JP3167421B2 - Polyamic acid film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a polyamic acid film that can be used as a substrate for a layer flexible printed circuit.

[0002]

2. Description of the Related Art The use of a two-layer flexible printed circuit board without an adhesive layer has been increasingly used as electronic devices have become smaller and lighter. The use of substrates having holes in a support film such as a carrier tape for TAB is also increasing. On the other hand, as a method of manufacturing a substrate for a flexible printed circuit having holes formed in a support film layer used for TAB or the like and having conductor wiring, a hole is formed in the support film layer in advance by punching or the like, and an adhesive is used. After laminating the conductor layer, a method of forming a wiring circuit, a polyamic acid solution was directly applied to the conductor layer, and drying and imidization were performed, or the conductor layer was formed on the support film layer by an evaporation method or a sputtering method. Thereafter, a method of forming a hole in the support film layer by using a laser or a strong alkaline solution and then forming a wiring circuit is used.

However, these conventional methods each have disadvantages in heat resistance, adhesion, workability and chemical resistance. First, in the case of a three-layer flexible printed circuit board having an adhesive layer, the heat resistance of the adhesive layer is low. It has the disadvantage of being determined by gender. When the conductor layer is formed by vapor deposition or sputtering,
The disadvantage of low adhesion between the support film layer and the conductor layer, or when the resin layer is made thicker, for example, by applying and drying polyamic acid directly to form a thick film, the stress due to the shrinkage accompanying imidization is reduced. Exceeds the supporting force of the conductor layer,
Causes large curls during drying. On the other hand, if the polyamic acid solution is directly applied and dried on the conductor layer several times and then imidized, curling during the process is reduced, but the heat history is reduced in the portion close to the conductor layer and the opposite side of the conductor layer. Therefore, the imidization ratio and the residual amount of the solvent in the film are different, and the curl and the dimensional change of the film after copper foil etching are increased. In addition, when using a laser, especially when using an excimer laser, it is excellent in fine workability and damage to the copper foil is small, but a strong imide bond must be cut, and it takes time to process and the productivity is low, There is a problem that running cost is high. Alternatively, polyimides having a molecular structure that can be alkali-etched after imidization have the disadvantage that solvent resistance is slightly reduced, and that a highly alkaline solution is used as an etchant, which is dangerous and that wastewater treatment cannot be easily performed. ing.

[0004] Although the progress of semiconductor packaging technology in recent years is remarkable,
Among them, TAB is capable of easily forming a conductor pattern at an extremely high density, so that it can easily cope with an increase in the number of pins. In addition, it is possible to wire-connect the entire lead to the semiconductor element at once without using a wire at the time of bonding. Because it is possible,
Currently, high-density packaging technology is required, and development is being actively pursued.

[0005] There are two types of TAB tapes, a two-layer structure and a three-layer structure. A three-layer structure (hereinafter abbreviated as "three-layer TAB") generally includes a conductor foil such as a copper foil and a heat-resistant resin film. Is bonded with an adhesive, and even if a polyimide film with excellent properties such as heat resistance and chemical resistance is used as the film, it has an adhesive layer with poor heat resistance. I could not do it.

On the other hand, a two-layer TAB (hereinafter, abbreviated as a two-layer TAB) generally has excellent heat resistance as a TAB because it does not have an adhesive layer on a base film, but is difficult to use due to the difficulty in its production method. It was rarely offered. That is, as a method for manufacturing the two-layer TAB, a conductive layer is provided on a heat-resistant film such as polyimide by using a thin film forming technique such as sputtering, vapor deposition, and plating, and then the base film and the conductive layer are subjected to an etching treatment to obtain a device. A method of forming a predetermined opening such as a hole or a sprocket hole, and a conductor pattern, and directly applying a varnish of a heat-resistant resin such as a polyimide on a conductor foil such as a copper foil and drying to form a two-layer substrate, and then forming a resin layer And a method of forming a predetermined opening or a conductor pattern by performing an etching treatment on a conductor foil. In the former, a rolled foil having excellent flexibility and a Fe-Ni alloy foil having excellent strength are used. There is a problem that it cannot be used, and since it is necessary to provide an opening using an etching method for forming the opening of the base film, a punching method of a three-layer TAB is required. Compared to productivity is significantly lowered.
On the other hand, also in the latter, in order to prevent the occurrence of curls and wrinkles, it is necessary to match the linear expansion coefficient of the resin used with the copper foil as the conductor layer, but such resins are generally rigid and have excellent solvent resistance. For this reason, alkali etching is often difficult, and dry etching such as excimer laser must be performed in order to provide openings in the film layer, which has a problem that productivity and cost are disadvantageous. .

