JPH05283865A - Manufacture of multilayer flexible printed-circuit board - Google Patents

Abstract

PURPOSE:To provide excellent heat resistance, dimensional stability, thinner and flexible by curing polyimide precursor after coating an entire board formed with a circuit pattern to form a polyimide layer, and forming a conductive layer on the surface-treated polyimide layer. CONSTITUTION:A circuit pattern 7 is formed on a copper foil 1 of a copper-clad board 3 in which polyimide resin is used as a base material 2. The entire board 3 formed with the pattern 7 is coated with polyimide precursor, and cured to form a polyimide layer 8. The layer 8 is surface-treated with oxygen plasma 9, and a conductive layer made of copper is formed by electroless plating and electroplating. A circuit pattern 10 is formed on the conductive layer, and an opening 6 to become a conduction hole 5 with the other layer is formed at the layer 8 by etching. A conductive part is formed in the opening 6 by electroless plating and copper electroplating. The steps after coating of the precursor are repeated to manufacture a circuit board.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite part having wiring, cable and connector functions for moving parts of various electronic devices such as computers and communication devices, and a multi-layer used for a circuit module for mounting LSI. The present invention relates to a wiring board, particularly a multilayer flexible printed wiring board.

[0002]

2. Description of the Related Art A flexible printed wiring board is a thin flexible base film provided with metal wiring.
It is useful for saving mounting space and improving reliability, and is widely used in computer-related equipment, audio products, communication equipment, etc. As electronic devices have become smaller, lighter, thinner, and higher in density in recent years, flexible printed wiring boards are required to have multiple layers as with rigid printed wiring boards. Since the printed wiring board has multiple layers, the printed wiring board has several layers of printed wiring inside as well as on the front and back.
By using it together with integrated circuits such as I and VLSI, it has become possible to shorten the distance between electronic circuit components and to greatly reduce the number of components and connection parts.

Although a multilayer flexible printed wiring board has been conventionally manufactured by various manufacturing methods, an example of the manufacturing process is shown in FIG. 3 taking a three-layer flexible printed wiring board having three metal conductive layers as an example. ..

First, as shown in FIG. 3A, a circuit pattern 33, which is an inner layer after another layer is laminated, is photo-etched on a double-sided copper-clad substrate having a copper foil 31 as an insulating layer such as polyimide as a base material 32. Formed by a method or the like, and after forming a hole for conducting the inner layer and the outer layer, electroless copper plating is performed after the surface of the polyimide resin is activated, and then electrolytic copper plating is performed to form the conductive hole 34. .. And FIG. 3 (b)
As shown in FIG. 2, a glass plate in which a circuit pattern formed on one side of a double-sided copper-clad substrate and an insulating layer 36 side of a single-sided copper-clad substrate 35 having an insulating layer such as polyimide as a base material are impregnated with epoxy or acrylic resin. Prepreg 3 made of fiber cloth
Then, the layers are laminated with each other through 7, and as shown in FIG. 3C, a heat press 38 pressurizes and cures under heating. Next, as shown in FIG. 3D, through holes 39 for forming conduction between the front and back conductor layers and the inner conductor layer are provided, and after the activation treatment, electroless copper plating and electrolytic copper plating are performed, and further Three
As shown in (e), a circuit pattern is formed on the front and back copper foils 31 by a photo-etching method.

[0005]

However, in such a method, since the prepreg used for lamination uses an epoxy or acrylic material, heat resistance and dimensional stability are problematic. In addition, a copper-clad substrate having an insulating layer such as polyimide as a base material has an insulating layer thickness of 35 to 50 μm, and a copper foil as a conductor has a thickness of 18 to 35 μm. The total thickness of the substrates after lamination becomes thick, which not only violates thinning, but also may lower flexibility, which is a characteristic of the flexible printed wiring board. Further, since the front and back conductor layers and the inner conductor layer are electrically connected to each other by the through holes, the inner wall portion is likely to be disconnected due to the concentration of stress on the through hole portions during bending. Further, the land diameters of the front and back surfaces and the inner layer are increased in order to secure the stacking alignment accuracy, wiring of the conductors of the front and back surfaces and the inner layer is limited, and high-density wiring is difficult, and the design is also limited.

