JP3089264B2 - Processing method of flexible printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for processing an inexpensive back-bearing flexible printed wiring board by simplifying the processing steps and increasing the yield.

[0002]

2. Description of the Related Art Electronic devices equipped with a liquid crystal display panel such as a personal computer and a video camera are increasingly required to be reduced in size and weight. Backbeard flexible printed wiring boards (hereinafter referred to as BBFPCs) are lightweight, bend freely, and can be connected from both sides. Recently, the demand for flexible printed wiring boards, which are indispensable for connection between a display panel such as a liquid crystal panel, a driver thereof, and a board such as a controller, is rapidly increasing. In addition, this market demands that the circuit width be 100
A major feature is that it is a fine wire circuit of μm or less.

[0003] However, the conventional processing method has a disadvantage that the processing steps are longer and more complicated than ordinary FPC, resulting in low productivity and low yield, resulting in an increase in cost.

Conventionally, a BBFPC processing method is to first make a round or square hole with a mold or the like in a portion of a base insulating film where a circuit is to be exposed, and then bond the insulating film with a copper foil. I do. Next, an etching resist is buried in the hole by screen printing or the like, and etching is performed by a normal method, and the etching resist is removed to form a circuit board. Further, a cover lay film for circuit protection is bonded and subjected to surface treatment such as plating to obtain BBFPC.

[0005] In such a conventional method, a conventional FP is used, such as die-cutting of an insulating film, exposure to light aligned with a hole, embedding of an etching resist, and removal of a resist.
The processing step is longer and more complicated than that of C, and a decrease in productivity is inevitable. Also, since the copper foil at the boundary of the hole made in the insulating film becomes uneven, the followability of the photosensitive dry film resist is poor and the etching circuit is locally thinned, or in extreme cases it is disconnected. Yield decreases. In particular, this phenomenon is remarkable in the case of a fine line circuit having a circuit width of 100 μm or less. Such low productivity and yield have caused an increase in cost.

[0006] Recently, a method of exposing the circuit by forming a circuit and then removing the insulating film by laser irradiation after laser irradiation has been attempted. However, the removal of carbon residue generated after laser irradiation has not been solved. In addition, the equipment is expensive and the running cost is high, so it has not been adopted.

[0007]

SUMMARY OF THE INVENTION The present invention has been made as a result of various studies to solve the problems such as low productivity and low product yield as described above. After fabrication, a support sheet is attached to the circuit surface, the insulating film is scraped off from the back side of the circuit, and the circuit back is exposed, simplifying the process and increasing productivity, and also improving the product yield and reducing the cost of BBFPC.
It is intended to provide.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a BBFPC circuit exposing process in which a part of a terminal circuit of an FPC is exposed on an opposite circuit surface. A method of processing an FPC, which comprises exposing the back surface of a circuit by counterbore processing from a support sheet, wherein the support sheet is an organic sheet having a softening point of 80 ° C or higher. It is.

The BBFPC is lightweight and freely bendable, and has a structure having terminals on both sides as shown in FIG. 1, so that it is suitable for connection between a glass electrode of a liquid crystal display panel and an IC substrate for driving and controlling the liquid crystal. However, the cost is high, and the expansion of applications has been limited.

According to the present invention, after a circuit is formed by a usual method, a support sheet is stuck on a circuit surface, vacuum-adsorbed firmly to a bed of a counterbore machine, and an insulating film is rounded or squared from the back side of the circuit with an end mill. Sitting on the shape of
This is a BBFPC processing method for exposing the back surface of the circuit.

When processing is performed without attaching the support sheet, the vacuum suction cannot be performed firmly due to the unevenness of the circuit surface, resulting in a displacement during the operation of the end mill. Further, the support of the terminal circuit becomes extremely small near the end point of the spot facing, and the circuit is deformed or cut.

