CN114615813A

CN114615813A - Production process of flexible circuit board with locally thin and thick circuit layer

Info

Publication number: CN114615813A
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: 2022-06-10
Anticipated expiration: 2042-03-12
Also published as: CN114615813B

Abstract

The invention provides a production process of a flexible circuit board with a locally thin and thick circuit layer, which is characterized by comprising the following steps of: and (3) adopting three photosensitive dry film pasting, exposure and developing processes to complete pad hole, via hole copper plating metallization, circuit etching and partial circuit copper plating thickening processes to obtain a flexible circuit board semi-finished product with two-side circuits conducted through hole copper, a thin local circuit and a thick local circuit, and then carrying out covering film pasting, nickel gold plating, appearance processing and other processes to obtain the required flexible circuit board finished product with the local thin and local thick circuit layer. The invention solves the problem that some flexible circuit boards are locally thin and some flexible circuit boards are locally thick so as to meet the performance requirements of electronic products.

Description

Production process of flexible circuit board with locally thin and thick circuit layer

Technical Field

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

Background

With the progress of electronic technology, electronic products are more and more developed in multi-function and miniaturization aspects, because flexible circuit boards have bendable and bendable performance, and are more and more widely applied to electronic products, many electronic products need to be thin in circuit layout due to chip, structure, circuit performance and other reasons, some local circuits need to be thin, such as some high-density signal lines, or some parts need to be better flexible, some parts need to be circuits resistant to larger current, the thickness of copper foil needs to be increased to increase the circuit sectional area when the line width layout is limited, namely, the current-carrying capacity of the circuits, such as power lines, ground lines, bonding pads and other parts, are increased by increasing the sectional area, and therefore, the flexible circuit boards with different circuit thicknesses of local thin and local thick need to be manufactured to meet the needs of the electronic products. Generally, the thinner the copper foil thickness, the easier the etching of the fine line, and when the line width is less than 2 times the copper foil thickness, the etching is difficult, and if a copper foil with a thicker thickness is used for the thick line, the etching of the fine line is obviously impossible, so a method must be found to solve the contradiction.

Disclosure of Invention

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

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

the production process of the flexible circuit board with the locally thin and thick circuit layer is characterized in that:

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

step 2: pasting a first dry film after the hole is blackened, exposing and developing through a laser direct imaging system to obtain a semi-finished product, wherein only the bonding pad part, the hole passing disc part and the electroplating pinch point part expose the copper foil, and other parts are protected by the first dry film;

and step 3: copper plating is carried out on the semi-finished product obtained in the step 2 according to the requirement of the thickness of the hole copper, and a copper layer with a specified thickness is plated on the copper-plated pad part, the copper-plated pad hole, the copper-plated through-hole plate part and the copper-plated through hole;

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

and 5: c, pasting a second dry film with a thickness larger than that of the first dry film on the semi-finished product obtained in the step 4 after the hole is plated with copper and metalized, exposing and developing through a laser direct imaging system, and forming a semi-finished product with copper foil to be etched exposed after developing and other circuits required being protected by the dry film;

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 thin circuits, line spacing, copper-plated pad parts, copper-plated pad holes, copper-plated via holes and process leads on two sides;

and 7: pasting a third dry film which is thicker than the first dry film to the semi-finished product obtained in the step 6, exposing and developing through a laser direct imaging system to form a semi-finished product with a structure that only the copper foil and the process lead of the part of the local wide circuit are exposed, and other circuits are protected by the third dry film;

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

and step 9: removing the third dry film to obtain a semi-finished flexible circuit board with a thin local thin circuit, a thick local wide circuit plated with a thickened copper layer and a thick process lead plated with the thickened copper layer on two sides, wherein the two sides of the semi-finished flexible circuit board are conducted through a copper-plated pad part, a copper-plated pad hole, a copper-plated via hole disc part and a related circuit of the copper-plated via hole;

step 10: aligning and attaching the adhesive layer covering film on the semi-finished product obtained in the step 9 by using a jig according to the positioning hole, pressing, and baking to obtain a semi-finished product with the copper-plated bonding pad exposed and the gold finger positioned on the thick thickened copper-plated local wide circuit;

step 11: electroplating nickel gold or chemically plating nickel gold on the semi-finished product obtained in the step 10, so as to respectively plate a nickel layer on the copper-plated pad part, the copper-plated pad hole and the gold finger part, thereby forming a nickel-gold-plated copper-plated pad, a nickel-gold-plated copper-plated pad hole and a nickel-gold-plated gold finger;

step 12: and punching the appearance by using a die, and removing the thick process lead plated with the thickened copper layer to obtain a finished product of the flexible circuit board with a circuit layer having a local thin part and a local thick part.

The glue thickness of the glue layer covering film is more than or equal to 0.8 x (the thickness of the copper foil plus the thickness of the copper plating layer of the bonding pad).

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

The invention has the advantages that:

the invention ensures the etching of a thin circuit and the local copper plating to increase the thickness of the copper foil through the thickness of the thin copper foil so as to improve the sectional area of the copper foil, thereby solving the needs that some flexible circuit boards need to be locally thin and some flexible circuit boards need to be locally thick so as to meet the performance requirements of the electronic products.

