CN114615813B

CN114615813B - Flexible circuit board production process with local thin and local thick circuit layers

Info

Publication number: CN114615813B
Application number: CN202210243528.6A
Authority: CN
Inventors: 杨贤伟; 叶华; 敖丽云
Original assignee: Fujian Shizhuo Electronic Technology Co ltd
Current assignee: Fujian Shizhuo Electronic Technology Co ltd
Priority date: 2022-03-12
Filing date: 2022-03-12
Publication date: 2023-12-15
Anticipated expiration: 2042-03-12
Also published as: CN114615813A

Abstract

The invention provides a flexible circuit board production process with local thin and local thick circuit layers, which is characterized in that: the three-time photosensitive dry film pasting, exposing and developing processes are adopted to finish the processes of copper plating metallization of a bonding pad hole and a via hole, circuit etching and copper plating thickening of part of the circuit, thus obtaining a semi-finished product of the flexible circuit board with two-sided circuit through hole copper conduction, thin part of the circuit and thick part of the circuit, and then the semi-finished product of the flexible circuit board with the required circuit layer and thin part of the circuit layer is manufactured through the working procedures of film pasting, nickel plating, contour machining and the like. The invention solves the need that some parts of flexible circuit boards are thinner and some parts are thicker so as to meet the performance requirements of the electronic products.

Description

Flexible circuit board production process with local thin and local thick circuit layers

Technical Field

The invention relates to a flexible circuit board, in particular to a production process of a flexible circuit board with locally thin and locally thick circuit layers.

Background

With the progress of electronic technology, electronic products are increasingly developed towards multifunctional and miniaturization, and as flexible circuit boards have flexible and bendable performances, the flexible circuit boards are increasingly widely applied to electronic products, and many electronic products have very thin local circuits on circuit layout, such as high-density signal wires or circuits with higher flexibility at certain positions, and circuits with higher current resistance at certain positions, such as power wires, ground wires, bonding pads and the like, and the copper foil thickness is required to be increased to increase the circuit sectional area when the circuit width layout is limited, namely, the circuit current carrying capacity is increased by increasing the sectional area, so that the flexible circuit boards with different local thin and local thick circuit thicknesses are required to be manufactured to meet the requirements of the electronic products. Generally, the thinner the copper foil is, the easier the thin circuit is etched, and when the line width is less than 2 times the thickness of the copper foil, the etching is difficult, and if the copper foil with a thicker thickness is used for the thick circuit, the thin circuit is obviously not etched, so a method must be found to solve the contradiction problem.

Disclosure of Invention

The invention provides a flexible circuit board production process with locally thin and locally thick circuit layers, which aims to solve the defects in the prior art and solve the requirements that some flexible circuit boards are locally thin and some are locally thick so as to meet the performance requirements of electronic products.

The technical scheme adopted for solving the technical problems is as follows:

the flexible circuit board production process with local thin and local thick circuit layers is characterized in that:

step 1: adopting a double-sided flexible copper-clad plate with copper foil covered on a polyimide substrate, and carrying out numerical control or laser drilling of a bonding pad hole, a via hole and an exposure positioning hole according to a design file;

step 2: attaching a first dry film after the black hole, exposing and developing by a laser direct imaging system to obtain a semi-finished product with only a bonding pad part, a via disc part and an electroplating clamping point part exposed out of the copper foil and other parts protected by the first dry film;

step 3: plating copper on the semi-finished product obtained in the step 2 according to the thickness requirement of the hole copper, wherein a copper layer with a specified thickness is plated on the copper-plated bonding pad part, the copper-plated bonding pad hole, the copper-plated via disc part and the copper-plated via hole;

step 4: removing the first dry film to obtain a semi-finished product after hole copper plating metallization;

step 5: the semi-finished product of the hole copper plating metallization obtained in the step 4 is pasted with a second dry film with a thickness larger than that of the first dry film, and is exposed and developed through a laser direct imaging system, so that a semi-finished product with only copper foil to be etched exposed after development and other needed circuits protected by the dry film is formed;

step 6: etching the semi-finished product obtained in the step 5, removing the second dry film after etching the part of the exposed copper foil to obtain a circuit layer semi-finished product with local wide circuits, local fine circuits, wire spacing, copper-plated bonding pad parts, copper-plated bonding pad holes, copper-plated via disc parts, copper-plated via holes and process wires on two sides;

step 7: the semi-finished product obtained in the step 6 is pasted with a third dry film with a thickness larger than that of the first dry film, and is exposed and developed through a laser direct imaging system, so that a semi-finished product with a structure that only copper foil and process wires of a part with a local wide circuit are exposed and other circuits are protected by the third dry film is formed;