In order to solve these problems, we first form a semi-cured polyamic acid film on a release film, and provide an opening by punching or the like with the release film. It has been found that a two-layer flexible printed circuit board with an opening can be easily manufactured by thermocompression bonding and heat drying and imidization. There is a problem that the film after etching is curled due to the curl of the substrate or the residual stress generated between the copper foil and the film.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a two-layer flexible printed circuit board without an adhesive layer, which has inherent alkali resistance, solvent resistance and heat resistance.
A polyamic acid for a substrate for a flexible printed circuit, having a predetermined thickness without deteriorating electrical properties and having a perforated film layer as necessary.
Provide a film .

[0009]

According to the present invention, the coefficient of linear expansion after imidization is 1 × 10 ^-6 (1 / K) higher than that of metal foil for printed circuits.
Larger semi-cured polyamic acid layer and 1 × 10 ^-6
(1 / K) is formed from a semi-cured polyamic acid layer that is smaller than or equal to, and after imidization, the difference in linear expansion coefficient between the entire layer and the metal foil is 5 × 10 ⁻⁶ (1 / K) or less. Some polyamic acids
A film, wherein the layer having a small linear expansion coefficient is
It is a polyamic acid film that is used by thermocompression bonding, and a polyamic acid film provided with a predetermined opening as required, and a polyamic acid film formed on a release film in contact with a layer having a large linear expansion coefficient. is there.

[0010] The polyamic acid film of the present invention is a semi-cured polyamic acid in which the linear expansion coefficient after imidization on the release film is 1 × 10 ⁻⁶ (1 / K) or more larger than that of the metal foil for printed circuits. Forming a semi-cured polyamic acid layer having a linear expansion coefficient after imidization of 1 × 10 ⁻⁶ (1 / K) or more smaller than that of the metal foil for printed circuit on the polyamic acid layer. Or the linear expansion coefficient after imidization on the release film is 1
Form a semi-cured polyamic acid layer that is larger than × 10 ^-6 (1 / K) or more, and the linear expansion coefficient after imidization on other release films is 1 × 10 ^-6 than that of metal foil for printed circuits. After forming a semi-cured polyamic acid layer that is smaller than (1 / K) or more, both are heated and pressed together with the surface of the amic acid layer aligned,
It can be manufactured by peeling off the release film on the polyamic acid side where the linear expansion coefficient becomes small.

A two-layer flexible printed circuit board without curl can be obtained by thermocompression bonding a polyamic acid layer having a small linear expansion coefficient of the film to a conductive foil plate. Since the polyamic acid film of the present invention has a linear expansion coefficient close to that of a metal foil after imidization as a whole, there is almost no curl as a substrate with a metal foil due to cooling after heat curing. If the difference in linear expansion coefficient from the metal foil is greater than 5 × 10 ⁻⁶ (1 / K), curling will occur. In addition, since the polyamic acid layer having a large linear expansion coefficient is located on the outermost layer to cancel the residual stress generated between the metal foil and the polyimide film interface, curling of the film after removing the metal foil can be prevented.
At this time, curl prevention can be achieved by making the layer whose linear expansion coefficient is 1 × 10 ⁻⁶ (1 / K) or more larger than the metal foil the outermost layer and the smaller layer a layer in contact with the metal foil. 1 × 10 ^-6 (1
If the difference from the metal foil is smaller than (/ K), the force for canceling the residual stress is weak and curl occurs.

In the present invention, in order to form a semi-cured polyamic acid film on a release film, a known coating means such as a roll coater, a rotary coater, a knife coater, a doctor blade, a flow coater or the like is formed on the release film. And then heat-dried after casting to a uniform thickness of 0 to 100 μm from the upper end of the release film.

