[in Japanese]

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Ionic migration occurs under the influence of an applied electric field, when water adheres to the bridge site between conductive patterns such as lead solder and lead-free solder. To investigate the ionic migration of hot dipped lead-free solder, new measurement method has been developed by the authors, which enables in situ monitoring of the migration process by quartz crystal microbalance (QCM) . As a result, in the case of Sn-3.5Ag solder, Sn-0.8Cu solder and Sn-58Bi solder, the deposit on the cathode electrode was tin. And that of Sn-9Zn solder was zinc. Compound (AgSn, CuSn) or element (Bi) of these solders does not dissolve in the solution. Therefore, tin dissolved selectively on the anode electrode. In the case of Sn-9Zn solder, zinc (less noble metal against tin) reacted predominantly on the anode electrode. It is thought that the migration growth of lead-free solder is influenced by the anodic dissolution characteristics.

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We present a novel hybrid-integrated twin laser-diode (LD) coupling function unit for use in CD-R (Compact Disc Recordable) read-compatible DVD (Digital Versatile Disc) optical pickup head. A 635nm-wavelength A1GaInP-LD chip and a 780nm-wavelength A1GaAs-LD chip are individually mounted in opposition to each inlet-surface of a micro prism. In this configuration, vertical and axial directional alignments are made semi-automatically. The remaining horizontal alignment can easily be made via a passive alignment procedure. As this unit emits two perpendicularly polarized laser beams, 635nm-wavelength TM-mode laser and 780nm-wavelength TE-mode laser, efficient light coupling can be achieved by using a PBS prism. Tentative fabrication and experimental efforts have been made, and good pickup servo behavior obtained.

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Electrodeposited Sn-Cu-Ag ternary alloy is a promising candidate to replace Sn-Pb solder coatings and provide superior thermal fatigue resistance. The ternary alloy film (Sn-0.7Cu-0.3Ag, mass%) of the desired constituent was deposited at 0.5-5A/dm² in a methanesulfonate bath using the additives toris-3-hydroxypropyl phosphin (T3HPP), polyoxyethylene-a-naphthol (POEN) and 2, 2, -dithiodianiline (DTDA) . The addition of T3HPP markedly improved the bath stability. The ternary alloy film consists of β-Sn, Cu₆Sn₅ and Ag₃Sn phases, and its solidus temperature was about 225°C. Whisker were not observed on the ternary alloy film of the copper substrate after six months of aging at room temperature.

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The influence of alloy composition on mechanical properties and solder joint reliabilities of the low-melting Sn-Bi-Cu lead-free solder alloys were investigated. The optimum alloy composition is Sn-4OBi-0.1Cu (mass%) . By containing 40mass%Bi, the low ductility is improved and the fillet-lifting is prevented, which are problems of the lead-free solder with Bi. The addition of copper improves the ductility of Sn-40Bi. Sn-Bi and Sn-Bi-Cu with 30-45mass%Bi show super plasticity. That is, the elongation of Sn-40Bi reaches 121% at 25°C, and that of Sn-40Bi-0.1Cu reaches 171% at 25t and 516% at 80°C which are 2.5 times those of the conventional Sn-37Pb solder alloy. The joint strength, thermal fatigue resistance and copper leaching resistance for PWB of the Sn-4OBi-0.1Cu solder joints are superior to those of Sn-37Pb.

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We have developed an environmentally friendly epoxy-glass laminate for PWB (printed wiring board) that contains no halogen, phosphorous derivatives, or other toxic flame-retarding additives. Flame retardancy and practicality of this PWB are, nonetheless, excellent. The epoxy resin and hardener in the new PWB contain aromatic substituents in novolac resin structures (phenol-ρ-xylene-type), in addition to a limited amount of safe metal hydroxide, and the PWB can be safely disposed of by incineration or reclamation. Moreover, it can also be thermally recycled. Additionally, the PWB exhibits high practicality, notably excellent electric properties, resistance to soldering heat, and processability.

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Bumpless ILB (Inner Lead Bonding) technology is characterized by the use of ultrasonic bonding method to bond gold plated inner leads directly to the aluminum electrodes of semiconductor device without forming metallic bumps on the electrodes. This paper describes development of high speed bonding technology with bumpless semi-gang ILB method that allows multiple leads to be bonded simultaneously using single-point bounder. High productivity, low cost and short manufacturing cycle times are achieved by this method.

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The deposition behavior of the electroless nickel plating in the nm order region was examined using optical fiber probe for a near-field optical microscopy. A tip part of optical fiber probe is about tens of nm. In such a minute area, initiation of nickel deposition reaction is difficult. However, the deposition reaction is started by the increment of the adsorbed amount of palladium on to a minute region. In addition, the diameter of aperture without nickel deposition on the tip can be controlled by the addition of various stabilizers to the plating bath. The minute probe of aperture diameter about 50nm was obtained by the addition of 100ng/dm³ of bismuth ion in the plating bath and operated at pH 6.0 for 15 minutes.

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The hybrid-integration of electro-mechanical components and opto-electronic devices have been designed and put through initial trial tests. The beam scanning unit, which guides the laser beam by tilting a micro-mirror prism with a piezoelectric actuator, has been fabricated and its basic performance has been confirmed. By applying 300Vp-p sinusoidal signal to the piezoelectric device, the laser beam scanning function has been stable up to 1kHz. The result suggests that it is possible to use the laser beam scanning function to control the optical spot's high-speed fine tracking.

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The eutectic Sn-3.5wt.%Ag solder alloy is expected to be one of the candidates for Pb-free solder bump materials. But it is difficult for the conventional Sn-Ag alloy plating method to obtain eutectic composition with good uniformity within wafer, and to control the composition of plating solution for long term product run. Therefore, we have developed the 2-step electro-plating bump process using separate plating reactors for Ag and Sn. The eutectic Sn-Ag alloy bumps were easily obtained by annealing the Ag/Sn metal stacks sequentially electroplated. It is easy to control the Sn-Ag alloy composition by changing the thickness ratio of Ag layer to Sn layer in an Ag/Sn metal stack. Furthermore, the 2-step electroplating bump process does not need to control the content ratio of Ag to Sn in a plating solution. The eutectic Sn-Ag solder bump process described here is confirmed to be easily applied to mass production.

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We have developed a chip stacking technology using Flip Chip Connection between active area of IC chips with Wire-Bumps made of gold wire. This packaging technology will introduce systematization of IC chip functions, and produce various System-Integration-Packages including plural IC chips. In this paper, we will mainly explain process reliability of chip stacking, and application example.

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Conventional methods of evaluating ionic migration have been confined to evaluating electrical characteristics such as changes in insulation resistance. However, this type of evaluation cannot provide the initiation process by ionic migration. This research has focused on the AC impedance method to study the process of ionic migration for various types of lead-free solder. As a result, the migration generation process is composed of the charge transfer process and the mass transfer process. Moreover, two semicircles in the charge transfer process appeared before the short circuiting between electrodes. The migration generation can be forecast by monitoring the charge transfer resistance of two semicircles.

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