TWI772095B - Release film for fabricating printed circuit board - Google Patents

Abstract

This invention relates to a release film, which has a buffer layer configured between two release resin layers. The release resin layer is composed of thermoplastic resin with a melting point above 250℃. The buffer layer is composed of curable resin with a cross-linked structure. The storage elastic modulus of the curable resin after curing is 6 MPa or less at 23℃ and 0.6 MPa or less at 300℃. The release film of this invention can be used to fabricate a flexible printed circuit board in a high temperature environment without causing contamination of molds and other supplies.

Description

Release film for printed circuit board manufacturing

The present invention relates to a release film, which is used in the production process of printed circuit boards such as flexible printed circuit boards (FPC).

The commonly used release film contains a buffer layer, which is located in the middle section of the height direction to absorb the unevenness of the cover film and the copper foil substrate (CCL) during heating and stamping. The buffer layer is made of a flexible resin film, for example, a thermoplastic resin such as polyethylene and high-density polyethylene (HDPE) (refer to the following Patent Document 1). The thermoplastic resin film should have its melting point, and when heated above the melting point, the resin has fluidity.

However, the materials used for printed circuit boards, especially the materials used for flexible printed circuit boards, have improved performance, so the processing temperature tends to be higher in recent years. For example, if the resin used in the thermocompression processing of the cover film and CCL, if it is a general-purpose product (FR4) made of epoxy resin, the processing temperature is 150 °C; if it is a heat-resistant product using polyimide resin (FR4) FR5), the processing temperature is 170 °C; while the use of LCP (liquid crystal polymer) (FR6), the processing temperature is 250 °C. Furthermore, the aforementioned "FR" refers to the flame retardant grade of the copper foil substrate of the printed circuit board, which is currently divided into FR1~FR6.

In addition, in order to improve processing efficiency and shorten processing time, it can be performed at high temperature even if the material is FR4 or FR5.

It is generally believed that the processing temperature will be higher in the future.

However, if a homogeneous polymer with a specific gravity of 0.97 is used, the melting point of HDPE is about 136°C; therefore, if HDPE is used as the buffer layer, when the temperature of the release film is heated above the melting point, it will cause The polymer dissolves and contaminates the mold or product.

Patent Document 1: Japanese Patent Laid-Open No. 2007-98816.

So far, it is common knowledge in the industry that the buffer layer is made of resin film, but there are limitations in preventing contamination of tools such as molds.

Therefore, since the present invention uses a curable adhesive as a buffer layer, even in a high-temperature environment, there will be no contamination of articles such as molds.

In order to achieve the above purpose, the release film of the present invention is provided with a buffer layer between two resin layers, and at least one of the two resin layers is a release resin layer composed of thermoplastic resin, and its melting point is above 200 ℃; The buffer layer is made of a curable resin having a cross-linked structure, and the elastic storage rate after curing is 10 MPa or less at 23°C.

The above structure sandwiches the buffer layer between the resin layers, and the buffer layer has a cross-linked structure that prevents the elution of the curable resin. In addition, the curable resin with low elastic storage rate is very soft, so it is possible to ensure the conformability of the unevenness of the release resin layer during hot stamping. The release resin layer of at least one of the resin layers has high heat resistance and can exhibit the function of mold release.

Because the buffer layer of the release film of the present invention is made of curable resin with a cross-linked structure, it will not contaminate articles such as molds even if it is used in a high temperature environment, and at the same time, good unevenness can be obtained.

11: Release film

12: Release resin layer

13: Buffer layer

14: Release coating

15, 16: Resin layer

21a: Single-sided copper foil substrate

21b: Double-sided copper foil substrate

22: cover film

23: Heating plate

FIG. 1 is a cross-sectional view of the release film of the present invention.

FIG. 2 is a sectional view of the separation state of an embodiment of the release film of the present invention.

FIG. 3 is a cross-sectional view of an embodiment of the release film of the present invention during stamping.

4 is a cross-sectional view of another embodiment of the release film of the present invention.

FIG. 5 is a cross-sectional view of another embodiment of the release film of the present invention.

6 is a cross-sectional view of another embodiment of the release film of the present invention.

7 is a cross-sectional view of another embodiment of the release film of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view of the release film 11 . The structure of the release film 11 is that there is a buffer layer between two resin layers, and at least one of the two resin layers is a release resin layer composed of thermoplastic resin.

The release film 11 shown in FIG. 1 has a buffer layer 13 between the two release resin layers 12 , so the release film has at least three layers. The release film 11 has excellent heat resistance and is suitable for high temperature environments exceeding 200°C or 250°C.

The release resin layers 12 are respectively located on the upper and lower outermost layers, which are made of thermoplastic resin with good tensile strength and elongation, and are in contact with the mold or product and have a mold release function.