The invention designs three different exposure files, adopts three photosensitive dry film pasting, exposure and development processes to complete the processes of pad hole, via hole copper plating metallization, circuit etching and partial circuit copper plating thickening, obtains a semi-finished flexible circuit board with circuits on two sides conducted through hole copper, thin local circuits and thick local circuits, and then obtains the required flexible circuit board finished product with thin local circuit and thick local circuit layers through the procedures of covering film pasting, nickel gold plating, appearance processing and the like.

Drawings

The invention is further illustrated with reference to the following figures and examples.

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

FIG. 2 shows the bonding pad and the via pad exposed after the first dry film pasting and developing;

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

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

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

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

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

FIG. 8 is a cross-sectional view of a thickened portion of a 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 wiring layer after laminating a cover film;

fig. 11 shows a finished product obtained by cutting the two-end process wire after nickel-gold plating.

Detailed Description

In order to more clearly illustrate the technical solution of the present invention, the drawings used in the description will be briefly introduced, and it is obvious that the drawings in the description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other embodiments can be obtained according to the drawings without creative efforts. In order to facilitate an understanding of the invention, the invention is described in more detail below with reference to the accompanying drawings and specific examples.

It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may be present. As used in this specification, the terms "upper," "lower," "inner," "outer," "bottom," and the like are used in the orientation or positional relationship indicated in the drawings for convenience in describing the invention and simplicity in description, and do not indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and are not to be considered limiting of 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 file of the perforated bonding pad and the via hole disc of the circuit layers on the two sides is a negative file, the bonding pad and the via hole disc are exposed after the first exposure and development, and the other parts are protected by a first dry film;

second exposure file: the circuit file of the circuit layers on the two sides is a positive file, after the second exposure and development, the required circuit, the bonding pad and the via hole disc are protected by the second dry film, and the exposed part of the copper foil is etched;

third exposure file: and partially protecting the circuit file, namely a positive and negative file, exposing the circuits to be thickened and the bonding pads on the circuits after third exposure and development, and protecting other unnecessary circuits by a third dry film.

The porous bonding pad, the porous pad and the copper plating in the hole are realized through the exposure and development of the first exposure file, the black hole and the copper plating; circuit etching is realized through exposure, development and etching of the second exposure file; and local line thickening is realized through third exposure file exposure and development and process wire copper plating.

The method comprises the following specific steps:

1. the main materials are selected: for a flexible circuit board with a fine circuit, the thinner copper foil is better, and the flexible copper clad plate with the thinnest copper foil of 9um or 12um in the current market is selected to be manufactured.

2. Because the two sides of the double-sided board or the multi-layer board need to be conducted through the hole copper with a certain thickness, the whole hole is drilled and then the black hole copper plating is carried out, however, the copper foil on the two sides of the whole board is plated thickly, and the etching of a fine line is not facilitated.

According to the invention, a dry film is pasted after black holes are adopted, a semi-finished product only exposing a hole-containing bonding pad and a hole-containing pad is obtained by exposure and development through a laser direct imaging system, copper plating is carried out, then the dry film is removed, the dry films are pasted on two sides of the semi-finished product, exposure and development are carried out through the laser direct imaging system, the hole-containing bonding pad, the hole-containing pad and the hole-containing pad as well as required circuits are protected by the dry film, other parts needing etching are exposed out of copper foil, and required circuit layer patterns are obtained after etching and film stripping.

As shown in fig. 1:

a double-sided flexible copper clad laminate with a copper foil 2 covered on a polyimide substrate 1 is adopted, and a pad hole 3, a via hole 4 and an exposure positioning hole are numerically controlled or laser drilled according to a design file, and the structure is shown in figure 1.

As shown in fig. 2:

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

As shown in fig. 3:

then, the semi-finished product is plated with copper according to the requirement of the thickness of the hole copper, and as carbon powder with black holes in the hole is conductive, the copper-plated pad part 6 '(obtained by plating copper on the pad part 6), the copper-plated pad hole 8 (obtained by plating copper on the pad hole 3), the copper-plated via disc part 7' (obtained by plating copper on the via disc part 7) and the copper-plated via hole 9 (obtained by plating copper on the via hole 4) are plated with a copper layer 20 with a specified thickness, as shown in fig. 3.

As shown in fig. 4:

after copper plating, 3-5% sodium hydroxide solution is used for removing the first dry film 5, and a part which is not plated with the copper, except the copper-plated pad part 6 'and the copper-plated pad hole 8, the copper-plated via hole part 7' and the copper-plated via hole 9, is plated with a copper layer 20 with a specified thickness, and the other parts protected by the dry film 5 are obtained, the thickness of the part is unchanged and still is a semi-finished product of the original thin copper foil 2, so that the copper plating metallization process of the pad hole 3 and the via hole 4 is completed, and the structure is shown in fig. 4.

