KR101332416B1 - Method for machining flexible printed circuitboard - Google Patents

Abstract

The present invention discloses a flexible circuit board processing method capable of preventing the lifting of the epoxy resin layer and the unevenness of the cut surface and the damage of the members constituting the flexible circuit board when cutting a thin flexible circuit board. do. A flexible circuit board processing method according to the present invention comprises the steps of: forming an epoxy resin layer on a second surface opposite to the first surface of the circuit board on which the conductive pattern is formed; Forming a protective film layer on the first surface of the circuit board; Curing the protective film layer; Cutting the circuit board to a set standard; And removing the protective film layer. The protective film layer formed on the first surface of the circuit board is made of a mixed material of a binder polymer and a monomer, preferably the binder polymer is a thermoplastic polymer, and the monomer is an acrylic monomer which is a photosensitive monomer. Meanwhile, the protective film layer may further include an adhesion enhancer and / or a plasticizer for imparting adhesion between the protective film layer and the first surface of the circuit board. In addition, the protective film layer curing step is performed by ultraviolet irradiation, In addition, the circuit board cutting step is performed by a routing process or a press process.

Description

Method for machining flexible printed circuit board

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for processing a flexible circuit board, and more particularly, to a method for processing a flexible circuit board capable of suppressing whitening (burr) occurring at a processing edge portion of a flexible circuit board during a cutting process.

An electronic device such as a computer or a mobile phone is mounted with a flexible printed circuit board (FPCB) on which a conductive pattern is formed on a surface thereof and on which electronic elements are mounted.

With the miniaturization and slimming of electronic devices such as mobile phones, the flexible circuit boards mounted in the electronic devices are also decreasing in area and thickness. However, the thin flexible circuit board having such a small thickness has a weakness of weak strength.

In order to reinforce the strength of such a thin flexible circuit board, a manufacturer uses a method of forming an epoxy resin layer on a second surface opposite to the first surface after forming a conductive pattern on the first surface of the flexible circuit board. .

Epoxy resins have strong physical properties against conditions such as temperature changes, and therefore, have optimum conditions as reinforcement elements of flexible circuit boards that are affected by heat generated from mounted electronic devices and peripheral devices.

Generally, after forming an epoxy resin layer on the 2nd surface of the flexible circuit board of a predetermined area, a hardening process is advanced. After the epoxy resin layer is cured, the flexible circuit board is processed into a flexible circuit board having a predetermined standard that meets the requirements of the electronic device manufacturer.

Generally, the cutting of the flexible circuit board proceeds through a press process or a router processing process.

In the process using the press equipment, while the flexible circuit board having the epoxy resin layer formed on the second surface is placed on the lower die of the press equipment, the upper die corresponding to the outer portion of the lower die is moved downward on the lower die. Located flexible circuit boards are instantaneously cut.

1 is a photograph of a flexible circuit board processed to a predetermined standard through the above press process, and shows an epoxy resin layer formed on a second surface.

As shown in FIG. 1, a photograph of a flexible circuit board processed through a pressing process is a photograph of a whitening phenomenon at an edge portion of a flexible circuit board, that is, an edge portion of an epoxy resin layer formed on a second surface of the flexible circuit board. burr) is generated.

In the process of temporarily processing (cutting) the flexible circuit board seated on the lower die by the downwardly moving upper die, the epoxy resin layer formed on the second surface of the flexible circuit board is impacted by the upper die. By this, the epoxy resin layer is partially separated from the second surface of the flexible circuit board (that is, the portion to which the impact force is applied).

In particular, when the epoxy resin layer and the flexible circuit board are cut by the upper die, the epoxy resin layer in a state separated from the second surface of the flexible circuit board is not cut in a straight line and has an irregular shape as shown in FIG. 1. And is cut.

This partial lifting and irregular cutting state of the epoxy resin is called "burr", and the flexible circuit board on which such whitening has occurred is regarded as defective and must be discarded or manually removed. Therefore, this whitening phenomenon acts as an uneconomical waste of excessive material consumption and unnecessary labor input.

In order to supplement the problems of the press process, a method of processing (cutting) a flexible circuit board through a router process is being implemented.

Unlike the press process using the upper mold and the lower mold, the router process is a path set for the flexible circuit board fixed on the router base (conductive pattern is formed on the first surface and the epoxy resin layer is formed on the second surface). It is a process of cutting to a predetermined size using a cutting tool (bit: bit) that moves along and rotates at high speed.

FIG. 2 is a photograph of a flexible circuit board processed through a router process. FIG. 2A illustrates a second surface on which an epoxy resin layer is formed, and FIG. 2B illustrates a first surface on which a conductive pattern is formed.

In a flexible circuit board processed by a cutting tool moving along a predetermined path, the edge portion of the second surface on which the epoxy resin layer is formed is hardly lifted by the epoxy resin layer and the processing line (cutting line) is relatively straight. (State of Fig. 2a).

