The identification of the elastic-plastic-creep constitutive equation for the lead-free solder bump is very important to design the structure of semiconductor packages. Through the shearing tests in the scanning electron microscope (SEM), it has been clarified that the displacement of the generating crack increases as the testing temperature increases. With a simplex method, an identification method of the elastic-plastic-creep constitutive parameters has been developed such that the computational results for the shear force at the specific shear deformation coincide with those obtained by experiments of bump. Very good correspondence between the computationally predicted results for a series of the shearing test by the different shaped bump and those due to experiment, has been proved, which indicates the capability of the proposed identification method for design of semiconductor packages.

View full abstract

We proposed that the differential thermal gravimetry analysis (DTGA) for method of flux material development. The reaction of cupric oxide (powder) and the organic acid was exam-ined by DTGA as a model type corresponding to the metal oxidation membrane removal action which was a main flux action. The reaction with each change point was explained from the X-ray difraction of the sample corresponding to the change point of the heat behavior and the weight behavior. The fluxreaction temperature, the flux potency, the flux residue weight and the information of after-oxidation can be read from DTGA. The result showed that DTGA data guessed compatibility as the flux of the material. Also, we examined the influence given to solder or the substrate metal of organic acid system flux residue by a similar method.

View full abstract

Vertical integration of planar single-mode optical waveguides and their interconnectiorr were discussed and demonstrated. A pair of grating couplers were used for transferring guided power from one waveguide to the other via a bridging mode. Utilization of a bridging mode enables efficient coupling of waveguides stacked far between as well as selective coupling among multistory structure. Wavelength dispersion of the grating couplers and mode discontinuity of the guided modes provide sharp wavelength selectivity. Prototype devices were designed, fabricated and characterized for two types of interconnection, namely, wavelengthdivision demultiplexing via radiation modes among stacked three waveguides and optical drol demultiplexing via supermode between stacked two waveguides.

View full abstract

A method of 90° optical path conversion is a key of Optical Surface Mount Technology (O-SMT) which was proposed to provide a possible solution for growing serious problems in manufacturing process of opto-electronic products. We have proposed a new method that can change the optical path from the vertical to the horizontal using an optical pin with a micro mirror. An optical pin was fabricated by cutting a multi-mode fiber at 45°. We studied reflection characteristics of an optical pin with a micro mirror and found that the optical ray components which leaked through the 45° mirror existed. The insertion loss between a polymeric optical waveguide and an optical pin with a micro mirror was measured to be 30%. It is clarified that an optical pin with a micro mirror has a useful function of changing the beam direction from the vertical to the horizontal and vice versa.

View full abstract

[in Japanese]

View full abstract

We developed a highly reliable fan-out-type chip scale package (CSP) for a microcomputer or an ASIC (Application Specific IC) . We found that the solder joint reliability of the CSP under temperature cycling is equal to that of a quad flat package (QFP) and that its mechanical strength (determined from a board-bending test) is much higher than that of a QFP. The fatigue life of a Sn-Ag-Cu lead-free CSP solder joint determined from a cyclic board-bending test is almost equal to that of a Sn-37Pb CSP solder joint. Moreover, compared to a QFP, the occupied area of a CSP is decreased by 75% and its weight is decreased by 90%.

View full abstract

Thermal fatigue life of Flip Chip packages (Direct Attach Aurum bump type) is studied both analytically and experimentally. In this analysis we found the law of thermal fatigue life which is ruled by equivalent-stress of aurum bump and clarified a sensitivity of thermal fatigue life related to material and structural size.

View full abstract

The requirement of high-density packaging has becoming strongly in the portable electronic products with progressing for miniature, lightweight, high speed, and high function. The use of the miniature semiconductor package, such as Chip Size Package, has been growing very rapidly. The portable products are subjected to mechanical stress as it is pressed keypad and it is dropped. Therefore mechanical reliability is very important in the portable products. Then, we have performed with the repeatedly bending test of the CSP mounted on the circuit board. As a result, the first failures occurred in the CSP's corner pads. And the correlation between the life cycle times and the destruction mode was made clear. It was found out that a exfoliation between solder and PWB's pad, and a broken wire of PWB were occurred earlier than the solder crack in case of comparing Sn-Ag-Cu solder with Sn-Pb eutectic solder. It was found out that the life cycle of the Sn-Ag-Cu solder was better than that of the Sn-Pb eutectic solder.

View full abstract

We have developed a new technique of adjusting propagation delay time of Multi-Wire Boards (MWBs) . MWBs use polyimide insulated copper wires for signal connection. The wires will intersect each other. Therefore, in high-density wiring, improper variation in the delay time will be caused by intersections of wires, adjacent through holes, folded wires, and via holes in the middle of wiring. A new estimation method was proposed and the influence of these factors on the variation of the delay time was investigated. It was found that about 73% of the variation is caused by the intersection of wires. With this new technique, it is possible, after finishing the routing design, to control the length of the wiring, and adjust the propagation delay time so that it is equal to that calculated by a newly developed software. We confirmed that the variation time of the boards designed in this way decreases to one-third or less of that of the conventional MWBs.

View full abstract

A new conducting method of ultrafine polymer particles by using direct metallization technology was proposed in this paper. Carboxyl groups, as a cation exchange group, were formed onto the particle surfaces through NaOH hydrolysis treatment. Nickel ions absorbed to the cation exchange groups were reduced by sodium borohydride. Size of metal nickel nuclei after the reduction treatment depended on pH, particle concentration, and sodium borohydride concentration. In an acid solution, minute metal nickel nuclei deposited on the particle surfaces. Subsequent electroless Ni-P plating could form complete Ni films on the surfaces of particles reduced in the acid solution.

View full abstract