Chi-Shiung Hsi

Formation and Morphology of Zn2Ti3O8 Powders Using Hydrothermal Process without Dispersant Agent or Mineralizer

Synthesis of Zn2Ti3O8 powders for attenuating UVA using TiCl4, Zn(NO3)2·6H2O and NH4OH as precursor materials by hydrothermal process has been investigated. The X-ray diffractometry (XRD) results show the phases of ZnO, anatase TiO2 and Zn2Ti3O8 coexisted when the zinc titanate powders were calcined at 600 °C for 1 h. When calcined at 900 °C for 1 h, the XRD results reveal the existence of ZnO, Zn2TiO4, rutile TiO2 and ZnTiO3. Scanning electron microscope (SEM) observations show extensive large agglomeration in the samples. Transmission electron microscope (TEM) and electron diffraction (ED) examination results indicate that ZnTiO3 crystallites formed with a size of about 5 nm on the matrix of plate-like ZnO when calcined at 700 °C for 1 h. The calcination samples have acceptable absorbance at a wavelength of 400 nm, indicating that the zinc titanate precursor powders calcined at 700 °C for 1 h can be used as an UVA-attenuating agent.

Sintering of titanate based dielectrics doped with lithium fluoride and calcium borosilicate glass

The effect of LiF and CBS glass additives on the microstructure and dielectric property of BaTiO3 (BT) ceramics was studied. The phase of BaLiF3 was observed from the interaction between BT and LiF when the samples were sintered at 900 °C for 1 h. Crystal grains with Ba and F in atomic ratios of 1:3 were observed from the SEM and TEM analysis of the microstructures. Abnormal grain growth (AGG) was observed to occur in the BT ceramics sintered at 950 °C. Further improvement to the composition was achieved by employing a two-stage process. This included CBS glass shell coating of the BT particles in the first stage, and the addition of LiF in the second stage. The composition thus formed had very good permittivity (1725) and an extremely low dielectric loss value (0.008).

Co2Y-NiCuZn ferrite composites for high frequency applications

It is very important and urgent to develop a magnetic material that has a higher initial permeability and quality factor above 200-300 MHz for use in making high frequency inductors. This study produced a Co2Y-NiCuZn ferrite composite with high permeability by coating NiCuZn ferrites onto the surface of Co2Y ferrites using a heterogeneous nucleation process. The NiCuZn ferrites addition effects on the densification behavior, micro-structure and magnetic property of Co2Y-NiCuZn ferrite composites were investigated. A NiCuZn ferrites coating onto the surface of Co2Y ferrites can effectively enhance the densification and improve the magnetic property of Co2Y ferrites. Co2Y-NiCuZn ferrite composites sintered at 1200° show a sintered density of 5.34g/cm3, high initial permeability of 4 and quality factor above 30 in the 300-600 MHz frequency, which can be used in inductors for high frequency applications.

RF Properties of LTCC BST Thick Film Made by MicroPen

The direct-writing technique by MicroPen provides maskless fabrication method for complex and multilayer structures. In this work, low-temperature co-firing ceramic (LTCC) BST paste was fabricated and structures for high frequency evaluation were formed by MicroPen. The results showed uniform microstructures with some porosity after sintering at 900 °C. The dielectric properties were characterized in the frequency range of 0.5 to 13.5 GHz using coplanar waveguides. The ϵ r and tanδ of the LTCC BST thick film were 57.5–41 and 0.013–0.007 with applied electric field of 0-10 V/μm, respectively at 5 GHz. The tunability obtained was 28 % at 10 V/μm.

Solder joint strengths and interfacial reactions in various Pb-free solder joints

Two kinds of Pb-free solders, Sn8Zn3Bi and Sn9ZnAl, were used to mount passive components onto OSP and ENIG PCB using a reflow soldering process. The component mounted boards were stored at 150degC for 200, 400, 600, 800, and 1100 h. The microstructures of the interfaces between the solders and pads of the aged assemblies were observed using scanning electron microscopy (SEM) and the chemical compositions of the intermetallic compounds (IMCs) formed at the interfaces were analyzed using energy dispersive spectrometry (EDS). After shear testing, both solders showed acceptable solderability on the OSP and ENIG layers, but the shear strengths of the Sn8Zn3Bi solder joints were better than those of the Sn9ZnAl solder joints. All of the solder joint strengths deteriorated during the aging process, but the degradation of the OSP solder joints was more evident than that of the ENIG solder joints. Scallop-shaped epsiv-Cu0.2Zn0.8 IMC and flat gamma-Cu5Zn8 IMC formed between the solders and Cu pad of the OSP board after reflowing with an increase of aging time, all of theepsiv-Cu0.2Zn0.8 layers transformed into gamma-Cu5Zn8 and the IMC layer became thicker. The Zn-depletion zone and Cu6Sn5 IMC were observed in the solders due to the interaction between the tin and zinc compounds. Both solder joints on the ENIG boards had similar interfacial microstructures; very thin gamma2-AuZn3 layers were formed at the interface of the solders and Ni-P layers. The gamma2-AuZn3 layer transformed into gamma2-AuZn8 IMC with a consistent thickness during aging. The Zn phase redeposited above the IMC layer and the size of the Zn phase grew with increasing aging time.

