CN116347750A

CN116347750A - Flexible circuit board, circuit board end reinforcing structure and manufacturing method thereof

Info

Publication number: CN116347750A
Application number: CN202310291388.4A
Authority: CN
Inventors: 张仁金; 莫欣满; 赵前波; 赵前高
Original assignee: Shenzhen Capel Technology Co ltd
Current assignee: Shenzhen Capel Technology Co ltd
Priority date: 2023-03-17
Filing date: 2023-03-17
Publication date: 2023-06-27

Abstract

The invention discloses a flexible circuit board, a circuit board end reinforcing structure and a manufacturing method thereof, which belong to the technical field of printed circuit boards, and the circuit board end reinforcing structure comprises two layers of flexible boards and reinforcing plates, wherein the reinforcing plates are arranged between the two layers of flexible boards; one side surface of the two layers of flexible plates is respectively connected with the reinforcing plate, the two layers of flexible plates are provided with welding surfaces relative to the other side surface connected with the reinforcing plate, and welding pieces for welding are arranged on the welding surfaces. Through the arrangement of the end reinforcing structure of the circuit board, the problems that the conventional unilateral reinforcing structure cannot be welded on two sides, but the non-reinforcing type double-sided weldable soft board is insufficient in thickness and hardness support are solved, and an end part with a certain thickness and hardness can be formed, wherein the top surface and the bottom surface of the end part are both provided with exposed bonding pads or golden fingers which can be welded on two sides or pulled out and plugged in.

Description

Flexible circuit board, circuit board end reinforcing structure and manufacturing method thereof

Technical Field

The invention relates to the technical field of printed circuit boards, in particular to a flexible circuit board, a circuit board end reinforcing structure and a manufacturing method thereof.

Background

The flexible circuit board (hereinafter referred to as flexible board) is mainly a polyimide film (PI) at present, and has the characteristics of uniform medium, light and thin material, flexibility, bending property and three-dimensional assembly, so that the flexible circuit board is widely applied to electronic products. However, because of the thin and soft characteristics, when the board surface is used in applications such as welding operation, wire-arranging plug plugging and unplugging, etc., the flexible circuit board is soft and unsupported, and is not easy to weld devices, and when the thickness and the hardness are insufficient, the flexible circuit board is difficult to be plugged and unplugged, so that a reinforcing plate (Stiffener) with certain thickness/hardness is generally added on the back of a local bonding pad and an end golden finger position of the flexible circuit board so as to be suitable for the applications.

As shown in fig. 1, the flexible board structure with reinforcement commonly used in industry generally has several forms of lower reinforcement, upper reinforcement and upper-lower staggered reinforcement according to the bonding position of reinforcement (the number of the reinforcements can be 1 or more according to the position requirement of the reinforcement area required by the design); the specific processing method is that the flexible circuit board is processed firstly, then the reinforcing plate with a certain shape is processed, then the adhesive coated part of the reinforcing plate is attached to the appointed surface and the appointed position of the circuit board in a contraposition mode, and the reinforcing type flexible plate is formed through pressing at a certain temperature and pressure.

In three forms shown in fig. 1 (a), b and c), a windowed pad or a golden finger can be designed on the non-reinforced side of the flexible board, and the disadvantage is that only single-sided welding or single-sided finger pulling and inserting can be realized. On the one hand, the welding is designed on one side, the density is limited, and on the other hand, when the design of double-sided contact plug-in is needed, for example, a Type C interface of USB and a Lightning interface adapter plate are needed, and at the moment, the design of arranging golden fingers on two sides is needed, and at the moment, the two-sided welding or plug-in cannot be realized because the three structural forms (a), b and C) are shielded by a reinforcing plate on one side; if the reinforcement is removed to make a double-sided flexible board with a double-sided exposed bonding pad or a golden finger, the thickness of the intermediate dielectric layer (1-1) of the raw material is limited, and is generally only below 0.1mm, and the thicker and more expensive, so the selection of the general industry is not more than 0.1mm, and the thickness of the end part cannot be thickened to the thickness of pluggable or support welding at the moment, so the design without reinforcement cannot meet the requirement.

