TWI663901B - Flexible printed circuit board and method for manufacturing the same - Google Patents

Abstract

A flexible circuit board includes: a polyimide substrate, which is provided with at least one through hole therethrough, and grooves are formed on opposite surfaces of the polyimide substrate; and a polyimide conductive film is formed. A first polyimide conductive layer on the inner wall of the through hole is provided on the opposite surfaces of the polyimide substrate except the groove and the inner wall of the through hole; And a second polyimide conductive layer other than the first polyimide conductive layer; two conductive circuit layers formed on the surface of the second polyimide conductive layer, each conductive circuit layer having A circuit opening corresponding to the groove position, and a conductive portion in the through hole is used to electrically connect the two conductive circuit layers; two cover films are formed on the surfaces of the two conductive circuit layers and fill the grooves.

Description

Flexible circuit board and manufacturing method thereof

The invention relates to a flexible circuit board and a manufacturing method thereof.

As electronic products such as smart phones, tablet computers, and wearable devices are becoming smaller and more versatile, flexible circuit boards also need to meet the requirements of high density. Improved semi-additive method (MSAP) is a relatively common process for making high-density flexible circuit boards. MSAP uses ultra-thin copper on the surface of the polyimide (PI) substrate to reduce the thickness of the copper to the required thickness, and then compresses the dry film to form an electroplated copper layer on the copper by exposure and development technology. The dry film was removed, and the underlying copper between the electroplated copper layers was etched away.

However, during the etching of the underlying copper, the sidewalls of the electroplated copper layer may also be etched, resulting in an increase in the line pitch of the circuit and difficulty in obtaining a high-density flexible circuit board. In addition, since the base copper is generally electrolytic copper, the material itself is denser than that of electroplated copper, and the difference in the corrosion rate between the two will cause an undercut at the bottom of the copper circuit, causing the circuit to skew. In addition, the surface of the PI substrate has a certain roughness, and the surface of the PI substrate is usually formed with a seed layer by sputtering to overcome the problem of poor adhesion between the copper substrate and the PI substrate. It is difficult to remove during the etching process, resulting in residuals and the risk of short circuits.

In view of this, the present invention provides a flexible circuit board and a manufacturing method thereof, which can solve the above problems.

The invention provides a method for manufacturing a flexible circuit board, which includes: providing an insulating polyimide substrate, and at least one through-hole is formed in the polyimide substrate; A wall and a surface of the polyimide substrate form a polyimide conductive film, and the polyimide conductive film includes a first polyimide conductive layer located on an inner wall of the through hole, and a polyimide conductive film. A second polyimide conductive layer other than the first polyimide conductive layer; covering each surface of the second polyimide conductive layer away from the polyimide substrate with a photosensitive material A pattern opening is formed in each photosensitive layer by using an exposure and development technology, and the pattern opening is used to expose a through hole where the first polyfluorene imide conductive layer is formed, and Part of the second polyimide conductive layer; copper is plated on the exposed portion of the second polyimide conductive layer to form two conductive circuit layers, and the first polyimide is conductively formed. Copper is plated in the through holes of the layer to form a conductive portion electrically connecting the two conductive circuit layers; each photosensitive layer is removed to expose a circuit opening located in the conductive circuit layer; and the second polyimide is conductive. A portion of the layer corresponding to the circuit opening and a portion of each surface of the polyimide substrate corresponding to the circuit opening, and the surface of the polyimide substrate after etching forms the circuit opening A corresponding groove; and covering a surface of each of the conductive circuit layers away from the polyimide substrate with a cover film, and then pressing the cover film to flow to the groove, thereby making the Flexible circuit board.

The present invention also provides a flexible circuit board, comprising: a polyimide substrate with at least one through hole formed therethrough, grooves formed on opposite surfaces of the polyimide substrate; and a polyimide A conductive film is formed on the opposite surfaces of the polyimide substrate except the groove and an inner wall of the through hole, and the polyimide conductive film includes the through hole A first polyimide conductive layer on the inner wall and a second polyimide conductive layer in addition to the first polyimide conductive layer; two conductive circuit layers formed on the second polyimide The imine conductive layer is far from the surface of the polyfluorene imide substrate, and each conductive circuit layer has a line opening corresponding to the position of the groove, wherein a through hole of the first polyfluorene imide conductive layer is formed A conductive portion is provided to electrically connect the two conductive circuit layers; and two cover films are formed on a surface of the two conductive circuit layers away from the polyimide substrate, and the cover film fills the groove. .

Compared with the prior art, the manufacturing process of the above copper-clad substrate is a full addition method. By forming a polyimide conductive film on a polyimide substrate, the surface of the polyimide substrate is metallized. In the process of etching the polyfluorene imide conductive film located between the conductive circuit layers, the conductive circuit layer will not be etched, which can ensure a small line pitch while avoiding side etching; , A portion of each surface of the polyimide substrate corresponding to the circuit opening will also be etched to form a groove, thereby ensuring that the polyimide conductive film between the conductive circuit layers is etched away to avoid part Risk of short circuits due to residues.

