This paper describes a study to improve the quality factor (Q-factor) of a silicon-on-chip spiral inductor by determining the most appropriate shape and structure of inductor wires and a ground shield. Electro-magnetic field simulation is carried out under the condition that the spiral inductor is formed on a P-substrate with an electric conductivity of 10 [Ω^-1 m^-1] in assuming the use of a conventional CMOS process. After assessing the simulation results, we propose a new, ring-type structure for the wires and a comb-shaped ground shield that is placed under the inductor wires only. This comb-like shape reduces the stray capacitance between the shield and the inductor wires. As the Q-factor value of a spiral inductor depends on the distance between the ground shield and the inductor wires, as well as on the resistivity of the ground shield material, those influences are also clarified. As a result, we obtain 15% to 23% increases in the Q-factor values in the frequency range of 2 to 3.5 GHz for a 7 nH inductor. We also identify a material possessing the appropriate resistivity to serve as a ground shield.

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An optical board coupled with vertical-cavity surface-emitting laser (VCSEL) and photodiode (PD) for intra-board level optical interconnection was developed using a fluorinated polyimide waveguide film. The edges of the multimode waveguide film were butt-coupled to an 850nm multimode VCSEL and a PD by two passive alignment techniques developed. One was the method used the waveguide core shape, observed using transmission light through the waveguide, as a marker. The other was the method used the dent shape of the waveguide, observed from upside, as a marker. The sum of the two coupling losses among VCSEL, the waveguide and PD was obtained to be less than 2dB. The waveguide film coupled with the VCSEL and the PD was mounted on a conventional FR-4 printed wiring board (PWB), bending the waveguide film. We confirmed that the high-bit-rate data, 2.5Gbps non-return-to-zero (NRZ) pseudo random bit sequence (PRBS) of 2⁷-1 word length, was transmitted using the FR-4 PWB with the optical board.

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We have combined the conventional wettability tester (meniscograph tester) with the newly developed contact angle measuring equipment, which optically and in-situ measures the contact angle of molten solder. Using this new evaluation system, the wettability can be quantitatively evaluated and analyzed on the basis of physical parameters (contact angle and interfacial tension) . In the wettability evaluation of Sn-3.5Ag, which is the typical Pb-free solder, it was found that its contact angle (θ) is greater than that of Sn-37Pb and its wettability is significantly inferior. Moreover, this new system was applied to the detailed investigation of the influence of various factors such as alloying elements (1% Cu, 1% Zn, 5% Bi, 5% In), flux and Au coating on the Cu substrate on the wettability of the Sn-3.5Ag. It was clarified that the changes in its wettability are caused by the difference in the three interfacial tensions between the solder/flux, substrate/flux and substrate/solder, which are affected by the solder composition, flux, substrate surface and intermetallic compound formed at the solder/substrate interface.

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The reaction between molten lead-free solder and iron-based alloys has been investigated by evaluating the dissolution rate of iron-based alloys in molten solders. The dissolution rate of these alloys used for plating on tip of soldering iron and container materials of solder bath are about three times larger when tested in lead-free solder than in conventional Sn-Pb eutectic, which indicate that the iron plating of soldering iron tip and container materials for soldering bath are subjected to heavier damage in lead-free solders than in Sn-Pb eutectic. The rate showed little dependence on compositions of both solders and iron-base alloys. Heterogeneous dissolution was observed in stainless steels and the maximum dissolution depth was larger than that of alloyed steels. The decrease in reaction temperature and time and the small addition of iron into solder were found to be effective for suppression of dissolution.

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We studied interfacial reaction and joint strength of Sn-Ag solder ball and Sn-Ag-Cu solder ball bonded on electroless Ni-P plating with various thickness of Au coating. In Sn-Ag-Cu solder samples, no P-rich layer formed at the joint interface except for the samples with 250nm and 500nm Au coating. This is caused by (Cu, Ni) ₆Sn₅ layer formed at the interface, which suppresses diffusion of Ni into the solder. On the other hand, in Sn-Ag solder samples, P-rich layer formed at the interface regardless of thickness of Au coating, because no (Cu, Ni) ₆Sn₅ formed. In the samples with P-rich layer, the fracture occurred at the interface and thereby the joint strength degraded. Therefore the strength of the Sn-Ag-Cu solder joints was higher than that of the Sn-Ag solder. In Sn-Ag-Cu solder, 50nm thickness of Au layer accomplished the best joint.

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The reliability of the BGA joint is influenced by the reaction between the solder ball and the pad. In this study, the melting behavior of Cu core solder ball with Sn/Ag and the solderability of the BGA joint between this ball and the Ni/Au coated pad ware investigated. It was revealed that this ball started to melt at Sn-Ag-Cu eutectic temperature. β-Sn, Ag₃Sn, and Cu₆Sn₅ phase were formed inside the solder and the Cu₆Sn₅ reaction layer was formed at the interface after reflow soldering. It was also revealed that the BGA joint using Cu core solder ball could be prevented strength reduction because the Cu₆Sn₅ reaction layer at the solder/pad interface grew slowly during aging at 150°C.

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New measurement method for characteristic impedance of Printed Circuit Board was developed and its usability was demonstrated. This method is based on a conventional TDR method, but using burst sinusoidal wave modulated by step pulse as a input signal instead of direct step pulse. Characteristic impedances of 5m semi-rigid cable and 28cm Microstrip PCB are measured at 70 MHz-350MHz frequency randge using this new method. For the long cable the characteristic impedance can be measured consistently with the conventional method between 200MHz to 350MHz. For the short microstrip line however the measured values fluctuate in some extent. The reason for obtained results are discussed.

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