TWM455320U - Covering film for printed circuit board - Google Patents

Description

Cover film for printed circuit boards

The present invention relates to a cover film, and more particularly to a cover film for a printed circuit board having a low basis weight, low moisture absorption, and excellent curl resistance.

Printed circuit boards are an indispensable material in electronic products, and as the demand for consumer electronics grows, so does the demand for printed circuit boards. Due to the flexible and three-dimensional wiring of flexible printed circuit boards, it is widely used in computers and peripherals, communication, under the influence of the development of technology-based electronic products, which emphasizes lightness, shortness, and flexibility. Products as well as consumer electronics and more.

In general, a flexible printed circuit board is mainly composed of a copper foil substrate (FCCL) and a cover film (CL), and is generally formed by using a polyimide film to form a cover film, or by using a screen printing technique to form a thin film. The insulating ink layer serves as a cover film. However, these conventional cover films have problems such as cracking or peeling of the ink layer.

In addition, most of the cover films on the market currently use a common open polyimine film, and the release material also uses a heavy base paper having a relatively heavy basis weight (thickness). Due to the use of thicker release base paper, the amount of base paper used will increase, so it is necessary to cut down a large number of trees and cause environmental hazard. Therefore, in order to avoid waste of natural resources, environmental protection and sustainable development, and the trend of paperless electronic materials, the characteristics of the release material can be improved, and the use of the release paper can be reduced. At the same time, there is a need to provide the polyimide film with a cover film that meets the requirements for high-density opening, half-cutting, and flatness.

In order to achieve the above and other objects, the present invention provides a cover film for a printed circuit board, comprising: a polyimide layer; an adhesive layer formed on the polyimide layer to adhere the cover film to the cover film a release film formed on the adhesion layer, wherein the release film has a base paper basis weight of 40 to 50 g/m ² and the release force of the release film is 2 to 8 g /5cm.

In the cover film of the present invention, since the polyimine layer of the polyimide layer has heat resistance and chemical resistance, it can be used for a high temperature and high pressure processing process of a printed circuit board when bonded to a cover film, and has a high glass transition state. The advantages of temperature, high dimensional stability, high modulus of elasticity, and low coefficient of thermal expansion; the adhesion layer is cured by a resin, a rubber, and an inorganic filler, having a low dielectric constant and low dielectric consumption characteristics; and the release film includes Low base weight and low thickness of the base paper layer and polyethylene (PE) layer, therefore reducing the amount of base paper used, in line with environmental protection and sustainable development requirements.

A further technical solution of the present invention is that the cover film has low basis weight, low hygroscopicity and excellent curl resistance, and is particularly suitable for high-density small-pore and semi-cut flexible printed circuit boards.

11‧‧‧ Polyimine layer

12‧‧‧Adhesive layer

13, 23‧‧‧ release film

24‧‧‧ Release layer

25‧‧‧First polyethylene layer

26‧‧‧Original paper layer

27‧‧‧Second polyethylene layer

Figure 1 is a schematic cross-sectional view showing the cover film of the present invention; And Fig. 2 is a schematic view showing the cross-sectional structure of the release film in the cover film of the present invention.

The embodiments of the present invention are described by way of specific examples, and those skilled in the art can readily understand the advantages and effects of the present invention from the disclosure of the present disclosure. This creation can also be implemented in a variety of different ways, that is, it can be modified and changed without departing from the scope of this creation.

In the present specification, the glass transition temperature (Tg) is related to the heat resistance of the adhesive layer. In the context of the present invention, the glass transition temperature is one of transition temperatures, especially the phase change temperature of a material, specifically, the temperature of the material is high or low with heating or cooling. At temperature, the phase changes to a rubbery or brittle glass state.

The basis weight of the release film of the present invention may refer to the weight per unit area (g/m ² ) of the release agent layer, the first polyethylene layer, the base paper layer and the second polyethylene layer, and the basis weight value thereof is larger. The thicker the representative thickness; conversely, the smaller the basis weight value, the thinner the thickness.