10‧‧‧Polyimide substrate

11‧‧‧through hole

12‧‧‧ groove

20‧‧‧Polyimide conductive film

21‧‧‧ the first polyimide conductive layer

22‧‧‧Second polyimide conductive layer

30‧‧‧ Photosensitive layer

31‧‧‧ Graphic opening

40‧‧‧ conductive circuit layer

41‧‧‧Conductive Section

42‧‧‧line opening

50‧‧‧ cover film

100‧‧‧flexible circuit board

FIG. 1 is a flowchart of a method for manufacturing a flexible circuit board according to a preferred embodiment of the present invention.

FIG. 2 is a cross-sectional view of a polyimide substrate used in the production method shown in FIG. 1.

3 is a cross-sectional view of a polyfluorene imide substrate shown in FIG. 2 after a through hole is opened.

4 is a cross-sectional view of a polyimide conductive film formed on the inner wall of the through hole and the surface of the polyimide substrate in FIG. 3.

5 is a cross-sectional view of the second polyimide conductive layer of the polyimide conductive film shown in FIG. 4 after being covered with two photosensitive layers.

FIG. 6 is a cross-sectional view of the photosensitive layer shown in FIG. 5 after exposure processing.

FIG. 7 is a cross-sectional view after developing the photosensitive layer shown in FIG. 6 to form a pattern opening.

FIG. 8 is a cross-sectional view of a portion of the polyimide conductive film of the polyimide conductive film shown in FIG. 7 after being plated with copper to form a conductive circuit layer.

Figure 9 is a cross-sectional view after the photosensitive layer shown in Figure 8 is removed.

FIG. 10 is a cross-sectional view of the second polyimide conductive layer and the polyimide substrate shown in FIG. 9 after etching.

11 is a cross-sectional view of a flexible circuit board obtained by covering a surface of a conductive circuit layer shown in FIG. 10 with a cover film.

Referring to FIG. 1, a method for manufacturing a flexible circuit board 100 according to a preferred embodiment of the present invention includes the following steps:

Step S1, referring to FIG. 2, an insulating polyimide (PI) substrate 10 is provided.

Step S2, referring to FIG. 3, at least one through-hole 11 is formed in the polyimide substrate 10.

In this embodiment, the through hole 11 is formed by laser drilling.

Step S3, referring to FIG. 4, a polyimide conductive film 20 is formed on the inner wall of the through hole 11 and the surface of the polyimide substrate 10, so that the polyimide substrate 10 Metallized surface. The polyimide conductive film 20 includes a first polyimide conductive layer 21 located on an inner wall of the through hole 11 and a second polyimide other than the first polyimide conductive layer 21. Imine conductive layer 22.

In this embodiment, the polyfluorene imide conductive film 20 is mixed with metal or metal oxide particles. The polyfluoreneimide conductive film 20 may be formed by one of an in-situ dispersion method, an in-situ deposition method, a sol-gel method, and a surface-modified ion exchange method.

The in-situ dispersion method is specifically: providing a polyamic acid solution having a lower viscosity as a polyimide precursor, and adding a dispersant with metal or metal oxide particles to the polyamine The mixture is casted into an acid solution to obtain a mixture, and the mixture is cast into a film and thermally imidized at a certain temperature to obtain the polyfluorene imine conductive film 20. The in-situ dispersion method may further be specifically: providing a polyamidic acid solution, adding metal or metal oxide particles to the polyamidoimine solution to obtain a mixture, and then in the through hole 11 The wall and the surface of the polyimide substrate 10 are coated with the mixture and subjected to heat treatment, so that the solvent in the polyimide solution is volatilized and the polyimide cyclization reaction occurs to form polyimide, thereby obtaining The polyfluorene imide conductive film 20.

The in-situ deposition method is specifically: providing a polyamic acid solution as a polyimide precursor, adding a metal salt to the polyamino acid solution to prepare a mixture, and then casting into a film and performing The heat treatment causes the polyimide cyclization reaction to generate polyimide, and at the same time, the metal salt is decomposed in situ to form metal or metal oxide particles, thereby obtaining the polyimide conductive film 20.

The sol-gel method is specifically: providing a polyamidic acid solution having a lower viscosity as a polyimide precursor, and adding a metal organic alkoxide to the polyacrylic acid solution or polyimide solution to A mixture is obtained, which is then cast into a film and heat-treated, so that the polyimide cyclization occurs to form a polyimide, and the organometallic alkoxide is hydrolyzed to form a metal oxide through a sol-gel process, thereby obtaining The polyfluorene imide conductive film 20.

