JPH0346292A - Flexible printed board and manufacture thereof - Google Patents

Abstract

PURPOSE:To make a flexible printed board excellent in heat resistance, electrical property, adhesion, and breakage resistance and free of curl, wrinkles, and shrinkage by a method wherein a polyimide thin layer with specific structural units is directly bonded to a metal foil. CONSTITUTION:A polyimide thin layer possessed of structural units represented by a formula I is directly bonded to a metal foil to form a flexible printed board. The polyimide film with structural units represented by formula I can be manufactured by curing a polyamide acid precursor. In formulas I and II, m and n denote positive integers. By this setup, a flexible printed board free of curl, wrinkles, and the like, excellent in adhesive power, electrical property, and breakage resistance, and moreover simplified in manufacturing can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a flexible printed circuit board that is made of a thin polyimide layer and a metal foil and has excellent heat resistance, electrical properties, and mechanical properties, and a method for manufacturing the same.

[Prior Art] Conventionally, flexible printed circuit boards have generally been manufactured by laminating an insulating film such as a polyimide film to a metal foil such as copper foil using an adhesive. However,
Because the adhesive did not have sufficient heat resistance, it was not possible to take full advantage of the properties of polyimide.

Therefore, a method for manufacturing a flexible printed circuit board without using an adhesive is disclosed, for example, in US Pat. No. 3,179.
As seen in No. 834, it has been considered, but it has not been possible to obtain a flexible printed circuit board that has sufficient heat resistance, adhesiveness, and bending durability, and that does not curl, wrinkle, or jilt due to temperature changes. It was considered to be extremely difficult.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a product that has excellent heat resistance, electrical properties, adhesive properties, and folding durability, and that is free from curling. It is an object of the present invention to provide a flexible printed circuit board that does not cause wrinkles, jiggling, etc., and a method for manufacturing the same.

[Means for Solving the Problems] ゛In order to solve the above problems, the present inventors have conducted various studies, and by using polyimide having a specific structure, curls, wrinkles, and wrinkles can be reduced due to temperature changes. The present invention has been completed based on the discovery that a flexible printed circuit board that does not cause wrinkles and has sufficient heat resistance, electrical properties, adhesive properties, and folding durability can be obtained.

That is, the first invention provides general formula (I) [wherein, msn
is a positive integer] (I) A flexible printed circuit board characterized in that a polyimide thin layer having a structural unit represented by the formula (I) is directly bonded to a metal foil. anhydride to paraphenylenediamine and 4. -After directly coating metal foil with a polyamic acid solution obtained by reacting with diaminodiphenyl ether, heating,
This is a method for manufacturing a flexible printed circuit board characterized by dehydration and drying.

A polyimide film having a structural unit represented by the above general formula (I) is produced by curing a polyamic acid precursor having a structural unit represented by the following general formula (II) [where mSn is a positive integer] (n) It can be manufactured by

This polyamic acid precursor can be obtained by reacting paraphenylene diamine and 4,1-diaminodiphenyl ether with pyromellitic dianhydride.

Various patterns can be considered for the equivalent ratio of the two types of diamines used here and the polymerization mode with pyromellitic dianhydride, but regarding the equivalent ratio, if the ratio of para-phenylene diamine is too high, The flexibility of the polyimide film is impaired, making it impossible to provide a material suitable for flexible printed circuit boards. Also, 4,4°
- If the ratio of diaminodiphenyl ether is too high, the coefficient of linear expansion of the polyimide after curing will be larger than that of the metal, making the printed circuit board produced more likely to curl or wrinkle due to thermal history. The optimal polymerization ratio varies depending on the type of metal foil to be combined, but
Suitably, the molar ratio of phenylene diamine to 4,4'-diaminodiphenyl ether is between approximately 10:1 and 1=10, particularly preferably between 3:1 and 1:5. For copper foils, which are most commonly used for printed circuit boards, the most preferred polymerization ratio is between 1:5 and 1:1 paraphenylene diamine to 4,4[deg.]-diaminodiphenyl ether.

Further, as for the polymerization method, any polymerization method such as random copolymerization or block copolymerization can be employed, but the most preferable polymerization method is the following polymerization method using alternating copolymerization. That is, pyromellitic dianhydride is added in an excess molar ratio to the primary amine component to form an acid anhydride-terminated oligomer, and the secondary amine component is added to this in the molar amount of the primary amine component and the secondary amine component. This is a method of obtaining an alternating copolymer by adding so that the sum of the molar amounts of pyromellitic dianhydride is approximately the same as the molar amount of pyromellitic dianhydride. The thus obtained alternating polymer exhibits superior mechanical properties when formed into a film, compared to random copolymers and ordinary block copolymers.

Organic solvents used during polymerization reactions and coating include N,N-dimethylformamide, NIN-dimethylacetamide, N,N-diethylformamide, N
, N-diethylacetamide, N,N-dimethylmethoxyacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, tetrahydrofuran, pyridine, etc., and these solvents may be used alone or in combination of two or more. Moreover, a non-solvent such as toluene, benzene, xylene, etc. can be mixed with a part of the solvent.

As the metal foil used in the present invention, copper foil is generally used, but aluminum foil, nickel foil, etc. can also be used. The thickness of the metal foil used is 5 to 100μ,
The surface on which the polyamic acid is cast is preferably roughened.