Disclosure of Invention

1. Technical problem to be solved by the invention

The invention aims to solve the technical problem that the double-sided welding of a circuit board is difficult to realize due to the reinforcing form of the flexible circuit board in the prior art, and provides a flexible circuit board, a circuit board end reinforcing structure and a manufacturing method thereof.

2. Technical proposal

In order to achieve the above purpose, the technical scheme provided by the invention is as follows:

the invention relates to a circuit board end reinforcing structure, which comprises two layers of flexible boards and a reinforcing plate, wherein the reinforcing plate is arranged between the two layers of flexible boards; one side surface of the two layers of flexible plates is respectively connected with the reinforcing plate, the two layers of flexible plates are provided with welding surfaces relative to the other side surface connected with the reinforcing plate, and welding pieces for welding are arranged on the welding surfaces. Through the arrangement of the end reinforcing structure of the circuit board, the problems that the conventional unilateral reinforcing structure cannot be welded on two sides, but the non-reinforcing type double-sided weldable soft board is insufficient in thickness and hardness support are solved, and an end part with a certain thickness and hardness can be formed, wherein the top surface and the bottom surface of the end part are both provided with exposed bonding pads or golden fingers which can be welded on two sides or pulled out and plugged in.

Preferably, the flexible board comprises a film coating layer, a metal layer and a dielectric layer, and the film coating layer, the metal layer, the dielectric layer, the metal layer and the film coating layer are sequentially arranged along the direction from one side surface to the other side surface of the flexible board.

Preferably, a pure glue layer is arranged between the flexible plate and the reinforcing plate, and the flexible plate and the reinforcing plate are connected through the pure glue layer.

Preferably, the end part of the reinforcing plate close to the inner side is provided with a transition section, and the longitudinal sectional area of the reinforcing plate of the transition section is gradually reduced along the direction from outside to inside; through the setting of changeover portion, can alleviate the step height variation when stiffening plate and flexible board are pressed, do benefit to two flexible boards smooth transition bonding together.

Preferably, the transition section of the reinforcing plate is a bevel edge, the included angle between the bevel edge and the horizontal plane is alpha, and the alpha is more than or equal to 15 degrees and less than or equal to 45 degrees.

According to the flexible circuit board, the end part of the circuit board of the flexible circuit board is provided with the end part reinforcing structure, and the end part reinforcing structure is the end part reinforcing structure.

The invention relates to a manufacturing method of a circuit board end reinforcing structure, which is characterized by comprising the following steps:

step (1), respectively carrying out circuit etching on the metal layers of the two layers of flexible boards;

cutting the reinforcing plate into a shape of a part of the flexible plate, which needs to be reinforced;

step (3), coating a pure glue layer between the flexible board and the reinforcing plate, and pressing the two layers of flexible boards after clamping the reinforcing plate;

and (4) cutting the pressed circuit board to form the circuit board with the end reinforcing structure.

Preferably, when the flexible board needs to manufacture the inner layer circuit and the outer layer circuit, firstly manufacturing the inner layer circuit in the step (1); and (3) after the step (3) is finished, manufacturing an outer layer circuit.

Preferably, in the step (3), the lamination layers in the lamination process are sequentially as follows: pressfitting steel sheet, from type rete, silastic layer, from type rete, PE rete, from type rete, wait to press circuit board, from type rete, PE rete, from type rete, silastic layer, from type rete and pressfitting steel sheet layer. And pressing by adopting a pressing covering mode of PE film and silicon rubber, and pressing and combining the soft boards without the reinforcing areas together by using soft deformation to form extrusion filling of the groove areas.

Preferably, in the step (4), the shape of the flexible board is processed by a laser processing mode, and then the shape of the flexible circuit board with the reinforcing plate is milled by a milling machine; the process can avoid the problem of rough edges of the outer soft board caused by direct milling, and the board can be finally molded after being milled to form the required small piece.

