Hyo-Hoon Park

Effect of dihedral angle on the morphology of grains in a matrix phase

Minimum interface energy configurations of a uniformly intermixed grain-matrix aggregate are determined for various dihedral angles and matrix contents by numerical analysis of a model which consists of a rhombic dodecahedron grain in contact with matrix at its curved surfaces along truncated edges and corners. For dihedral angles, Φ, greater than 90 deg, the total interface energy,E, increases monotonically with the matrix volume fraction,Vm. For Φ= 0 deg,E decreases withVm until the grains become spherical atVm = 26 pct. For 0 deg Φ ≤ 75 deg,E vs Vm curves show the minima which represent the stable configurations to be obtained whenVm can be freely varied. For Φ ≤ 60 deg, the matrix is always continuous along the grain edges. For Φ 75 deg, the matrix becomes separated at the grain corners below certain critical values ofVm. The contiguity decreases monotonically withVm. The slope ofE vs Vm curve is shown to be an effective pressure on the specimen surface, which represents the driving force for changing the grain configuration with a corresponding change ofVm while keeping the grain volume constant. The implications of these results on solid state sintering, liquid phase sintering, and the penetration of liquid into liquid phase sintered alloys are discussed. Finally, the results of a previous analysis by Beere are shown to disagree with the present work for systems with low dihedral angles apparently because of inaccuracy in his calculation.

PCB-compatible optical interconnection using 45/spl deg/-ended connection rods and via-holed waveguides

In this paper, a new architecture for a chip-to-chip optical interconnection system is demonstrated that can be applied in a waveguide-embedded optical printed circuit board (PCB). The experiment used 45/spl deg/-ended optical connection rods as a medium to guide light paths perpendicularly between vertical-cavity surface-emitting lasers (VCSELs), or photodiodes (PDs) and a waveguide. A polymer film of multimode waveguides with cores of 100/spl times/65 /spl mu/m was sandwiched between conventional PCBs. Via holes were made with a diameter of about 140 /spl mu/m by CO/sub 2/-laser drilling through the PCB and the waveguide. Optical connection rods were made of a multimode silica fiber ribbon segment with a core diameter of 62.5 and 100 /spl mu/m. One end of the fiber segment was cut 45/spl deg/ and the other end 90/spl deg/ by a mechanical polishing method. These fiber rods were inserted into the via holes formed in the PCB, adjusting the insertion depth to locate the 45/spl deg/ end of rods near the waveguide cores. From this interconnection system, a total coupling efficiency of about -8 dB was achieved between VCSELs and PDs through connection rods and a 2.5 Gb/s /spl times/ 12-ch data link demonstrated through waveguides with a channel pitch of 250 /spl mu/m in the optical PCB.

Pore filling process in liquid phase sintering

Models for liquid flow into isolated pores during liquid phase sintering are described qualitatively. The grains are assumed to maintain an equilibrium shape determined by a balance between their tendency to become spherical and a negative capillary pressure in the liquid due to menisci at the specimen surface and the pore. With an increase of grain size, the grain sphering force decreases while the radius of liquid menisci increases to maintain the force equilibrium. When grain growth reaches a critical point, the liquid menisci around a pore become spherical and the driving force for filling the pore rapidly increases as liquid flows into it. The critical grain size required for filling a pore increases linearly with pore size. Experimentally, filling of isolated pores has been investigated in Fe-Cu powder mixture after liquid phase sintering treatment and after dipping into a molten matrix alloy. The observed pore filling behaviors agree with the qualitative predictions based on the models. In Fe-Cu alloy, pore filling is terminated by gas bubbles formed in liquid pockets.

Optical backplane system using waveguide-embedded PCBs and optical slots

As discussed in this paper, a practical optical backplane system was demonstrated, using a waveguide-embedded optical backplane board, processing boards, and optical slots for board-to-board interconnection. A metal optical bench was used as a packaging die for the optical devices and the integrated circuit chips in both the transmitter and the receiver processing boards. The polymer waveguide was produced by means of a hot-embossing technique and was then embedded following a conventional lamination processes. The average propagation loss of these waveguides was approximately 0.1 dB/cm at 850 nm. The dimension and optical properties of the waveguide in an optical backplane board were unchanged after lamination. As connection components between transmitter/receiver processing boards and an optical backplane board, optical slots were used for easy and repeatable insertion and extraction of the boards with a micrometer-scale precision. A 1/spl times/4 850-nm vertical-cavity surface-emitting laser array was used with 2 dBm of output power for the transmitter and a p-i-n photodiode array for the receiver. This paper successfully demonstrates 8 Gb/s of data transmission between the transmitter processing board and the optical backplane board.

