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  4. No.33 January,2004
Fujikura Technical Review

No.33 January,2004

Downsizing of electronic devices, especially digital electronic products and cellular phone, require smaller and thinner printed circuit board. R-F PCB is one of its solutions. It's stacked and unified flexible printed circuit board (FPC) and rigid printed circuit board (RPC). Multi-layered RPC portion can achieve component mounting as same as conventional RPC, and FPC portion is suitable for bending or high flexibility applications. It contributes downsizing of electronic devices. We are manufacturing R-F PCB not only in Japan but also in Thailand to support rapidly increasing demands.


1x4 Fused Taper Star Couplers

Optical splitters are important devices for the Passive Optical Network (PON). We propose two types of fused taper 1x4 couplers; low excess loss, dual window 1x4 couplers for the current PON system, and high uniformity type 1x4 couplers for BPON full-band operation. Wavelength flattened characteristics and excellent branching uniformity less than 0.4dB have been achieved in wavelength range from 1,200nm to 1,700nm. Their high reliability is also demonstrated. 

Subminiature Micro-Optic Devices with Mini Quartz-Rod-Lens

In order to miniaturize micro-optic devices, we have developed a novel mini quartz-rod-lens collimator by using plasma-activated chemical vapor deposition (PCVD) method and CO2 laser splicing technology. By employing these collimators, roughly 90% volume reduction has been achieved in micro-optic devices compared with conventional ones. 

Dispersion Compensating Fiber Modules for Dispersion-Shifted Fiber

Slope compensating and dispersion compensating fibers (SC-DCF) for a dispersion-shifted fiber (DSF) have been designed and fabricated. The SC-DCF has realized a targeted dispersion slope compensation ratio, which require the highest relative dispersion slope (RDS) among various types of SC-DCFs. The optical performance of the SC-DCF is similar to those of SC-DCFs for non-zero dispersion-shifted fibers (NZ-DSF). The nonlinearity of the SC-DCF is smaller than conventional SC-DCFs, since the fiber length of the SC-DCF to be used in a DCF module is shorter than those for conventional SC-DCF modules. In addition, the SC-DCFs have been packaged into modules. It has been confirmed that the modules have good optical performance and high reliability.

Laminated Tube Cable (LT Cable)

We have developed a new type of cable (LT cable) that will prove both economical and efficient in access network integration. The concepts behind the newly developed cable are as follows. (1) The new cable should provide compatibility with various common network systems. (2) It should be easily accessible for mid-span access. (3) It should lend itself to duct and aerial installation. In this report, we would like to introduce the new developed cable in terms of its construction, mechanical performance and characteristics.

InfiniBandTM Cable

We have developed InfiniBandTM connector, cable and assembly capable of transmitting data at 2.5Gbps/pair. In various tests conducted to examine the electrical and mechanical properties of the connector and the cable assembly, we have made sure that the products meet InfiniBandTM requirements and ensured excellent performance in crosstalk and impedance matching.

Film Antenna for Wireless LAN

Wireless LAN operating at the 2GHz band and 5GHz band will spread widely in the future. We have developed the multi band film antenna suited for mounting in mobile equipments. The antenna is very small and thin (55x5x0.1mm) , and can operate 2GHz and 5GHz with sufficient band width. The antenna has omnidirectional radiation pattern, and the average gain is 1.7dBi at 2GHz and 2.3dBi at 5GHz band.

Flame Retardant Membrane Switch with Eco-friendly Materials

We have been producing membrane switch modules which are combination of membrane switches and other various kinds of mechanical parts. These products are used for digital cameras and digital video cameras, UL certification is required for these products. In order to satisfy the flammability specified in UL94, the membrane switch is made flame-retardant with an over-coating of the plasticized polyvinyl chloride resin. From the viewpoint of the environmental consideration, however, polyvinyl chloride resin and other halogen compounds, which generate toxic dioxin gas by incomplete combustion, are recently limited to use for these products. This paper reports the development of flame retardant membrane switches without halogen compounds. The Eco-membrane switches possess the mechanical and electrical properties equivalent to the conventional membrane switches coated with polyvinyl chloride resin.