The surface modification ion exchange method is specifically: providing a semi-dry film of polyamic acid as a precursor of polyimide, subjecting the semi-dry film to ion exchange in an aqueous solution of an inorganic metal salt, and then Heat treatment in the air under tension causes the polyimide to undergo polyimide cyclization to form polyimide, and at the same time, metal ions are thermally induced to reduce to metal and partially migrate to collect on the two opposite sides of the semi-dry film Surface, thereby forming the polyfluorene imide conductive film 20 with high reflectivity and high conductivity on both sides.

Wherein, the metal includes silver (Ag), copper (Cu), nickel (Ni), lead (Pb), platinum (Pt), gold (Au), cobalt (Co), lithium (Li), zinc (Zn) And at least one of aluminum (Al) and the like. The metal oxide includes at least one of silver oxide, copper oxide, nickel oxide, lead oxide, platinum oxide, gold oxide, cobalt oxide, lithium oxide, zinc oxide, and aluminum oxide.

Step S4, referring to FIG. 5, a photosensitive layer 30 is covered on each surface of the second polyimide conductive layer 22 away from the polyimide substrate 10.

In this embodiment, the photosensitive layer 30 is a dry film.

In step S5, referring to FIG. 6, an exposure process is performed on each photosensitive layer 30.

Specifically, a circuit pattern is first covered on each photosensitive layer 30 and then subjected to ultraviolet light treatment, so that areas of the photosensitive layer 30 not covered by the circuit pattern are illuminated by ultraviolet light. It is cured by exposure to radiation (ie, is exposed), and the area of the photosensitive layer 30 covered by the circuit pattern is not cured (ie, is not exposed) because it is not irradiated with ultraviolet light.

In step S6, referring to FIG. 7, each exposed photosensitive layer 30 is subjected to a development process to form a pattern opening 31 in each photosensitive layer 30. The pattern opening 31 is used for exposing the first polymer layer. The through hole 11 of the imine conductive layer 21 and part of the second polyfluorene imine conductive layer 22.

Specifically, the product covered with the photosensitive layer 30 is immersed in a developing solution, and the unexposed areas of each photosensitive layer 30 are removed due to the reaction with the developing solution to form the pattern opening 31. The developing solution is a 1% NaCO ₃ solution.

Step S7, referring to FIG. 8, copper is plated on the exposed portion of the second polyimide conductive layer 22 to form two conductive circuit layers 40, and the first polyimide conductive layer 21 is formed Copper is plated in the through holes 11 to form a conductive portion 41 electrically connecting the two conductive circuit layers 40.

In this embodiment, the conductive circuit layer 40 is formed by electroless plating or electroplating.

In step S8, referring to FIG. 9, each photosensitive layer 30 is removed to expose the circuit openings 42 of the conductive circuit layer 40.

Step S9, referring to FIG. 10, etching a portion of the second polyimide conductive layer 22 corresponding to the circuit opening 42 and each surface of the polyimide substrate 10 corresponding to the circuit opening 42 In part, a groove 12 corresponding to the circuit opening 42 is formed on the surface of the polyimide substrate 10 after the etching.

In this embodiment, an alkaline chemical is used to etch the second polyimide conductive layer 22 and the polyimide substrate 10. During the etching process, polyimide undergoes ring-opening hydrolysis and is then oxidized by an oxidant. More specifically, the degree of etching of the polyimide substrate 10 can be controlled by controlling the content of the oxidant, the reaction temperature, and the reaction time, that is, the depth of the groove 12 can be controlled.

In another embodiment, the second polyimide conductive layer 22 and the polyimide substrate 10 are etched by laser. The laser may be a carbon dioxide laser or an ultraviolet laser.

In step S10, referring to FIG. 11, a surface of each conductive circuit layer 40 away from the polyimide substrate 10 is covered with a cover film 50, and then the cover film 50 is pressed to flow to fill the cover film 50. The groove 12, so that the flexible circuit board 100 is manufactured.

The manufacturing process of the above copper-clad substrate 100 is a full addition method. The polyimide conductive film 20 is formed on the polyimide substrate 10 to metalize the surface of the polyimide substrate 10, thereby improving The bonding force between the polyimide substrate 10 and the conductive circuit layer 40 is located at the etching position. During the process of the polyimide conductive film 20 between the conductive circuit layers 40 (see step S9 above), the conductive circuit layer 40 will not be etched, which can prevent side etching while ensuring a small line distance. . In addition, a portion of each surface of the polyimide substrate 10 corresponding to the circuit opening 42 is also etched to form a groove 12 (see step S9 above), so as to ensure the space between the conductive circuit layers 40. The polyfluorene imide conductive film 20 is removed by etching to avoid the risk of causing a short circuit caused by some residues.