In the present invention, the conditions for drying the polyamic acid solution to form a semi-cured polyamic acid film are preferably 80 to 200 ° C. and 5 to 30 minutes.
If the temperature is lower and the time is shorter than this, when heat-pressing with the conductor foil, the fluidity is large, the bleeding at the opening, the seepage is large, the variation in the film thickness is large, and the dimensional change after imidization is large. growing. If the temperature is higher than this and the time is longer, the fluidity is too small when heating and pressure bonding with the conductor foil, the peel strength with the conductor foil or the flexible printed circuit board is reduced, and the occurrence of voids is increased.
The imidation ratio in the polyamic acid film state is 10
5050%, preferably 20-40%. 10% imidation rate
If it is less than 1, the tackiness remains and the workability is poor, and after winding, it is difficult to isolate the film one by one by adhering to the back of the release film. Even if the polyamic acid surfaces are combined and thermocompression-bonded, they will not be sufficiently integrated.

The thickness of one polyamic acid film to be applied is suitably 50 μm or less after imidization.
If the thickness is larger than this, the stress due to the shrinkage due to imidization exceeds the supporting force of the release film, and a large curl is generated during drying. In addition, since the film layer is thick, the evaporation rate of the solvent is low, and the productivity is significantly reduced.

The conditions for heating and pressing the polyamic acid films together and the polyamic acid film on the conductor foil are as follows: 70 to 200 ° C., 5 to 100 kg / cm ² , 5
~ 30 minutes, 70 ~ 200 ℃ for roll laminator, 1 ~ 50
The condition of 0 kg / cm ² and 0.1 to 50 m / min is appropriate.
It is desirable to carry out the reaction at a temperature lower by 30 ° C. without generating volatile substances.

The polyamic acid film provided with the release film is formed by a conventional method, for example, punching, cutting, alkali etching, laser or the like to form a hole together with the release film or by opening only the polyamic acid film. However, punching is preferable in terms of productivity and cost. After the completion of the hole processing, the polyamic acid film is heated and pressed on the conductive foil, and then the release film is peeled off to sufficiently imidize.

The polyamic acid in the present invention is usually obtained by reacting a diamine with an acid anhydride.
Examples of the diamine include phenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, and diaminodiphenylether.Examples of the acid anhydride include trimellitic anhydride, pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, and benzophenonetetracarboxylic acid. Dianhydride and the like can be used.

In the present invention, the polyamic acid having a predetermined coefficient of linear expansion has an acid anhydride and a diamine of one kind.
Or copolymerizing the species or two or more species appropriately,
Alternatively, it can be obtained by blending two or more polyamic acid solutions.

Examples of the material that can be used as the release film include plastic films such as polypropylene, polyester, polyethersulfone, polyimide, and polyethylene.

Examples of the material that can be used for the conductor layer include metal foils such as Fe—Ni alloy and Fe—Cr—Al alloy in addition to simple metal foils such as copper, aluminum and nickel.

[0021]

According to the present invention, a semi-cured polyamic acid film composed of two layers having different linear expansion coefficients and having apertures as necessary formed on a release film is heated and pressed with a conductive foil, and the imide is formed. By completing the formation, it is possible to easily and inexpensively obtain a curl-free two-layer flexible printed circuit board having holes in the support film layer as required with good productivity and high yield.

[0022]

EXAMPLES (Synthesis Example 1) 200 g of purified anhydrous 4,4'-diaminodiphenyl ether was placed in a four-neck separable flask equipped with a thermometer, a stirrer, a reflux condenser, and a dry nitrogen gas inlet. To this, a mixed solvent of 90% by weight of anhydrous N-methyl-2-pyrrolidone and 10% by weight of toluene was added and dissolved in such an amount that the solid content in all the raw materials became 20% by weight. Dry nitrogen gas was allowed to flow throughout the entire process from the preparation of the reaction to the removal of the product. Next, 218 g of purified anhydrous pyromellitic dianhydride is added little by little with stirring, but because of an exothermic reaction,
Cold water of about 15 ° C. was circulated through the external water tank to cool it.
After the addition, the internal temperature was set to 20 ° C., and the mixture was stirred for 5 hours, and the reaction was completed to obtain a polyamic acid solution A.

