CN112533368A

CN112533368A - Rigid-flexible circuit board and manufacturing method thereof

Info

Publication number: CN112533368A
Application number: CN201910878519.2A
Authority: CN
Inventors: 李卫祥
Original assignee: Avary Holding Shenzhen Co Ltd; Qing Ding Precision Electronics Huaian Co Ltd
Current assignee: Avary Holding Shenzhen Co Ltd; Qing Ding Precision Electronics Huaian Co Ltd
Priority date: 2019-09-18
Filing date: 2019-09-18
Publication date: 2021-03-19

Abstract

A soft and hard combined circuit board comprises an inner layer substrate, wherein the inner layer substrate comprises a soft base layer and a circuit layer formed on the surface of the soft base layer; the rigid substrate covers part of the surface of the circuit layer, the part of the rigid substrate of the rigid-flexible circuit board is a reinforced layer area, the part of the rigid substrate which does not have the rigid substrate is a flexible area, and at least one first conductive block connected with the circuit layer is arranged in the rigid substrate; the outer layer substrate comprises an outer copper layer, a dielectric layer and a bonding layer, the bonding layer covers the surfaces of the circuit layer and the rigid substrate, the dielectric layer covers the surface of the bonding layer, and the outer copper layer covers the surface of the dielectric layer corresponding to the interlayer region; and a solder mask layer covering the surface of the outer copper layer. The soft and hard combined circuit board utilizes the dielectric layer and the bonding layer to replace the protective layer to cover the flexible area of the inner layer substrate, solves the problem of open circuit caused by uneven thickness of the layer adding area, and improves the bending performance of the flexible area. The invention also provides a manufacturing method of the rigid-flexible circuit board.

Description

Rigid-flexible circuit board and manufacturing method thereof

Technical Field

The invention relates to the field of circuit boards and manufacturing thereof, in particular to a rigid-flexible circuit board and a manufacturing method thereof.

Background

With the development of chip technology, the requirements for the quality and size of the rigid-flexible circuit board are becoming more and more stringent. The rigid-flex board is more and more widely used due to its advantages of easy assembly, good signal transmission reliability and lightness and thinness.

Referring to fig. 10, in order to control the aspect ratio of the conventional rigid-flex board, a protective layer 202 (CVL for short) of the flexible circuit board 201 is partially embedded, specifically, a section extends from the flexible circuit board 201 to the hard board 203. Therefore, the area of the embedded protection layer 202 in the hard board is thicker than the area not covered by the protection layer 202, and the uneven thickness causes the glue to remain in the blind holes when the blind holes are formed in the area of the embedded protection layer 202, so that the copper metal can not be plated during hole filling, and the open circuit is caused.

Disclosure of Invention

In view of the above, it is desirable to provide a rigid-flex circuit board and a method for manufacturing the same.

A rigid-flex circuit board comprising: the inner layer substrate comprises a soft base layer and a circuit layer formed on the surface of the soft base layer; the rigid substrate covers part of the surface of the circuit layer, the part of the rigid substrate, provided with the rigid substrate, of the rigid circuit board is an interlayer region, the part of the rigid substrate, not provided with the rigid substrate, is a flexible region, and at least one first conductive block connected with the circuit layer is arranged in the rigid substrate and is electrically connected with the circuit layer; the outer-layer substrate comprises an outer copper layer, a dielectric layer and an adhesive layer, the adhesive layer covers the surfaces of the circuit layer and the hard substrate, the dielectric layer covers the surface of the adhesive layer, and the outer copper layer covers the surface of the dielectric layer corresponding to the interlayer area; and the solder mask layer covers the surface of the outer copper layer.

A manufacturing method of a rigid-flexible circuit board comprises the following steps: providing an inner layer substrate, wherein the inner layer substrate comprises a soft base layer and a circuit layer formed on the surface of the soft base layer; covering a hard substrate on part of the surface of the circuit layer, forming a first via hole on the hard substrate to expose the circuit layer of the inner substrate, and filling the first via hole to form a first conductive block which enables the circuit layer to be electrically connected with the hard substrate; pressing a dielectric layer coated with an outer copper layer onto the hard substrate and the circuit layer of the inner substrate not covered by the hard substrate through an adhesive layer, electrically connecting the outer copper layer with the hard substrate, and removing the outer copper layer on the circuit layer of the inner substrate not covered by the hard substrate; and covering a solder mask layer on the surface of the outer copper layer.