Please refer to FIG. 11, a preferred embodiment of the present invention further provides a flexible circuit board 100 including a polyimide substrate 10. The polyimide substrate 10 is provided with at least one through hole 11 therethrough. A groove 12 is formed on two opposite surfaces of the polyimide substrate 10.

A polyimide conductive film 20 is formed on the opposite surfaces of the polyimide substrate 10 except for the groove 12 and the inner wall of the through hole 11. The polyimide conductive film 20 includes a first polyimide conductive layer 21 located on an inner wall of the through hole 11 and a second polyimide other than the first polyimide conductive layer 21. Imine conductive layer 22.

Two conductive circuit layers 40 are formed on a surface of the second polyimide conductive layer 22 away from the polyimide substrate 10. Each conductive circuit layer 40 has a circuit opening 42 corresponding to the position of the groove 12. Wherein, the through hole 11 in which the first polyimide conductive layer 21 is formed has a conductive portion 41 to electrically connect the two conductive circuit layers 40.

A cover film 50 is covered on a surface of each conductive circuit layer 40 away from the polyimide substrate 10, and the cover film 50 is filled into the groove 12.

Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solution of the present invention and are not limiting. Although the present invention has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be carried out. Modifications or equivalent replacements should not depart from the spirit and scope of the technical solution of the present invention.

Claims (8)

A method for manufacturing a flexible circuit board includes: providing an insulating polyimide substrate, wherein at least one through-hole is formed in the polyimide substrate; and an inner wall of the through-hole and A polyimide conductive film is formed on a surface of the polyimide substrate, and the polyimide conductive film includes a first polyimide conductive layer located on an inner wall of the through hole, and the first polyimide conductive layer is in addition to the first polyimide conductive film. A second polyimide conductive layer other than the polyimide conductive layer; covering each surface of the second polyimide conductive layer away from the polyimide substrate with a photosensitive layer; using The exposure and development technology forms a pattern opening in each photosensitive layer, and the pattern opening is used to expose the through-hole in which the first polyimide conductive layer is formed and a part of the second polyimide conductive layer; The exposed portion of the second polyfluorene imide conductive layer is plated with copper to form two conductive circuit layers, and copper is plated in a through hole where the first polyfluorene imide conductive layer is formed to form an electrical connection with the Conductive portions of two conductive circuit layers; removing each photosensitive layer to expose the conductive circuit layers Circuit opening; etching a portion of the second polyimide conductive layer corresponding to the circuit opening and a portion of each surface of the polyimide substrate corresponding to the circuit opening; the etched polyimide A surface of the fluorimide substrate forms a groove corresponding to the circuit opening; and a surface of each conductive circuit layer away from the polyimide substrate is covered with a cover film, and then the cover film is pressed so that It flows to the groove, so that the flexible circuit board is manufactured. The method for manufacturing a flexible circuit board according to item 1 of the scope of patent application, wherein the through hole is formed by laser drilling. The method for manufacturing a flexible circuit board according to item 1 of the scope of patent application, wherein the polyimide conductive film is mixed with metal or metal oxide particles. The method for manufacturing a flexible circuit board according to item 3 of the scope of the patent application, wherein the polyimide conductive film adopts an in-situ dispersion method, an in-situ deposition method, a sol-gel method, and a surface-modified ion exchange method One of these forms. The method for manufacturing a flexible circuit board according to item 3 of the scope of patent application, wherein the metal includes at least one of silver, copper, nickel, lead, platinum, gold, cobalt, lithium, zinc, and aluminum, and the metal The oxide includes at least one of silver oxide, copper oxide, nickel oxide, lead oxide, platinum oxide, gold oxide, cobalt oxide, lithium oxide, zinc oxide, and aluminum oxide. The method for manufacturing a flexible circuit board according to item 1 of the scope of patent application, wherein the conductive circuit layer is formed by chemical plating or electroplating. The method for manufacturing a flexible circuit board according to item 1 of the scope of patent application, wherein the second polyimide conductive layer and the polyimide substrate are etched by using an alkaline potion or a laser technique. A flexible circuit board includes: a polyimide substrate, which is provided with at least one through hole therethrough, and grooves are formed on opposite surfaces of the polyimide substrate; and a polyimide conductive film is formed. On a portion of two opposite surfaces of the polyimide substrate except the groove and an inner wall of the through hole, the polyimide conductive film includes A first polyimide conductive layer and a second polyimide conductive layer other than the first polyimide conductive layer; two conductive circuit layers formed on the second polyimide conductive layer A surface of the polyimide substrate away from the surface of each conductive circuit layer has a circuit opening corresponding to the position of the groove, wherein a conductive portion is formed in the through hole in which the first polyimide conductive layer is formed. The two conductive circuit layers are electrically connected; and two cover films are formed on surfaces of the two conductive circuit layers away from the polyimide substrate, and the cover films fill the grooves.