step 8: plating copper on the semi-finished product obtained in the step 7 by using a process wire electroplating method to thicken, plating a thickened copper layer with a specified thickness on a circuit connected with the process wire 1 to form a thick thickened copper layer plated local wide circuit and a thick thickened copper layer plated process wire, wherein other copper foils protected by a third dry film cannot be plated with copper;

step 9: removing the third dry film to obtain a flexible circuit board semi-finished product which is provided with a thin local fine circuit, a thick local wide circuit plated with a thickened copper layer and a thick technological wire plated with a thickened copper layer on two sides and is conducted on the two sides through copper-plated bonding pad parts, copper-plated bonding pad holes, copper-plated via hole disc parts and related circuits of the copper-plated via holes;

step 10: the glue layer covering film is aligned and attached to the semi-finished product obtained in the step 9 by using a jig according to the positioning holes, pressed and baked to obtain a semi-finished product with copper-plated bonding pad parts and golden finger parts on partial wide circuits of the thick thickened copper plating layer;

step 11: electroplating nickel gold or chemical nickel gold on the semi-finished product obtained in the step 10, so that nickel gold layers are respectively plated on the copper-plated bonding pad part, the copper-plated bonding pad hole and the gold finger part, and a nickel gold-plated bonding pad, a nickel gold-plated copper-plated bonding pad hole and a nickel gold-plated gold finger are formed;

step 12: and (3) punching the shape by using a die, and removing the thick technological wire plated with the thickened copper layer to obtain a flexible circuit board finished product with a local thin part and a local thick part of the circuit layer.

The thickness of the adhesive layer covering film is more than or equal to 0.8× (copper foil thickness+copper plating thickness of bonding pad).

The thickness of the copper foil of the double-sided flexible copper-clad plate is 9um or 12um.

The invention has the advantages that:

the invention solves the problem that some flexible circuit boards are partially thinner and some parts are thicker by ensuring the etching of fine lines and increasing the copper foil thickness by partially plating copper to increase the copper foil sectional area through the thickness of the thin copper foil so as to meet the performance requirements of the electronic products.

The invention designs three different exposure files, adopts three processes of pasting a photosensitive dry film, exposing and developing, completes the copper plating metallization of a bonding pad hole and a via hole, circuit etching and partial circuit copper plating thickening process, obtains a flexible circuit board semi-finished product with two-sided circuit through hole copper conduction, thin local circuit and thick local circuit, and then obtains the required flexible circuit board finished product with thin local circuit layer and thick local circuit through the working procedures of pasting a covering film, plating nickel gold, contour machining and the like.

Drawings

The invention will be further described with reference to the drawings and examples.

FIG. 1 is a cross-sectional view of a flexible copper clad laminate after drilling;

FIG. 2 shows the exposed pads and via pads after the first dry film development;

FIG. 3 is a cross-sectional view of a hole copper after copper plating of a black hole;

FIG. 4 is a cross-sectional view after the first dry film removal;

FIG. 5 is a cross-sectional view of the copper surface to be etched after the second dry film development;

FIG. 6 is a cross-sectional view of a circuit layer after etching to remove a second dry film;

FIG. 7 is a cross-sectional view of a circuit with a thickened portion to be plated with copper exposed after the third development of the dry film;

FIG. 8 is a cross-sectional view of the thickened portion circuit after copper plating;

FIG. 9 is a cross-sectional view of the circuit layer after the third dry film is removed;

FIG. 10 is a cross-sectional view of the circuit layer after lamination of the coverlay;

fig. 11 is a finished product obtained by cutting a two-head process wire after nickel plating.

Detailed Description

In order to more clearly illustrate the technical solutions of the present invention, the drawings that are needed in the description will be briefly introduced below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other embodiments may be obtained according to these drawings without inventive effort for a person skilled in the art. In order that the invention may be readily understood, a more particular description thereof will be rendered by reference to specific embodiments that are illustrated in the appended drawings.

It will be understood that when an element is referred to as being "fixed" to another element, it can be directly on the other element or one or more intervening elements may be present therebetween. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or one or more intervening elements may be present therebetween. The terms "upper," "lower," "inner," "outer," "bottom," and the like as used in this specification are used in an orientation or positional relationship based on that shown in the drawings, merely to facilitate the description of the invention and to simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the invention. Furthermore, the terms "first," "second," "third," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

The invention designs three exposure files:

first exposure file: the files of the hole bonding pads and the via pads of the two circuit layers are a negative file, the bonding pads and the via pads are exposed after the first exposure and development, and other parts are protected by the first dry film;

second exposure file: the circuit files of the two circuit layers are positive files, and after the second exposure and development, the required circuits, the bonding pads and the via pads are protected by the second dry film, and the exposed part of the copper foil is etched;

third exposure file: the circuit file is locally protected, which is a yin-yang file, after the third exposure and development, the circuit which needs to be thickened and the bonding pads on the circuit are exposed, and other unnecessary circuits are protected by the third dry film.