3. Advantageous effects

Compared with the prior art, the technical scheme provided by the invention has the following remarkable effects:

the invention relates to a circuit board end reinforcing structure, which comprises two layers of flexible boards and a reinforcing plate, wherein the reinforcing plate is arranged between the two layers of flexible boards; one side surface of the two layers of flexible plates is respectively connected with the reinforcing plate, the two layers of flexible plates are provided with welding surfaces relative to the other side surface connected with the reinforcing plate, and welding pieces for welding are arranged on the welding surfaces. Through the arrangement of the end reinforcing structure of the circuit board, the problems that the conventional single-side reinforcing structure cannot be welded on two sides, but the reinforcing-free double-side weldable soft board is insufficient in thickness and hardness support are solved, and an end part with a certain thickness and hardness can be formed, wherein the top surface and the bottom surface of the end part are provided with bare bonding pads or golden fingers which can be welded on two sides or pulled out and plugged in; the structure design of the reinforcement in the middle is adopted, the reinforcement thickness can be flexibly selected according to the requirement, so that the flexible plate with the end parts with different thicknesses is obtained, the flexible plate is positioned on the double outer sides, the double-sided welding of the end parts can be realized, or double-sided golden fingers are arranged to be pulled out and plugged, more pins can be connected compared with the single-sided design, and the wiring density is increased by more than twice of that of the single side.

Drawings

FIG. 1 is a schematic diagram of a prior art flexible circuit board reinforcement structure;

FIG. 2 is a schematic diagram of a flexible circuit board structure according to the present invention;

FIG. 3 is a schematic view of a reinforcing plate in the reinforcing structure of the end portion of the circuit board according to the present invention;

FIG. 4 is an enlarged schematic view of the end reinforcing structure of the circuit board according to the present invention;

FIG. 5 is a schematic flow chart of step (1) in the method for manufacturing a reinforcing structure at an end of a circuit board according to the present invention;

fig. 6 is a schematic flow chart of the outer layer circuit manufacture in the method for manufacturing the end reinforcing structure of the circuit board.

Reference numerals in the schematic drawings illustrate:

100. a flexible circuit board; 101. an end of the circuit board; 102. a welding surface;

111. a film coating layer; 112. a metal layer; 113. a dielectric layer; 114. a pure glue layer;

120. a reinforcing plate; 121. and a transition section.

Detailed Description

For a further understanding of the present invention, the present invention will be described in detail with reference to the drawings and examples.

The structures, proportions, sizes, etc. shown in the drawings are shown only in connection with the present disclosure, and are not intended to limit the scope of the invention, since any modification, variation in proportions, or adjustment of the size, etc. of the structures, proportions, etc. should be considered as falling within the spirit and scope of the invention, without affecting the effect or achievement of the objective. Meanwhile, the terms such as "upper", "lower", "left", "right", "middle" and the like are also used in the present specification for convenience of description, and are not intended to limit the scope of the present invention, but the changes or modifications of the relative relationship thereof are also regarded as the scope of the present invention which can be implemented without substantial modification to the technical content; in addition, the embodiments of the present invention are not independent of each other, but may be combined.

As shown in fig. 2, in a flexible circuit board 100 of the present embodiment, the circuit board end 101 of the flexible circuit board 100 is provided with an end reinforcing structure for reinforcing the position strength of the circuit board end 101, and in order to avoid the problem that the single-side reinforcing structure cannot be welded on both sides as in the prior art, i.e. the scheme in fig. 1, an end reinforcing structure is provided.

For the end reinforcing structure of the flexible circuit board 100, including two layers of flexible boards and a reinforcing plate 120, as shown in fig. 4, for the flexible boards, the flexible boards include a film coating layer 111, a metal layer 112 and a dielectric layer 113, and along the direction from one side surface to the other side surface of the flexible board, the film coating layer 111, the metal layer 112, the dielectric layer 113, the metal layer 112 and the film coating layer 111 are sequentially arranged. In this embodiment, the dielectric layer 113 is a PI dielectric layer 113, that is, a polyimide dielectric layer 113, and the metal layer 112 is a metal copper layer.

It should be noted that, in this embodiment, the stiffening plate 120 is disposed between two layers of flexible plates, one side surface of the two layers of flexible plates is connected with the stiffening plate 120, the two layers of flexible plates are provided with a welding surface 102 corresponding to the other side surface connected with the stiffening plate 120, and a welding piece for welding is provided on the welding surface 102.

