KR100951939B1 - Method of manufacturing flexible printed circuit board - Google Patents

Abstract

PURPOSE: A manufacturing method of a flexible PCB is provided to prevent deflection of a flexible PCB by attaching a carrier tape in the upper side of a first copper foil layer. CONSTITUTION: A carrier tape is attached on the upper side of a first copper foil layer of a polyimide substrate(S11). A via hole is formed in the polyimide substrate(S12). The surface of the polyimide substrate is processed(S13). A seed layer is formed on the surface of the polyimide substrate(S14). A second copper foil layer is formed on the surface of the seed layer(S15). The carrier tape is removed(S16). A circuit is formed in the first and the second copper foil layer(S17). The surface of the circuit is processed(S18).

Description

Method of manufacturing flexible printed circuit board {Method of manufacturing flexible printed circuit board}

The present invention relates to a method for manufacturing a printed circuit board, and more particularly, to a method for manufacturing a flexible printed circuit board having flexibility and flexibility.

Flexible printed circuit boards (FPCBs), which are easy to embed in more complex and narrow spaces, due to the development of semiconductor integrated circuits, the development of surface-mount technology for directly mounting small chip components, and the miniaturization of electronic equipment. This was developed.

Such a flexible printed circuit board is manufactured using a flexible copper clad laminate (hereinafter, FCCL) as a substrate material. FCCL is a flexible substrate that has a copper foil layer adhered to the surface of a polyimide film. In the past, many products of a three-layer structure (polyimide film-adhesive-copper foil) in which a polyimide film and a copper foil were glued were used. FCCL of the two-layer structure which directly bonded the mid film and the copper foil layer is used frequently.

1 is a cross-sectional view showing such a conventional FCCL, Figure 2 is a cross-sectional view showing a copper plating on the surface of the FCCL of FIG. Referring to FIG. 1, in the FCCL 10, the copper foil layer 12 is positioned on the upper and lower surfaces of the polyimide film 11, respectively, and the polyimide film 11 and the copper foil layers 12 are formed by drilling or the like. Through-holes 13 are formed.

After the through hole 13 is formed, the surface of the copper foil layer 12 may be chemically plated, electroplated, or the like to electrically conduct the upper and lower surfaces via the through hole 13 as shown in FIG. 2. The copper plating layer 14 is formed.

However, when the chemical copper plating and the electrocopper plating is used, the copper foil layer 12 is further thickened by the copper plating layer 14. In addition, the FCCL 10 thus formed has a thick thickness of the copper foil layer 12, making it difficult to form a fine circuit.

In addition, in order to prevent the thickness of the copper foil layer 12 from being thickened, a method of attaching a dry film to the surface of the copper foil layer 12 which does not require copper plating and copper plating only around the through hole 13 (so-called button plating) is However, the process of exposing and developing a dry film is added, and a process becomes complicated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a flexible printed circuit board having a thin thickness, which facilitates circuit formation of a fine pattern.

Method for manufacturing a flexible printed circuit board according to the present invention comprises the steps of: forming a via hole in a polyimide substrate having a first copper foil layer laminated on one surface; Surface treating the polyimide substrate; Forming a seed layer by evaporation so that copper may be plated on the surface of the polyimide substrate; Plating copper on the surface of the seed layer to form a second copper foil layer; Forming a circuit in said first copper foil layer and said second copper foil layer; And a post processing step of treating the surface of the circuit.

Here, the via hole may be formed through the first copper foil layer and the polyimide substrate, or may be formed only through the polyimide substrate. In addition, the surface treatment may be performed by at least one of an ion beam, a plasma, and a desmear.

In addition, the forming of the seed layer may be performed by at least one of a high frequency induction heating method, a resistance heating method, an electron beam method, and a plasma method. Furthermore, the seed layer may include nickel-chromium (Ni-Cr), copper (Cu), or nickel (Ni).

The method may further include attaching a carrier tape to an upper surface of the first copper foil layer before forming the via hole, and after forming the second copper foil layer, It may further comprise the step of removing.

Furthermore, in the forming of the circuits on the first copper foil layer and the second copper foil layer, the method may further include removing the seed layer and the second copper foil layer of the portion to be bent by etching.

According to the method of manufacturing a flexible printed circuit board of the present invention,

First, the seed layer is formed by evaporation, and the copper foil layer is formed by copper plating on the seed layer, so that the thickness of the substrate becomes thin.

Second, since the thickness of the substrate is thin, there is an advantage in that a circuit of a fine pattern is easily formed.

Third, the process is simpler than when button plating to prevent the copper foil layer from becoming thick.