The support sheet may be any organic sheet having a softening point of 80 ° C. or higher, but preferably has a proper adhesion to the copper circuit surface and a uniform thickness. For example, a sheet of vinyl chloride, polypropylene, polyester, or the like coated with an adhesive, a heat-sensitive adhesive film, a photosensitive dry film, a coverlay film used for circuit protection by FPC, and the like. Softening point of support sheet is 80 ℃
In the following, the sheet or the adhesive melts due to the frictional heat of the end mill, contaminates the exposed circuit, hinders metal plating, and impairs the reliability of electrical connection such as solder connection.

As for the procedure for attaching a support sheet and counterboring, a coverlay film is attached, and a procedure for attaching a coverlay film as a support sheet after circuit creation and performing a spot facing process is performed. For those that do not require the above, any procedure may be used, in which the support sheet is attached after the circuit is created, the counterbore processing is performed, and the support sheet is peeled off.

[0014] Further, a positioning device,
It has a sensor for determining the bottom dead center of the end mill, a vacuum groove for vacuum-adhering and fixing the product, and it may be processed one sheet at a time. And a winding device. The end mill is a single blade and the blade shape is preferably a half moon type.

[0015]

FIG. 1 is a conceptual sectional view of a BBFPC.
The mark is a portion where the circuit is exposed by spot facing. FIG. 2 shows an example of the processing steps of the present invention, and (1), (2),
(3) As a case using a coverlay film as a support sheet, as shown in FIG. 1 (1), first, a circuit having a width of 100 μm is etched by etching a copper-clad board in which an insulating film of a polyimide resin and a copper foil having a thickness of 35 μm are bonded. Was formed. As a support sheet, a polyester adhesive is applied to a polyester resin film having a thickness of 50 μm to 15 to 20 μm.
It was adjusted to a thickness of m and bonded to the circuit using a rubber roll heated to 120 ° C.

Then, as shown in FIG. 2 (2), the support sheet surface is fixed to the bed of the spot facing machine by vacuum suction, and the end mill has a diameter of 2 mm, a rotation speed of 8000 RPM, and a moving speed of 480 mm / min. The insulating film was cut out and the spot facing was performed until the back surface was exposed. To determine the bottom dead center of the end mill, a test terminal was previously provided in the circuit, a voltage was applied between the terminal and the end mill, the point at which the end mill contacted the test terminal was measured several times, and the zero point of the Z-axis coordinate was set. The appearance of the spotted copper foil surface was good and there was no problem in practical use. Also, the yield was able to be increased by about 10% as compared with the conventional method. Finally, solder plating was performed to obtain BBFPC.

On the other hand, FIGS. 2 (1), (4), (5),
(6) shows a case in which a coverlay film is not required. As shown in FIG. 4D, a photosensitive dry film (AQ4066 manufactured by Asahi Kasei Corporation) is attached to a circuit board, and cured by exposing to 70 mJ for 40 seconds. After that, after counterbore processing in the same manner as above, 5% as shown in FIG.
The support sheet was peeled off with a caustic soda solution to obtain BBFPC of the same quality as described above.

[0018]

According to the BBFPC processing method of the present invention, the conventional processing steps are simplified to increase the productivity, and a high yield can be achieved even in a fine line circuit having a circuit width of 100 μm or less, which is required in the display panel market for liquid crystal and the like. Inexpensive BBFPC
Can be provided.

[Brief description of the drawings]

FIG. 1 is a conceptual cross-sectional configuration diagram of a BBFPC.

FIG. 2 is a processing step diagram of the present invention, wherein (1), (2) and (3).
Is (1) if the support sheet is coverlay film
(4), (5) and (6) are the cases of photosensitive dry films.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating film 2 Circuit wiring 3 Cover lay film adhesive 4 Cover lay film 5 Photosensitive dry film

Claims (1)

(57) [Claims] 1. A method for processing a back-bearing flexible printed wiring board in which a part of a terminal circuit of the flexible printed wiring board is exposed on the opposite side of the circuit, wherein a support made of an organic sheet having a softening point of 80.degree. A method for processing a flexible printed wiring board, comprising: after affixing a sheet, performing counterbore processing from an insulating film side to expose a circuit.