Passively assembled optical interconnection system based on an optical printed-circuit board

We propose a passively assembled chip-to-chip optical interconnection system using fiber-optic technology. To demonstrate the system, three components were prepared: a fiber-embedded optical printed-circuit board (OPCB), optical transmitter/receiver modules, and 90/spl deg/-bent fiber connectors. All components were assembled using precise guide pins and holes so that complete passive alignment was achieved in the OPCB. An optical link of 5-Gb/s/ch signals with a total link loss of -1.5 dB has been successfully demonstrated from the assembled system.

High-coupling-efficiency optical interconnection using a 90/spl deg/-bent fiber array connector in optical printed circuit boards

A high-coupling-efficiency optical interconnection has been demonstrated using a 90/spl deg/-bent fiber array connector to deflect beams between surface-emitting lasers or surface-receiving photodiodes and optical layers embedded in a board. A 90/spl deg/-bent fiber array is mounted in a tetragonal body with a millimeter scale size to make it suitable for passive packaging in the board. The bending radius of silica fibers in the connector was controlled to have 1.5 mm resulting in bending loss of about 0.5 dB. An optical link of 2.5-Gb/s signals with a total interconnection loss of -1.3 dB was demonstrated using the connectors and a fiber-embedded board.

An analysis of the surface menisci in a mixture of liquid and deformable grains

The capillary force due to liquid menisci at the surface of a mixture of deformable grains and a limited amount of liquid (exemplified by liquid phase sintered alloys) is analyzed. Geometrical models for the grains and the menisci at the specimen surface are described. The menisci curvature required to keep the grains in the anhedral (contact flattened) shape with limited liquid content is calculated from the condition that the capillary force is counterbalanced by the sphering force of the grains. The radius of the menisci at equilibrium increases with liquid content. Its dependence on the dihedral angle, on the wetting angle, and on the ratio of the interfacial energies between the liquid-vapor and solid-liquid phases is also described. The grain-meniscus system maintains a shape geometrically similar with respect to change of grain size; hence, the meniscus radius increases in proportion to the grain radius. It is proposed that the difference between the capillary force and the sphering force is the meaningful driving force for grain shape accommodation during liquid phase sintering. Finally, some experimental evidence supporting the results of these analyses is discussed.

Two-Dimensional Optical Interconnection Based on Two-Layered Optical Printed Circuit Board

The demonstration of an optical platform based on an optical printed circuit board (OPCB) was shown for two-dimensional (2-D) chip-to-chip optical interconnection. The optical platform was designed for 96 Gb/s total throughput which was 2 layers times 4 channels times 4 parallel links times 3 Gb/s/ch and using a passive assembly technology. We fabricated three main components for the 2-D optical interconnection; two-layered six-channel fiber- and connector-embedded OPCB, two-layered six-channel 90deg-bent fiber connectors, and 2-D optical transmitter/receiver (Tx/Rx) modules. The total optical loss from the Tx to the Rx was measured to approximately be -5.3 dB. The optical interconnection using an optical platform was successfully achieved with 3-Gb/s/ch data transmission

Compact packaging of optical and electronic components for on-board optical interconnects

An optical interconnection plate was developed in order to achieve a compact and cost-effective interconnection module for an optical data link between chips on printed circuit boards. On the silica substrate, transmission lines and solder bumps are formed on the top surface of the substrate, and polymer waveguide array with 45/spl deg/ mirror planes is formed on the back side. This optical interconnection plate technique makes the alignment procedure quite simple and economical, because all the alignment steps between the optical components can be achieved in wafer processes and a high accuracy flip-chip bonding technique. We confirmed the sufficiently high coupling efficiency and low optical crosstalk using the simplified experimental setup. Flip-chip bonding of the vertical-cavity surface-emitting laser and photodiode arrays on the top surface of the optical interconnection plate was performed using indium bumps in order to avoid thermal damage of the polymer waveguide. The fully packaged optical interconnection plate showed an optical data link at rates of 455 Mb/s. Improvement of the mirror surface roughness and the mirror angle accuracy could lead to an optical link at higher rates. In addition, the interconnection system can be easily constructed by inserting the optical interconnection plate between the processing chips or data lines requiring optical links.

The critical grain size for liquid flow into pores during liquid phase sintering

A model of grain-liquid mixture containing a spherical pore is analyzed to describe the pore filling during liquid phase sintering. Since the radius of liquid menisci around a pore increases linearly with the grain size, the menisci form a spherical bubble at a critical grain size and the pore is rapidly filled with liquid flowing from numerous menisci at the specimen surface. The values of the critical grain size for pore filling are calculated for various dihedral angles, wetting angles, and liquid contents. Although the predicted critical grain size is subject to errors because of assumptions in the models, the values agree in an order of magnitude with some experimental results. The effect of entrapped gas on pore filling and the expected behavior of irregular pores are also briefly discussed.