Fourth, in the case of using the carrier tape, it is possible to reduce the upper and lower variations of the circuit pattern during etching, to prevent the spread of the plasma on the copper foil layer surface, and to solve the wrinkle phenomenon of the substrate.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the present specification and claims should not be construed as being limited to the common or dictionary meanings, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that it can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

3 is a flowchart illustrating a method of manufacturing a flexible printed circuit board according to an exemplary embodiment of the present invention, and FIGS. 4 to 10 are cross-sectional views illustrating a manufacturing process of a flexible printed circuit board according to an exemplary embodiment of the present invention.

3 to 10, a method of manufacturing a flexible printed circuit board according to the present invention includes steps S11 to S18.

In step S11, a polyimide substrate 110 (see FIG. 4) having the first copper foil layer 120 laminated on one surface is prepared, and a carrier tape 400 is attached to an upper surface of the first copper foil layer 120. (See FIG. 5). The polyimide substrate 110 in which the first copper foil layer 120 is laminated on one surface is also called a cross-sectional material. General copper foil may be used as the copper foil layer, and in particular, when there is a part requiring flexibility, a rolled foil or a special electrolytic foil having good flexibility may be used.

Attachment of the carrier tape 400 may be omitted as necessary, as will be described later.

In step S12, a via hole 130 penetrating the polyimide substrate 110 is formed (see FIG. 6).

The via hole 130 is formed by a UV laser drill. The UV laser drill is capable of processing 75 μm or less by generating 355 μm of an ultraviolet wavelength band using vanadium or the like as a laser source. The UV laser drill may form fine and sophisticated via holes 130.

In step S13, the surface of the polyimide substrate 110 is processed. Surface treatment may be performed by at least one of an ion beam, a plasma, and a desmear.

In particular, when the plasma is used to deposit the seed layer 200 to be described later, the plasma may be spread on the surface of the first copper foil layer 120, so that it may be difficult to improve the surface roughness of the polyimide substrate 110. When surface treatment is performed to prevent this, plasma is not spread through the first copper foil layer 120, so that even surface roughness of the polyimide substrate 110 is secured regardless of the presence or absence of the first copper foil layer 120. It is possible to improve the adhesion when the seed layer 200 is formed.

Next, in step S14, the seed layer 200 is formed by evaporation so that the copper copper 300 may be plated on the surface of the polyimide substrate 110 on which the via holes 130 are formed (see FIG. 7). The seed layer 200 is formed of nickel-chromium (Ni-Cr), copper (Cu), or nickel. Since the seed layer 200 is for forming the second copper foil layer 300 to be described later, it is not necessary to form the seed layer 200 in the first copper foil layer 120 as shown in FIG. 7. That is, the plasma for forming the seed layer 200 is generated toward the polyimide substrate 110, and the seed layer 220 is formed in the polyimide substrate 110 and the via hole 130. The sputtering method for forming the seed layer 200 in step S14 may be performed by at least one of a high frequency induction heating method, a resistance heating method, an electron beam method, and a plasma method.

The vapor deposition method is a technique in which an inert element such as argon is hit on a metal plate to drive out a metal molecule and then attach a film to the surface. When DC power is applied to the target while flowing argon (Ar) gas, which is an inert gas, in the vacuum chamber, a plasma is generated between the substrate to be deposited and the target. In such a plasma, argon gas is ionized into cations by a high output direct current ammeter. Argon cations are accelerated to the cathode by a DC ammeter and collide with the target surface. The collision of the target material causes the atoms to extrude out of the surface by exchanging momentum due to the full elastic impact. The released atoms move freely in the vacuum chamber and form a deposition layer on the surface of the object to be deposited. The released atoms have relatively high kinetic energy due to the transfer of momentum, so that when the deposition layer is formed on the surface of the target, surface diffusion occurs to a thermodynamically stable position, forming a very thin film of dense tissue. The seed layer 130 formed by such a deposition method is formed to a very thin thickness of 1000 두께 or less. This deposition method requires a high voltage of 600V or more, and the current that determines the deposition rate of the plating can only flow about 10A, so the deposition rate can not be very fast.

In the case of the deposition method, as described above, the surface of the first copper foil layer 120 may be spread with plasma, so that the surface treatment is preceded. In addition, the above-mentioned carrier tape 400 also serves to prevent the phenomenon of plasma spreading on the first copper foil layer 120.

In step S15, the copper foil is plated on the deposited seed layer 200 to form the second copper foil layer 300 (see FIG. 8). Since copper is also plated in the via hole 130, the first copper foil layer 120 and the second copper foil layer 300 are electrically conductive.

When plating copper on the surface of the seed layer 200 deposited in step S14, current must be applied to the upper and lower surfaces, and a small amount of current is also applied to the first copper foil layer 120 that does not require copper. For this reason, copper may be plated even on the first copper foil layer 120 thinly. In this case, since the thicknesses of the first copper foil layer 120 and the second copper foil layer 300 may be different from each other, the carrier tape 400 is attached to the upper surface of the first copper foil layer 120. In addition, during electroplating, the film-type substrate may be soft and creased and wrinkled. The carrier tape 400 may solve the wrinkle phenomenon of the substrate by maintaining a constant thickness.

