JPH11346039A - Flexible printed wiring board and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accuracy in terms of the design of a high-density circuit, by laminating photosensitive dry film resist onto the copper foil of both the surfaces of an insulation base, by exposing and developing a circuit pad part only, by masking the other parts, and by providing a continuity connection part where electric copper plating is deposited at the circuit pad part or the like for forming a conductor circuit. SOLUTION: In a method for manufacturing a flexible printed circuit board, a continuity hole 3 for connecting a front to a back is provided at a circuit part 10 of a copper-clad plate where copper foil 1 is laminated onto both the surfaces of an insulation base 2, photosensitive dry film resist is laminated onto the copper foil 1 of both the surfaces of the insulation base 2, only the circuit pad part 10 is exposed and developed, and the other parts are subjected to masking 7. Then, electric copper plating 6 is deposited at the circuit pad part 10 and the continuity hole 3 for providing a continuity connection part 9, the front and back are connected for continuity, and a specific conductive circuit 8 is formed. A conductor such as chemical copper plating, palladium, and carbon is allowed to adhere to the insulation base as pretreatment for depositing the electric copper plating 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible circuit board for controlling characteristic impedance, which can process a high-density circuit design with high precision and control characteristic impedance, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, a conductive connection between a front side and a back side of a flexible printed wiring board for impedance control is performed by (A) a copper-clad laminate obtained by laminating a copper foil coated with an adhesive on both sides of an insulating base material 2. (B) After conducting drilling in a predetermined position with a predetermined hole diameter by an NC drill to form a conductive hole 3 on the plate, and (C) performing a chemical copper plating process on the entire copper foil surface on both surfaces of the copper clad plate. Then, an electrolytic copper plating process is performed, and an electrolytic copper plating 6 is deposited on an inner wall of a portion drilled by an NC drill, thereby ensuring front and rear conductive connection. Next, (D) a photosensitive dry film resist is laminated on both sides of the copper-clad plate subjected to the electro-copper plating treatment, and the portions other than the portions to be circuits are exposed and developed. Of the conductive circuit 8 and the conductive connection portion 9.

[0003] However, in this processing method, chemical copper plating and electrolytic copper plating are applied to the entire surface of the double-sided circuit copper foil. It is necessary to remove the treated chemical copper plating and electrolytic copper plating. However, there is a limit to the width of conductor circuits and the spacing between conductor circuits that enable circuit formation from the viewpoint of etching accuracy, and furthermore, variations in the finished width after conductor circuits are formed due to the effects of variations in the thickness of electrolytic copper plating. Since it greatly changes, there are problems such as a decrease in the yield during the pattern design and the manufacturing process, and the conductor circuit width and thickness that are important in controlling the characteristic impedance vary as described above. There was a problem. In addition to the restriction of processing accuracy of the conductor circuit, since the copper foil surface bonded to the front and back of the insulating base material is subjected to electroplating for front and back conductive connection from the viewpoint of the structure, it has excellent bending characteristics as copper foil Even when a rolled copper foil is used, the bending characteristics are degraded due to an increase in the thickness of the conductor, and the bending characteristics of the rolled copper foil cannot be effectively utilized.

[0004] These restrictions pose a problem in the design and characteristics of products that require control of characteristic impedance. When carrying out, sandwich a shielding plate made by cutting out a glass base epoxy resin laminated board etc. in a predetermined shape with clips etc. on the front and back of the copper clad board, and deposit copper electroplating only on the parts where front and back conductive connection of the circuit is required There is a shield plating method to prevent deposition on the part where conductor circuit width accuracy is required, but it is necessary to prepare a shield plate for each product shape, and to attach and remove the shield plate in the electrolytic copper plating process There is a problem in that the number of man-hours for operations and the like, and the yield decreases due to an increase in the number of product handling steps and the like due to crevices, wrinkles, etc., lead to complicated processing steps and cost increase factors. In addition, since the shielding plate is sandwiched and processed by the copper clad plate, the position of the copper clad plate with respect to the predetermined position is misaligned, and during electroplating, the liquid spills from the mating surface of the copper clad plate and the shielding plate, so that the designed plating deposition part 10-15mm from the border
Therefore, it is necessary to design the circuit so as not to affect the characteristic impedance in consideration of variations in the width and thickness of the conductor circuit in this portion.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems and structural problems that occur when forming a conductive circuit in a characteristic impedance control flexible printed wiring board. The object of the present invention is to provide a flexible printed wiring board which does not require complicated processing steps, enables high-density circuit design with high accuracy, and improves control accuracy of characteristic impedance of a product, and a method of manufacturing the same.