In this embodiment, a pure glue layer 114 is disposed between the flexible board and the reinforcing plate 120, and the flexible board and the reinforcing plate 120 are connected through the pure glue layer 114.

In addition, the flexible boards on the two sides of the reinforcing board 120 can be designed into a single-sided, double-sided or multi-layer board form according to the requirement, so that the space is increased for the flexibility of design; meanwhile, the high-speed signal can directly travel on the surface layers at two sides without changing layers, and the structure is more beneficial to the integrity of the transmission signal.

In addition, a transition section 121 is arranged at the end part of the reinforcing plate 120 close to the inner side, and the longitudinal sectional area of the reinforcing plate 120 of the transition section 121 is gradually reduced along the direction from outside to inside; by the arrangement of the transition section 121, the step height change of the reinforcing plate 120 and the flexible plate during the lamination can be alleviated, and the two flexible plates can be smoothly transitionally bonded together. In this embodiment, as shown in fig. 3, the transition section 121 of the stiffening plate 120 is a bevel edge, an included angle between the bevel edge and a horizontal plane is α, and α is 15 ° or more and 45 ° or less, and in this embodiment, 30 °.

The manufacturing method of the circuit board end reinforcing structure is characterized by comprising the following steps:

step (1), respectively carrying out circuit etching on the metal layers 112 of the two flexible boards; as shown in fig. 5, the copper layer (i.e., metal layer, the same applies to the lower side) of the inner layer on the flexible board (i.e., flexible board, the same applies to the lower side), the inner layer pattern circuit is etched and manufactured by pattern transfer manufacturing method, then the inner layer covering film is attached, and the inner layer circuit is protected by fast press-fit curing. Then a thin layer of pure glue film (namely pure glue layer, the same applies below) is attached on the surface of the covering film.

Step (2), cutting the reinforcing plate 120 into a shape of a part of the flexible plate, which needs to be reinforced; and selecting a reinforcing plate with a certain thickness according to the thickness design requirement, cutting the reinforcing plate into a shape consistent with the flexible plate of the soft plate, and then locally hollowing the flexible plate by a gong machine to manufacture a certain pattern (namely hollowing a non-reinforcing area). Particularly, the edge of the reinforced hollow area is beveled by a bevel edge machine at a certain angle so as to alleviate the step height change when the soft boards are subsequently pressed, and the two soft boards are smoothly transitionally and adhered together.

Step (3), coating a pure glue layer 114 between the flexible board and the reinforcing plate 120, and pressing the two layers of flexible boards after clamping the reinforcing plate 120; laminating two flexible boards with inner layers and a middle reinforcing plate, and pressing at a certain temperature and pressure in a pressure transmission machine; because the reinforcing non-integral plane has the hollowed area, the lamination coating mode of PE film and silicon rubber is adopted during lamination, and specifically, the lamination layers in the lamination process are as follows: the method comprises the steps of pressing a steel plate, releasing a film layer, a silicon rubber layer, releasing the film layer, a PE film layer, releasing the film layer, waiting for a circuit board, releasing the film layer, the PE film layer, releasing the film layer, the silicon rubber layer, releasing the film layer and pressing the steel plate layer, wherein the soft deformation of the silicon rubber is utilized to limit the flow range of the PE film on one hand, and balance the pressure uniformity of the whole laminated plate surface, so that the circuit board, especially a non-reinforced concave soft board area, is uniformly subjected to the pressure effect, otherwise, the thin soft board area cannot be pressed due to the fact that the steel plate is in a hard plane state and has no deformation capability, so that the upper soft board layer and the lower soft board layer cannot be bonded together due to the fact that the soft board area is not pressed and is not pressed; and pressing and filling the soft deformation to form a groove area, and combining the soft boards without the reinforcing area together. Wherein the PE film (polyethylene film) can adopt the thickness of 0.15-0.3 mm, mainly plays a role of fusion filling the concave area at high temperature, and the silicone rubber can adopt 0.8-1.6 mm of red silica gel, can play a role of auxiliary balance pressure and enables the plate surface to be uniformly pressed. After a certain number of layers are laminated according to the sequence of the materials, the press can be pushed to press and form at specific temperature, pressure and time.