The soft and hard combined circuit board utilizes the dielectric layer and the bonding layer of the outer layer substrate to replace the protective layer to cover the flexible area of the inner layer substrate, solves the problem of open circuit caused by uneven thickness of the layer increasing area, and improves the bending performance of the flexible area.

Drawings

Fig. 1 is a schematic cross-sectional view of an inner substrate according to an embodiment of the invention.

FIG. 2 is a schematic cross-sectional view illustrating a rigid substrate laminated to the inner substrate shown in FIG. 1.

FIG. 3 is a schematic cross-sectional view illustrating a process of opening the rigid substrate of FIG. 2.

FIG. 4 is a schematic cross-sectional view of the opened rigid substrate of FIG. 3 after hole filling.

Fig. 5 is a schematic cross-sectional view of the rigid substrate of fig. 4 after being uncapped.

FIG. 6 is a cross-sectional view of the hard substrate of FIG. 5 with an outer substrate laminated thereon.

Fig. 7 is a schematic cross-sectional view of the outer substrate of fig. 6 being perforated and filled.

FIG. 8 is a cross-sectional view of the outer substrate of FIG. 7 being etched.

Fig. 9 is a schematic cross-sectional view of a protective layer covering the outer substrate of fig. 8.

Fig. 10 is a schematic cross-sectional view of a conventional rigid-flex board.

Fig. 11 is a flowchart of a method for manufacturing a rigid-flex board according to an embodiment of the present invention.

Description of the main elements

Soft-hard combined circuit board 100

Inner layer substrate 10

Soft base layer 11

Line layer 13

Conductive via 171

Conductive block 19

Flexible region 101

Increased zone 102

Rigid substrate 20

Hard base layer 21

Inner copper layer 23

Adhesive layer 25

Void 251

First via hole 30

First conductive block 31

Outer layer substrate 40

Outer copper layer 41

Dielectric layer 42

Adhesive layer 43

Second via hole 50

Second conductive block 51

Solder mask layer 60

Flexible circuit board 201

Protective layer 202

Hard board 203

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

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Some embodiments of the invention are described in detail below with reference to the accompanying drawings. The embodiments described below and the features of the embodiments can be combined with each other without conflict.

Referring to fig. 1 to 9 and fig. 11, a method for manufacturing a rigid-flex circuit board according to a first embodiment of the invention includes:

step S1: providing an inner layer substrate, wherein the inner layer substrate comprises a soft base layer and a circuit layer formed on the surface of the soft base layer, and the circuit layer is positioned at the outermost side of the inner layer substrate;

step S2: covering a hard substrate on part of the surface of the circuit layer, forming a first via hole on the hard substrate to expose the circuit layer of the inner substrate, and filling the first via hole to form a first conductive block which enables the circuit layer to be electrically connected with the hard substrate;

step S3: pressing the dielectric layer coated with the outer copper layer onto the hard substrate and the circuit layer of the inner substrate not covered by the hard substrate through the bonding layer;

step S4: electrically connecting the outer copper layer with the rigid substrate;

step S5: removing the outer copper layer on the circuit layer of the inner substrate which is not covered by the rigid substrate;

step S6: and covering a solder mask layer on the surface of the outer copper layer.

Specifically, the manufacturing method of the rigid-flexible circuit board comprises the following steps:

referring to fig. 1, an inner substrate 10 is provided, where the inner substrate 10 includes a flexible base layer 11 and circuit layers 13 respectively formed on two opposite surfaces of the flexible base layer 11, and the two circuit layers 13 are electrically connected to each other. The inner substrate 10 does not include a shield layer 202 for protecting the wiring layer 13.

The inner substrate 10 is divided into a flexible region 101 and build-up regions 102 connected to two opposite sides of the flexible region 101. The flexible region 101 is a portion of the rigid-flex circuit board 100 according to this embodiment, which includes only the inner substrate 10, and the additional layer region 102 also includes a portion of a hard plate.

In one embodiment, the two circuit layers 13 are electrically connected by drilling a through hole in the flexible base layer 11 and electroplating to form a conductive hole 171. In another embodiment, the two circuit layers 13 are electrically connected through the conductive bumps 19 penetrating through the flexible base layer 11 and having two ends respectively extending into the corresponding circuit layers 13. In the present embodiment, the above two modes are simultaneously adopted.