Exposing and developing the first exposure file, and realizing hole bonding pads, via holes and copper plating in holes by black holes and copper plating; the circuit etching is realized through the exposure, development and etching of the second exposure file; and (3) realizing local line thickening through exposing and developing the third exposure file and plating copper on the process lead.

The method comprises the following specific steps:

1. the main materials are selected as follows: for a flexible circuit board with a fine line, the thinner copper foil is, and the flexible copper-clad plate with the thickness of 9um or 12um of the current copper foil with the thinnest thickness in the market is selected to manufacture.

2. Because the two sides of the double-sided board or the multi-layer board need to be conducted by hole copper with certain thickness, the copper plating of the black holes is realized by the way of whole drilling, however, the copper foil on the two sides of the whole board is plated with the thickness, which is not beneficial to etching of fine lines.

The invention adopts a dry film sticking method after black holes, exposes and develops the dry film through a laser direct imaging system to obtain a semi-finished product with only the hole welding disk and the via hole disk exposed, then carries out copper plating, then removes the dry film, and then integrally pastes the dry film on two sides, the hole welding disk, the via hole disk and the required circuit are protected by the dry film through the laser direct imaging system, and other parts needing etching expose copper foil, and the required circuit layer pattern is obtained after etching and film stripping.

As shown in fig. 1:

the double-sided flexible copper-clad plate with copper foil 2 covered on polyimide substrate 1 is adopted, and numerical control or laser drilling of bonding pad holes 3, via holes 4 and exposure positioning holes is carried out according to design files, as shown in the structure of figure 1.

As shown in fig. 2:

removing the glue slag in the hole by plasma, carrying out a black hole process to form a layer of nano conductive carbon layer in the hole, micro-etching the copper surface by sulfuric acid hydrogen peroxide on the copper surface to enable carbon powder on the copper surface to fall off, washing and drying, pasting photosensitive dry films on the two surfaces for the first time, then pasting a Gerber file with a designed hole welding disk or via hole, adopting a laser direct imaging system, utilizing data output by a CAM workstation, automatically aligning through the designed positioning hole, directly driving a laser direct imaging device on the surface covered with the first dry film 5, developing, and forming a semi-finished product with only a bonding pad part 6, a via hole disk part 7 and an electroplating pinch point part exposed out of the copper foil 2, and protecting other parts by the first dry film 5, wherein the semi-finished product is structured as shown in figure 2.

As shown in fig. 3:

this semi-finished product is then copper plated as required by the thickness of the hole copper, and since the carbon powder with the black hole in the hole is conductive, the copper plated pad sites 6 '(copper plated from the pad sites 6) and copper plated pad holes 8 (copper plated from the pad holes 3), copper plated via pad sites 7' (copper plated from the via pad sites 7) and copper plated via holes 9 (copper plated from the via holes 4) are each plated with a copper layer 20 of a prescribed thickness, as shown in the structure of fig. 3.

As shown in fig. 4:

after copper plating, the first dry film 5 is removed by 3-5% sodium hydroxide solution to obtain a copper plated metal layer 20 with a prescribed thickness in the pad part 6 'and the copper plated pad hole 8, the copper plated via hole disk part 7' and the copper plated via hole 9, and the other parts protected by the dry film 5 have unchanged thickness and are still semi-finished products of the original thin copper foil 2, thus completing the copper plating metallization process of the pad hole 3 and the via hole 4, and the structure is shown in fig. 4.

3. As shown in fig. 5:

and (3) carrying out secondary dry film pasting on the semi-finished product with the holes plated with copper and metallizing, wherein the bonding pad and the via hole disk are plated with a layer of copper to form a copper-plated bonding pad hole 8 and a copper-plated via hole 9, so that a secondary dry film 10 thicker than the primary dry film 5 is selected, and the dry film emulsion is filled at the height. The designed circuit Gerber file is subjected to laser direct imaging system, data output by a CAM workstation is utilized, the designed positioning holes are utilized to automatically align, the laser direct imaging device is directly driven to accurately expose a circuit pattern on the plate surface covered with the second dry film 10, and the circuit pattern is developed, so that a semi-finished product with only the copper foil 2 to be etched exposed after development and other needed circuits protected by the dry film 10 is formed, and the structure is shown in fig. 5.

As shown in fig. 6:

the developed semi-finished product is etched, and the copper foil 2 is still thin copper of 9um or 12um, so that the thin line is easy to etch, and the etching of line width of more than 18um or 24um can be satisfied, after the part of the exposed copper foil 2 is etched, the second dry film 10 is removed, and the circuit layer semi-finished product with partial wide lines 12, partial thin lines 13, line spacing 14, copper plated pad parts 6', copper plated pad holes 8, copper plated via disc parts 7', copper plated via holes 9 and process wires 11 on two sides is obtained, and the structure is shown in fig. 6.