(Synthesis Example 2) 108 g of purified anhydrous paraphenylenediamine was placed in a four-neck separable flask equipped with a thermometer, a stirrer, a reflux condenser and a dry nitrogen gas inlet, and anhydrous N was added thereto. -Methyl-2-pyrrolidone
A mixed solvent of 90% by weight and 10% by weight of toluene was added and dissolved in such an amount that a solid content ratio in all the raw materials became 20% by weight. Dry nitrogen gas was allowed to flow throughout the entire process from the preparation of the reaction to the removal of the product. Then, 294 g of purified anhydrous 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride is added little by little with stirring, but since the reaction is exothermic, circulate cold water at about 15 ° C to the external water tank. This was allowed to cool. After the addition, the internal temperature was set at 20 ° C., and the mixture was stirred for 5 hours, and the reaction was completed to obtain a polyamic acid solution B.

Example 1 C was obtained by mixing and stirring the polyamic acid solutions A and B so that the solid content ratio became A / B = 10/90. Further, D was obtained by mixing and stirring so that A / B = 40/60. Using these polyamic acid solutions, directly apply on the glossy surface of the copper foil so that the thickness after imidization becomes 25 μm, 30 minutes at 100 ° C., 30 minutes at 200 ° C., 30 minutes at 300 ° C.
After heating and drying at 350 ° C. for 30 minutes for imidization, the entire surface of the copper foil was etched to obtain C and D polyimide films. The coefficient of linear expansion of the obtained film is represented by T
When measured in the range of 50 to 150 ° C. using MA, C was 12 × 10 ⁻⁶ (1 / K) and D was 24 × 10 ⁻⁶ (1 / K).

This polyamic acid solution D was applied on a commercially available release film (polyester film) using a roll coater so that the thickness after imidization became 15 μm, and
Drying was performed at 15 ° C. for 15 minutes to form a polyamic acid layer having a large linear expansion coefficient on the release film. Further, a polyamic acid solution C was applied on the polyamic acid layer by a roll coater so that the thickness after imidization became 10 μm,
Drying was performed at 15 ° C. for 15 minutes to obtain a polyamic acid film with a release film. Drill holes (device holes) using a mold, overlay the surface of the polyamic acid film on the roughened surface of a commercially available copper foil, and press at 90 ° C.
Heating / compression bonding was performed at 40 kg / cm ² for 15 minutes. Thereafter, the release film was peeled off, and heating was performed at 380 ° C. for 1 hour to complete imidization, thereby obtaining a two-layer substrate having device holes.

The two-layer substrate thus obtained has an adhesive strength (JIS C6481) of 1.5 kg / cm and a dimensional change rate (JIS C6481).
Is no curl at 0.02%, and the film after the copper foil is removed by etching has no curl at all, and has a tensile strength (JIS K6
760) is excellent at 31 kg / mm ² and elongation (JIS K6760) is 41%, and the coefficient of linear expansion of this film is 16 × 10 ^-6 (1 /
K), the coefficient of linear expansion of the copper foil was 17 × 10 ⁻⁶ (1 / K), and the difference was 1 × 10 ⁻⁶ (1 / K).

(Example 2) The polyamic acid solution C of Example 1 was applied on a commercially available release film (polyester film) with a roll coater so that the thickness after imidization became 15 μm, and the temperature was adjusted to 110 ° C. and 15 ° C. Drying was carried out to form a polyamic acid layer having a small linear expansion coefficient on the release film. Next, the solution D was imidized to a thickness of 10 μm as in Example 1.
To form a polyamic acid layer having a large linear expansion coefficient on the release film. The two are superimposed so that the surfaces of the polyamic acid face each other, and heated and pressed at 100 ° C. and 20 kg / cm ² for 10 minutes using a press to obtain a polyamic acid laminated film. The release film on the small side was peeled off to obtain a polyamic acid film. Drilling using a mold (device hole)
Performing, laminating the polyamic acid film surface on the copper foil roughened surface, using a roll-type laminator, 90
Heating and pressure bonding were performed at 100 ° C., 100 kg / cm ² and 0.5 m / min. After that, peel off the release film and perform heating at 380 ° C for 1 hour.
The imidization was completed, and a two-layer substrate having device holes was obtained.

