JPH03275724A - Flexible printed circuit substrate having low thermal expansion - Google Patents

Abstract

PURPOSE:To obtain the circuit substrate having excellent heat resistance and dimensional stability by using a polyimide film having a low coefficient of linear thermal expansion prepared by polymerizing an aromatic tetracarboxylic acid dianhydride with a specific aromatic diamine. CONSTITUTION:One or more of aromatic tetracarboxylic acid dianhydrides and a diamine comprising a mixture of 4,4'-diaminobenzanilide and/or 3,4'- diaminobenzanilide (30-100mol% contained) and 4,4'-diaminodiphenyl ether are subjected to polycondensation in an aprotic polar solvent, cast onto a glass plate, etc., dried, released and heated to give a polyimide film having <=15X10<-6> (1/K) coefficient of linear expansion. Then, copper foils or aluminum foils are stuck to one side or both sides of the film with an adhesive, preferably polyimide resin to give the objective circuit substrate.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a polyimide film with low thermal expansion and excellent heat resistance, and a flexible film with a low coefficient of linear expansion, which is made by laminating this film and metal foil with an adhesive. This invention relates to a printed circuit board.

(Prior Art) In recent years, with the development of the electronic and electrical industry, there has been a demand for simpler, smaller, and more reliable packaging methods for communication and consumer equipment, and the use of printed circuit boards has become desirable. In particular, the use of flexible printed circuit boards that are lightweight and can be mounted three-dimensionally is advantageous and is attracting attention.

Conventional flexible printed circuit boards are made by bonding copper foil and polyimide film with a linear expansion coefficient of 20x 1O-6 (1/K) or more with adhesive, and are used for flexible printed circuits with a high linear expansion coefficient. It was the board. For this reason, microfabrication of patterns often results in defects due to dimensional changes.

In addition, by casting a polyamic acid solution directly onto the metal foil,
There is a method of manufacturing a flexible circuit board without an adhesive layer by heating and curing it, but although heat resistance can be ensured,
Unless special measures are taken, it has been difficult to obtain a flexible printed circuit board with a sufficiently small coefficient of linear expansion.

(Problems to be Solved by the Invention) As a result of careful consideration in order to overcome the above-mentioned drawbacks, the present invention provides a linear expansion bow length coefficient using an aromatic diamine diaminobenzanilide using an adhesive. The inventors have discovered that a flexible circuit board with excellent low thermal expansion can be obtained by laminating a polyimide film with a low thermal expansion coefficient and a metal foil, leading to the completion of the present invention.

(Means for Solving the Problems) The present invention provides a polyimide film obtained by a polycondensation reaction of aromatic tetracarboxylic dianhydride and aromatic diamine, in which aromatic tetracarboxylic dianhydride ( One or more aromatic tetracarboxylic dianhydrides selected from A) and aromatic diamine (B
) consists of 4,4'-diaminobenzanilide and/or a mixture of 3,4'-diaminobenzanilide and 4,4'-diaminodiphenyl ether, and 4,
4'-diaminobenzanilide and/or 3.4'
- diaminobenzanilide is the aromatic amine component
A low thermal expansion polyimide film made of aromatic diamine consisting of ~100 mol% and having a linear expansion coefficient of 15X 1O-6 (1,/K) or less, and bonding this low thermal expansion polyimide film with metal foil and an adhesive. Therefore, the coefficient of linear expansion after etching the metal foil is 15x jO-6 (1/
K) It is a low thermal expansion bow length flexible printed circuit board with r.

(Function) The aromatic tetracarboxylic dianhydride of the polyimide film used in the present invention is 1,2,4.5-benzenetetracarboxylic dianhydride, 3.3', 4.4'-biphenyltetracarboxylic dianhydride, Acid dianhydride, 3.3',4.4'-benzophenonetetracarboxylic dianhydride, diphenylsulfone-3,3',4.4'-tetracarboxylic dianhydride and 3.3',4. 4"-diphenyl ether tetracarboxylic dianhydride, etc., and one or a mixture of two or more of these can be used. Among them, 1, 2,
4.5-benzenetetracarboxylic dianhydride acts as a rigid component, and 3.3', 4.4'-biphenyltetracarboxylic dianhydride and 3.3', 4.4'-diphenyl ether tetracarboxylic dianhydride Acid dianhydride acts as a component with high flexibility. The diamine used as the aromatic diamine component in the present invention is 4,4'-diaminodiphenyl ether, which has a highly flexible ether bond in the molecule, and diaminobenzanilide, which has a rigid bond.
It is a mixture of different diamines.

