CN110545625B

CN110545625B - Flexible circuit board and manufacturing method thereof

Info

Publication number: CN110545625B
Application number: CN201810531170.0A
Authority: CN
Inventors: 胡先钦; 沈芾云; 何明展
Original assignee: Hongqisheng Precision Electronics Qinhuangdao Co Ltd; Avary Holding Shenzhen Co Ltd
Current assignee: Hongqisheng Precision Electronics Qinhuangdao Co Ltd; Avary Holding Shenzhen Co Ltd
Priority date: 2018-05-29
Filing date: 2018-05-29
Publication date: 2021-11-02
Anticipated expiration: 2038-05-29
Also published as: CN110545625A

Abstract

A manufacturing method of a flexible circuit board comprises the following steps: providing a double-sided copper-clad substrate; etching the first copper layer to obtain two first circuit layers; covering a first glue layer, a first insulating layer and a second copper layer on each first circuit layer, and etching the second copper layer to obtain two second circuit layers; covering a second glue layer and a second insulating layer on each second circuit layer; forming a third copper layer on the surface of each second insulating layer, and etching the third copper layer to obtain two third circuit layers; covering a third glue layer and a protective layer on each third circuit layer; and forming a first groove and a second groove in the protective layer and the adjacent third adhesive layer, and forming a groove from one of the protective layer to the second adhesive layer positioned on the other side of the base layer at a position corresponding to the second groove, so that the second insulating layer positioned on one side of the second groove and the corresponding third circuit layer form a single panel area at a part corresponding to the groove.

Description

Flexible circuit board and manufacturing method thereof

Technical Field

The present invention relates to printed circuit board technology, and more particularly, to a flexible circuit board and a method for manufacturing the same.

Background

Nowadays, more and more electronic products such as smart phones, tablet computers, etc. employ Active Matrix Organic Light Emitting Diode (AMOLED) screens. For high integration requirements of such screens, high density wiring of a flexible wiring board for driving the screen will face many challenges.

The conventional flexible circuit board includes an inner layer circuit and an outer layer circuit, and an electronic chip for driving the screen is mounted on the inner layer circuit. To meet the alignment requirement of the pin pitch of the electronic chip, the line width and line pitch of the inner layer lines are usually required to be less than 10 μm/10 μm. However, after the inner circuit is manufactured, the size of the multilayer circuit board will be greatly changed due to a series of subsequent processes, so that the electronic chip cannot be aligned accurately.

Disclosure of Invention

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

The embodiment of the invention provides a manufacturing method of a flexible circuit board, which comprises the following steps: providing a double-sided copper-clad substrate which comprises a flexible base layer and first copper layers formed on two opposite surfaces of the base layer, and etching the first copper layers to obtain two first circuit layers; sequentially covering a first adhesive layer, a first insulating layer and a second copper layer on each first circuit layer, and etching the second copper layer to obtain two second circuit layers; covering a second adhesive layer and a second insulating layer on each second circuit layer in sequence; forming a third copper layer on the surface of each second insulating layer, and etching the third copper layer to obtain two third circuit layers; covering a third glue layer and a protective layer on each third circuit layer in sequence; and forming a first groove and a second groove for exposing part of the third circuit layer in the protective layer and the adjacent third adhesive layer, and forming a slot at the position corresponding to the second groove from one of the protective layers to a second adhesive layer positioned at the other side of the base layer, so that the bottom of the slot is sealed by the second insulating layer, and the second insulating layer positioned at one side of the second groove and the corresponding third circuit layer form a single panel area at the part corresponding to the slot.

The embodiment of the invention also provides a flexible circuit board, which comprises a flexible base layer, first circuit layers formed on two opposite surfaces of the base layer, a first adhesive layer, a first insulating layer, a second circuit layer, a second adhesive layer, a second insulating layer, a third circuit layer, a third adhesive layer and a protective layer which are sequentially formed on each second circuit layer, a first groove and a second groove for exposing part of the third circuit layer are arranged in the protective layer and the adjacent third adhesive layer, a slot is arranged from one of the protective layer to a second adhesive layer positioned on the other side of the base layer at a position corresponding to the second groove, so that the bottom of the slot is sealed by the second insulating layer, so that the second insulating layer and the corresponding third circuit layer on one side of the second groove form a single panel area at the part corresponding to the slot.