Referring to FIG. 1, the cover film for a printed circuit board of the present invention comprises: a polyimide layer 11; an adhesion layer 12 formed on the polyimide layer 11 for adhering the cover film to printing a release film 13 formed on the adhesion layer 12, wherein the release film 13 has a base paper basis weight of 40 to 50 g/m ² and the release film is separated The force is 2 to 8 g/5 cm.

In the present creation, the polyimide layer has a thickness of 5 to 50 μm; the adhesion layer has a thickness of 1 to 70 μm; and the release film has a thickness of 90 to 100 μm.

In order for the cover film to have better folding resistance, the thickness of the adhesive layer and the polyimide layer may be the same or the sum of the thicknesses of both is equal to 12 microns.

In the cover film structure of the present invention, a viscous liquid containing a resin, a rubber and an inorganic filler is coated on the polyimide layer, and after drying and curing, an adhesive layer is formed, wherein the resin may be an epoxy resin. The rubber may be a nitrile rubber, and the inorganic filler may be a mixture of one or more selected from the group consisting of titanium dioxide, cerium oxide, aluminum hydroxide, boron nitride, and barium sulfate.

2 is a schematic view showing the structure of a release film in a cover film for a printed circuit board of the present invention, the release film 23 including a release agent layer 24; and a first polyethylene formed on the release agent layer 24. a layer 25; and a base paper layer 26 and a second polyethylene layer 27 formed on the first polyethylene layer 25, wherein the first polyethylene layer 25 is sandwiched between the release agent layer 24 and the base paper layer 26. The base paper layer 26 is interposed between the first polyethylene layer 25 and the second polyethylene layer 27.

The thickness of the release agent layer used in the present application is generally less than 1 micrometer; the thickness of the first polyethylene layer is 15 to 22 micrometers; the thickness of the base paper layer is 50 to 70 micrometers; and the thickness of the second polyethylene layer It is 15 to 22 microns.

In the trend of paperlessness, in order to make the cover film of this creation meet environmental protection requirements, the release base paper used needs to be lighter and thinner to reduce the amount of base paper used, thereby reducing the felling of trees to facilitate sustainable development goals. As this creation A further improvement is that the release film used consists of a base paper layer of low basis weight and low thickness, and a polyethylene layer of low basis weight and low thickness, thereby reducing material cost.

In the basis weight test of the cover film, compared with the comparative example, the base paper layer of the release film of the cover film of the present invention has a small basis weight, thereby reducing the amount of the base paper used and effectively controlling the material cost.

The cover film of the present invention can be completed, for example, by the following process steps: First, a polyimine layer is provided, and epoxy resin, nitrile rubber and dioxide are coated on either surface of the polyimide layer. A viscous liquid composed of strontium. Next, the viscous liquid is cured or semi-cured to form an adhesive layer. Thereafter, the release film was taken, and the release film was attached to the adhesion layer to obtain a finished cover film.

The cover film of the invention can be prepared by a simple process, and the thickness of the adhesive layer and the polyimide layer can be adjusted to achieve high folding density and small density in order to achieve better folding resistance of the cover film. Hole or half cut printed circuit board. In addition, the cover film of the present invention also has a low basis weight and a low release force, which can reduce the amount of base paper used.

Based on the above characteristics, the polyimide film, the adhesive layer and the release film of the cover film of the present invention have good flatness in the downstream flexible printed circuit board, and can withstand the influence of temperature and humidity on the curl.

Example

The inventive cover film was prepared according to the data in Table 1 below using the above-mentioned preparation method for the following test examples. A conventionally used cover film was additionally used as a control.

Further, the release force of the release film of the present invention was tested to be between 2 and 8 g/5 cm.