[0006]

According to the present invention, there is provided a flexible printed wiring board having conductive circuits formed on both surfaces of an insulating base material, wherein only the surface of the circuit pad portion for front / back connection and the conductive connection portion of the printed wiring board are electrically connected. This is a flexible printed wiring board for characteristic impedance control characterized by being copper-plated, and a conduction hole for front and back connection is made in the circuit pad part of the copper clad board with copper foil laminated on both sides of the insulating base material. After that, a photosensitive dry film resist is laminated on the copper foil on both sides of the insulating substrate, only the circuit pads are exposed and developed, and the other parts are masked, and electrolytic copper plating is deposited on the circuit pads and the conductive holes To provide a conductive connection,
A method for manufacturing a flexible printed wiring board for controlling characteristic impedance, comprising forming a predetermined conductor circuit after conducting a front-to-back connection.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. The material of the flexible printed wiring board for characteristic impedance control in which conductive circuits are formed on both sides of the insulating base material used in the present invention is a copper foil such as a rolled copper foil on both sides of an insulating base material such as a polyester resin film or a polyimide resin film. Are integrally molded by heating and pressing. Also, for photosensitive dry film resist (hereinafter referred to as DFR) laminated on copper foil on both sides of insulating base material,
There is no particular limitation as long as it is the same as the acrylic resin film conventionally used in this field. This DFR has also conventionally been used in this field.

Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. FIG. 1 (A)
1 to (F) are schematic cross-sectional views of a flexible printed wiring board for characteristic impedance control having conductor circuits on both surfaces. FIG. 1 (A): This is a copper clad board material obtained by laminating a rolled copper foil 1 on an insulating base material 2 and integrally molding the front and back sides. FIG. 1 (B): The copper-clad plate is formed with a conduction hole 3 for conducting a predetermined front and back surface by an NC drill. 1 (A) and 1
The step (B) is the same as the conventional flexible printed wiring board manufacturing step and is not particularly limited. FIG. 1 (C): DFR is laminated on both sides of the copper-clad plate having the conduction holes obtained in FIG.
And a mask 4 intended to cover the other surface. FIG. 1 (D): A conductive connection portion 9 and a circuit pad portion 10 for depositing an electrolytic copper plating 6 at a predetermined location and electrically connecting the front and back sides are provided. FIG. 1E: After peeling off the mask (residual DFR) 4, laminating a DFR for forming a conductor circuit, forming a predetermined image, exposing and developing portions other than the circuit and the circuit pad portion, and developing the circuit and the circuit pad portion. Is turned into a mask 7. FIG. 1 (F): After performing the etching operation, the mask 7 is peeled off, and a predetermined conductor circuit 8 is formed.

DFR is laminated on both surfaces of the copper-clad plate thus drilled, and an opening is formed by performing a developing operation after exposure except for a portion where a front-to-back conductive connection is made. In the electrolytic copper plating method for making the front and back conductive connection of the copper foil, a pretreatment for depositing the electrolytic copper plating on the insulating base material of the perforated inner wall is required. The pretreatment is performed by attaching a conductor such as chemical copper plating, palladium, carbon, and graphite to the insulating base material. After that, in order to deposit electrolytic copper plating only on the predetermined circuit pad portion for front and back connection, DFR
After masking the portions other than the corresponding portions by using the method described above, 5 to 15 μm of electrolytic copper plating may be deposited to ensure a conductive connection only to the front and back connection circuit pad portions. In the method of partially depositing electrolytic copper plating using a conventional shielding plate, the minimum plating area is about 100 to 150 mm ² due to restrictions such as processing accuracy of the shielding plate and alignment at the time of electrolytic copper plating. Position accuracy with the hole is about ± 10-15mm,
There are also restrictions such as a rectangular or circular shape.

In the present invention, since the electrolytic copper plating is selectively deposited using the DFR as a mask, it has an irregular shape with a minimum plating area of 0.3 to 1.0 mm ² and a positional accuracy of ± 0.05 to Processing of 0.20 mm becomes possible. As a result, it becomes possible to selectively deposit electrolytic copper plating for conductive connection only on the front and back connection circuit pad portions. As a result, there is no deposition of electrolytic copper plating in the conductor circuit portions other than the front and back conductive connection circuit pad portions, and the thickness can be etched without being affected by the above-described plating, so that the circuit width is 0.03 to 0.10 mm. , A high-density conductor circuit can be formed with high yield and high precision, and the characteristic impedance of the conductor circuit portion can be easily controlled.

[0011]

In the flexible printed wiring board according to the present invention in which conductive circuits are formed on both sides of the insulating base material, only the surface of the circuit pad portion for front and back connection and the conductive connection portion of the printed wiring board are electroplated with copper. In addition, it is possible to stably obtain a conductive circuit requiring characteristic impedance control at a high density.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a flexible printed wiring board for controlling characteristic impedance according to the present invention.

FIG. 2 is a schematic cross-sectional view of a conventional flexible printed wiring board for controlling characteristic impedance.

Claims (2)

[Claims] 1. A flexible printed wiring board in which conductive circuits are formed on both sides of an insulating base material, wherein only the surface of the front and back connection circuit pads and the conductive connection portion of the printed wiring board are plated with copper. Flexible printed wiring board for controlling characteristic impedance. 2. A conductive dry film resist is formed on the copper foil on both sides of the insulating base material after forming conductive holes for front and back connection in the circuit pad portion of the copper clad board in which copper foil is laminated on both surfaces of the insulating base material. After laminating, only the circuit pad portion is exposed and developed, the other portions are masked, electrolytic copper plating is deposited on the circuit pad portion and the conductive hole, a conductive connection portion is provided, and the front and back conductive connection is made, and then a predetermined A method for producing a flexible printed wiring board for controlling characteristic impedance, comprising forming a conductor circuit.