Polyimide and circuit substrate comprising the same

Details Polyimide and circuit substrate comprising the same Polyimide and circuit substrate comprising the same

2002-04-11

2004-05-11

Hightower, P. Hampton (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From phenol, phenol ether, or inorganic phenolate

C528S125000, C528S126000, C528S128000, C528S172000, C528S173000, C528S176000, C528S183000, C528S185000, C528S188000, C528S220000, C528S229000, C528S350000, C528S351000, C528S353000, C525S282000, C524S600000, C524S607000, C428S457000, C428S458000, C428S411100, C428S473500, C428S901000

Reexamination Certificate

active

06734276

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a polyimide that comprises specific repeating structural units and has good thermal resistance, mechanical properties and chemical resistance. Additionally, for polyimide/metal leaf laminates that are said to be especially important in the field of electronic materials, the invention relates to a useful polyimide which is so designed that its linear expansion coefficient approximates that of metal leaf and which can be a polyimide circuit substrate material capable of keeping flat, neither shrinking nor expanding in its laminate.
BACKGROUND ART
The linear expansion coefficient (thermal expansion coefficient) of most organic polymers is at least 50 ppm/K even in a temperature range not higher than the glass transition temperature thereof, and is much higher than that of metals and inorganic substances. Therefore, metal/polymer composites, for example, metal leaf/organic polymer laminates involve serious problems of warping, deformation, delamination, cracking of the polymer layer and disruption of the substrate itself because of the difference in the linear expansion coefficient between the constituent components.
In that problematic situation, polyimide having good thermal resistance and good mechanical properties has heretofore been used as an organic polymer that solves the problems.
For example, the polyimide represented by the formula (A):
has been known as a typical example. This is a resin having good thermal resistance and good mechanical properties, and is widely used for electronic materials. However, its linear expansion coefficient is about 40 ppm/K (in the temperature range of 100 to 200° C.), and the polyimide is still unsatisfactory for a constituent component of laminates.
On the other hand, the polyimide represented by the formula (B):
also has good thermal resistance and good mechanical properties, and its linear expansion coefficient is extremely low. Concretely, however, the linear expansion coefficient of the polyimide is at most 10 ppm/K (in the temperature range of 100 to 200° C.), and contrary to the above, it is lower than the linear expansion coefficient of metal.
Recently, other polyimides having a low linear expansion coefficient (low stress) have been developed to solve these problems. For example, in Japanese Patent Laid-Open Nos. 191830/1988, 199236/1988, 16829/1989, 20232/1989, 33134/1989 and 38437/1989, alkyl chains such as methyl groups are introduced into rigid polyimide main chain skeletons to lower the linear expansion coefficient of the thus-modified polyimides. However, these polyimides (or their precursors, polyamic acids) are problematic in that the polymer component deposits in the varnish thereof when stored long. Another problem with them is that, since they have many alkyl groups introduced thereinto, the methyl groups therein are oxidized when they are exposed to high temperatures.
In Japanese Patent Laid-Open Nos. 153934/1990 and 251584/1990, disclosed are polyimides having rigid hetero rings such as imidazole introduced thereinto. However, the hetero ring-having monomers for them require complicated steps in their production, and their costs inevitably increase.
A polyimide having a controlled linear expansion coefficient useful for polyimide/metal leaf has not as yet been realized. In that situation, a technique for controlling the linear expansion coefficient of polyimide through stretching and orientation is known. However, the technique requires an additional secondary step, and is therefore problematic in practical use.
As mentioned hereinabove, a polyimide satisfactory for laminates of polyimide/metal leaf is not as yet found out, and a polyimide that solves the problems noted above is desired.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide a polyimide having a suitable linear expansion coefficient that corresponds to the linear expansion coefficient of metal leaf (in this case, in the range of 10 to 20 ppm/K at the temperature range of 100 to 200° C.) in addition to good properties inherent to polyimides, that is, good thermal resistance, mechanical properties and chemical resistance. More precisely, it is to provide a useful polyimide which can be a polyimide circuit substrate material capable of keeping flat, neither shrinking nor expanding in its laminate.
The present inventors have assiduously studied to attain the object mentioned above and, as a result, have found that a polyimide obtained through thermal imidation of a polyamic acid copolymer, which is prepared by reacting a) pyromellitic acid dianhydride selected for a tetracarboxylic acid dianhydride component with b) a diamine component of essentially paraphenylenediamine combined with 4,4′-oxydianiline or two diamines selected from 4,4′-oxydianiline, metaphenylenediamine and diaminomethyl-bicyclo[2.2.1]heptanes in a specific composition ratio, satisfies the necessary linear expansion coefficient and therefore solves the problems noted above. On the basis of this finding, the present invention has been completed.
Specifically, the invention relates to the following:
1) A polyimide, which is a random copolymer having repeating units represented by the formula (1):
 wherein R
1
and R
2
each represent a divalent group selected from
 and R
1
and R
2
may be the same or different; and x=0.60 to 0.80, y+z=0.40 to 0.20, and x+y+z=1.00, and which has a linear expansion coefficient of the range of 10 to 20 ppm/K at 100 to 200° C.;
2) The polyimide of above 1, which is a random copolymer having repeating units represented by the formula (2):
 wherein x1=0.60 to 0.80, y1=0.40 to 0.20, and x1+y1=1.00, and which has a linear expansion coefficient of the range of 10 to 20 ppm/K at 100 to 200° C.;
3) The polyimide of above 1, which is a random copolymer having repeating units represented by the formula (3):
 wherein x2=0.60 to 0.80, y2=0.35 to 0.05, z2=0.05 to 0.15, and x2+y2+z2=1.00, and which has a linear expansion coefficient of the range of 10 to 20 ppm/K at 100 to 200° C.;
4) The polyimide of above 1, which is a random copolymer having repeating units represented by the formula (4):
 wherein x3=0.65 to 0.75, y3=0.30 to 0.10, z3=0.05 to 0.15, and x3+y3+z3=1.00, and which has a linear expansion coefficient of the range of 10 to 20 ppm/K at 100 to 200° C.;
5) The polyimide of above 1, which is a random copolymer having repeating units represented by the formula (5):
 wherein x4=0.65 to 0.75, y4=0.05 to 0.15, z4=0.30 to 0.10, and x4+y4+z4=1.00, and which has a linear expansion coefficient of the range of 10 to 20 ppm/K at 100 to 200° C.;
6) The polyimide of above 1, of which the precursor, polyamic acid has a number-average molecular weight (Mn) of at least 40,000, a weight-average molecular weight (Mw) of at least 60,000, and a molecular weight distribution (Mw/Mn) being in the range of 1.6 to 2.3;
7) A process for preparing the polyimide of above 1, which comprises reacting 1 equivalent mol of pyromellitic acid dianhydride of the formula (6):
 with from 0.9 to 1.1 equivalent mols of a diamine mixture that comprises from 60 to 80 mol % of a diamine of the formula (7):
 and from 40 to 20 mol % of diamines of the formulae (16) and (17):
H
2
N—R
1
—NH
2
  (16)
H
2
N—R
2
—NH
2
  (17)
 wherein R
1
and R
2
each represent a divalent group selected from
 and R
1
and R
2
may be the same or different, in an organic solvent, followed by thermally imidizing the resulting random copolymer, polyamic acid having repeating units represented by the formula (15):
 wherein R
1
and R
2
each represent a divalent group selected from
 and R
1
and R
2
may be the same or different; and x=0.60 to 0.80, y+z=0.40 to 0.20, and x+y+z=1.00;
8) A process for preparing the polyimide of above 2, whi

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