The composition ratio of the diamine component is preferably in the range of 30 to 100 mol % of diaminobenzanilide based on the aromatic diamine.

If the diaminobenzanilide content is 30 mol % or less, the effect of introducing the rigid molecule + M structure is not exhibited, so the coefficient of linear expansion becomes large.

The reaction between the aromatic tetracarboxylic dianhydride (A) and the aromatic diamine (B) is carried out in an aprotic polar solvent. Aprotic polar solvents include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (D
MAc), N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), diglyme, and the like. Only one type of aprotic polar solvent may be used, or two or more types may be used in combination. At this time, L
A mixture of non-polar solvents that are compatible with the above aprotic polar solvent may be used. In particular, aromatic hydrocarbons such as toluene, xylene, and solvent naphtha are often used for the purpose of flattening the surface of the coating film. The proportion of the nonpolar solvent in the mixed solvent is preferably 30% by weight or less. This is because if the nonpolar solvent exceeds 30% by weight, the solvent's dissolving power decreases and polyamic acid precipitates. The most preferred solvent in the present invention is a combination of DMF and an aromatic hydrocarbon having a relatively high boiling point.

The polycondensation reaction of polyimide consists of two methods: (a) a random copolymerization method in which all amine components are first dissolved in a solvent, and then an acid component is added and reacted; and (b) a method in which one specific type of amine and an acid are first dissolved. A block copolymerization method in which the polymer is reacted to form an amine-terminated or acid-terminated polymer, which is then grown, and the remaining amine component and acid component are added to complete the polymerization; There is a blending method in which polyamic acids obtained by reacting acids and amines separately are mixed without chemical reaction.

In the present invention, a composition for flexible circuits having excellent properties that satisfies the purpose can be obtained by a random copolymerization method, a block copolymerization method, or a blending method. Therefore, in the present invention, any of the polymerization methods (a), (b), and (c) can be employed. The polyamic acid solution thus obtained is cast onto a glass plate, stainless steel plate, etc., and dried at a temperature ranging from 60°C'' to 150°C for 1 to 2 hours.

After that, peel it off and fix it with an iron frame at 150°C to 350°.
A polyimide film can be obtained by heating in a temperature range of C.

The metal foil used in the present invention is generally copper foil, but aluminum foil, nickel foil, stainless steel foil, tungsten foil, etc. can also be used.

There is a method of casting a polyamic acid solution directly on metal foil and applying a heating effect to produce a flexible circuit board without an adhesive layer, but although heat resistance can be ensured, the wires are sufficiently small unless special measures are taken. It has been difficult to obtain a flexible circuit board with a non-expansion coefficient. Therefore, by applying an adhesive to one or both sides of a copper foil and a low thermal expansion polyimide film and bonding them together, a low thermal expansion printed circuit board can be produced. Moreover, it can also be made into a prepreg by impregnating a base material such as glass cloth.

The adhesive used in the present invention is NBR/phenol resin,
Examples include phenol resin/butyral resin, NBR/epoxy resin, bismaleimide/acrylic resin, polyimide resin, etc., and bismaleimide/acrylic resin and polyimide resin are particularly desirable for applications requiring heat resistance.

The above adhesives can be used as is, but antimony trioxide, aluminum hydroxide, barium borate,
Flame retardants such as brominated epoxy or inorganic fillers such as silica alumina, mica, titanium oxide, zirconia, and magnesium oxide may be added as appropriate. However, if a large amount is added, the adhesive strength will decrease.

The present invention will be explained in more detail below using synthesis examples and comparative examples.

(Synthesis Example) Purified anhydrous 4,4'-diaminobenzanilide 1. ．． 70
．． Take 4 g (75 mol% of the amine component) and add a mixed solvent of 80% by weight of anhydrous N,N-dimethylformamide and 2[1jfii%] of xylene to it until the solid content in the total raw materials is 15% by weight. Add as much as possible and dissolve while flowing nitrogen gas.

