Masahide Tokuda

Fluxless and virtually voidless soldering for semiconductor chips

A novel soldering technique using a solder washer preform has been developed. A conventional vacuum-release process is used in the soldering procedure. That is, after curing of the assembly in vacuum ( approximately 1 torr) the fused washer preform wets the specimens (e.g. chip and heat sink) to seal up the through-hole area of the washer preform with approximately 1 torr. Subsequently, the vacuum is released to make the fluid pure solder flow into the through-hole area in such a manner that most of the oxide film of the washer preform is destroyed. It is demonstrated that the procedure results in an ideal bond with pure solder in a vacuum, without using flux. It also demonstrated that the above technique can be used to reduce voids to less than 5% on average in solder bonds with 1-cm/sup 2/ chips or 3-in wafers. Improved solder bond strength due to the new technique is also confirmed. >

Fluxless and substantially voidless soldering for semiconductor chips

A soldering method for reliability fabricating a composite structure is presented. This method, which need not use flux, provides a substantially voidless layer of solder that has low thermal resistance and excellent mechanical strength. A detailed description of soldering procedure, which uses a square, washer-shaped solder preform, is given. The experimental results show that the voids in the solder layer were reduced to less than 5% in bonds of silicon chips with a size of 1 cm/sup 2/. When 3-in silicon wafer chips were used, a similar void reduction took place. Moreover, pure solder flowed into the vacant region within the preform in such a manner that the native oxide film at the surface of the preform was removed. This resulted in an average solder bond shear strength that was greater than that obtained in the conventional manner using flux. The method was successfully applied to the fabrication of a multichip module. It was also used to make a high-voltage diode composed of ten silicon chips piled up vertically and connected with solder.<<ETX>>

A module of a blue-violet laser diode and photodiodes for adaptive compensation of spherical-aberration

Much research and development has been reported for high-density optical disc systems using a blue-violet laser diode (LD) and a high numerical-aperture (NA) objective. The next phase is now underway - studying ways to mass produce them. We previously described adaptive compensation of spherical-aberration (SA) and a single-element objective, for overcoming the narrow tolerance of the substrate thickness error in high NA optics, and the narrow working distance of a conventional two-element objective, respectively. To facilitate their use in assembling a miniaturized optical pickup, we recently developed a module that integrates a blue-violet LD, photo-diodes (PD) and an etched mirror on a silicon substrate. For precise alignment of the module, we used the junction-down arrangement for the LD. We confirmed the ability of this blue-violet LD module to compensate for the SA and give good signal quality for the Blu-ray Disc format (23 GB).

4-channel/spl times/10-Gbit/s parallel laser-diode module for high-capacity optical interconnects

A 4-channel/spl times/10-Gbit/s parallel LD module for next-generation high-capacity optical interconnects was developed. To suppress the inter-channel crosstalk, a PPLC platform with a channel-pitch conversion function was also developed. Four un-cooled 1.3-/spl mu/m InGaAlAs FP-LDs were mounted on separated electrodes of the PPLC platform by passive alignment; thus, the module is compact and low cost. Crosstalk is as low as -40 dB. The module has a total throughput of 40 Gbit/s over 300-m transmission without suffering any degradation caused by inter-channel crosstalk. Our proposed 4-channel/spl times/10 Gbit/s parallel LD module can be applied to next-generation high-capacity optical interconnects.