The polyamic acid solution can be applied to the metal foil by casting to a uniform thickness of 30 to 1000 microns using a known coating means such as a roll coater, knife coater, doctor blade, or flow coater. Subsequently, the solvent of the polyamic acid is removed by heating, but since rapid heating causes foaming and twitching, and also causes deterioration of physical properties, it is preferable to heat from a low temperature and gradually increase the temperature.

The maximum temperature is preferably in the range of 200 to 550°C.

Although heating can be carried out in air, it is more preferable to carry out under reduced pressure or in an atmosphere of an inert gas such as nitrogen.

Note that in order to relieve residual stress in the polyimide thin layer and prevent curling of the flexible printed circuit board, annealing treatment and slow cooling may be performed after firing at the maximum temperature. The thickness of the polyimide film is ultimately controlled to 5-200μ. Furthermore, since the metal foil may be oxidized by heating, the foil may be treated with an acid after firing. Further, the foil may be subjected to anti-rust treatment.

[Example] Next, the present invention will be specifically explained with reference to Examples.

The viscosity of the polyamic acid in the examples was measured using a B-type viscometer. Various performances as a printed circuit board were measured by the following methods.

(I) Beer strength It was carried out according to the method of IPC-FC-241A.

(2) Surface resistance It was conducted according to JIS C6481.

(3) Solder resistance Samples treated according to JIS C6481 at 300℃
After being immersed in a solder bath for 60 seconds, the shape was visually observed.

(4) Folding Durability Measured according to JIS P-8115, with a radius of curvature of the folded surface of 0.8 mm and a static load of 500 g.

(5) Dimensional stability Dimensional stability was measured according to the method of IPC-FC-241A, and expressed as shrinkage percentage.

Example I 815 g of N,N-dimethylformamide was mixed with ODA (4
, 4°-diaminodifenino ether) 70.28 g
After dissolving 102.07 g of PMDA (pyromellitic dianhydride) and stirring for 1 hour, p-P
Approximately 12.65 g of DA (rose phenylene diamine) was added and the viscosity was adjusted to 2500 voids. ODA: p
- PDA ratio is 3:1. This polyamic acid solution was applied uniformly to a thickness of 270μ on copper foil, and heated at 80°C and 100°C.
, 150℃, 200℃, 250℃, 300℃, 350℃
, 400° C., and 450° C. for 5 minutes each to dry. The properties of the obtained substrate were as shown in Table 11.

Example 2 ODA (4
, 4'-diaminodiphenyl ether) was dissolved, and PMDA (pyromellitic dianhydride) was dissolved therein.
After adding 104.09g and stirring for 1 hour, p-PD
A (rose phenylenediamine) approx. 17.20. was added to adjust the viscosity to 2500 voids. ODA: p-
PDA-2: 1. This polyamic acid solution was applied uniformly to a thickness of 270μ on copper foil, and heated at 80°C and 100°C.
, 150℃, 200℃, 250℃, 300℃, 350℃
, 400° C., and 450° C. for 5 minutes each to dry. The properties of the obtained substrate were as shown in Table 1.

Comparative Example 2 ODA (4
, 4'-diaminodiphenyl ether) was dissolved, and PMDA (pyromellitic dianhydride) was dissolved therein.
94.33 g was added to adjust the viscosity to 2500 poise. This polyamic acid solution was applied uniformly to a thickness of 270μ on copper foil, and heated at 80℃, 100℃, 150℃, 200
℃, 250℃, 300℃, 350℃, 400℃, and 4
It was dried by heating at 50° C. for 5 minutes each. The properties of the obtained substrate were as shown in Table 1.

Table 1 Item Unit Example 1 Example 2 Comparative Example 1 Pill strength ) cgf/cm 1.7 1.7 1
．． 6 Surface resistance Ω 1.7 Xl0161.8
XIO” 1.8 Xl016 solder resistance
No abnormality No abnormality No abnormality Folding durability
times 280 250 280 dimensional stability
% 0.08 0. 060.14 [Effects of the Invention] The flexible printed circuit board of the present invention does not cause curls, wrinkles, etc., has sufficient adhesive strength, electrical properties, and bending durability, and can simplify the manufacturing process. Therefore, it is extremely useful as an industrial material.

Claims (1)

[Scope of Claims] 1) A flexible printed circuit board characterized in that a polyimide thin layer having a structural unit represented by general formula (I) is directly bonded to metal foil. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ 2) The flexible printed circuit board according to claim 1, wherein m/n is between 5 and 1. 3) The flexible printed circuit board according to claim 1 or 2, wherein the film has a thickness of 5 to 200μ, and the metal foil has a thickness of 5 to 100μ. 4) The flexible printed circuit board according to any one of claims 1 to 3, wherein the metal foil is a copper foil. 5) A flexible product characterized by directly coating metal foil with a polyamic acid solution obtained by reacting pyromellitic dianhydride with paraphenylene diamine and 4,4'-diaminodiphenyl ether, followed by heating, dehydration, and drying. Method of manufacturing printed circuit boards. 6) The method for manufacturing a flexible printed circuit board according to claim 5, wherein the equivalent ratio of 4,4'-diaminodiphenyl ether to paraphenylenediamine is between 5:1 and 1:1. 7) The method for manufacturing a flexible printed circuit board according to claim 5 or 6, wherein the metal foil is a copper foil.