The present invention has been made to solve the above-mentioned problems, and is excellent in heat resistance and dimensional stability, thinner, more flexible, and capable of relieving physical stress. An object of the present invention is to provide a method for manufacturing a flexible printed wiring board.

[0007]

According to the present invention, after a circuit pattern is formed on a copper foil on a copper clad substrate having a polyimide resin as a base material, a polyimide precursor is applied to the entire surface of the circuit pattern-formed substrate. After forming the polyimide layer by curing treatment, after the surface treatment of the polyimide layer by oxygen plasma, after forming a conductive layer made of copper by electroless plating and electroplating on the surface-treated polyimide layer, the circuit pattern on the conductive layer Along with forming a polyimide layer by etching to form an opening to be a conduction hole with another layer, a method of forming a conductive portion in the opening by electroless plating and electrolytic copper plating, after the application of the polyimide precursor It is a method of manufacturing a flexible wiring board, which is repeated a number of times corresponding to the layers of the multilayer wiring board which requires steps.

That is, the present invention uses a double-sided copper-clad substrate having a polyimide resin as a base material, and (a) a step of providing a predetermined opening on the copper foil surface of the double-sided copper-clad substrate, and (b) the opening. After the step of selectively removing only the more exposed polyimide resin portion, and (c) activation for the purpose of conducting electricity between the front and back copper foils at the portion where the polyimide resin portion is selectively removed,
A step of performing electroless copper plating and electrolytic copper plating, (e)
The circuit-formed surface of the double-sided copper-clad substrate on which the predetermined circuit has been formed is coated with a solvent-containing polyimide-based paste, and the double-sided copper-clad substrate coated with the polyimide-based paste is heat-treated to accelerate the curing of the polyimide-based paste. Process and (f)
A step of subjecting the surface of the polyimide insulating film formed by thermosetting a polyimide paste to an oxygen plasma treatment, and (g) activating the surface-treated polyimide insulating film, followed by electroless plating and A step of forming a metal foil by electrolytic copper plating; (h) a step of providing an opening in a predetermined portion of the metal copper foil; and (i) selectively removing the polyimide insulating film exposed from the opening. And (j) electroless copper plating and electrolysis after activation treatment for the purpose of conducting the first predetermined circuit portion and the metal copper foil through the opening where the polyimide is selectively removed. The present invention achieves the above-described object by enabling a copper plating process and (k) a step of forming a second predetermined circuit on the metal copper foil surface formed by the copper plating, thereby forming a multilayer structure.

[0009]

According to the manufacturing method of the present invention, it is possible to provide a highly reliable multilayer FPC which has excellent heat resistance and dimensional stability, is thinner, is more flexible, has less physical stress, and enables high-density wiring. ..

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a manufacturing process of a three-layer flexible printed wiring board which is a multilayer flexible printed wiring board in the present invention.

As shown in FIG. 1 (a), one copper foil of a copper laminated substrate 3 in which a copper foil 1 is laminated on both sides of a polyimide base film 2, a copper foil to be an inner layer of an electric circuit and a copper layer on the surface layer. Holes 4 are etched into the copper foil for the via holes to provide via holes for electrical continuity with the foil. Figure 1
As shown in (b), using the copper foil as a mask, the base film 2
Then, a hole 5 for a via hole is formed. For the etching liquid,
An alcohol solution containing an alkali metal hydroxide such as potassium hydroxide can be used. As shown in FIG. 1C, in order to electrically connect the inner layer conductor and the back layer conductor,
After activating the surface of the base film with palladium chloride, stannous chloride, etc., electroless plating is performed, and then copper is electroplated on the copper thin film obtained by electroless plating to form via holes. Complete 6. As shown in FIG. 1D, a predetermined circuit pattern 7 is formed on the conductive layer for the inner layer by etching, and as shown in FIG. 1E, the predetermined circuit is formed on the substrate by heating. After applying a coating material such as a polyamic acid or the like such as a polyimide-based coating material from which a polyimide film is obtained, the solvent is heated and removed, and then heating is further performed to perform a curing treatment to form a polyimide layer 8.

