Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2001-02-16
2003-06-10
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S402000, C428S457000
Reexamination Certificate
active
06576334
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to bonding materials for connecting members to be connected having opposite electrodes, particularly to bonding materials suitable for connecting members to be connected having electrodes undergoing high voltage and high current.
PRIOR ART
Anisotropic conductive films have been substituted for solders conventionally used as bonding materials for connecting members to be connected having opposite electrodes. These anisotropic conductive films are bonding materials comprising conductive particles dispersed in a thermosetting resin and they are inserted between members to be connected for thermocompression bonding so that the conductive particles come into contact with electrodes to establish electric connection between the electrodes while the resin is cured with the conductive particles dispersed therein to ensure insulation between adjacent electrodes and mechanical bonding between members to be connected in regions where electrodes are not present.
Such anisotropic conductive films have anisotropic conductivity allowing opposite electrodes to be electrically connected while adjacent electrodes are insulated. They are used to mount a semiconductor element on a printed wiring board or to connect a printed wiring board to another printed wiring board such as a flexible printed wiring board or to connect a printed wiring board to an ordinary liquid crystal display device.
However, these anisotropic conductive films are generally considered to be suitable for connecting electrodes at low voltage and low current but ineffective for ensuring electric connection or insulation when high voltage or high current is applied across electrodes. For example, it is difficult to connect a plasma display panel and a flexible printed wiring board via an anisotropic conductive film but solder is still used for this purpose because plasma display panels undergo high voltage and high current at 50 V through 500 V and 500 mA through 2 A.
Investigations into the causes of unsuitability of anisotropic conductive films for high voltage or high current applications revealed that a major cause is short circuit between adjacent electrodes due to migration of metal ions from electrodes under conduction. Such migration was found to increase with voltage or current.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a bonding material with excellent adhesion, electric connection and insulation properties, which can be used to connect members to be connected having opposite electrodes for high voltage or high current applications without inducing short circuit between adjacent electrodes even under the application of high voltage or high current.
The present invention provides a bonding material for connecting members to be connected having opposite electrodes, the bonding material comprising conductive particles, metal ion scavenger particles for scavenging metal ions liberated from the electrodes, and a resin component based on a thermosetting resin, wherein the metal ion scavenger particles have an average particle diameter smaller than that of the conductive particles.
In the bonding material of the present invention, the metal ion scavenger particles comprise at least one of a bismuth-based ion exchanger and a vinyl triazine compound.
In the bonding material of the present invention, the metal ion scavenger particles are present 1.5 parts by weight or more but 60 parts by weight or less per 100 parts by weight of the resin component.
In the bonding material of the present invention, the metal ion scavenger particles are present 3 parts by weight or more but 50 parts by weight or less per 100 parts by weight of the resin component.
In the bonding material of the present invention, the conductive particles have an average particle diameter of 1 &mgr;m or more but 60 &mgr;m or less and the metal ion scavenger particles have an average particle diameter of 0.1 &mgr;m or more but less than 10 &mgr;m.
In the bonding material of the present invention, the metal ion scavenger particles have a specific surface area of 0.8 m
2
/g or more but 100 m
2
/g or less.
The present invention also provides a bonded assembly comprising opposite electrodes and a bonding material inserted between the electrodes and heat-cured to at least electrically connect the electrodes, the bonding material comprising conductive particles, metal ion scavenger particles for scavenging metal ions liberated from the electrodes, and a resin component based on a thermosetting resin, wherein the metal ion scavenger particles have an average particle diameter smaller than that of the conductive particles and wherein the voltage applied across the opposite electrodes is 50 V or more but 500 V or less.
Members to be connected according to the present invention are any members having opposite electrodes, particularly a number of electrodes, but the present invention is suitable for connecting members having electrodes undergoing a high voltage of 50 V or more but 500 V or less, especially 70 V or more but 300 V or less or a high current of 100 mA or more but 10 A or less, especially 200 mA or more but 5 A or less. Connections between such members include connection between a plasma display panel as described above or a printed wiring board for driving it and a flexible printed wiring board to be connected thereto.
These members to be connected have a substrate such as a glass or resin substrate, and flexible printed wiring boards often have a resin substrate made of a polyimide resin. Electrodes formed on these substrates may contain metals dissociating as metal ions such as silver, copper, nickel or chromium but may also contain non-dissociating metals.
Bonding materials of the present invention comprises a thermosetting resin, conductive particles and a metal ion scavenger, and they are inserted between members to be connected and pressurized from both sides so that opposite electrodes are forced into contact with the conductive particles while the resin is concentrated and cured with the conductive particles dispersed therein to bond the members in regions where electrodes are not present, whereby electric connection and mechanical bonding are achieved.
Base resins of thermosetting resins used in bonding materials of the present invention may be any resins that are cured under heating or irradiation such as UV in combination with curing agents, such as epoxy resins, urethane resins, phenol resins, hydroxyl-containing polyester resins or hydroxyl-containing acrylic resins, but preferably epoxy resins in view of the balance of the curing temperature, curing time, storage stability, etc.
Suitable epoxy resins include bisphenol-type epoxy resins, epoxy-novolac resins or epoxy compounds having two or more oxirane groups in their molecule or the like. These resins are commercial available.
The above base resins of thermosetting resins may be generally cured in combination with curing agents, but curing agents may be omitted when a functional group contributing to curing reaction is attached to the base resins. Suitable curing agents are those capable of inducing curing reaction with base resins under heating or irradiation, such as imidazole, amines, acid anhydrides, hydrazides, dicyandiamide and modifications thereof, and are also commercially available. These curing agents are preferably latent curing agents.
Latent curing agents induce curing reaction under heat and pressure (thermocompression bonding) or irradiation such as UV at the curing temperature but not during preparation and storage at normal temperatures and drying under relatively low-temperature conditions in the range of 40° C. through 100° C. Especially preferred such latent curing agents are the above curing agent components such as imidazole or amines microencapsulated and are also commercially available. Heat-activatable curing agents preferably begin curing at a temperature range of 80° C. through 150° C.
Suitable conductive particles include metal particles such as solders or nickel; conductive materi
Resan Stevan A.
Sony Chemicals Corp.
Uhlir Nikolas J
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