Compared with the prior art, in the embodiment of the invention, because the third circuit layer (namely, the outer conductive circuit) is manufactured by adopting a semi-additive method and is formed by electroplating copper and etching during the circuit, the defect that the circuit distance is easily limited by the copper thickness in the conventional subtractive method manufacturing process is overcome, so that the full-additive method is more suitable for manufacturing a fine circuit; because the electronic chip for driving the display screen can be arranged on the outer conductive circuit, and the outer layer circuit is a thin circuit, the alignment requirement of the pin center distance of the electronic chip is met, and the influence of the size change of a product on the alignment is reduced; because the part of the flexible circuit board for fixing the display screen is a single panel area, the flexible effect is better.

Drawings

Fig. 1 is a schematic structural diagram of a double-sided copper-clad substrate according to a preferred embodiment of the invention.

Fig. 2 is a schematic structural view of the double-sided copper-clad substrate shown in fig. 1 after a first through hole is formed and copper is plated.

FIG. 3 is a schematic structural diagram of the double-sided copper-clad substrate shown in FIG. 2 after etching to form a first circuit layer.

Fig. 4 is a schematic structural diagram of the first circuit layer shown in fig. 3 covered with a first glue layer, a first insulating layer and a second copper layer in sequence.

Fig. 5 is a schematic structural view of the first adhesive layer, the first insulating layer and the second copper layer shown in fig. 4 after a second through hole is formed therein and copper is plated.

Fig. 6 is a schematic diagram illustrating the second copper layer shown in fig. 5 after etching to form a second circuit layer.

Fig. 7 is a schematic structural diagram of the second circuit layer shown in fig. 6 covered with a second glue layer and a second insulating layer in sequence.

Fig. 8 is a schematic structural diagram of the second adhesive layer and the second insulating layer shown in fig. 7 after a third through hole is formed therein and a seed layer is formed on the second insulating layer.

Fig. 9 is a schematic structural diagram of the seed layer shown in fig. 8 after a third copper layer is formed on the seed layer and a third circuit layer is formed by etching.

Fig. 10 is a schematic structural diagram of the third circuit layer shown in fig. 9 covered with a third glue layer and a protective layer in sequence.

Fig. 11 is a schematic structural view of a flexible circuit board formed after forming a first groove and a second groove in the third adhesive layer and the protective layer shown in fig. 10, opening a cover, and then mounting and forming an anisotropic conductive film.

Description of the symbols

The following detailed description will further illustrate the invention in conjunction with the above-described figures.

Detailed Description

In order to further explain the technical means and effects of the present invention adopted to achieve the predetermined objects, the following detailed description will be made on the specific embodiments, structures, features and effects of the method for manufacturing a flexible circuit board according to the present invention with reference to the accompanying drawings and preferred embodiments.

Referring to fig. 1 to 11, the present invention provides a method for manufacturing a flexible printed circuit board 100. The order of the steps of the method for manufacturing the flexible circuit board 100 may be changed, and some steps may be omitted or combined according to different requirements. The manufacturing method of the flexible circuit board 100 comprises the following steps:

referring to fig. 1, a double-sided copper-clad substrate 10 is provided. The double-sided copper-clad substrate 10 includes a flexible base layer 11 and first copper layers 12 formed on opposite surfaces of the base layer 11.

The material of the base layer 11 may be selected from one of Polyimide (PI), Polyethylene Terephthalate (PET), Polyethylene Naphthalate (PEN), and the like.

Referring to fig. 2, at least one first through hole 13 penetrating through the base layer 11 and each first copper layer 12 is opened in the double-sided copper-clad substrate 10 (not shown), and copper is plated in the first through hole 13 to form a first conductive portion 14 electrically connected to the first copper layers 12 on two opposite surfaces of the base layer 11.

Wherein the first through hole 13 is formed by means of laser drilling.

Referring to fig. 3, a desired conductive circuit is etched in the first copper layer 12 (not shown) by using an exposure and development technique, so as to obtain a first circuit layer 20.

Referring to fig. 4, a first glue layer 30, a first insulating layer 31 and a second copper layer 32 are sequentially covered on each first circuit layer 20, and the first glue layer 30 flows to fill the gap formed by the first circuit layers 20.

The first adhesive layer 30 may be made of an insulating adhesive resin, such as at least one of polypropylene (PP), epoxy resin, polyurethane, phenolic resin, urea resin, melamine-formaldehyde resin, unsaturated resin, and polyimide adhesive resin. The first insulating layer 31 may be made of polyimide.