Cutting the pressed circuit board to form a circuit board with an end reinforcing structure; the milling machine and the laser processing mode are adopted, in particular, the shape of the soft board is excited by the front and back laser, the reinforced thick board area is milled by the milling machine, the problem of the rough edges of the soft board on the outer side caused by direct milling is avoided, and the board can be finally formed after being milled to form the required small piece.

As shown in fig. 6, when the flexible board needs to manufacture the inner layer circuit and the outer layer circuit, the inner layer circuit is manufactured in step (1); then, after the step (3) is finished, manufacturing an outer layer circuit; the method comprises the steps of drilling holes in the thick area of the end part, copper deposition electroplating, and manufacturing an outer layer circuit by using a pattern transfer method, wherein preferably, vacuum film pasting is adopted during film pasting of the outer layer, and meanwhile, soft roller air compression is adopted, so that a dry film at the step of the outer layer is compacted. And forming an outer layer circuit after etching, then pasting a covering film with a windowed outer layer, protecting the outer layer circuit by fast pressing, curing and finally carrying out surface technology (gold deposition and gold plating) on the exposed copper surface.

The descriptions of the steps (1) and (2) are not limited to the order. The following describes in detail the implementation process of a method for manufacturing a reinforcing structure at an end of a circuit board:

step 1, respectively manufacturing single-sided circuits as inner layers of upper and lower soft board sub-boards through film pasting, exposure, development and etching, then pasting a cover film on the whole board, pressing by a quick press (at 160 ℃/60 min), and pasting a layer of pure glue of 15-40 um for later use;

step 2, selecting an FR4 optical plate (without copper) material (preferably, the reinforcing thickness is between 0.2 and 0.5mm, the lamination gradient is reduced), cutting the material into the size equal to that of a soft plate, then, hollowing and milling the reinforcing of a non-reinforcing area by a milling machine, and obliquely cutting the vertical edge into an oblique edge of 15 to 45 degrees, preferably, 30 degrees by an oblique edge machine;

and 3, laminating the soft board manufactured in the step 1 and the FR4 reinforced optical board manufactured in the step 2 by a vacuum press after sequentially laminating and riveting the upper soft board, the reinforced and lower soft board, and laminating by adopting 2 three-in-one laminating films (combination of release film, PE film and release film), and adding a piece of red silica gel to carry out lamination so as to assist filling up the reinforced hollowed-out area and facilitate the butt-pressing bonding of the soft boards together. The pressing parameters are four sections, the pressure is controlled to be 150psi at the primary pressure, 280psi at the secondary pressure, 400psi at the high pressure at the third and fourth sections, the temperature is controlled to be 100 ℃ at the primary temperature, 140 ℃ at the secondary temperature, 170 ℃ at the high temperature, 70 ℃ at the fourth temperature reducing section, and the total pressing time is controlled to be 180 minutes, so that the multi-layer board mother board with the middle reinforcing structure is obtained after pressing;

and 4, carrying out conventional numerical control drilling, copper deposition and electroplating on the mother board, and then entering an outer layer pattern for manufacturing. Vacuum film pressing production is adopted, the vacuum pumping degree is 4hPa/30sec, the film pressing temperature is 110-120 ℃, the film pressing pressure is 100psi, after the film is taken out of the machine, the film is subjected to air pressing once by a pressing roller with the hardness of 60-70 ℃, then exposure is carried out, and after standing for 30min, development and etching are carried out; and (3) laminating the cut outer layer covering film in alignment after forming the outer layer circuit, and pressing by adopting an air bag type vacuum quick press, wherein the quick press parameters are as follows: vacuumizing for 5-10s, pressing at 250psi and 185 deg.C for 120-160s. After pressing, performing post curing at 150-170 ℃ for 60-90min; and then silk screen printing and surface process treatment (preferably gold deposition) are carried out to obtain the intermediate local reinforced soft board semi-finished product.

And 5, adopting a milling machine and laser processing mode, preferably using laser to control the depth to excite the shape of the soft board (the depth is controlled to be the thickness of the single-side soft board) on the front side and the back side, designing the milling belt to compensate 0.1mm+ milling cutter radius outside the outer shape line, milling the reinforced thick board area by using the milling machine, and using the laser to excite the soft board bonding area to coincide with the hard board area outline, thereby finally forming to obtain the flexible board finished product with the structure.