However, on the first surface on which the conductive pattern is formed, a composite film in which a base film and a coverlay (polyimide film) of a flexible circuit board are coated with a heat curable flame-retardant epoxy adhesive, which is used to protect and insulate the exposed surface of the circuit. The member attached thereto is torn by the moving cutting tool.

Therefore, as illustrated in FIG. 2B, damage portions at which the base film and the coverlay are torn are generated at the edge portion of the first surface of the flexible circuit board processed through the router process. As such, the flexible circuit board having the damaged area is regarded as defective and discarded, thereby causing a problem of waste of material and deterioration of process efficiency.

The present invention is to solve the above problems in the process of cutting a thin flexible circuit board (with an epoxy resin layer formed on one surface) through a press process or a router process, the number of epoxy in the cut line region SUMMARY OF THE INVENTION An object of the present invention is to provide a method for processing a flexible circuit board which can prevent the lifting of the ground layer, the unevenness of the cut surface, and the damage of the members constituting the flexible circuit board.

Flexible circuit board processing method according to the present invention for achieving the above object comprises the steps of forming an epoxy resin layer on the second surface of the first surface of the circuit board on which the conductive pattern is formed; Forming a protective film layer on the first surface of the circuit board; Curing the protective film layer; Cutting the circuit board to a set standard; And removing the protective film layer.

The protective film layer formed on the first surface of the circuit board is made of a mixed material of a binder polymer and a monomer, preferably the binder polymer is a thermoplastic polymer, and the monomer is an acrylic monomer which is a photosensitive monomer.

On the other hand, the protective film layer may further include an adhesion enhancer and / or a plasticizer for imparting adhesion between the protective film layer and the first surface of the circuit board.

At the same time, the protective film layer curing step is performed by ultraviolet irradiation, and the circuit board cutting step is performed by a routing process or a pressing process.

According to the present invention having the above characteristics, even in the process of cutting a thin flexible circuit board through a press process, the epoxy resin layer does not lift in the cutting line region and a uniform cut surface can be obtained.

In addition, even after the router process, damage such as tearing of the base film and the overlay, which are the constituent members of the flexible circuit board, can be prevented, thereby obtaining a complete flexible circuit board.

1 is a photograph of a flexible circuit board processed to a predetermined standard through a pressing process.
2 is a photograph of a flexible circuit board processed through a router process, FIG. 2A illustrates a second surface on which an epoxy resin layer is formed, and FIG. 2B illustrates a first surface on which a conductive pattern is formed.
FIG. 3 is a corresponding photograph of FIG. 2B, showing a first surface on which a conductive pattern is formed of a flexible circuit board processed through the method according to the present invention. FIG.

Hereinafter, the flexible circuit board processing method according to the present invention will be described in detail.

A flexible circuit board processing method according to the present invention includes the steps of: forming a conductive pattern on a first surface of a circuit board, and forming an epoxy resin layer on a second surface opposite to the first surface of the circuit board; Forming a protective film layer on the first surface of the circuit board; Curing the protective film layer; And cutting the flexible circuit board to a set standard. And removing the protective film layer.

Each step will be described in detail as follows.

A conductive pattern is formed on the first surface of the circuit board (hereinafter, referred to as "substrate") using a conductive material to electrically connect the electronic device to be mounted. The process of forming the conductive pattern is generally carried out through a known method, and thus, a detailed description thereof will be omitted below.

An epoxy resin layer having a predetermined thickness is formed on the second surface, which is the surface opposite to the first surface of the substrate. Epoxy resins have physical properties that do not deform under conditions such as temperature changes, and thus the epoxy resin layer functions as a reinforcing member for thin circuit boards that are affected by heat generated in mounted electronic devices and peripheral devices.

After forming an epoxy resin layer on the 2nd surface of a board | substrate, a hardening process is advanced. The curing process for the epoxy layer can be carried out in various ways known to those skilled in the art.

After the hardening process with respect to an epoxy layer, a protective film layer is formed in the 1st surface of a board | substrate. Together with the epoxy resin layer formed on the second surface of the substrate, the protective film layer formed on the first surface performs the function of the reinforcing member for improving the strength of the substrate.

In particular, the protective film layer protects the conductive pattern formed on the first surface of the substrate and at the same time serves to prevent damage to the structural members of the substrate, that is, the base film and the coverlay, during the subsequent cutting of the substrate. Perform.

Thereafter, a process of curing the protective film layer formed on the first surface of the substrate and a process of cutting to a predetermined size of the substrate proceed.

Finally, a process of separating and removing the protective film layer present on the first surface of the processed substrate is performed.

Hereinafter, the protective film layer forming step, the protective film layer curing step, the substrate cutting step, and the protective film layer removing step, which are considered as the most characteristic steps of the present invention, will be described in detail.

The protective film layer formed on the first surface of the substrate (with the conductive pattern formed) can be easily separated and removed from the substrate, the mechanical strength after curing, the firm adhesion to the substrate surface to protect the substrate during the cutting process, and the like. It is desirable to have physical properties that are present.

In order to have such a characteristic, in this invention, the material which mixed the binder polymer, the monomer, the initiator, and the adhesion promoter can be used as a material of a protective film layer.