Step five, referring to fig. 5, at least one second via hole 33 penetrating through the second copper layer 32, the first insulating layer 31 and the first adhesive layer 30 is opened in the second copper layer 32, and copper is plated on the bottom and inner wall of the second via hole 33 and the periphery of the second copper layer 32 located at the second via hole 33, so as to form a plated through hole 34 electrically connecting the second copper layer 32 and the first circuit layer 20.

Wherein the second through hole 33 is formed by means of laser drilling.

Referring to fig. 6, a desired conductive circuit is etched in the second copper layer 32 by using an exposure and development technique, so as to obtain a second circuit layer 40.

Step seven, referring to fig. 7, a second adhesive layer 50 and a second insulating layer 51 are sequentially covered on each second circuit layer 40, and the second adhesive layer 50 flows to fill the gaps formed by the second circuit layers 40 and the plated through holes 34.

In the present embodiment, the material of the second adhesive layer 50 may be an insulating adhesive resin, such as at least one of polypropylene (PP), epoxy resin, polyurethane, phenol resin, urea resin, melamine-formaldehyde resin, unsaturated resin, and polyimide adhesive resin. The second insulating layer 51 may be made of polyimide.

Step eight, referring to fig. 8, at least one third via 52 penetrating through the second insulating layer 51 and the second adhesive layer 50 is opened in the second insulating layer 51, and a seed layer 60 is formed on the bottom and inner wall of the third via 52 and the surface of the second insulating layer 51. The seed layer 60 is a nano silver coating.

Wherein the third through hole 52 is formed by means of laser drilling.

The seed layer 60 is used for conducting when an outer conductive circuit is formed by electroplating. Wherein, because the conductivity of the nano silver coating is similar to that of copper, the plating is easy to be carried out during the electroplating. The seed layer 60 may be formed by spraying or printing, for example, by printing a nano silver paste and curing. The nano silver paste is a solution or suspension liquid comprising nano silver particles, a bonding agent, a solvent and an auxiliary agent. The nano silver particles are approximately spherical and have uniform particle size distribution, and the average particle size is less than 100 nm.

Step nine, referring to fig. 9, a third copper layer (not shown) is formed on the surface of each seed layer 60, and the third copper layer is filled in the third through holes 52 to form a third conductive portion 70 electrically connecting the third copper layer and the second circuit layer 40, and then the required conductive circuit is etched in the third copper layer by using an exposure and development technique to obtain two third circuit layers 80, and the portion of the seed layer 60 exposed to the third circuit layer 80 is also etched and removed.

In this embodiment, the line width and the line pitch of the third wiring layer 80 are not more than 10 μm/10 μm.

Step ten, referring to fig. 10, a third glue layer 91 and a protective layer 92 are sequentially covered on each third circuit layer 80, and each third glue layer 91 is made to flow to fill the gap formed by the third circuit layer 80.

In this embodiment, the third adhesive layer 91 may be made of an insulating adhesive resin, such as at least one of polypropylene (PP), epoxy resin, polyurethane, phenol resin, urea resin, melamine-formaldehyde resin, unsaturated resin, and polyimide adhesive resin. The material of the protection layer 92 may be solder mask ink.

Referring to fig. 11, a first groove 93 and a second groove 95 for exposing a portion of the third circuit layer 80 are formed in the protective layer 92 and the adjacent third adhesive layer 91, wherein the first groove 93 and the second groove 95 may be respectively located on two sides or the same side of the base layer 11. A groove 101 is formed from one of the protective layers 92 to a second adhesive layer 50 on the other side of the base layer 11 at a position corresponding to the second groove 95 (i.e., a decapping step), so that the bottom of the groove 101 is closed by the second insulating layer 51, and thus the second insulating layer 51 on the one side of the second groove 95, and the corresponding seed layer 60 and the corresponding third circuit layer 80 form a single panel region 102 at a portion corresponding to the groove 101.

In this embodiment, the first groove 93 and the second groove 95 are respectively located on both sides of the base layer 11.

An anisotropic conductive film 96 (i.e., ACF) electrically connected to the third circuit layer 80 is formed in the second groove 95,

step twelve, an electronic chip 200 electrically connected to the third circuit layer 80 is mounted in the first groove 93, and a first solder mask layer 94 is formed between the first groove 93 and the electronic chip 200. An anisotropic conductive film 96 (i.e., ACF) electrically connected to the third circuit layer 80 is formed in the second groove 95, and a second solder resist layer 97 is formed between the second groove 95 and the anisotropic conductive film 96, thereby manufacturing the flexible circuit board 100.