The material of the flexible substrate 11 may be selected from one of Polyimide (PI), Polypropylene (PI), Liquid Crystal Polymer (LCP), Polyetheretherketone (PEEK), Polyethylene Terephthalate (PET), and Polyethylene Naphthalate (PEN).

Referring to fig. 2, a rigid substrate 20 is pressed on the circuit layers 13 on both sides of the flexible base layer 11, and the rigid substrate 20 is used as a rigid board portion of the rigid-flex circuit board and includes a rigid base layer 21 and an inner copper layer 23 formed on a surface of the rigid base layer 21. The rigid substrate 20 is pressed against the wiring layer 13 of the build-up zone 102 by the adhesive layer 25. The portion of the adhesive layer 25 corresponding to the flexible region 101 is cut and removed.

The rigid substrate 20 may be a single-layer board or a multi-layer board, and it is understood that when the rigid substrate 20 is a multi-layer board, the rigid substrate 20 may include a plurality of inner copper layers and a dielectric layer disposed between the inner copper layers, the rigid base layer 21 is the dielectric layer closest to the inner substrate 10, and the inner copper layers 23 may have different metal patterns to form a circuit structure required for the normal operation of the rigid substrate 20.

The hard base layer 21 is made of one of FR-4 grade Polyimide (PI), Polypropylene (PI), Liquid Crystal Polymer (LCP), Polyetheretherketone (PEEK), Polyethylene Terephthalate (PET), Polyethylene Naphthalate (PEN), and the like.

The material of the adhesive layer 25 is a viscous resin, and more specifically, the resin may be at least one selected from polypropylene (PP), epoxy resin, polyurethane, phenol resin, urea resin, melamine-formaldehyde resin, polyimide, and the like.

When in pressing, a gap 251 can be formed between the circuit layer 13 and the rigid base layer 21 corresponding to the flexible region 101 by controlling the pressing force and the usage amount of the adhesive layer 25, and a gap 251 can also be formed between the circuit layer 13 of the flexible region 101 and the rigid base layer 21 by controlling the pressing position.

Thirdly, referring to fig. 3, a hole forming process is performed to form at least one first via hole 30 in a portion of the hard substrate 20 corresponding to the interlayer region 102 along the stacking direction of the inner copper layer 23, the hard base layer 21 and the adhesion layer 25. The first via holes 30 extend to the corresponding wiring layers 13, so that the wiring layers 13 are exposed at the first via holes 30.

Fourthly, referring to fig. 4, the rigid substrate 20 is electroplated to form a first via block 31 in the first via hole 30, so that the inner copper layer 23 is electrically connected to the corresponding circuit layer 13.

In the previous step, when the first via hole 30 is opened, the thickness of the increased layer region 102 is uniform, and there is no other layer causing thickness variation, such as the protection layer 202, so that the colloid of the adhesive layer 25 does not remain in the first via hole 30 due to the non-uniform thickness, so that the first via block 31 formed in the present step cannot electrically connect the inner copper layer 23 and the circuit layer 13.

Fifthly, referring to fig. 5, a cover opening process is performed to remove the rigid substrate 20 corresponding to the flexible region 101 to expose the inner substrate 10 located in the flexible region 101.

Since the adhesive layer 25 corresponding to the flexible region 101 is removed in advance and the gap 251 is formed between the circuit layer 13 of the flexible region 101 and the hard base layer 21 in step S2, a larger working space is provided when the lid opening process is performed in this step, and damage to the inner substrate 10 caused by the lid opening process is reduced.

Sixthly, referring to fig. 6, providing two outermost external substrates 40, where the external substrates 40 include an external copper layer 41, a dielectric layer 42, and an adhesive layer 43, and pressing the two external substrates 40 onto the hard substrate 20 and the exposed inner substrate 10 of the flexible region 101. After the lamination, the adhesive layer 43 fills the gap of the circuit layer 13 at the flexible region 101 to protect the circuit layer 13.

The material of the dielectric layer 42 is preferably Polyimide (PI). The material of the adhesive layer 43 is preferably Thermoplastic Polyimide (TPI), which is convenient for molding and processing and has better flexibility after molding.

In this step, a vacuum press-fit method is preferable.