Ultrasonic Flip Chip Bonding on FPC

Small form factor and high density of printed circuit boards (PCB) have been achieved by flip chip (F/C) bonding technology. However, the requirement for finer pitch of PCB is still increasing with integration of semiconductor devices. Hence, conventional F/C bonding technology will not provide sufficient capability or productivity to meet future demands. Fujikura has adopted novel ultrasonic F/C bonding technology, which can provide fine pitch bonding and evaluated reliability and bondability to flexible printed circuits. In conclusion, ultrasonic technology is most suitable for fine pitch chip on flex products as it provides high productivity with reduced bonding time.

Flexible Printed Circuit on Suspension of Hard Disk Drive

Fine printed circuit formed on suspension, currently becomes more common in HDD; Hard Disk Drive. There are various methods of forming the circuit on suspension. The FPC; Flexible Printed Circuit method, adheres to suspension, has the advantages of lower cost and high transmission rate compared with the others, so HDD made use of this method is suitable for electric household applications. Therefore, we developed the FPC, formed on suspension, build-in HDD of Audio Visual appliances, which is expected to rapidly expand the HDD market from now on. For the above-mentioned FPC, we employed wet-etching technology, which is able to have dust-free and pattern resolution in 100㎛.

Heat Resistant Double-Layered TCO

New TCO films, FTO films coated on ITO films, were developed for DSC. These films were prepared by a SPD method at a substrate temperature of 350°C in ITO and 400°C in FTO. For ITO deposition, an ethanol solution of InCl3·4H2O and SnCl2·2H2O [Sn/(In+Sn), 5 at.%] was sprayed on a glass substrate. After the deposition of ITO, FTO films were consecutively deposit-ed for protecting oxidation of ITO films. FTO deposition was carried out by an ethanol solution of SnCl4·5H2O within the saturated water solution of NH4F. These films achieved the lowest resistivity of 1.4x10-4Ωcm and the optical transmittance of more than 80% in the visible range of the spectrum. The electrical resistance of these films increased by less than 10% even though exposed to high temperatures of 300 to 600°C for 1 hour in the air. The 100x100 mm2 large size DSC composed of the films were fabricated to confirm the availability of them. Energy conversion efficiency of h=3.7% was obtained. As the result, the FTO/ITO films showed heat-resisting property in sintering TiO2 for the DSC.

Dye-sensitized Solar Cells Using Ionic Liquid-based Electrolytes

Because of low fabrication costs, simple manufacturing process, using no toxic materials and so on, a dye-sensitized solar cell (DSC) composed of nanocrystalline TiO2, organic dyes and electrolytes is expected to be a large-scale prevalent solar cell. It is necessary to improve cell stability and develop large sized cell fabrication technology for its practical use. In this report, developments of DSC using an ionic liquid electrolyte and its upscaling technology are introduced. For application of ionic liquids as electrolytes of DSC, short-circuit current (Jsc) and open-circuit voltage (Voc) of cells using ionic liquids were evaluated as a function of I-/I3- redox couples in the electrolyte. At optimized electrolyte composition, h=4.5 % of energy conversion efficiency was obtained. Based on the result, a 100 x 100 mm2 sized DSC using an ionic liquid electrolyte was fabricated and h=2.7 % (based on active area) was obtained. Fabrication of a DSC using an ion-gel electrolyte, which was a gelated ionic liquid electrolyte, was also described.

High-density Through-hole Interconnections in a Silicon Substrate

Fabrication technologies of through-hole interconnections in a Si substrate have attracted much attention as one of next-generation packaging technologies. We demonstrated through-hole interconnections in a Si substrate, which can be applied to image sensors or Micro Optical Electro-Mechanical System (MOEMS) devices such as micro mirror. We evaluated some basic characteristics of the through-hole interconnections including electrical or mechanical charac-teristics. Especially, we analyzed stress distributions of the through-hole interconnections by Finite Element Method (FEM). The result showed that the estimated stress value was so small and would cause no crack in through-hole interconnections.