Thus, when the flexible circuit board 100 needs to be connected to a display screen (not shown), the flexible circuit board 100 can be fixed to the display screen through the anisotropic conductive film 96.

In this embodiment, the flexible circuit board 100 is a three-layer circuit board. In other embodiments, the same manufacturing process may be used to manufacture more than three layers of circuit boards.

Referring to fig. 11, a flexible circuit board 100 applied to a display screen (not shown), such as an AMOLED screen, is also provided in accordance with a preferred embodiment of the present invention. The flexible circuit board 100 includes a flexible substrate 11, first circuit layers 20 formed on two opposite surfaces of the substrate 11, a first adhesive layer 30, a first insulating layer 31, a second circuit layer 40, a second adhesive layer 50, a second insulating layer 51, a seed layer 60, a third circuit layer 80, a third adhesive layer 91, and a protective layer 92 sequentially formed on each second circuit layer 40. The seed layer 60 is a nano silver coating. A first groove 93 and a second groove 95 for exposing a portion of the third circuit layer 80 are formed in the protective layer 92 and the corresponding third glue layer 91, wherein the first groove 93 and the second groove 95 may be respectively located on two sides or the same side of the base layer 11. A slot 101 is formed from one of the protective layers 92 to a second adhesive layer 50 on the other side of the base layer 11 at a position corresponding to the second groove 95, so that the bottom of the slot 101 is sealed by the second insulating layer 51, and the second insulating layer 51 on one side of the second groove 95, the corresponding seed layer 60, and the corresponding third circuit layer 80 form a single panel region 102 at a portion corresponding to the slot 101. An electronic chip 200 electrically connected to the third circuit layer 80 is installed in the first groove 93. A first solder mask layer 94 is formed between the first recess 93 and the electronic chip 200. An anisotropic conductive film 96 (i.e., ACF) electrically connected to the third circuit layer 80 is formed in the second groove 95. A second solder mask layer 97 is formed between the second groove 95 and the anisotropic conductive film 96.

At least one first through hole 13 is formed in the base layer 11, and a first conductive portion 14 electrically connected to the first circuit layer 20 on two opposite surfaces of the base layer 11 is formed in the first through hole 13. At least one plated through hole 34 electrically connecting the second circuit layer 40 and the first circuit layer 20 is formed in the first adhesive layer 30. At least one third through hole 52 is opened in the second insulating layer 51 and the second glue layer 50. The seed layer 60 is also formed on the bottom and inner wall of the third via hole 52. A third conductive part 70 electrically connecting the third circuit layer 80 and the second circuit layer 40 is formed in the third via 52 having the seed layer 60.

Since the third circuit layer 80 (i.e., the outer conductive circuit) is manufactured by a semi-additive process (SAP), the circuit is formed by electroplating copper and etching, thereby overcoming the defect that the circuit pitch is easily limited by the copper thickness in the conventional subtractive process, and making the full-additive process more suitable for manufacturing fine circuits. Because the electronic chip 200 for driving the display screen is located at the outer side conductive circuit, and the outer layer circuit is a thin circuit, the alignment requirement of the pin center distance of the electronic chip 200 is met, and the influence of the product size change on alignment is reduced. The flexible circuit board 100 has a single panel area for fixing the display screen, so that the flexible effect is better. The seed layer 60 is a nano silver coating, and the conductivity of the nano silver coating is similar to that of copper, so that plating is easy to start during electroplating, and the nano silver particles are small, thereby being beneficial to formation of fine lines.

Although the present invention has been described with reference to the above preferred embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A manufacturing method of a flexible circuit board comprises the following steps:

providing a double-sided copper-clad substrate which comprises a flexible base layer and first copper layers formed on two opposite surfaces of the base layer, and etching the first copper layers to obtain two first circuit layers;

covering a first glue layer, a first insulating layer and a second copper layer on each first circuit layer in sequence;

forming at least one second through hole penetrating through the second copper layer, the first insulating layer and the first adhesive layer, and plating copper on the bottom and inner wall of the second through hole and around the second through hole where the second copper layer is located, thereby forming a plated through hole electrically connecting the second copper layer and the first circuit layer, the plated through hole having a hole ring around the second copper layer where the second copper layer is located;