The invention has been described in detail hereinabove with reference to specific exemplary embodiments thereof. It will be understood that various modifications and changes may be made without departing from the scope of the invention as defined by the appended claims. The detailed description and drawings are to be regarded in an illustrative rather than a restrictive sense, and if any such modifications and variations are desired to be included within the scope of the invention described herein. Furthermore, the background art is intended to illustrate the status and meaning of the development of the technology and is not intended to limit the invention or the application and field of application of the invention.

More specifically, although exemplary embodiments of the present invention have been described herein, the present invention is not limited to these embodiments, but includes any and all embodiments that have been modified, omitted, e.g., combined, adapted, and/or substituted between the various embodiments, as would be recognized by those skilled in the art in light of the foregoing detailed description. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the foregoing detailed description or during the prosecution of the application, which examples are to be construed as non-exclusive. Any steps recited in any method or process claims may be executed in any order and are not limited to the order presented in the claims. The scope of the invention should, therefore, be determined only by the appended claims and their legal equivalents, rather than by the descriptions and examples given above.

Claims

1. The end reinforcing structure of the circuit board is characterized by comprising two layers of flexible boards and a reinforcing plate (120), wherein the reinforcing plate (120) is arranged between the two layers of flexible boards; one side surface of the two layers of flexible plates is respectively connected with the reinforcing plate (120), the welding surface (102) is arranged on the two layers of flexible plates relative to the other side surface connected with the reinforcing plate (120), and a welding piece for welding is arranged on the welding surface (102).

2. The circuit board end reinforcing structure according to claim 1, wherein the flexible board comprises a film coating layer (111), a metal layer (112) and a dielectric layer (113), and the film coating layer (111), the metal layer (112), the dielectric layer (113), the metal layer (112) and the film coating layer (111) are sequentially arranged along the direction from one side surface to the other side surface of the flexible board.

3. The circuit board end reinforcing structure according to claim 1, wherein a pure glue layer (114) is provided between the flexible board and the reinforcing plate (120), and the flexible board and the reinforcing plate (120) are connected through the pure glue layer (114).

4. A circuit board end reinforcing structure according to claim 1, wherein the end of the reinforcing plate (120) near the inner side is provided with a transition section (121), and the longitudinal sectional area of the reinforcing plate (120) of the transition section (121) is gradually reduced in the direction from the outside to the inside.

5. A circuit board end reinforcing structure according to claim 4, wherein the transition section (121) of the reinforcing plate (120) is a sloping side, the angle between the sloping side and the horizontal plane is α, and the angle α is 15 ° or less and 45 °.

6. A flexible circuit board, characterized in that a circuit board end (101) of the flexible circuit board (100) is provided with an end reinforcing structure, which is the end reinforcing structure according to any one of claims 1-5.

7. The manufacturing method of the circuit board end reinforcing structure is characterized by comprising the following steps:

step (1), respectively carrying out circuit etching on metal layers (112) of the two flexible boards;

cutting the reinforcing plate (120) into a shape of a part of the flexible plate, which needs to be reinforced;

step (3), coating a pure glue layer (114) between the flexible board and the reinforcing plate (120), and pressing the two layers of flexible boards after clamping the reinforcing plate (120);

8. The method of claim 7, wherein when the flexible board needs to manufacture the inner layer circuit and the outer layer circuit, the inner layer circuit is manufactured in step (1); and (3) after the step (3) is finished, manufacturing an outer layer circuit.

9. The method for manufacturing a reinforcing structure for an end portion of a circuit board according to claim 7, wherein in the step (3), the lamination layers are sequentially formed by: pressfitting steel sheet, from type rete, silastic layer, from type rete, PE rete, from type rete, wait to press circuit board, from type rete, PE rete, from type rete, silastic layer, from type rete and pressfitting steel sheet layer.

And (3) laminating the PE film and the silicone rubber in a laminating mode.

10. The method according to claim 7, wherein in the step (4), the shape of the flexible board is processed by laser processing, and then the shape of the flexible board (100) with the reinforcing plate (120) is milled by a milling machine.