The two-layer substrate thus obtained has an adhesive strength (JIS C6481) of 1.3 kg / cm and a dimensional change rate (JIS C6481).
Is no curl at 0.02%, and the film after the copper foil is removed by etching has no curl at all, and has a tensile strength (JIS K6
760) is excellent at 32 kg / mm ² and elongation (JIS K6760) is 43%, and the coefficient of linear expansion of this film is 16 × 10 ^-6 (1 /
K), the coefficient of linear expansion of the copper foil was 17 × 10 ⁻⁶ (1 / K), and the difference was 1 × 10 ⁻⁶ (1 / K).

Example 3 E was obtained by mixing and stirring the polyamic acid solutions A and B of Example 1 so that the solid content ratio was A / B = 20/80. Using this polyamic acid solution E, it was directly applied on a glossy surface of a copper foil so as to have a thickness of 25 μm after imidization.
After heating and drying at 350 ° C. for 30 minutes for 30 minutes and imidization, the entire surface of the copper foil was etched to obtain a polyimide film E. When the linear expansion coefficient of the obtained film was measured in the range of 50 to 150 ° C. using TMA, 15 × 10 ⁻⁶ ( ^1/1 )
K).

On a commercially available release film (polyester film), the polyamic acid solution D of Example 1 was applied by a roll coater so as to have a thickness of 10 μm after imidization, and dried at 110 ° C. for 15 minutes. A polyamic acid layer having a large linear expansion coefficient was formed on the release film. Next, a polyamic acid solution E was applied to the polyamic acid layer side by a roll coater so that the thickness after imidization became 15 μm,
Drying was performed at 110 ° C. for 15 minutes to obtain a polyamic acid film having a release film. A two-layer substrate was obtained in the same manner as in Example 1 except that this polyamic acid film was used.

The two-layer substrate thus obtained has an adhesive strength (JIS C6481) of 1.4 kg / cm and a dimensional change rate (JIS C6481).
Is no curl at 0.07%, and the film after the copper foil is removed by etching has no curl, and has a tensile strength (JIS K6
760) is excellent at 30 kg / mm ² and elongation (JIS K6760) is 40%, and the coefficient of linear expansion of this film is 19 × 10 ^-6 (1 /
K), the coefficient of linear expansion of the copper foil was 17 × 10 ⁻⁶ (1 / K), and the difference was 2 × 10 ⁻⁶ (1 / K).

(Comparative Example 1) The polyamic acid solution D of Example 1 was applied on a commercially available release film (polyester film) using a roll coater so that the thickness after imidization became 25 μm. The mixture was dried for a minute to obtain a polyamic acid film with a release film. A two-layer substrate was obtained in the same manner as in Example 1 except that this polyamic acid film was used.

The thus obtained two-layer substrate has an adhesive strength (JIS C6481) of 1.5 kg / cm and a dimensional change rate (JIS C6481).
However, there is a curl with a diameter of 5 cm outside the copper foil surface at 0.20%, and the film after etching away the copper foil curls to a diameter of 1 cm, and there is a problem in workability when used as a substrate for a flexible printed circuit. is there.

[0034]

According to the present invention, a curl-free two-layer flexible print excellent in heat resistance, chemical resistance, dimensional stability, etc., provided with openings such as device holes by punching with excellent productivity. A circuit board can be obtained, and a two-layer flexible printed circuit board using a rolled foil that cannot be used by an evaporation method or the like can be manufactured. INDUSTRIAL APPLICABILITY The present invention can be easily applied to a continuous process using a continuous sheet, and can be used for a two-layer TAB or the like for an industrial two-layer flexible printed circuit board .
It is suitable as a polyamic acid film .

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H05K 1/03 610 B32B 15/08 C08J 5/18 CFG C08L 79:08

Claims (3)

(57) [Claims] 1. A semi-cured polyamic acid layer having a coefficient of linear expansion after imidization of at least 1 × 10 ⁻⁶ (1 / K) higher than that of a metal foil for printed circuits, and 1 × 10 ⁻⁶ (1 / K). ) And a semi-cured polyamic acid layer that is smaller than the above, and after imidization, the difference in linear expansion coefficient between the entire layer and the metal foil is 5 × 10 ⁻⁶
K) a polyamic acid film that is:
A polyamic acid film in which a layer having a small expansion coefficient is thermocompression-bonded to a metal foil . 2. The polyamic acid film according to claim 1, wherein the polyamic acid film is formed on a release film in contact with a layer having a large linear expansion coefficient. 3. The polyamic acid film according to claim 2, wherein a predetermined opening is provided.