4. As shown in fig. 7:

and the semi-finished product after the circuit etching is subjected to the third dry film pasting, and the copper plating and thickening of the pad part 6 and the via disc part 7 become copper plated pad part 6 'and copper plated via disc part 7', and the height difference between the circuit and the line after the etching is carried out, so that the third dry film 15 thicker than the first dry film 5 is selected, and the dry film emulsion is filled at the height. The designed local protection circuit Gerber file is subjected to laser direct imaging system, the data output by the CAM workstation is utilized, the designed positioning holes are utilized to automatically align, the laser direct imaging device is directly driven to accurately expose the protection circuit pattern on the plate surface covered with the third dry film 15, and development is carried out, so that a semi-finished product of a structure in which only the copper foil 2 (namely the copper foil of the part of the local wide circuit 12) and the process wire 11 needing copper plating and other circuits are protected by the third dry film 15 is formed, and the structure is shown in fig. 7.

As shown in fig. 8:

the developed semi-finished product is plated with copper and thickened by a process wire electroplating method, a circuit connected with the process wire 11 is plated with a thickened copper layer 21 with a specified thickness, a local wide circuit 12 'plated with the thickened copper layer and a thick process wire 11' plated with the thickened copper layer are formed, and other copper foil 2 protected by a third dry film 15 cannot be plated with copper, so that the structure is shown in fig. 8.

As shown in fig. 9:

and removing the third dry film 15 to obtain a flexible circuit board semi-finished product with thin local fine lines 13, thick local wide lines 12 'plated with thick thickened copper layers and thick process wires 11' plated with thickened copper layers on two sides, wherein the two sides are conducted through the copper-plated bonding pad parts 6', the copper-plated bonding pad holes 8, the copper-plated via hole disc parts 7' and the copper-plated via holes 9, and the related lines are structured as shown in fig. 9.

5. As shown in fig. 10:

the adhesive layer covering film 16 with the adhesive thickness of not less than 0.8× (thickness of copper foil 2+thickness of copper plating layer 20 of bonding pad) is selected, and is aligned according to the jig for positioning holes, attached to the semi-finished product of fig. 9, and pressed, and the low part can be filled up due to the fluidity of the adhesive during pressing, and the high and low parts are filled up and then baked, so that the semi-finished product of gold finger part 2 'on the thick copper plating partial wide line 12' is obtained, as shown in fig. 10.

6. As shown in fig. 11:

the semi-finished product is electroplated with nickel gold or electroless nickel gold, so that a nickel gold layer 22 is respectively plated on the copper-plated bonding pad part 6', the copper-plated bonding pad hole 8 and the gold finger part 2', thereby forming a nickel-plated gold-plated bonding pad 6", a nickel-plated gold-plated copper-plated bonding pad hole 8 and a nickel-plated gold-finger 2".

After the outline is punched by a die, the thick and thickened copper layer plating process lead 11 'outside the thick and partially copper plated wide circuit 12' is removed, and a finished flexible circuit board product with a complete circuit layer and a partially thin part and a partially thick part is obtained, and the structure is shown in fig. 11.

The flexible circuit board finished product has the structure that: copper foil 2 is covered on two sides of polyimide substrate 1, copper foil 2 is provided with thick local wide circuit 12 'plated with thick copper layer and thin local thin circuit 13, and the thickness of copper of thin local thin circuit 13 is smaller than that of copper of thick local wide circuit 12' plated with thick copper layer; the circuits on the two sides are conducted through the copper-plated bonding pad part 6', the copper-plated bonding pad hole 8, the copper-plated through hole disc part 7' and the copper-plated through hole 9; the local wide circuit 12 'of the thick copper plating layer is provided with a gold finger 2' plated with nickel, the copper plating pad part 6 'is plated with nickel to form a pad 6', and the copper plating pad hole 8 is plated with nickel to form a copper plating pad hole 8 plated with nickel; the flexible circuit board is covered with an adhesive layer covering film on both sides except the golden finger 2 'and the bonding pad 6'.

In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The flexible circuit board production process with local thin and local thick circuit layers is characterized in that:

2. The process for producing a flexible wiring board having a locally thin and a locally thick wiring layer according to claim 1, wherein: the thickness of the adhesive layer covering film is more than or equal to 0.8× (copper foil thickness+copper plating thickness of bonding pad).

3. The process for producing a flexible wiring board having a locally thin and a locally thick wiring layer according to claim 1, wherein: the thickness of the copper foil of the double-sided flexible copper-clad plate is 9um or 12um.