Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2000-04-28
2002-11-12
Talbott, David L. (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S260000, C174S264000, C361S760000, C361S779000, C361S803000, C029S832000, C257S698000, C428S313500
Reexamination Certificate
active
06479763
ABSTRACT:
TECHNICAL FIELD
This invention relates to conductive paste, etc. to be used for mounting to substrates of electronic parts or inter-electrode joint, etc.
BACKGROUND ART
Conventionally, conductive adhesive agents which have been used for mounting onto substrates of electronic parts or for inter-electrode joint, whose purpose is fixation and electrical connection, therefore, generally have comprised metal particles such as conductive silver and copper, etc., having been made to disperse in a viscous resin for fixation or cure-type resin paste.
To make joint effective, it is important that an adhesive agent and the surface of adherend gets sufficiently closer on a micro level. In case of an adhesive type, resins which are flexible, easily deformed and has high affinity with the surface of adherend have been used, while in case of a cure type, resins which have high fluidity and wetness has been used. This enables an adhesive agent to enter the recess and salient of adherend having unit of a micro level and attain good joint in case of either adhesive type or cure type.
On the other hand, for conductive particles, particles in various shapes have been used according to their use, those of adhesive type as well as cure type have been required to be with low resistance so that good electric connection is obtainable, and have been arranged so as to improve the content ratio of conductive particles in the adhesive agent, and remove bubbles, and increase volumetric occupation ratio of conductive particles.
In addition, as concerns cure type, because volume shrinkage takes place at the time of curing, for the purpose of relieving the resultant internal stress, addition of plasticizers, etc., has been implemented as well.
In general, an electrical joining method involving conductive adhesive agents is being used in various fields for its simple nature, and recently, since resins themselves or additions of plasticizers show flexibility, the method is being in wide use as an electric connection method for portions where thermal as well as mechanical strain is apt to occur. In addition, the electric joint method using conductive adhesive agents is remarkably applied and extended to terminal electrodes for small-sized electronic parts and mounting of electronic parts onto substrates. As an example, an embodiment of mounting onto substrates has been disclosed in Japanese Patent Laid-Open No. 1-232735 specification.
However, in case of conventional conductive adhesive agents, whose conductivity is maintained by contact among conductive particles, there was a problem that stress was generated when expansion and shrinkage took place due to heating or when the substrates were bent, and at the time of stress relief thereof the contact among particles was removed to heighten resistance.
In addition, since electric connection to electrodes to be connected has been conducted with contact between conductive particles and electrodes, there has been a problem that not only being weak against stress as described above but also in some cases, surface resistance between electrodes and adhesive agents would become greater from the initial period.
On the other hand, in recent years, in correspondence with miniaturization as well as higher performance of electronic equipment, not only for industrial use but also in a vast field of equipment for commercial use, it has been strongly desired that multilayer wiring circuit substrates on which semiconductor chips such as LSI, etc., can be mounted with higher density are supplied. In such a multilayer wiring circuit substrate, it is important that electric connection can be attained with highly connection reliability among wiring patterns of plural layers formed with fine wiring pitch.
To comply with such demand from the market, in stead of metal-plated conductor on the inner wall of through hole, which has been the main stream of inter-layer connection of conventional multilayer wiring substrate, there is an inner via hole connection method that enables optional electrode on a multilayer print wiring substrate to be interlayer-connected in optional wiring pattern position, that is, whole layer IVH structural resin multilayer substrate (Japanese Patent Laid-Open No. 06-268345 specification). This one, in which conductive body filling in via holes of a multilayer print wiring substrate can connect only respective necessary layers and inner via hole can be disposed right under the part land, thus, can realize miniaturization of substrate sizes as well as mounting with high density.
However, a general inner via hole connection method is implemented by squeegee-printing the conductive paste which fills in inside the via holes, and especially for filling conductive paste toward via holes with micro diameters the viscosity characteristics of conductive pastes are supposed to play an important role. In conductive pastes for via hole filling, printing characteristics and conductivity in inter-layer connection oppose each other from the point of view of structural materials.
That is, when composition ratio of conductive particle among fine particles is increased for the purpose of improving conductivity, resin components are absorbed on the surface of conductive particle, resulting in increase in viscosity of the paste, and thus printing becomes less easy. In addition, when conductive particles with small surface area, that is, greater particle diameter are used, or structural ratio of conductive particles is decreased for the purpose of lowering viscosity of the paste to improve printing characteristics, contact surface area between conductive particles themselves becomes smaller, thus a problem on connection reliability occurs. That is, as concerns conductivity in a conductive paste, with conductive particles coming into point contact each other, and since electric connection between electrode foils disposed on the upper surfaces of via holes and conductive particles depends on point contact between conductive particles and the electrode foils as well, thus, when in particular the wiring pattern in terms of line width as well as distance between lines have been made minute, accordingly diameters of via holes have been made minute as well, it becomes extremely difficult to secure high connecting reliability in inter-layer connection among multilayer wirings.
DISCLOSURE OF THE INVENTION
The purpose of the present invention is to solve issues such as the foregoing to provide conductive paste, etc., which has low resistance and can tolerate stress so as to enable the conductive structure to be formed.
First and foremost, conductivity of, for example, an adhesive agent, which is a typical example of conductive paste, is given by mutual contact of conductive particles dispersed in the adhesive agent. In addition, electrical connection with electrodes to be connected is given by contact between conductive particles in the adhesive agent and electrodes. Accordingly, as the contact area between conductive particles as well as the contact area between conductive particles and electrodes is greater, better electric connection with smaller resistance can be obtained.
In a conductive adhesive agent, foamable resin powder, for example, is contained as a foamable material, and when the foamable resin powder foams by heating or decompression, as a macro structure, the volume content ratio of conductive particles in the adhesive agent decreases. However, micro-structurally, contact area between conductive particles as well as between conductive particles and electrodes can be made equal to or more than the contact area in the case where no foamable resin powder is contained. This can be attained by adopting a method of construction such as in the method of the present invention, that the foamable resin powder undergoes foaming prior to curing of the resin, and subsequently undergoes curing in the case where the cure type of the conductive adhesive agent of the present invention is used in such a place that it can expand freely. At that time, the contact between conductive particles, whic
Igaki Emiko
Suzuki Takeshi
Tanahashi Masakazu
Matsushita Electric - Industrial Co., Ltd.
Patel I. B.
RatnerPrestia
Talbott David L.
LandOfFree
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