As shown in FIG. 1 (f), oxygen plasma 9
The surface of the polyimide layer was treated with to improve the adhesion of copper on the polyimide layer. As shown in FIG. 1 (g), after the surface of the polyimide layer 7 was activated, electroless plating of copper was performed, and a copper foil was formed on the obtained copper thin film by electroplating.

As shown in FIG. 1 (h), the copper foil 1 has
By a method similar to the method shown in (a), the holes 4 corresponding to the via holes between the multiple layers are formed, and as shown in FIG.
Similarly to the method shown in (b), the holes 5 were formed in the polyimide layer 7 using the copper foil having the holes obtained in the step of FIG. 1 (h) as a mask. Further, as shown in FIG.
Similar to the method shown in (c), the via hole 6 which forms the conduction between the multiple layers was formed. Then, as shown in FIG. 1K, the copper foils on both surfaces were etched to form a circuit pattern 10.

Through the above steps, a thin and more flexible multi-layer flexible printed wiring board FPC which has excellent heat resistance and dimensional stability and does not require an adhesive layer, and which is capable of high-density wiring, is provided unlike the method using a prepreg. It can be manufactured.

Further, after the step shown in FIG.
A multilayer wiring board having three or more layers can be manufactured by repeating the same steps as in (d) to FIG. 1 (j). FIG. 2 shows an example of a multilayer wiring board having a total of 6 conductive layers.

A conductive layer 2 is formed on the polyimide film 22.
2a is formed, the polyimide layer 23a is provided on the conductive layer 22a, and the conductive layer 22b, the polyimide layer 23b, and the conductive layer 22 are further provided on the polyimide layer.
c, polyimide layer 23c, conductive layer 22d, polyimide 2
3d is provided.

A circuit pattern 24 is formed on both surfaces of the multilayer substrate, and a via hole 25 is formed for conducting each conductive layer.

Example 1 A polyimide insulating layer having a copper foil of 18 μm thick laminated on both sides of a 35 μm thick copper foil laminated polyimide film (trade name: Espanex double-sided plate manufactured by Nippon Steel Chemical Co., Ltd.) In order to provide a via hole for electrically connecting the conductor circuit to be the conductor layer and the conductor circuit to be the surface layer, a hole having a diameter of 300 μm for the via hole was formed in the copper foil by the photoetching method. The etching is performed by using an aqueous ferric chloride solution having a concentration of 42 ° Be as an etching agent at a temperature of 40 ° C and a spray pressure of 1.0.
It was performed by spray etching of kgf / cm ² .

Then, using the copper foil having the holes as a mask, ethanol of 1N potassium hydroxide and water were mixed at 8: 2.
Using an alcohol solution mixed at a ratio of 1 as the etching agent, the polyimide resin layer in the via hole forming portion was selectively removed by etching at a temperature of 70 ° C. and under irradiation of ultrasonic waves.

Next, a conductive layer was formed inside the via hole. First, palladium chloride (PdCl ₂ ): 0.2 g /
1, stannous chloride (SnCl ₂ · 2H ₂ O): 20 g /
1, hydrochloric acid (HCl, 35%): 200 ml / l of pure water to make 1000 ml, and immersed in an activating liquid at a liquid temperature of 40 ° C. for a dipping time of 2 minutes to activate the surface of the polyimide resin and sulfuric acid. Copper (CuSO ₄ .5H ₂ O): 5 g / l,
Rochelle salt (KNaC ₄ H ₄ O ₆ ): 25 g / l, formalin (HCHO): 10 ml / l, sodium hydroxide (NaOH): 7 g / l Electroless plating was performed at a temperature of 20 ° C. Subsequently, copper sulfate (CuSO ₄ .5H ₂ O): 24
0 g / l, sulfuric acid (H ₂ SO ₄ , specific gravity 1.83): 50 g
/ L, cathode current density: 3 A / dm ² , cathode: anode = 1:
Copper was electroplated under the conditions of 1, anode: electrolytic copper, bath voltage: 3 V, and liquid temperature: 30 ° C.

