CN112969306B

CN112969306B - Process for improving surface tension of polyimide cover film of flexible circuit board

Info

Publication number: CN112969306B
Application number: CN202110158759.2A
Authority: CN
Inventors: 杨贤伟; 叶华; 吴邦华
Original assignee: Fujian Shizhuo Electronic Technology Co ltd
Current assignee: Fujian Shizhuo Electronic Technology Co ltd
Priority date: 2021-02-05
Filing date: 2021-02-05
Publication date: 2022-06-03
Anticipated expiration: 2041-02-05
Also published as: CN112969306A

Abstract

The invention provides a process for improving the surface tension of a polyimide cover film of a flexible circuit board, which comprises the steps of opening a window on the polyimide cover film according to a specified position, then pasting and pressing a copper foil on one side of the cover film with glue to form a semi-finished product with the copper foil exposed at the position of the window on the cover film, and baking the semi-finished product at 160 ℃ for 1 hour, wherein the surface tension dyne value of the cover film is 30; the method is characterized in that: then the semi-finished product is soaked and sprayed by 3-5% sodium hydroxide (NaOH) solution, and is cleaned and dried, and the surface tension dyne value of the covering film is 52 at the moment; and then a dry film with the surface tension dyne value of 38 is pasted on the copper foil at the position of the covering film and the window through a film pasting machine with the temperature of 100-110 ℃. The invention can effectively improve the surface tension of the polyimide covering film, ensures that no air bubbles are generated at the right-angled part of the step formed between the windowing part of the covering film and the copper foil, and improves the product quality.

Description

Process for improving surface tension of polyimide cover film of flexible circuit board

Technical Field

The invention relates to a processing method of a flexible circuit board, in particular to a method for improving the polyimide surface tension of the flexible circuit board by adopting a low-concentration sodium hydroxide solution.

Background

In the production process of the flexible circuit board, sometimes, a window is opened on a polyimide cover film according to a specified position, then a pure copper foil is pasted and pressed on the surface of the cover film with glue to form a semi-finished product with the copper foil exposed at the position of the window of the cover film, a layer of photosensitive dry film is pasted on the cover film, and the circuit in the cover film window is manufactured through the working procedures of film alignment, exposure, development, etching and the like. In the process of pasting the photosensitive dry film, the surface tension of the covering film is low, the covering film is high in tension and easy to stretch at a certain temperature, the bonding quality of the dry film can be hindered, particularly, bubbles are easy to generate at right angles of steps formed between the windowing part of the covering film and the copper foil, liquid medicine can seep during etching, circuit breakage or corrosion is caused, and the product quality is influenced.

As shown in fig. 1

According to the product type and design requirements, a window 5 is opened on a polyimide covering film 2 according to a specified position, then a pure copper foil 1 is pasted and pressed on one side of the covering film 2 with glue, a semi-finished product of the copper foil 1 is exposed at the windowing position of the covering film 2, namely the position of the window 5, the semi-finished product is baked at 160 ℃ for 1 hour, the surface tension of the covering film 2 is tested by a dyne pen, and the dyne value is 30. The semi-finished product is pasted with the photosensitive dry film 3 at 110 ℃ by adopting a film drying machine 100, because the tension of the dry film 3 is greater than the tension of the cover film 2, the cover film 2 and the dry film 3 can generate similar wavy resistance in the film pasting process, so that the dry film 3 can be stretched in the film pasting process, at the corner 4, namely a right angle of a step formed between the windowing part of the cover film 2 and the copper foil 1, and due to the combined action of temperature and stretching, bubbles 41 are easily generated, so that liquid medicine can seep during etching, and the circuit is broken or bitten, and the product quality is influenced.

Disclosure of Invention

The invention provides a process for improving the surface tension of a polyimide cover film of a flexible circuit board, which aims to overcome the defects in the prior art, effectively improve the surface tension of the polyimide cover film, ensure that no bubbles are generated at the right-angled part of a step formed between an open window part of the cover film and a copper foil and improve the product quality.

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

a process for improving the surface tension of a polyimide cover film of a flexible circuit board comprises the steps of opening a window on the polyimide cover film according to a specified position, then pasting and pressing a copper foil on one side of the cover film with glue to form a semi-finished product with the copper foil exposed at the position of the window on the cover film, baking the semi-finished product at 160 ℃ for 1 hour, and then, ensuring that the surface tension dyne value of the cover film is 30;

the method is characterized in that:

then the semi-finished product is soaked and sprayed by 3-5% sodium hydroxide (NaOH) solution, and is cleaned and dried, and the surface tension dyne value of the covering film is 52 at the moment;

then a dry film with the surface tension dyne value of 38 is pasted on the copper foil at the position of the covering film and the window through a 100-plus-110 ℃ film pasting machine;

the specific flow of cleaning and drying is as follows:

the plate is put → 3-5% of sodium hydroxide solution is soaked → 3-5% of sodium hydroxide solution is sprayed → the first countercurrent washing → the second countercurrent washing → new water washing → water absorption → hot air drying.

