JPH06164084A - Polyimide wiring board and method for etching the same - Google Patents

Abstract

PURPOSE:To form a high precision hole by etching in the polyimide resin films of a double-side copper clad laminated film, by forming the polyimide layer from a plurality of layers having different properties. CONSTITUTION:As polyimide films, films having different etch rates are laminated, and if the number of laminations is 2, a polyimide film 1 of a lower etch rate and a polyimide film 2 of a higher etch rate are laminated and a copper foil 3 is laminated on both sides thereof. A photoresist pattern is formed on the copper foil in a portion where a hole is to be formed, and etching is performed to form a hole 4 in the copper foil 3. With the copper foil 3 as a mask, etching is performed from the layer of a lower etch rate to the layer of a higher etch rate, thereby forming a via hole 5. In addition, for three or more layers, a polyimide film 6 of a lower etch rate is etched from both sides. This allows the making of a hole which has a uniform shape and no side etch, and which is excellent in reliability and properties.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board used for a flexible circuit board, a lead frame, a lead frame for a multi-chip package and the like and a processing method thereof, and more particularly to a polyimide wiring board in which polyimide is laminated in multiple layers and an etching method thereof.

[0002]

2. Description of the Related Art Processing of a high-definition polyimide resin film for forming a small-diameter through hole in a copper foil laminated film using polyimide as a base material for flexible circuit boards, etc.
It was done mechanically by a puncher with a high spinning spindle head. This is because it was considered that polyimide was chemically stable and etching was technically difficult.

In recent years, there has been an increasing demand for polyimides to be subjected to etching, and various investigations have been conducted at various places. As a result, it has been found that the polyimides are dissolved in hydrazine-based and highly alkaline solutions, and it seems that the polyimides are etched. Became.

Also for copper foil laminated films, conventionally, copper foil and polyimide as a base material have been pasted together with an epoxy adhesive, and the etching process of the poex adhesive as an adhesive layer has been performed. Since it is difficult to etch, the polyimide layer of the copper foil laminated film has not been etched.

However, a technique for directly laminating a copper foil and a polyimide, such as a method for casting a copper foil and a polyimide on a polyimide surface, a sputtering method on the surface of the polyimide, or laminating the copper foil and the polyimide with a thermoplastic polyimide, has been established. As a result, it has become possible to apply the etching technology to polyimide-based wiring boards.

However, as shown in FIG. 2, a pattern is formed with a photoresist on the copper foil of the double-sided copper foil laminated film (a) in which the copper foil 22 is laminated on both sides of the polyimide film 21. , The copper foil is etched to form holes 23 in the copper foil (b). Next, the polyimide film 21 is etched using the copper foil as a mask (c). As the etching progressed, the side etching 24 proceeded (d), and at the time when the etching progressed to the other copper foil and the via hole 25 was formed, the side etching further proceeded greatly (e). .

The hole in which the large side etching has occurred cannot be used as a product because it causes a hindrance when forming a via hole, a through hole or the like.

[0008]

DISCLOSURE OF THE INVENTION According to the present invention, the shape of a hole due to side etching or the like in a polyimide layer generated when a polyamide layer composed of a multilayer laminated copper foil film having copper foil laminated on both sides is etched is uniform. The purpose is to solve the problem that
It is an object of the present invention to apply an etching method capable of excellent etching with a small hole shape such as side etching.

[0009]

DISCLOSURE OF THE INVENTION The present invention provides a copper foil laminated film made of polyimide and a method for etching a copper foil laminated film, which is a laminate of a polyimide film having a slow etching rate and a polyimide film having a high etching rate. When the number of laminated polyimides is 3 or more, the outer polyimide film is a copper foil laminated film in which the etching rate is slower than that of the inner polyimide film, and the number of laminated polyimides is 2. In this case, one side is etched from the side of the polyimide film having a slow etching rate, and when the number of laminated polyimide films is three or more, the polyimide is etched from both sides, so that the hole shape is uniform and the side etching is performed. A hole having a small number of holes is formed in the polyimide film.

Polyimide films laminated with copper foils are manufactured by various methods. For example, in the case of the casting method, a double-sided laminated film cannot be manufactured at one time, so a polyimide film laminated with copper foils on one surface is used. BACKGROUND ART Films are laminated and laminated with polyimide having excellent adhesive properties. To this end, FIG.
As shown in the cross-sectional view of the double-sided copper foil laminated polyimide film 1, the copper foil 2 is provided on both sides, the inner polyimide film is composed of a plurality of layers 3, and the polyimide film of each layer has different characteristics. ing. And, since these multi-layer films also have different etching characteristics, it was found that the cause is that the side etching and the like greatly progress due to the difference in the etching rate of each layer in the etching, and a hole having an unfavorable hole shape is formed. .

Therefore, when films having different etching rates are laminated as a polyimide film and the number of laminated layers is two, as shown in FIG. 1A, a polyimide film 1 having a slow etching rate and a polyimide film having a high etching rate are formed. The film 2 is laminated, and the copper foil 3 is laminated on both sides (a). A photoresist pattern is formed on the copper foil at the portion where the hole is to be formed, and the copper foil is etched to form the hole 4 in the copper foil (b). Etching is performed from the layer 1 having a slow etching rate to the layer 2 having a high etching rate using the copper foil as a mask (c) and (d), and the via hole 5 is formed (d). FIG. 1B shows a case where through holes are formed from both sides when the number of laminated polyimides is three or more. A polyimide film having an etching rate slower than that of the inner polyimide film 7 is arranged on the outer polyimide film 6 and the copper foil 3 is laminated on both surfaces (a). The hole 4 is formed by etching. Using copper foil as a mask, etching is performed from both sides (c) and (d) to form through holes 8 (e).