Then purified 1,2,4,5-benzenetetracarboxylic dianhydride 152. ], g (75 mol% of acid component
) was added little by little while stirring (↑, but since it was an exothermic reaction, it was cooled by circulating cold water at about 15°C in an external water tank. After the addition, the internal temperature was set at 20°C, and Time reacted.

Next, 50.1 g of purified anhydrous 4,4"-diaminodiphenyl ether (25 mol% of the amine component) was added little by little with stirring, and then purified 1, 2,
4.5-benzenetetracarboxylic dianhydride 50.7g
(25 mol % of the acid component) was added little by little with stirring. After the addition, the internal temperature was set at 20°C and stirred for 5 hours to complete the reaction.

The acid/amine (molar ratio) in the reaction is 0.93,
The intrinsic viscosity of a 0.5% by weight solution in N,N-dimethylformamide was 1.30 (at 30<0>C).

This polyamic acid solution was applied onto glass so that the film thickness was 25 μm, dried at 80°C for 2 hours, and then peeled off from the glass and fixed with an iron frame.
Continuous heating from °C to 350 °C, 350 °C
By heating at C for 30 minutes, a polyimide film with low thermal expansion is obtained. This polyimide 7 (/L4)
F? jl1141 coefficient c5.5x 1O-6 (1/K)
Teat it.

(Example) A bismaleimide adhesive solution was cast onto a 25 μm low thermal expansion polyimide film so that the total thickness after pressing was 30 μm, and then dried, and the adhesive-applied surface was coated with a thickness of 35 μm. A flexible printed circuit board was obtained by overlapping the copper foils.

The 180°C peel strength of this single-sided copper-clad laminate is 2.0
kg/cm, and the linear expansion coefficient of the polyimide film after etching is 7. Ox 1O-6 (1/K).

(Comparison f(1) After casting the polyamic acid solution synthesized by the above method onto copper foil, put it in a dryer and dry it at 100°C for 30 minutes.
50°C for 30 minutes, 200°C for 30 minutes, 250°
After heating at C for 20 minutes and at 300°C for 10 minutes, it was wrapped around a 90mmφ cylinder and heated from 300°C to 35°C.
The temperature was continuously raised to 0°C over 1 hour for annealing. The 180°C peel strength of the flexible printed circuit board manufactured in this way is 0.7 kg/am.
and the linear expansion coefficient i of the polyimide film after etching, t 20 x 1O-a (1/K)
=.

(Comparative Example 2) A bismaleimide adhesive solution was cast onto a 25 μm commercially available polyimide film (Kapton, manufactured by DuPont) so that the total thickness after pressing was 30 μm, and then dried to remove the adhesive. A 35 μm thick copper foil was superimposed on the coated surface to obtain a flexible printed circuit board.

The 180°C peeling strength of this single-sided m-strung carcass is 1.
It was 5 kg/cm. The linear expansion coefficient of the polyimide film after etching was 27 x 1O-6 (17K).

(Effects of the Invention) According to the present invention, a curl-free flexible circuit board with excellent heat resistance and dimensional stability can be obtained.

Procedural amendment June 14, 1990

Claims (2)

[Claims] (1) In a polyimide film obtained by a polycondensation reaction of an aromatic tetracarboxylic dianhydride and an aromatic diamine, (A) one type selected from aromatic tetracarboxylic dianhydrides as the acid anhydride; or an aromatic tetracarboxylic dianhydride consisting of a mixture of two or more, (B) 4,4'-diaminobenzanilide and/or 3,4'-diaminobenzanilide and 4,4'-diaminodiphenyl ether as diamines; and 4,4'-diaminobenzanilide and/or 3,4'-diaminobenzanilide are reacted with an aromatic diamine consisting of 30 to 100 mol% of the aromatic amine component. The linear expansion coefficient is 1
A polyimide film with a low thermal expansion of 5×10^-^6 (1/K) or less. (2) By laminating the low thermal expansion polyimide film according to claim 1 with metal foil and an adhesive,
Linear expansion coefficient after metal foil etching is 15×10^-^6
A flexible printed circuit board characterized by low thermal expansion of (1/K) or less.