3. As shown in fig. 5:

and (3) pasting a dry film for the second time on the semi-finished product after the hole is plated with copper and metalized, wherein the bonding pad and the via hole plate 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 second dry film 10 thicker than the first dry film 5 is selected, and the dry film latex can be filled in the high and low positions. The designed circuit Gerber file is automatically aligned through a designed positioning hole by adopting a laser direct imaging system and utilizing data output by a CAM workstation, a circuit pattern is accurately exposed on the surface covered with the second dry film 10 by directly driving a laser direct imaging device, and is developed, so that a semi-finished product with only the copper foil 2 needing to be etched exposed after development and other circuits needing to be protected by the dry film 10 is formed, and the structure is shown in figure 5.

As shown in fig. 6:

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

4. As shown in fig. 7:

the semi-finished product after the circuit etching is pasted with the dry film for the third time, and because the pad part 6 and the via hole disc part 7 have the copper plating thickening to become the copper plated pad part 6 'and the copper plated via hole disc part 7' and there is the difference in height between the circuit and the line spacing after the etching, the third dry film 15 thicker than the first dry film 5 is selected for use, and the dry film latex is favorable for filling the high-low position. The designed partial protection circuit Gerber file is subjected to automatic alignment by a laser direct imaging system through a designed positioning hole by utilizing data output by a CAM workstation, a laser direct imaging device is directly driven to accurately expose a protection circuit graph on a board surface covered with a third dry film 15, and the protection circuit graph is developed, so that a semi-finished product of a structure that only a copper foil 2 (namely a copper foil of a part of a partial wide circuit 12) needing copper plating and a process lead 11 are exposed, and other circuits are protected by the third dry film 15 is formed, and the structure is shown in figure 7.

As shown in fig. 8:

and (3) plating copper and thickening the developed semi-finished product by using a process lead electroplating method, plating a thickened copper layer 21 with a specified thickness on a circuit connected with the process lead 11 to form a thick thickened copper layer plated local wide circuit 12 'and a thick thickened copper layer plated process lead 11', and plating copper on other copper foils 2 protected by the third dry film 15, wherein the structure is shown in figure 8.

As shown in fig. 9:

and removing the third dry film 15 to obtain a semi-finished flexible circuit board with thin local fine circuit 13 on two sides, thick local wide circuit 12 'with a thick plated thick copper layer, and thick process lead 11' with a thick plated thick copper layer, wherein the two sides of the semi-finished flexible circuit board are conducted through the copper-plated pad part 6 'and the copper-plated pad hole 8, the copper-plated via plate part 7' and the associated circuits of the copper-plated via hole 9, and the structure is as shown in fig. 9.

5. As shown in fig. 10:

selecting an adhesive layer covering film 16 with the adhesive thickness of more than or equal to 0.8 x (the thickness of the copper foil 2 and the thickness of the copper-plated layer 20 of the pad), aligning by using a jig according to a positioning hole, attaching the adhesive layer covering film to the semi-finished product in the figure 9, performing press fitting, filling the adhesive layer to a low part due to the flowability of the adhesive during the press fitting, filling the high and low parts, and then baking to obtain a semi-finished product with the exposed copper-plated pad part 6 ' and the gold finger part 2 ' on the thick copper-plated local wide line 12 ', wherein the structure is shown in figure 10.

6. As shown in fig. 11:

and electroplating nickel and gold or chemically plating nickel and gold on the semi-finished product, so that nickel layers 22 are respectively plated on the copper-plated pad part 6 ', the copper-plated pad hole 8 and the gold finger part 2 ', and the nickel-gold-plated copper-plated pad 6 ', the nickel-gold-plated copper-plated pad hole 8 and the nickel-gold-plated gold finger 2 ″ are formed.

And (3) punching the appearance by using a die, and removing the thick process lead 11 'plated with the thickened copper layer except the thick local copper-plated wide circuit 12', thereby obtaining a complete flexible circuit board finished product with a circuit layer having a local thin part and a local thick part, wherein the structure is shown in fig. 11.

This flexible line way board finished product, the structure is: covering copper foils 2 on two sides of a polyimide substrate 1, wherein the copper foils 2 are provided with thick local wide lines 12 'plated with thick copper layers and thin local thin lines 13, and the thickness of copper of the thin local thin lines 13 is smaller than that of the thick local wide lines 12' plated with the thick copper layers; the circuits on the two sides are conducted through the copper-plated pad part 6 'and the copper-plated pad hole 8, the copper-plated via hole part 7' and the associated circuits of the copper-plated via hole 9; the gold finger 2 plated with nickel and gold is arranged on the local wide line 12 ' of the thick plated thickened copper layer, the nickel and gold plated bonding pad part 6 ' is plated with nickel and gold to form a bonding pad 6 ', and the nickel and gold plated copper bonding pad hole 8 is formed on the copper plated bonding pad hole 8; except the golden finger 2 'and the bonding pad 6', the two sides of the flexible circuit board are covered with glue layer covering films.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred 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 production process of the flexible circuit board with the locally thin and thick circuit layer is characterized in that:

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

step 10: aligning and attaching an adhesive layer covering film on the semi-finished product obtained in the step 9 by using a jig according to the positioning hole, pressing, and baking to obtain a semi-finished product exposing a copper-plated bonding pad part and a gold finger part positioned on a thick plated thickened copper layer local wide line;

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

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