An innovative packaging process for low power loss solar modules

This paper presents an innovative interconnecting process for the 5 inch × 5 inch photovoltaic (PV) modules based on single crystalline silicon solar cells using epoxy-based conductive adhesive (CA), and a conventional soldering type solar cell is also performed for comparison. The electrical performance of solar modules with innovative interconnecting process (Inno 1, 2, and 3) was characterized by a flasher system in AAA class, and the long-term durability of the solar modules was verified by thermal cycling test in accordance with IEC 61215 standard. The result shows that the power loss for innovative stringing solar cell with epoxy-based CA exhibits a two-stage degradation mechanism, in which a higher lossrate occurs before TC 600 times. For Sn-Pb solder solar module, a linear degradation is observed during the 1600 thermal cycling test, suggesting a single degradation mechanism. Compare the power loss of the solar modules, the innovative modules are around 4.31% to 5.21%, while a high power loss of 7.49% is obtained in soldering type module after 1600 TC test. According to the cross-sectional images focusing on the solder joints, a better performance of the epoxy-based CA solar module was due to the good adherence and stability of the soldering interfaces between the cell metallization and the interconnecting element. Electroluminescence (EL) detection was applied to identify the defects and high series resistance area which may degrade the power of the cell. Some dark failure area on the central region after 1600 thermal cycling test (TCT) is shown in soldering type sample. And a high contrast of the emission intensity is obtained, which implies a mismatch of minor carrier diffusion length in the solar cell. The dark regions observed in the soldering type sample indicated that a higher Rs was generated in the module. On the other hand, CA sample showed a clear image on the cell itself and the p-n junction borderline area.

Investigations of Lead-Free Glasses for Post-Fired and Embedded Thick Film Resistors

Lead-free thick film resistors (TFRs) were prepared by mixing of ruthenium oxide (RuO2) and CaO-B2O3-SiO2 based-glass. The resistors were post-fired on alumina and co-fired in LTCC substrates. Different metal oxides were added into the glass phase, such as Nb2O5, MnO2, MoO3, Fe2O3, TiO2. They were used as temperature coefficient of resistor (TCR) adjustment agents of the resistors. The microstructures variations and interactions at the interface between resistors and substrates were investigated. The additives made glass structure loose and conductivity of resistor decrease, the TCR values of the resistors moved toward negative direction. When 4wt% MnO2 was added into the glass, the thick-film resistors embedded in LTCC had conductivity of 2.46 (Ω-cm)-1, the temperature coefficient of resistor decreased to 12 ppm/°C. The conductivities of the resistors films were depended on the volume fractions of conductor-agglomeration (RuO2), microstructures, and TCR additives of the resistor layers

Effects of ZnO-B2O3-SiO2 addition on the microwave dielectric properties of Ba(Nd1-xBix) 2Ti4O12 ceramics

ZnO- B2O3 -SiO2 glass effects on both the sintering behavior and microwave dielectric properties of BaO. (Nd1-xBix)2O3. 4TiO2 (BNBT) ceramics were investigated in developing low-temperature-fired dielectric ceramics for microwave devices. Glass wetting characteristics on the BNBT surface, X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and a dilatometer were used to examine the ZnO-B2O3-SiO2 glass effect on BNBT densification and the chemical reaction between the glass and BNBT. The results indicate that ZnO-B2O3-SiO2 glass can be used as a sintering aid to reduce the densification temperature of BNBT from 1300°C to 900°C. The substitution of Bi for Nd in BNBT affected the densification behavior, microstructure, and dielectric properties. BNBT ceramics with 8 wt% ZnO- B2O3 -SiO2 glass sintered at 900°C show a relative density of 98%, a high dielectric constant of 61.2, a quality factor (Q×f) of 7924, and a temperature coefficient of resonant frequency of 9 ppm/°C.

Low Temperature Cofired Soft Ferrites for High Frequency Applications

The demand for small-sized multilayer LC filters has rapidly increased. One of the most important processes in manufacturing defect-free integrated multilayer magnetic components involves magnetic materials, high-dielectric-constant LTCC material and silver cofiring at a low temperature. This study develops low sintering temperature (below 900°C) Ba2Zn0.95Co0.8Cu0.4Fe11.98O22 (Co2Y) ferrites with superior magnetic properties added with Zn-B-Si glass. The cofiring behaviour and interfacial interactions between high-dielectric-constant BaO·(Nd0.8Bi0.2)2O3·4TiO2 ceramics (BNBT) ceramics/Co2Y ferrites at 900°C were studied using XRD, dilatometer, SEM, EPMA and TEM. It was observed that 4wt% Zn-B-Si glass addition can effectively promote Co2Y ferrite densification and magnetic properties. The interfaces between the 4wt% Zn-B-Si glass-added Co2Y ferrites and BNBT ceramics layers after cofiring were free of delamination or gaps, indicating that the Co2Y ferrites and BNBT ceramics exhibited excellent physical and chemical compatibilities during cofiring.

A Low-Temperature-Fired Multifunctional Varistor-Magnetic Ferrite Material-CuCr0.2Fe1.8O4

A novel low temperature-fired (950°) multifunctional varistor-magnetic ferrite material can be obtained by adding V2O5 into CuCr0.2Fe1.8O4 ferrite. The relationship between the grain-boundary composition and varistor properties were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersion spectroscopy (EDS), and X-ray photoelectric spectroscopy (XPS). The addition of V2O5 can effectively reduce the sintering temperature of CuCr0.2Fe1.8O4 ferrites to temperatures of lower than 950°. Moreover, the V^(5+) ions dissolved into spinel structure and acted as donor dopant, which resulted in the semi-conductive grain. The copper-rich observation at the grain boundary based on the TEM and EDS results implied that copper oxide would possibly develop at the grain boundary as the acceptor state, forming double Schottky barriers with the n-type semiconductor grains.