Test Example 1: Basis weight test

The release film test pieces of Example 1 and Comparative Examples 1 to 3 were cut to a size of 100 mm × 100 mm, and immersed in 1 liter (L) of 2 M sodium hydroxide solution (purchased from Yixing Hongkang Material Co., Ltd.). After separating the layers of each of the release film test pieces, the thickness test was performed using a spiral micrometer (model: m37570), and an analytical balance (model: TG328A(S)) and a precision oven (model: KD-9145A) were used. The basis weight test was carried out and the test results are recorded in Table 2.

Test Example 2: Dipping test

The cover film of Example 1 and Comparative Examples 1 to 3 was subjected to a dipping test, and the test procedure was as follows:

Step 1: Cut the cover film into MD × TD = 28 × 25 cm

Step 2: Place the above cover film on the FPC punching machine (model: AP-320A) for punching

Step 3: Take out the punched film to see the appearance

As a result, the punching result pictures of the glue test are shown in Annexes 1 to 4, wherein Annex 1, Attachment 2, Attachment 3 and Annex 4 are Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3, respectively. Test Results.

The results show that the cover film of this creation (Attachment 1) can meet the requirements of full-cut or semi-cutting of high-density and small-aperture opening of flexible printed circuit boards, which can avoid the appearance of the coating film and cause the appearance of the cover film to be damaged and tear the edge of the small aperture opening. problem.

Test Example 3: Water absorption test

The cover films of Example 1 and Comparative Examples 1 to 3 were subjected to a water absorption test. Each of the cover films was taken out from the sealed bag, and quickly cut into square test pieces of 100 mm × 100 mm, and weighed (W1) using an analytical balance (Model: TG328A(S)), using a precision oven (Model: KD- 9145A) Baking was carried out at 105 ° C for 3 hours, and the test piece taken out after baking was again weighed (W2) using an analytical balance, and repeated 3 times, and the obtained water absorption rate is shown in Table 3.

The water absorption rate is calculated as follows: water absorption %=(W1-W2)×100%/W1

From the results shown in Table 3, the cover film of the present invention has low water absorbency as compared with Comparative Examples 1 to 3.

In addition, the mechanical properties of the inventive cover film were tested. The results show that the cover film of the present invention can satisfy the curl height of the flexible printed circuit board under normal temperature and high humidity. 1.0cm technical requirements.

The above description and examples are merely illustrative of the principles and functions of the present invention and are not intended to limit the present invention. The scope of protection of this creation shall be as set forth in the scope of the patent application described later.

11‧‧‧ Polyimine layer

12‧‧‧Adhesive layer

13‧‧‧ release film

Claims (10)

A cover film for a printed circuit board, comprising: a polyimide layer; an adhesion layer formed on the polyimide layer for bonding the cover film to a printed circuit board; and forming the adhesion layer The release film of the release film, wherein the base paper of the release film has a basis weight of 40 to 50 g/m ² , and the release force of the release film is 2 to 8 g/5 cm. The cover film of claim 1, wherein the adhesive layer is formed by curing a resin, a rubber, and an inorganic filler. The cover film of claim 1, wherein the polyimide layer has a thickness of 5 to 50 μm. The cover film of claim 1, wherein the adhesive layer has a thickness of 1 to 70 μm. The cover film of claim 1, wherein the release film has a thickness of 90 to 100 μm. The cover film of claim 1, wherein the release film comprises a release agent layer; a first polyethylene layer formed on the release agent layer; and a first polyethylene layer formed on the first polyethylene layer a base paper layer and a second polyethylene layer, the first polyethylene layer is interposed between the release agent layer and the base paper layer, and the base paper layer is sandwiched between the first polyethylene layer and the second polyethylene layer Between the layers. The cover film of claim 6, wherein the release agent layer has a thickness of less than 1 micrometer. The cover film of claim 6, wherein the first polyethylene layer has a thickness of 15 to 22 microns. The cover film of claim 6, wherein the base paper layer has a thickness of 50 to 70 μm. The cover film of claim 6, wherein the second polyethylene layer has a thickness of 15 to 22 microns.