Seventhly, referring to fig. 7, at least one second via hole 50 is formed in a portion of the outer substrate 40 corresponding to the increased layer region 102 along the stacking direction of the outer copper layer 41, the dielectric layer 42 and the adhesive layer 43. The second via hole 50 extends to the inner copper layer 23 of the rigid substrate 20, thereby exposing the inner copper layer 23 at the second via hole 50. Filling the second via hole 50 to form a second via block 51 for electrically connecting the inner copper layer 23 and the outer copper layer 41.

In an eighth step, referring to fig. 8, a film pressing, exposing, developing, Etching, and Stripping (DES) process is performed on the outer copper layer 41 of the outer substrate 40 to remove a portion of the outer copper layer 41 corresponding to the flexible region 101.

Ninth, referring to fig. 9, solder mask is printed on the outer copper layer 41 of the outer substrate 40, and is exposed and developed to form a solder mask layer 60.

In the present embodiment, the solder mask 60 may be a solder mask (solder mask) or a cover layer (CVL) commonly used in the art.

Alternatively, the manufacturing process of the present invention can also be applied to manufacturing a soft-hard combined circuit board having a circuit structure on only one side.

Referring to fig. 9, an embodiment of the invention further provides a rigid-flex circuit board 100, which includes an inner substrate 10, a rigid substrate 20 covering two side surfaces of two ends of the inner substrate 10, an outer substrate 40 covering two sides of the inner substrate 10 and the rigid substrate 20, and solder mask layers 60 covering two side surfaces of two ends of the outer substrate 40.

The inner substrate 10 includes a flexible base layer 11 and circuit layers 13 respectively formed on two opposite surfaces of the flexible base layer 11, and the two circuit layers 13 are electrically connected. Specifically, the two circuit layers 13 are electrically connected through the conductive blocks 19 penetrating through the flexible base layer 11 and having two ends respectively extending into the corresponding circuit layers 13 and/or the conductive holes 171 formed on the hole walls of the through holes 17 penetrating through the two circuit layers 13 and the flexible base layer 11.

The inner substrate 10 is divided into a flexible region 101 and build-up regions 102 connected to two opposite sides of the flexible region 101.

The rigid substrate 20 includes a rigid base layer 21, and an inner copper layer 23 and an adhesive layer 25 respectively formed on two opposite surfaces of the rigid base layer 21. The rigid substrate 20 is covered on the surfaces of the two ends of the corresponding circuit layer 13 through the bonding layer 25. The inner copper layer 23 is electrically connected to the corresponding circuit layer 13. Specifically, the rigid substrate 20 further includes at least one first conductive block 31. The first conductive block 31 penetrates through the hard base layer 21 and the adhesive layer 25, and has one end connected to the inner copper layer 23 and the other end connected to the circuit layer 13.

The portion of the adhesive layer 25 corresponding to the flexible region 101 is cut and removed.

The rigid substrate 20 may be a single-layer board or a multi-layer board, and it is understood that when the rigid substrate 20 is a multi-layer board, the rigid substrate 20 may include a plurality of inner copper layers and a dielectric layer disposed between the inner copper layers, the rigid base layer 21 is a dielectric layer closest to the inner substrate 10, and the inner copper layers may have different metal patterns to form a circuit structure required for the normal operation of the rigid substrate 20.

The outer layer substrate 40 includes an outer copper layer 41, a dielectric layer 42, and an adhesive layer 43. The dielectric layer 42 and the adhesive layer 43 cover the inner copper layer 23 of the rigid substrate and the circuit layer 13 of the inner substrate 10. The outer copper layer 41 covers the surfaces of the two ends of the dielectric layer 42. The outer copper layer 41 is electrically connected to the inner copper layer 23. Specifically, the outer substrate 40 further includes at least one second via block 51. The second via 51 penetrates the dielectric layer 42 and the adhesive layer 43, and has one end connected to the inner copper layer 23 and the other end connected to the outer copper layer 41.

The solder mask 60 covers the corresponding outer copper layer 41.

It is understood that the inner copper layer 23 and the outer copper layer may also be a circuit layer.

In the rigid-flex circuit board 100, the dielectric layer 42 and the adhesive layer 43 of the outer substrate 40 are used to replace the protective layer 202 to cover the flexible region 101 of the inner substrate 10, so that the problem that the first conductive block 31 cannot electrically connect the inner copper layer 23 and the circuit layer 13 due to uneven thickness of the build-up region 102 is solved, and the flexibility of the flexible region 101 is improved because the dielectric layer 42 is preferably made of polyimide and the adhesive layer 43 is made of thermoplastic polyimide.

