Kiyokazu Yasuda

New Process of Self-Organized Interconnection in Packaging Using Conductive Adhesive with Low Melting Point Filler

A model experiment of the novel self-organized joining process using conductive adhesive with low melting point alloy was demonstrated to break through the limitation of conventional solders and adhesives used in electronics packaging. Basic properties of the adhesive paste, joint morphology, the formation of the conduction path, and the self-organization characteristics were examined. Melting fillers were preserved in their initial spherical form in resin without oxygen-reduction capability, although enlargement of the alloy domain occurred in the case of oxygen-reduction polymer. The formation of the conduction path could be controlled accurately by varying the resin performance and the process parameters such as the gap distance of the joint and the volume fraction of filler. Self-organization due to capillary wetting of melting alloy was observed on the copper-line-patterned glass-epoxy substrate. The pair of lines on the faced substrates was selectively interconnected with an alloy joint.

Visual Inspection of Soldering Joints by Neural Network with Multi-angle View and Principal Component Analysis

With the development of microelectronics technology, the demands of the automatic inspection system are ever increasing. The current trends toward miniaturization of components, denser packing of boards, surface mounting technology, and highly automated assembly equipment make the task of inspecting these defects more critical and more difficult for humans. In this paper, we achieved 0% of misjudgment by implementing training category intermediate samples. We also achieved cutting down the processing time and an increase of correct judgments by the improvement of inputs using principle component analysis and multi-angle image.

Numerical Analysis of Self-Organizing Interconnection Process by 3 Dimensional Flow Dynamics

The growing importance of high integration on electronics demands novel interconnection methods replacing high-cost solder bumping or less reliable conductive adhesives. Self-organizing interconnection process using resin containing solder fillers has a possibility to achieve high-density joints satisfying both needs. Numerical study visualized the process and revealed that surface tension of molten fillers and resin viscosity determine the speed of conductive path formation.

Movement of solder fillers because of the unevenness of interfacial tension in self-organization assembly process

Soldering or anisotropic conductive adhesives (ACAs) are used for assembling of devices with high-density area-array terminals. However, solder bump processes are high-cost and interconnects of ACAs are less-reliable. The purpose of this study is to develop a novel method. Self-organization assembly method that uses active resin containing solder fillers may allow reliable interconnects at low-cost. Fundamental process of Self-organization assembly are movement, coalescence, and wetting of molten fillers in resin. The focus of this paper is on the movement of fillers. In-situ observations of coalescence behavior for 40μm molten fillers in the resin revealed irregular movement of the fillers at a velocity of several μm/s. Numerical analysis, using improved volume fraction method, indicated that a 10% degradation of interfacial energy on one side of a 40μm filler could move the filler at a velocity of several mm/s. This degradation of the interfacial energy was resulted the remaining oxide film.

Estimation of Thermal Fatigue Resistance of Sn-Bi (-Ag) and Sn-Ag-Bi-Cu Lead-Free Solders Using Strain Rate Sensitivity Index

A tensile test was conducted to evaluate thermal fatigue resistances of Sn-Bi (-Ag) and Sn-Ag-Bi-Cu lead-free solder alloys. The test is based on the strain rate change method to obtain a strain rate sensitivity index (SRSI), m. The m values were investigated at various strains during the tensile test, until fracture. The plots of m and strain where m is measured showed a linear relationship. Therefore, the m value at zero strain, m0, and the gradient of the fitting line, k, were obtained by extrapolation. Using m0 and k values, an estimation of the thermal fatigue resistance of the solder joint was attempted. It was believed that m0 and k can be taken as a guide for developing a new lead-free solder with the excellent thermal fatigue resistance. Moreover, the influences of the aging treatment on m0, k and the microstructure of the solder were also investigated.

Interface Properties of Thin Film Bonding by Low Melting Point Metal for MEMS devices

Low temperature metal bonding is promising for assembling micro devices because the interface can easily achieve high mechanical reliability by the formation of metallurgical and electronically high conductive interfaces. For gaining high strength of micro joints with low temperature process, vacuum deposited low melting point metal (Snxln1-x) thin films were applied to solid-liquid diffusion bonding of copper. The effects of Sn content on the growth of reaction layer and on the shear strength were investigated. It was found that the sufficient initial Sn supply was important to achieve high strength interface characteristics to enhance solid-liquid diffusion.

Evaluation of wettability for microelectronic materials by reflow-mode wetting balance test

The reflow-mode wetting balance test is a promising method for evaluating the wettability of various kinds of chip devices and newly developed solders for Pb-Sn solder substitution. In this method, solder metal is applied as paste on to a micro pod, and the geometric boundary constraint limits the meniscus shape and varies with shape and size of specimen. It is crucial to understand the meaning of force curve and wettability parameters extracted from curves acquired by this method from a physical viewpoint. In this report, we introduce our test instrumentation and some experimental results. Moreover, extensive numerical analysis is conducted to realize the meniscus geometry and wetting force in the equilibrium wetting state of solder liquid on copper lead models. Both calculated wetting height and force acting on the specimen are increased with decreasing contact angle as for boundary conditions. These relationships are found to be insensitive to specimen dipping depth, even for constant solder volume. Although dipping depth slightly influences overall solder meniscus geometry, it drastically increases the maximum contact angle that could be formed at an early force curve stage just after solder melting; consequently, nonwetting force also increases. These results show good agreement with experimental data. It is concluded that the internal pressure force which is proportional to lead cross section and inversely proportional to global radius of curvature of the solder surface should be taken into account to evaluate wettability.

Surface Layer Modification of Metal Nanoparticle Supported Polymer by Irradiation of Laser-Driven Extreme Ultraviolet Light

Creation and control of interfacial structures between polydimethilsiloxane (C2H6OSi)n and nanoparticles allow us to create functional materials. Such technology is beneficial for fabrication of wearable devices. One of the concerns of modification of such materials is the effect of particle or heat loads on the sample when discharge plasma or visible to infrared light source is used for the processing. Extreme ultraviolet light could realize heat and particle load free fabrication of such materials because interaction of extreme ultraviolet radiation and materials is known for direct photoionization without thermal process. This study shows surface modification and creation of interfacial structure of AuPd nanoparticle supported polydimethylsiloxane by irradiation of high-fluence pulsed extreme ultraviolet light. It was observed that the size of nanoparticles increases as the number of EUV shots increases, and a layer of mixed Au and Si appeared after EUV irradiation.

Surface characterization of resilience sheet as a packaging material for the metallic ink printing

Self-resilience properties of metal-elastomer interface is important for bio-interface devices for health monitoring. Metallic fine line traces on a silicone sheet by means of the metal ink deposition was needed with good print capability and adhesion. To meet these demands, surface treatment of the silicone sheet by scanning CO2 laser was conducted to modify the surface property for the metal-elastomer interface fabrication. Micro texture with fibrous structures on the silicone surface was observed by the laser irradiation (typically ~7.2W/mm2), causing high hydrophilicity which was found to be suitable for the ink printing of metal particle solutions.

Influence of die adhesion properties on delamination of stacked chip interconnection encapsulated in plastic package

The chip-on-chip (COC) package in which a controller IC chip is adhered to a power MOSFET chip with a polyimide film is described. In the heat cycle test, the polyimide film showed a good performance but the mold resin used was delaminated from the IC chip surface. From the experimental and the thermal stress simulation, we demonstrate that the resin delamination is prevented by the polyimide film with a small thermal expansion coefficient. Thus we have successfully developed the high reliable COC package promising for automotive application.