The principle of the invention is as follows:

comparing the state of the semi-finished product (dyne value 30) which is not treated by sodium hydroxide with the state of the semi-finished product (dyne value 52) which is treated by sodium hydroxide after pasting a photosensitive dry film (dyne value of the dry film is 38):

as shown in FIG. 1, the untreated dry film pasting structure in the prior art has a similar wavy resistance in the film pasting process due to the fact that the tension of the dry film 3 is greater than the tension of the cover film 2, the dry film 3 is stretched when the photosensitive dry film 3 passes through a 100-plus-110 ℃ film pasting machine, bubbles 41 are easily generated at the corner 4 of the windowed window (i.e. the window 5) due to the combined action of temperature and stretching, and the chemical liquid is permeated during etching, so that the circuit is broken or bitten, and the product quality is affected.

The tension coefficient of the semi-finished product treated by the sodium hydroxide (NaOH) solution is obviously higher than that before treatment, as shown in figure 2, the semi-finished product after treatment is used for sticking a dry film, because the surface tension of the covering film 22 is large, the tension of the dry film 33 is unchanged, the sticking resistance of the dry film 33 is small, the chance of stretching the dry film 33 is small, when the photosensitive dry film 33 passes through a 100-plus-110 ℃ sticking film machine, because the tension is small, the covering film 22 and the photosensitive dry film 33 are in a plane state in the film sticking process, the dry film 33 is smoothly stuck on the surface of the covering film 22 and the corner 1 in a window (namely a window 55), particularly when the photosensitive dry film passes through a step formed between the window part of the covering film and a copper foil, bubbles can not be generated due to the combined action of temperature and stretching. Therefore, the circuit is prevented from being broken or bitten when the circuit at the windowing part of the covering film is etched, and the product quality is improved.

The invention has the advantages that:

the semi-finished product with the copper foil exposed at the windowing position of the polyimide cover film is soaked, sprayed and cleaned and dried by adopting a 3-5% low-concentration sodium hydroxide solution, so that the surface tension of the polyimide cover film is improved, the condition that the tension of the cover film is lower than that of a dry film is changed, the problem that bubbles are generated at corners in the process of pasting the photosensitive dry film is solved, the circuit breakage or biting corrosion of a circuit at the windowing position of the cover film during etching is avoided, the working procedures are reduced, and the production efficiency and the product quality are improved.

Drawings

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

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

fig. 2 is a structural view of a flexible circuit board of the present invention.

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 following 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 inventive labor. 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.

As shown in fig. 2:

according to the type and design requirements of the product, a window 55 is opened on the polyimide covering film 22 according to the specified position, then the pure copper foil 11 is pasted and pressed on the side with glue of the covering film 22 to form a semi-finished product with the copper foil 11 exposed at the position of the window of the covering film 22, the semi-finished product is baked at 160 ℃ for 1 hour, and then is soaked in 3-5% sodium hydroxide (NaOH) solution and sprayed, and is cleaned and dried.

The specific cleaning and drying process comprises the following steps: the plate is put → 3-5% of sodium hydroxide solution is soaked → 3-5% of sodium hydroxide solution is sprayed → the first countercurrent washing → the second countercurrent washing → new water washing → water absorption → hot air drying.

And then a dry film 33 is pasted on the copper foil 11 at the positions of the covering film 22 and the window 5 through a 100-110 ℃ laminator.

In the semi-finished product processed by the sodium hydroxide (NaOH) solution, the surface tension of the cover film 22 is tested by a dyne pen, the dyne value is 52, the tension coefficient after processing is obviously higher than the tension coefficient before processing, the dry film 33 is pasted by the processed semi-finished product, because the surface tension of the cover film 22 is large, the resistance for obstructing the pasting of the dry film 33 is small, and the chance for stretching the dry film 33 is small, when the photosensitive dry film 33 passes through a laminator with the temperature of 100 ℃ and 110 ℃, because the tension of the dry film 33 is lower than that of the cover film 22, the dry film 33 acts on the surface of the cover film 22 and the dry film 33 in the pasting process to be a plane condition, the dry film 33 can be smoothly pasted on the surface of the cover film 22 and the copper foil 11 in a windowing, and particularly, when the dry film 33 passes through a step formed between the windowing part of the cover film 22 and the copper foil 11, the dry film 33 is not stretched too much. Therefore, no air bubble is generated at the corner 44 due to the combined action of temperature and stretching, and the circuit breakage or the corrosion of the circuit at the windowing part of the covering film 22 during etching is avoided, thereby improving the product quality.

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. A process for improving the surface tension of a polyimide cover film of a flexible circuit board comprises the steps of opening a window on the polyimide cover film according to a specified position, then pasting and pressing a copper foil on one side of the cover film with glue to form a semi-finished product with the copper foil exposed at the position of the window on the cover film, baking the semi-finished product at 160 ℃ for 1 hour, and then, ensuring that the surface tension dyne value of the cover film is 30; the method is characterized in that: then the semi-finished product is soaked and sprayed by 3-5% sodium hydroxide (NaOH) solution, and is cleaned and dried, and the surface tension dyne value of the covering film is 52 at the moment; then a dry film with the surface tension dyne value of 38 is pasted on the copper foil at the position of the covering film and the window through a 100-plus-110 ℃ film pasting machine; the specific flow of cleaning and drying is as follows: the plate is put → 3-5% of sodium hydroxide solution is soaked → 3-5% of sodium hydroxide solution is sprayed → the first countercurrent washing → the second countercurrent washing → new water washing → water absorption → hot air drying.