etching the second copper layer to obtain two second circuit layers;

covering a second adhesive layer and a second insulating layer on each second circuit layer in sequence, wherein the second adhesive layer is also filled in the plated through holes;

forming a third copper layer on the surface of each second insulating layer, and etching the third copper layer to obtain two third circuit layers, wherein the third copper layer is further filled in a third through hole, the third copper layer in the third through hole forms a conductive part electrically connected with the third circuit layers and the second circuit layers, and the bottom of the conductive part and the hole ring of the plated through hole are staggered with each other and the bottom of the conductive part is connected with the second circuit layers along the thickness direction of the base layer;

covering a third glue layer and a protective layer on each third circuit layer in sequence; and

and arranging a first groove and a second groove for exposing part of the third circuit layer in the protective layer and the adjacent third adhesive layer, and arranging a notch from one protective layer to a second adhesive layer positioned on the other side of the base layer at a position corresponding to the second groove, so that the bottom of the notch is sealed by the second insulating layer, and the second insulating layer positioned on one side of the second groove and the corresponding third circuit layer form a single panel area at a part corresponding to the notch.

2. The method of manufacturing a flexible circuit board according to claim 1, further comprising:

installing an electronic chip in the first groove and electrically connecting the electronic chip with the third circuit layer; and

and forming a first solder mask layer between the first groove and the electronic chip.

3. The method of manufacturing a flexible circuit board according to claim 2, further comprising:

forming an anisotropic conductive adhesive film in the second groove, wherein the anisotropic conductive adhesive film is electrically connected with the third circuit layer; and

and forming a second solder mask layer between the second groove and the anisotropic conductive adhesive film.

4. The method of manufacturing a flexible circuit board according to claim 1, wherein the first groove and the second groove are respectively located on both sides of the base layer.

5. The method of claim 1, wherein after sequentially covering a second adhesive layer and a second insulating layer on each second circuit layer, the method further comprises:

covering a seed layer, wherein the seed layer is a nano silver coating;

and when the third copper layer is etched, the part of the seed layer exposed to the third circuit layer is also etched and removed.

6. The method of manufacturing a flexible circuit board according to claim 1, wherein the line width and line pitch of the third wiring layer is not more than 10 μm/10 μm.

7. A flexible circuit board comprises a flexible base layer, first circuit layers formed on two opposite surfaces of the base layer, a first adhesive layer, a first insulating layer, a second circuit layer, a second adhesive layer, a second insulating layer, a third circuit layer, a third adhesive layer and a protective layer sequentially formed on each first circuit layer,

the flexible circuit board is provided with at least one second through hole penetrating through the second circuit layer, the first insulating layer and the first adhesive layer, copper plating is arranged on the bottom and the inner wall of the second through hole and the second circuit layer positioned around the second through hole, so that a plated through hole electrically connected with the second circuit layer and the first circuit layer is formed, the second adhesive layer is further filled in the plated through hole, and the plated through hole is provided with a hole ring positioned around the second circuit layer positioned around the second through hole;

the flexible circuit board is also provided with at least one third through hole penetrating through the second insulating layer and the second adhesive layer, a conductive part electrically connected with the third circuit layer and the second circuit layer is arranged in the third through hole, the bottom of the conductive part and the ring of the plated through hole are staggered with each other along the thickness direction of the base layer, and the bottom of the conductive part is connected with the second circuit layer;

a first groove and a second groove which are used for exposing a part of the third circuit layer are formed in the protective layer and the adjacent third glue layer, and a notch is formed from one of the protective layer to a second glue layer positioned on the other side of the base layer at a position corresponding to the second groove, so that the bottom of the notch is sealed by the second insulating layer, and the second insulating layer positioned on one side of the second groove and the corresponding third circuit layer form a single panel area at a part corresponding to the notch.

8. The flexible circuit board of claim 7, wherein an electronic chip is mounted in said first recess, said electronic chip being electrically connected to said third circuit layer, and a first solder mask layer is formed between said first recess and said electronic chip.

9. The flexible circuit board of claim 8, wherein an anisotropic conductive film electrically connected to the third circuit layer is formed in the second groove, and a second solder resist layer is formed between the second groove and the anisotropic conductive film.

10. The flexible circuit board of claim 7, wherein the first recess and the second recess are located on both sides of the base layer, respectively.

11. The flexible circuit board of claim 7, wherein the line width and line spacing of the third circuit layer is not more than 10 μm/10 μm.