Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2002-09-19
2004-03-02
Dawson, Robert (Department: 1712)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S275500, C523S440000, C523S442000, C523S457000, C523S458000, C523S459000
Reexamination Certificate
active
06699351
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an anisotropically conductive adhesive composition and to an anisotropically conductive adhesive film formed from it.
BACKGROUND OF THE INVENTION
Anisotropically conductive adhesives that contain epoxy resin-based adhesives are known for adhesives used to bond circuit substrates, such as FPC (flexible printed circuits), or TAB (tape automated bondings) and PCB (printed circuit boards) or glass circuit boards, together while allowing electrical connection between the electrodes. The principal property demanded of such adhesives is the ability to harden within a short time at relatively low temperature so that the circuit substrate undergoes no thermal damage. An additional property is to provide a reliable electrical connection.
For example, Japanese Unexamined Patent Publication (Kokai) No. 7-90237, discloses a circuit connection material comprising conductive particles dispersed in an adhesive component, comprising an aromatic sulfonium salt added in a prescribed amount to a cationic polymerizable substance such as an epoxy resin. Also, Japanese Unexamined Patent Publication (Kokai) No. 10-273635 discloses a circuit bonding member comprising conductive particles and an adhesive composition the essential components of which are epoxidized polybutadiene, a naphthalene-based epoxy resin, an aromatic sulfonium salt and a phenoxy resin. The conductive adhesives disclosed in these publications are both described as being capable of thermocompression bonding within 20 seconds at 130° C. and within 20 seconds as 140° C. However, since the highly reactive curing agent and epoxy resin are stored in admixture, there is a risk of impaired shelf life at room temperature. Another problem is that the high temperature (about 80° C.) applied in the drying step during production of the adhesive film accelerates cationic polymerization. In order to avoid this, it is necessary to carry out the drying step for a longer period at low temperature, thus lowering production efficiency.
Other examples of anisotropically conductive adhesives are disclosed in Japanese Unexamined Patent Publication (Kokai) No. 11-35903 and Japanese Unexamined Patent Publication (Kokai) No. 10-269853, which employ an organic peroxide and a vinyl ester or the like, an acrylate, methacrylate or the like. According to the examples in Japanese Unexamined Patent Publication (Kokai) No. 11-35903, the disclosed adhesive can be thermocompression bonded within 15 seconds at 130° C. According to the examples in Japanese Unexamined Patent Publication (Kokai) No. 10-269853, its adhesive can be thermocompression bonded within 30 seconds at 160° C. These technologies, however, not only present the aforementioned problem of lower production efficiency due to the drying step, but also they employ a peroxide as a raw material, raising the concern of explosion occurring by contact with metals. Therefore, since the facilities for production must be strictly prescribed, manufacturing costs increase.
An additional technology for accomplishing thermocompression bonding at lower temperature is disclosed in National Publication No. 8-511570. That case disclosed an anisotropically conductive adhesive composition comprising a cationic polymerizable monomer such as a glycidyl epoxy resin; a thermoplastic resin; multicomponent thermal initiating agent comprising an organometallic complex cation, a stabilizing additive and a curing accelerator; and conductive particles. This publication states that the adhesive can harden rapidly at 120° C.
Another example is Japanese Unexamined Patent Publication (Kokai) No. 11-60899, which discloses a conductive epoxy resin composition comprising (a) a cycloaliphatic epoxy resin, (b) a diol, (c) a styrene-based thermoplastic elastomer with an epoxy group in the molecule, (d) an ultraviolet activatable cationic polymerization catalyst and (e) conductive particles at 1-50 parts by weight to 100 parts by weight of the cycloaliphatic epoxy resin. Also, Japanese Unexamined Patent Publication (Kokai) No. 11-116778 discloses a conductive epoxy resin composition comprising (a) a cycloaliphatic epoxy resin, (b) a tackifier with an aromatic ring in the molecule, (c) a styrene-based thermoplastic elastomer with an epoxy group in the molecule, (d) an ultraviolet activatable cationic polymerization catalyst and (e) conductive particles at 1-50 parts by weight to 100 parts by weight of the cycloaliphatic epoxy resin. These publications teach that their disclosed adhesives are capable of being cured within 30 seconds at temperatures of 70-120° C. and 70-150° C., respectively.
In the conductive adhesives disclosed in these publications, a cationic polymerization catalyst of a Lewis acid or its complex is highly reactive in combination with the cycloaliphatic epoxy resin, and therefore curing occurs rapidly; however, the high reactivity also results in the problem of a short shelf life in the case of ordinary cationic polymerization catalysts. For this reason, an “ultraviolet activatable cationic polymerization catalyst” is used which has low activity as a catalyst unless subjected to ultraviolet irradiation, and exhibits higher activity upon ultraviolet irradiation. Such conductive adhesives, however, produce cationic active species such as Lewis acids after ultraviolet irradiation which results in high reactivity at relatively low temperatures in combination with the cycloaliphatic epoxy resin. It is believed that these conductive adhesives have a short working life after ultraviolet irradiation.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to overcome these problems of the prior art and to provide an anisotropically conductive adhesive composition and an anisotropically conductive adhesive film that exhibit superior properties. Specifically, the invention provides an anisotropically conductive adhesive composition and an anisotropically conductive adhesive film formed using the composition simultaneously endowed with the properties that (1) the composition has a long shelf life at room temperature (for example, the composition remains usable for at least about 30 days), (2) the composition before activation can be heated at relatively high temperature, since its curing reaction does not yet proceed at about 80° C., and the resulting adhesive film can be produced more efficiently for a short time compared to the prior art, since drying process for the film formation can be shortened (3) the composition has a sufficiently long working life, which is defined as time length for which the composition can be left from activation by ultraviolet irradiation to thermocompression bonding, thus providing the sufficient time required for the thermocompression bonding procedure, which is preferably at least about 10 minutes, more preferably at least about 30 minutes and even more preferably at least about 60 minutes considering the maintenance time, etc. in the semiconductor device mounting step for actual use, (4) the composition rapidly cures at a low temperature of about 100 to about 130° C. during thermocompression bonding after ultraviolet activation, i.e. curability preferably within one minute, more preferably within about 30 seconds and even more preferably within about 10 seconds, and (5) the composition provides excellent connection stability after connection between substrates (for example, the resistance is not raised or remain the same, even after the high temperature/high humidity test as shown in table 1 of the working examples.).
“Anisotropically conductive adhesive composition” as used throughout the present specification refers to an adhesive composition capable of bonding two circuit substrates together, when the two circuit substrates are laminated together for electrical connection between conductors on the circuit substrates. Conductivity is exhibited in the direction normal to the substrate so as to provide electrical connection between conductors facing each other on the circuit substrates, but without exhibiting conductivity in th
Hata Michiru
Hiroshige Yuji
Kitamura Tetsu
Yamaguchi Hiroaki
3M Innovative Properties Company
Aylward D.
Dawson Robert
Harts Dean M.
LandOfFree
Anisotropically conductive adhesive composition and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Anisotropically conductive adhesive composition and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Anisotropically conductive adhesive composition and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3205380