In step S16, the carrier tape 400 is removed (see Fig. 9). In the present embodiment, the carrier tape is used, but the thickness of the first and second copper foil layers may be adjusted by controlling the current applied to the first and second copper foil layers without using the carrier tape. In this case, step S16 may also be omitted.

In step S17, a circuit is formed on the first copper foil layer 120 and the second copper foil layer 300 through a process such as exposure, development, and corrosion. In the corrosion process of the circuit forming step, the seed layer and the second copper foil layer corresponding to the bent portion A are removed. (See FIG. 9) A copper foil layer is formed by copper plating the seed layer 200 formed by deposition. This may cause problems in the bendability of the portion (A) to be bent in the finished substrate. Therefore, in order to eliminate this problem, the seed layer 200 and the second copper foil layer of the portion A to be bent are removed by etching during circuit formation.

When the circuit shape step is completed, in the post-treatment step of S18, PSR ink is applied to the surface of the circuit or the coverlay film 500 or the like is bonded (see FIG. 10).

11 is a cross-sectional view of a flexible printed circuit board manufactured by a method of manufacturing a flexible printed circuit board according to another embodiment of the present invention. In FIG. 11, unlike the via hole 130 formed only through the polyimide substrate 110 in the above-described embodiment, another embodiment of the present invention provides a carrier tape 400, a first copper foil layer 120, and a polyimide substrate. Through holes formed through all of the 110 are formed. In this case, since the same process as described above S12 to S18 is applied, repeated description is omitted.

As described above, according to the method of manufacturing the flexible printed circuit board, since the seed layer 200 is formed by evaporation and the second copper foil layer 300 is formed by copper plating on the seed layer 200, the thickness of the substrate is thin. It is easy to form a circuit of a fine pattern. In addition, the process is simpler than when button plating to prevent the thickness of the copper foil layer from becoming thick. In the case of using the carrier tape, it is possible to reduce the upper and lower deviations of the circuit pattern during etching, to prevent the spread of the plasma on the copper foil layer surface, and to solve the wrinkle phenomenon of the substrate.

1 is a cross-sectional view showing a conventional FCCL.

FIG. 2 is a cross-sectional view showing copper plating on the surface of the FCCL of FIG. 1.

3 is a flowchart illustrating a method of manufacturing a flexible printed circuit board according to an exemplary embodiment of the present invention.

4 to 10 are cross-sectional views illustrating a manufacturing process of a flexible printed circuit board according to an exemplary embodiment of the present invention.

11 is a cross-sectional view illustrating a manufacturing process of a flexible printed circuit board according to another exemplary embodiment of the present invention.

<Brief description of the main parts of the drawing>

110 ... polyimide substrate 120 ... first copper foil layer

130 ... via hole 200 ... seed layer

300 ... second copper foil layer 400 ... carrier tape

500 ... Coverlay Film

Claims (8)

Forming a via hole in a polyimide substrate having a first copper foil layer laminated on one surface thereof; Surface treating the polyimide substrate; Forming a seed layer by evaporation so that copper may be plated on the surface of the polyimide substrate; Plating copper on the surface of the seed layer to form a second copper foil layer; Forming a circuit in said first copper foil layer and said second copper foil layer; And a post-processing step of treating the surface of the circuit, wherein the seed layer is formed by at least one of a high frequency induction heating method, a resistance heating method, an electron beam method, and a plasma method. Method of manufacturing flexible printed circuit board. The method according to claim 1, The via hole is The method of manufacturing a flexible printed circuit board, characterized in that formed through the polyimide substrate. The method according to claim 1, The via hole is A method of manufacturing a flexible printed circuit board, characterized in that formed through the first copper foil layer and the polyimide substrate. The method according to claim 1, The surface treatment step, A method of manufacturing a flexible printed circuit board comprising at least one of an ion beam, a plasma, and a desmear. delete The method according to claim 1, The seed layer, A method for manufacturing a flexible printed circuit board comprising nickel-chromium (Ni-Cr), copper (Cu) or nickel (Ni). The method according to claim 1, Prior to forming the via hole, Attaching a carrier tape to an upper surface of the first copper foil layer; After the step of forming the second copper foil layer, Removing the carrier tape further comprises the step of manufacturing a flexible printed circuit board. The method according to any one of claims 1 to 4, 6 and 7, In the step of forming a circuit in the first copper foil layer and the second copper foil layer, A method of manufacturing a flexible printed circuit board, wherein the seed layer and the second copper foil layer of the portion to be bent are removed by etching.

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