It is preferred that the thermoplastic polymer be used as the binder polymer. Thermoplastic polymers contain carboxyl groups (-COOH), which impart moldability and mechanical strength to the film.

As a monomer, the acryl-type monomer which is a photosensitive monomer is preferable, This acryl-type monomer gives the mechanical strength of a film, and affects the performance of a resist.

An initiator, in particular a polymerization initiator, generates radicals by exposure energy.

On the other hand, the adhesion promoter included in the material of the protective film layer is a material that imparts adhesion between the protective film layer and the first surface of the substrate.

A mixture of the above materials is coated on the first surface of the substrate to form a protective film layer of a predetermined thickness.

That is, after applying a mixture of the above materials to a predetermined thickness on the first surface of the substrate, the substrate is passed between the rotating upper and lower rolls while maintaining a predetermined temperature. That is, the substrate is passed between the upper roll and the lower roll rotating in opposite directions at conditions of a temperature of 105 to 115 ° C. and a speed of 1.0 meter / minute. At this time, the pressure applied to the substrate by the upper roll and the lower roll is preferably 6 kgf.

Under such conditions, a protective film layer of uniform thickness is firmly formed on the first surface of the plate by pressure and temperature.

After forming a protective film layer on the 1st surface of a board | substrate as mentioned above, hardening, Preferably, a protective film layer is hardened using an ultraviolet-ray.

When ultraviolet rays are irradiated to the protective film layer formed on the first surface of the substrate, the thermoplastic polymer and the acrylic monomer cause an ultraviolet curing reaction, whereby the protective film layer is cured.

Meanwhile, a plasticizer may be included in the material for forming the protective film layer. The plasticizer is used as a criterion for visually judging the degree of exposure used in the curing step by discoloring with exposure. The plastic material is discolored by the amount of ultraviolet rays irradiated during the curing of the thermoplastic polymer and the acrylic monomer, so that the process manager can recognize the optimal curing state according to the degree of discoloration of the plastic material.

The cured protective film layer is attached on the first surface, in particular by the adhesion promoter, the protective film layer remains firmly attached on the first surface.

After the protective film layer is cured, the routing process for the circuit board is performed.

In a router process, a cutting bit moves along a set path with respect to a circuit board fixed on a router base (with an epoxy resin layer formed on the second surface and a conductive pattern and a protective film layer formed on the first surface). Then, the circuit board is cut to a predetermined size by rotating at a high speed.

Since the protective film layer is firmly adhered to the overlay on the base film constituting the circuit board, when the base film and the overlay are cut by the cutting tool, the cut portion of the base film and the overlay is supported by the protective film layer. Therefore, the cutting and tearing of the base film and the overlay by the cutting tool that rotates and moves at high speed does not occur.

Meanwhile, the cutting step of the circuit board may be performed through a pressing process.

The protective film layer is separated and removed from the flexible circuit board cut to the predetermined size, that is, the first surface. Separation and removal of the protective film layer is performed through various processes, for example, a stripping process using an aqueous solution of soda, deionized water, plasma gas, an organic solvent, and the like.

For example, the protective film layer formed on the 1st surface of a board | substrate is peeled and removed by spraying a 3% caustic soda (NaOH) aqueous solution of 50 degreeC temperature on the 1st surface of a board | substrate.

3 is a corresponding photograph of FIG. 2B, showing a first surface on which a conductive pattern is formed of a flexible circuit board processed through the method according to the present invention.

Compared to FIG. 2B, the edges of the first surface of the flexible circuit board processed according to the present invention had no damage such as tearing of the base film and the overlay, which are the constituent members of the flexible circuit board, and thus the flexible circuit board Has a uniform shape edge.

The embodiments disclosed herein are only selected and presented as the most preferred embodiments in order to help those skilled in the art among various possible examples, and the technical spirit of the present invention is not necessarily limited or limited only by these embodiments, Various changes, additions, and changes are possible without departing from the spirit of the present invention, as well as other equivalent embodiments.

Claims (7)

Forming an epoxy resin layer on a second surface opposite to the first surface of the circuit board on which the conductive pattern is formed;
Forming a protective film layer on the first surface of the circuit board;
Curing the protective film layer;
Cutting the circuit board to a set standard; And
Removing the protective film layer from the first surface of the circuit board. The method of claim 1,
The protective film layer is a circuit board processing steel method which consists of a mixed material of a binder polymer and a monomer. 3. The circuit board processing method according to claim 2, wherein the binder polymer is a thermoplastic polymer and the monomer is an acrylic monomer which is a photosensitive monomer. 3. The circuit board processing method according to claim 2, wherein the protective film layer further comprises an adhesion enhancer for imparting adhesion between the protective film layer and the first surface of the circuit board. The method of claim 2 or 4, wherein the protective film layer further comprises a plasticizer. The method of claim 1, wherein the protective film layer curing step is performed by ultraviolet irradiation. The method of claim 1, wherein the cutting of the circuit board is performed by a routing process or a pressing process.

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