The copper foil laminated polyimide film and the etching method of the present invention can be applied to the case where a via hole or a through hole is formed by using a hole provided in a copper foil as a mask, but a resist formed on the polyimide film is used. Etc. may be etched with a mask.

Further, the etching of polyimide is carried out by using various hydrazine-based solutions such as an alcohol solution of an alkali metal hydroxide such as potassium hydroxide or an aqueous solution of an alkali metal hydroxide, hydrazine or a mixed solution of potassium hydroxide and hydrazine. Etching solutions such as the above can be used, and etching can be performed by immersing the polyimide-based wiring board in these solutions or by spraying from a nozzle. Furthermore, during etching by immersion in an etching solution containing a high concentration of alkali, after pulling out from the high concentration etching solution and washing with water, it is immersed again in the etching solution or in an etching solution having a different concentration. By performing the etching, the etching rate can be increased and the hole shape can be made uniform by removing the polyamic acid and the like generated on the opening surface by the etching of the polyimide.

[0014]

The present invention provides a wiring board in which a polyimide film and a copper foil are laminated, such as a double-sided copper foil laminated film,
When a plurality of polyimide films having different etching characteristics are laminated and the number of laminated films is 3 or more, the polyimide wiring board is a polyimide wiring board in which a polyimide film having a slow etching rate is laminated on the outer side of a polyimide film having a high etching rate. If two or more layers are laminated, by etching one side from the polyimide film side with a slow etching rate, and if three or more layers, by etching a polyimide film with a slow etching rate from both sides, A hole having a uniform shape and no side etching and excellent reliability and characteristics can be formed by etching.

[0015]

Example 1 A novolac photoresist (OFPR-800C manufactured by Tokyo Ohka Kogyo Co., Ltd.) was formed on the copper surface of a double-sided copper-clad polyimide film having two layers of polyimide films having different etching rates laminated on the side of the polyimide film having a slow etching rate. Was applied to a thickness of 5 μm by roll coating, and a resist pattern was formed by ultraviolet exposure and alkali development.

Copper was etched with an aqueous solution of ferric chloride according to the pattern thus formed, and 200 holes having a diameter of 200 μm were formed in a grid pattern on the copper in a portion of 10 cm in length and width.

The patterned polyimide film was etched at 70 ° C. for 30 minutes in a first etching tank filled with a 1N potassium hydroxide aqueous solution containing 80% by volume of ethanol.

Next, after washing with water in a first washing tank at 25 ° C. for 1 minute under ultrasonic irradiation, the solution was washed with water at a temperature of 25 ° C.
Etching was carried out for 1 minute under ultrasonic irradiation in a second etching tank filled with a 3N aqueous potassium hydroxide solution, and further water washing was carried out under ultrasonic irradiation for 5 minutes in a second water washing tank. Out of 200 holes formed by the polyimide film, 180 holes were excellent in shape without side etching.

Comparative Example 1 A polyimide film was etched in the same manner as in Example 1 except that a resist pattern was formed on the copper foil surface on the side of the polyimide film having a high etching rate and etching was performed.

20 holes are formed in the polyimide film.
Of the 0 holes, side etching was formed in 150 holes to form defective ones.

[0021]

EFFECTS OF THE INVENTION The present invention is capable of etching a polyimide wiring board composed of two polyimide layers having different etching characteristics from the surface having a slow etching rate,
Alternatively, when arranging three or more polyimide layers, a polyimide layer having a slow etching rate is provided on the surface closest to the etching surface, and a polyimide layer having a high etching rate is arranged from the surface farthest from the etching surface. Therefore, large side etching is not formed in the polyimide layer in the portion close to the surface affected by the etching, and etching having an excellent shape can be performed.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an etching process of the present invention.

FIG. 2 is a view showing a hole formed by conventional etching.

[Explanation of symbols]

1 ... Polyimide film with slow etching rate, 2 ... Polyimide film with fast etching rate, 3 ... Copper foil, 4
... holes, 5 ... via holes, 6 ... outer layer polyimide film,
7 ... Outer layer polyimide film, 8 ... Through hole, 21 ...
Polyimide film, 22 ... Copper foil, 23 ... Hole, 24 ... Side etching, 25 ... Via hole

Claims (4)

[Claims] 1. A polyimide wiring board in which a polyimide layer and a conductive layer are laminated, wherein the polyimide layer is formed of a plurality of layers having different etching characteristics. 2. The layer formed near the surface on which the etching liquid acts is composed of three or more polyimide layers in which a layer having an etching rate slower than that of a layer formed far from the surface on which the etching liquid acts. The polyimide wiring board according to claim 1, which is formed. 3. A method for etching a polyimide layer of a polyimide-based wiring board having a polyimide layer and a conductive layer laminated, wherein a wiring board having polyimide layers laminated with different etching characteristics is etched by applying an etching solution from a surface having a slow etching rate. An etching method comprising: 4. The polyimide layer formed in a portion of the wiring board closer to the surface on which the etching liquid acts is composed of three or more polyimide layers in which polyimide layers having a slower etching rate than the polyimide layer formed in a distant portion are laminated. The etching method according to claim 3, wherein the etching method is configured.