Then, using a ferric chloride aqueous solution of 42 ° Be as an etching solution, the temperature is 40 ° C. and the spray pressure is 1.0 k.
After a predetermined circuit was formed on the copper foil as the inner layer by spray etching of g / cm ² , a polyimide precursor (trade name, manufactured by Nippon Steel Chemical Co., Ltd., polyimide paste SPI-200N) was provided on the side where the conductor of the inner layer was formed. Was applied to a uniform thickness of 24 μm by a screen printing method using a 150 mesh plate to form an insulating layer. After that, NMP (N-methyl-2-pyrrolidone) which is a solvent component is evaporated by heating at 130 ° C for 10 minutes in a conveyor type far infrared furnace, and the polyimide paste is completely cured by heating at 270 ° C for 2 minutes. To form a polyimide layer. The surface of the obtained polyimide layer was surface-treated with oxygen plasma. The treatment with oxygen plasma was carried out using MATRIX-102 manufactured by Drytech Co., Ltd. under the conditions of an oxygen gas pressure of 1.2 Torr, an oxygen gas flow rate of 150 ml / min, and a treatment time of 120 seconds.

Next, the surface of the polyimide layer is activated by the same method as the method of forming copper for obtaining conductivity on the surface of the via hole, and then electroless copper plating and electrolytic copper plating are performed. Copper foil was laminated on the polyimide layer. By simultaneously etching the front and back copper foils in a predetermined pattern, a multilayer wiring board having three conductor layers was obtained. The obtained multilayer wiring board did not use an adhesive, was excellent in heat resistance and dimensional stability, and was thin and flexible.

[0023]

As described above, according to the method for producing a multi-layer FPC of the present invention, it is possible to produce a non-adhesive type multi-layer FPC, so that the heat resistance is excellent. In addition, the thickness of the polyimide insulation layer and the conductor layer can be changed arbitrarily, making it thinner.
A more flexible flexible printed wiring board can be provided. Furthermore, since front and back conduction is possible without forming any through holes by the drilling method, accuracy can be improved by the photolithography method, and batch formation is possible regardless of the number of via holes.
It is possible to easily provide a higher density multilayer flexible printed wiring board.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an embodiment of a method for manufacturing a multilayer flexible wiring board according to the present invention.

FIG. 2 is a diagram illustrating an example of a multilayer flexible wiring board having six conductive layers manufactured by the method of the present invention.

FIG. 3 is a diagram illustrating a conventional method for manufacturing a multi-layer FPC.

[Explanation of symbols]

1 ... Copper foil, 2 ... Base film, 3 ... Copper laminated substrate, 4 ... Hole (copper foil), 5 ... Hole (base film), 6 ... Via hole, 7
... Circuit pattern, 8 ... Polyimide layer, 9 ... Oxygen plasma, 10 ... Circuit pattern, 21 ... Polyimide film,
22a, 22b, 22c, 22d ... Conductive layers, 23a, 2
3b, 23c, 23d ... Polyimide layer, 24 ... Circuit pattern, 25 ... Via hole, 31 ... Copper foil, 32 ... Base material, 33
... Circuit pattern, 34 ... Conductive hole, 35 ... Single-sided copper clad board
36 ... Insulating layer, 37 ... Prepreg, 38 ... Heat press, 39 ... Through hole

Claims (1)

[Claims] 1. A circuit pattern is formed on a copper foil on a copper-clad substrate using a polyimide resin as a base material, and a polyimide precursor is applied to the entire surface of the circuit pattern-formed substrate and then cured to form a polyimide layer. After that, the surface treatment of the polyimide layer by oxygen plasma, after forming a conductive layer made of copper by electroless plating and electroplating on the surface-treated polyimide layer, together with forming a circuit pattern in the conductive layer, the polyimide layer A method of forming an opening that becomes a conduction hole with another layer by etching, and forming a conduction portion in the opening by electroless plating and electrolytic copper plating, which corresponds to a layer that requires a step after the application of the polyimide precursor. A method for manufacturing a multilayer flexible wiring board, characterized in that the number of times of repeating is repeated.