Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2000-04-25
2002-01-01
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S125000, C528S128000, C528S172000, C528S173000, C528S179000, C528S185000, C528S188000, C528S220000, C528S229000, C528S350000, C528S353000, C428S473500
Reexamination Certificate
active
06335416
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a polyimide film having well-balanced physical properties, which may exhibit low warpage and provide high dimensional stability to a metal-clad product, especially to a copper-clad product.
BACKGROUND OF THE INVENTION
As a polyimide film has such properties as heat resistance, thermal insulation, solvent resistance, and low temperature resistance, it has been widely used as material for parts of a computer and an electric and electronic device controlled by an integrated circuit.
Because of the current trend towards downsizing and slimming of these computers and devices, material for wiring boards and IC packages has been increasingly required to be downsized and slimmed. For this reason, since wiring patterns are more densely formed on these boards and packages, the dimension of polyimide film which is used for flexible wiring boards and TAB (tape-automated bonding) carrier tapes as polyimide laminates is required not to change in dimension under the influence of heat, tension, and moisture absorbance. In addition, it is necessary to provide sufficient strength and stability to a slimed-down laminate.
In order to satisfy the above needs, polyimide film is required to have a low coefficient of linear expansion, a high elastic modulus and a low coefficient of hygroscopic expansion. However, since a polyimide film is laminated onto copper foil in a process of producing a flexible wiring board or an IC package, it is preferable that the coefficient of linear expansion of the film is not quite different from that of copper. If there is a big difference in the coefficient of linear expansion between the film and the copper, the resultant product warps so that it may be difficult to handle. As the result, its dimensional accuracy and yields are deteriorated. For this reason, it is preferable to use a polyimide film having a coefficient of linear expansion approximate to that of copper.
Various attempts have been made to obtain a polyimide film having such properties as described above. For example, a monomer of a rigid structure, namely, a higher linear structure, has been widely used to obtain a polyimide film having a high elastic modulus. However, a large amount of monomers having a higher linear structure reduces a coefficient of hygroscopic expansion of a film, so that the film is no more suitable to be used for a copper-clad laminate.
Alternatively, in order to obtain a polyimide film having a relatively high elastic modulus and not too low coefficient of linear expansion, a polyimide film can be produced by thermally curing a monomer of a relatively linear structure without using chemical imidization agent, thereby releasing orientation stress in the surface direction of the film. However, longer heating time is required in the thermal curing method than in the chemical curing method, so that productivity is decreased. In addition, the use of monomers having a rigid and high linear structure generally spoils the flexibility of the film and therefore decreases bendability, which is one of the advantage of a flexible wiring board.
For semiconductor packaging uses, a polyimide film is desired to have as low a water absorption as possible in terms of reliability of semiconductors, and as low a coefficient of hygroscopic expansion as possible in terms of dimensional stability. In order to reduce a water absorption and a coefficient of hygroscopic expansion, it is effective to reduce imide groups in a molecular structure. For this reason, a long-chain monomer including a plurality of flexible chain in its main chain may often be used to produce a polyimide film. However, the use of such monomer causes the reduction of an elastic modulus and the excessive increase of a coefficient of linear expansion, and consequently spoils the dimensional stability. In extreme cases, the glass transition temperature of the polyimide film falls less than 200° C., so that it is no more suitable to be used as a base film. The monomer of a long linear structure makes it difficult to fold molecular chains, so that sufficient toughness cannot be exhibited. In some cases, it is hard to form a film.
It is well-known that, at temperatures exceeding a glass transition temperature Tg, the storage modulus of a viscoelastic body such as a polyimide film is one order, or, in some cases, two or three orders of magnitude lower than the one at the room temperature. For this reason, where a storage modulus is excessively low at normal film-forming temperatures (e.g. 300° C. or more to 400° C. or less), the film sags too much, which may often make it difficult to produce a flat, unslacked film.
Thus, there are many considerations in the properties of a polyimide film except for a high elastic modulus, a low coefficient of linear expansion, and the reduction of water absorption. However, polyimide film is allowed to have some properties by sacrificing other properties, so that it has been very hard to produce a polyimide film having a plurality of good properties.
DISCLOSURE OF THE INVENTION
As the result of intensive studies to overcome the above disadvantages and to find a polyimide film having such properties as a high elastic modulus, a linear expansion coefficient close to that of copper, sufficient toughness, low water absorption, and a low coefficient of hygroscopic expansion, which is suitable for flexible wiring board with thin wirings and for TAB carrier tape, the present inventors have eventually found the present invention.
In consideration of the above requirements, the present inventors found that a polyimide film of a specific composition has various well-balanced properties and also found the process for producing the same.
The polyimide film of the present invention is produced from polyamide acid prepared through the reaction of p-phenylenebis(trimellitic acid monoester anhydride), oxydiphthalic acid dianhydride, p-phenylenediamine, and 4,4′-diaminodiphenylether in an organic solvent.
In the polyamide film, the content of p-phenylenebis(trimellitic acid monoester anhydride) in the total amount of acid anhydrides is 0 to 90 mol % or more, and preferably 1 to 90 mol %. The content of oxydiphthalic acid dianhydride in the total amount of acid anhydrides is 10 or more to 100 mol %, preferably 10 to 99 mol %. The content of p-phenylenediamine in the total amount of diamines is 25 to 90 mol %, and the content of 4,4′-diaminodiphenylether in the total amount of diamines is 10 to 75 mol %.
The polyimide film of the present invention has an average coefficient of linear expansion of 15 to 30 ppm at the temperature range of 100 to 200° C., a tensile elastic modulus of 4.5 to 8.5 GPa, an elongation at break of 20% or more, a coefficient of hygroscopic expansion of 10 ppm or less, and a glass transition temperature Tg of 200° C. or more.
In the method for producing a polyimide film according to the present invention, a polyimide film can be obtained by dehydration with ring-closure of a polyamide acid polymer obtained by dissolving each of monomers in an organic solvent.
Preferably, in the method of producing a polyimide film according to the present invention, the above dehydration with ring-closure is carried out under the presence of imidization agent of acid anhydride and tertiary amine.
Combined with p-phenylenebis(trimellitic acid monoester anhydride) monomer (hereinafter referred to as TMHQ) and p-phenylenediamine (hereinafter referred to as PDA), polyimide takes on a rodlike structure, which makes it possible to produce a film having a high elastic modulus. The TMHQ has an ester bond in its principal chain, which is rather thermally flexible. Therefore, the coefficient of linear expansion of the polyimide does never decrease sharply, compared to that of polyimide using pyromellitic acid dianhydride. In addition, the ester bond relieves the polarization of imide ring, and has the effect of reducing a water absorption and increasing a coefficient hydroscopic expansion. However, combined with PDA, TMHQ becomes structurally too rigid, and
Nojiri Hitoshi
Tanaka Koichiro
Hampton-Hightower P.
Kaneka Corporation
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