It is understood that various other changes and modifications may be made by those skilled in the art based on the technical idea of the present invention, and all such changes and modifications should fall within the protective scope of the claims of the present invention.

Claims

1. A rigid-flex circuit board comprising:

the inner layer substrate comprises a soft base layer and a circuit layer formed on the surface of the soft base layer;

the rigid substrate covers part of the surface of the circuit layer, the part of the rigid substrate, provided with the rigid substrate, of the rigid circuit board is an interlayer region, the part of the rigid substrate, not provided with the rigid substrate, is a flexible region, and at least one first conductive block connected with the circuit layer is arranged in the rigid substrate and is electrically connected with the circuit layer;

the outer-layer substrate comprises an outer copper layer, a dielectric layer and an adhesive layer, the adhesive layer covers the surfaces of the circuit layer and the hard substrate, the dielectric layer covers the surface of the adhesive layer, and the outer copper layer covers the surface of the dielectric layer corresponding to the interlayer area; and

and the solder mask layer covers the surface of the outer copper layer.

2. The rigid-flex circuit board of claim 1, wherein the dielectric layer is made of polyimide, and the bonding layer is made of thermoplastic polyimide.

3. The rigid-flex circuit board of claim 1, wherein the rigid substrate comprises a rigid base layer and an inner copper layer formed on a surface of the rigid base layer, the rigid substrate is covered on the circuit layer by an adhesive layer, and the first conductive bump penetrates through the rigid base layer and the adhesive layer to electrically connect the inner copper layer and the circuit layer.

4. The rigid-flex circuit board of claim 3, wherein the outer substrate further comprises at least one second conductive block, the second conductive block penetrates through the dielectric layer and the adhesive layer, one end of the second conductive block is connected with the inner copper layer, and the other end of the second conductive block is connected with the outer copper layer.

5. The rigid-flex circuit board of claim 4, wherein the number of the circuit layers of the inner substrate is two, and the two circuit layers are respectively formed on two opposite surfaces of the flexible base layer; the number of the hard substrates is two, and the hard substrates are covered on the corresponding circuit layers respectively; the number of the outer layer substrates is two, and the two outer layer substrates are respectively covered on the corresponding hard substrates and the corresponding circuit layers; the number of the welding-proof layers is two, and the two welding-proof layers are respectively covered on the corresponding outer-layer base plates.

6. A manufacturing method of a rigid-flexible circuit board comprises the following steps:

providing an inner layer substrate, wherein the inner layer substrate comprises a soft base layer and a circuit layer formed on the surface of the soft base layer;

covering a hard substrate on part of the surface of the circuit layer, forming a first via hole on the hard substrate to expose the circuit layer of the inner substrate, and filling the first via hole to form a first conductive block which enables the circuit layer to be electrically connected with the hard substrate;

pressing a dielectric layer coated with an outer copper layer onto the hard substrate and the circuit layer of the inner substrate not covered by the hard substrate through an adhesive layer, so that the outer copper layer is electrically connected with the hard substrate, and removing the outer copper layer not covered by the hard substrate; and

and covering a solder mask layer on the surface of the outer copper layer.

7. The method for manufacturing the rigid-flex circuit board according to claim 6, wherein the dielectric layer coated with the outer copper layer is vacuum laminated on the rigid substrate.

8. The method as claimed in claim 6, wherein the step of providing the rigid substrate includes providing the rigid substrate having a rigid base layer and inner copper layers and adhesive layers respectively formed on two opposite surfaces of the rigid base layer, and pressing the rigid substrate onto the circuit layers through the adhesive layers during the pressing step to electrically connect the inner copper layers and the corresponding circuit layers.

9. The method of claim 8, wherein a second via hole is formed through the dielectric layer and the adhesive layer and extends to the inner copper layer, and then a second via block is formed in the second via hole to electrically connect the inner copper layer and the corresponding outer copper layer.

10. The method for manufacturing a rigid-flex circuit board according to claim 9, wherein the circuit layers are formed on two opposite surfaces of the flexible base layer; covering the hard substrate on the two circuit layers respectively; covering the two circuit layers and the hard substrate with dielectric layers covered with the outer copper layers respectively; and covering the two outer copper layers with the solder mask layers respectively.