 M sodium halide (NaF, NaCl, NaBr, or NaI). We compared the structures and properties of the as-obtained hematite photoanodes with those of the material prepared in 1.0 M NaNO3, the most widely adopted electrolyte in previous studies. Among our studied systems, we found that the hematite photoanode prepared in NaCl solution was the only one possessing properties similar to those of the sample obtained from the NaNO3 solution-most importantly in terms of photoelectrochemical performance (ca. 0.2 mA/cm(2) with +0.4 V vs SCE). The hematites obtained from the NaF, NaBr, and NaI solutions exhibited much lower (by approximately 2 orders of magnitude) photocurrent densities under the same conditions, possibly because of their relatively less ordered crystallinity and the absence of rodlike morphologies. Because the synthetic protocol was identical in each case, we believe that these two distinct features reflect the environments in which these hematite photoanodes were formed. Consistent with the latest studies reported in the literature of the X-ray photoelectron spectra of fast-frozen hematite colloids in aqueous solutions, it appears that the degree of surface ion loading at the electrolyte-hematite interface (Stern layer) is critical during the development of hematite photoanodes. We suspect that a lower ion surface loading benefits the hematite developing relatively higher-order and a rodlike texture, thereby improving the photoelectrochemical activity.