Stock material or miscellaneous articles – Structurally defined web or sheet – Including aperture
Reexamination Certificate
1999-06-22
2001-10-23
Copenheaver, Blaine (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including aperture
C428S901000, C428S209000, C428S413000, C428S418000, C430S280100, C430S311000, C522S025000, C522S083000, C522S170000
Reexamination Certificate
active
06306481
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a high density multilayer circuit board, each of the layers of which is accessible by blind via-holes, and more particularly, the invention relates to a high density multilayer circuit board prepared by a photo via-hole forming process, using an incombustible aqueous developing solution, and a photosensitive epoxy resin composition having a preferable resolution, plating solution resistance and heat resistance.
Various photosensitive epoxy resin compositions are well known widely such as the ones disclosed in JP-B-49-17040 (1974), JP-A-50-158694 (1975), JP-A56-55420 (1981),
JP-A-63-71840 (1988), and others.
Most of the photosensitive epoxy resin compositions require organic solvents for their development. Chlorine group organic solvents cause many problems, such as water pollution, and therefore, an organic solvent for general use must be used at present. However, the use of an organic solvent inherently has the danger of producing a fire and explosion.
In accordance with the method disclosed in JP-A-63-71840 (1988), development with an alkaline aqueous solution is possible by using polyphenol resin as a base polymer. However, when the photosensitive layer contains so many hydroxyl groups as to be dissolved by the alkaline aqueous solution, the prepared relief pattern is caused to swell or become deformed in a chemical plating solution, which is a kind of alkaline aqueous solution, or there is a possibility that the plating solution will become contaminated by dissolving polyphenol into the plating solution.
On the other hand, the mounting of parts on the surface of a printed circuit board by a solder-reflow process has been used widely in order to mount the parts with a high density. Therefore, a thermally stable thermosetting resin, such as an epoxy resin and the like, has been used as the material of the substrate.
SUMMARY OF THE INVENTION
One of the objects of the present invention is to provide a thermally stable high density multilayer circuit board.
Another one of the objects of the present invention is to provide an epoxy group photosensitive resin composition, which is adequate for forming insulating films among the layers of the multilayer circuit board, which is capable of being developed with an incombustible aqueous developing solution, and which is capable of being plated without swelling or being dissolved into the chemical developing solution, which is an alkaline aqueous solution.
The present invention provides a multilayer circuit board, each of the layers of which is accessible via blind via-holes having a resolution of 25~80 &mgr;m, and an aspect ratio of 2.0 ~0.6, and particularly, the glass transition temperature of the insulating layers having the via-holes, which insulate the layers of the multilayer circuit board from each other, is in the range of 150~220° C.
The above mentioned insulating layers having the via-holes, which insulate the layers of the multilayer circuit board, can be formed, for example, by curing a photosensitive resin composition, and the insulating layers can be formed, for example, by laminating two kinds of photosensitive resin composition having different transmission characteristics for near ultraviolet light with respect to each other.
Furthermore, the present invention provides a photosensitive resin composition containing (a): 60~90 parts by weight of polyfunctional epoxy resin, (b): 10~40 parts by weight of resin having a phenolic hydroxyl group, (c): 3~30 parts by weight of a photo-acid generating agent to 100 parts by weight of the sum of (a) and (b), and (d): 1~5 parts by weight of a release agent to 100 parts by weight of the sum of (a) and (b). The photosensitive resin composition was used to prepare a photosensitive layer
1
, which will be mentioned later.
As the above component (a), a mixture of (al) 10~50 parts by weight of bifunctional epoxy resin having an epoxy equivalent of 130~300 g/eq, and (a2) 80~10 parts by weight of at least trifunctional epoxy resin having an epoxy equivalent of 160-300 g/eq can be used. As the above compound (a1), at least one resin selected from a group consisting of bisphenol type epoxy resin, aliphatic epoxy resin, and alicyclic epoxy resin, and, as the above compound (a2), a novolak type epoxy resin or its substituted resin can be used.
As the above component (b), at least one resin selected from a group consisting of novolak resin, resole resin, hydroxystyrene polymer or its copolymer, hydroxyphenyl maleimide polymer or its copolymer, and a self condensation type resin having a phenolic hydroxyl group can be used.
As the above component (d) of the release agent, at least one hydrophobic oil selected from a group consisting of polysiloxane, polyether, or its copolymer can be used.
Furthermore, the present invention provides a photosensitive resin composition containing, in addition to the above components (a)~(d), (e): 3~100 parts by weight of hydroxide, oxides, and carbonates of IIa group, IIIa group, and IVa group elements to 100 parts by weight of the sum of (a) and (b), (f): 3~30 parts by weight of a rubber component to 100 parts by weight of the sum of (a) and (b), and (g): 0.1~10 parts by weight of a thermal curing agent to 100 parts by weight of the sum of (a) and (b). The photosensitive resin composition is used to prepare a photosensitive layer 2, which will be mentioned later.
As the above component (e), at least one inorganic compound selected from a group consisting of calcium carbonate, magnesium hydroxide, aluminum hydroxide, and silicon oxide can be used. As the above component (f) of the rubber component, a rubber component containing fine particles of rubber can be used. As the above component (g), an onium salt can be used.
In the processes of BGA (Ball Grid Array) and bare chip mounting, which are receiving attention in the field of high density surface mounting, the multilayer circuit board is required to have a treat resistance, because the multilayer circuit board itself is treated as a mounted body in the process of mounting, such as reflowing, gold wire bonding, and others. Various characteristics, such as an adhesive force with a conducting wire at a high temperature, an elastic modulus at a high temperature, a thermal expansion coefficient, and others are required. However, the above characteristics are generally decreased in the temperature region higher than the glass transition temperature. Accordingly, in order to prevent the characteristics from decreasing at the high temperature which occurs in the mounting process and in a repairing process, the glass transition temperature must be raised to as high a level as possible. It was found that, if the insulating film between the layers having the blind via-holes was formed with an epoxy resin composition having a glass transition temperature after curing of 150~220° C., any defects of the multilayer circuit board were hardly generated at the time of mounting and repairing. The glass transition temperature can be regarded as an index indicating a degree of cross linkage density of the resin. Therefore, if the cross linkage of the resin exceeds a definite value, the decreasing rate of the characteristics of the circuit board at a high temperature is assumed to be restricted to a small value. That means that, if the glass transition temperature is lower than 150° C., the insulating film (photosensitive layer) between the layers is softened significantly by the heating during the mounting process. Therefore, when a component, such as in a LSI, is mounted at the wiring pad on the photosensitive layer with gold wire bonding, the photosensitive layer is deformed by the pressure of the bonding, and a defect in the insulation can result. On the contrary, if the glass transition temperature is higher than 220° C., no problems are generated in a mechanical strength and the like. However, in order to raise the glass transition temperature to higher than 220° C., a multifunctional epoxy resin having a rigid molecular structure must be used mainly. Therefore, t
Amou Satoru
Fukai Hiroyuki
Kawamoto Mineo
Kobayashi Shiro
Miyazaki Masashi
Antonelli Terry Stout & Kraus LLP
Boss Wendy
Copenheaver Blaine
Hitachi , Ltd.
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