As mentioned above, in order to be able to use in a high temperature environment exceeding 200 ° C, it is necessary to use appropriate materials, specifically, such as: polyethylene terephthalate (PET), polyethylene naphthalate Alcohol ester (PEN), polybutylene terephthalate (PBT), polyarylate (PAR), polyimide (PI), polyamide (PA), polyimide (PAI), Polyetherimide (PEI), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), etc.; the suitable material is formed of at least one of the aforementioned materials, and its melting point may be 200°C or above 250°C.

The thickness of the release resin layer 12 can be appropriately set according to its material or desired function, for example, it can be set at more than 4 μm and less than 50 μm; and from the viewpoint of the conformability of the unevenness, it can also be set at more than 6 μm and 25 μm. the following.

The side of the release resin layer 12 that is in contact with the buffer layer 13 can be subjected to surface treatment according to requirements, such as surface modification through corona discharge treatment, plasma treatment, primer coating, etc., thereby improving the contact with the buffer layer 13. 's cohesiveness.

The surface opposite to the contact surface of the release resin layer 12 with the buffer layer 13 can also be laminated with other suitable films, or laminated with several layers of the same release resin layer 12 .

The buffer layer 13 is a layer for absorbing the unevenness of the object, and is composed of a curable resin having a cross-linked structure; in other words, the curable resin has a cross-linked structure by curing. In the present invention, the buffer layer 13 uses an adhesive, especially a heat-resistant adhesive whose viscoelastic body has heat resistance. The adhesive is a low elastic storage rate, that is, an adhesive with a small hardness value; for example, when measured at 23°C (room temperature), a frequency of 10Hz, and a heating rate of 5°C/min, the elastic storage rate after curing is measured. 0.1MPa or more and 10MPa or less. Preferably, within the upper limit of 23°C (room temperature), the elastic storage rate is 0.6 MPa or more and 6 MPa or less; or when measured at 300° C., the elastic storage rate is 0.012 MPa or more and 0.6 MPa or less.

The resins used in the aforementioned adhesives have functional groups that contribute to the curing reaction, such as hydroxyl groups, mercapto groups, carboxyl groups, oxetanyl groups, amine groups, vinyl groups, and the like.

Furthermore, its curing methods include isocyanate curing, epoxy resin curing, melamine curing, metal curing, oxazoline curing, free radical curing generated by heat and initiator, ultraviolet and photoinitiator. Radical curing or cation curing, electron beam curing, etc.

The adhesive can also be added with monomers according to requirements to supplement the lack of physical properties; and by adding this, the adhesive can be customized for the purpose of use. For example, in order to improve the adhesive force of the buffer layer 13, a monomer with a low glass transition temperature can be added; if the problem of insufficient heat resistance is considered, a monomer with a high glass transition temperature or a multi-functionality can be added.

From the viewpoint of buffering properties, the thickness of the buffer layer 13 is preferably 5 μm or more and 100 μm or less, and more preferably 25 μm or more and 50 μm or less.

The overall thickness of the release film 11 can be set according to expectations, for example, it can be set at about 13 μm to 200 μm; while the thickness of the most commonly used release film 11 is set at about 25 μm to 75 μm.

Although the thickness varies depending on the required cushioning properties, optimum cushioning properties, or the properties of the release resin layer 12, if the overall thickness of the release film 11 is assumed to be 100, the thickness of the buffer layer 13 can be set to, for example, 20~ around 75%.

The manufacturing method of the release film 11 having the above-mentioned release resin layer 12 and the buffer layer 13 is described below.

An adhesive is coated on one side of one release resin layer 12 . After the adhesive is dried, the adhesive is attached to the other release resin layer 12 at a temperature above 5° C. and below 200° C.

When the adhesive is applied, the reactive resin compound of the adhesive is diluted into an organic solvent or an aqueous solvent. In the organic solvent or aqueous solvent, in addition to water, ethanols such as ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol methyl ether, ethylene glycol ethyl ether, and ethylene glycol monoethyl ether can be used alone or in combination. Ethanol-based solvents such as alkanediol monoalkyl ethers such as butyl ether, propylene glycol methyl ether, propylene glycol monobutyl ether, etc., aromatic hydrocarbons such as toluene and xylene, esters of ethyl acetate and butyl acetate, etc. Ketones such as ketone and methyl isobutyl ketone.

The following methods can be appropriately used for the coating operation: gravure coating, roll coating, comma coating, pneumatic blade coating, contact coating, curtain coating, spin coating, wire bar coating, and the like.

During the drying operation, the solvent contained in the adhesive will volatilize. Although the drying temperature varies depending on the type of solvent used, it is usually set at 23°C or higher and 200°C or lower, and most can be set at 80°C or higher and 120°C or lower.

The lamination system uses the adhesive force of the adhesive layer after drying for dry lamination.

In this sequential production process of coating, solvent drying, and lamination, the adhesive coated on one of the release resin layers 12 will be cured.

The operation and time of curing will vary depending on the curing method. In the case of isocyanate curing, it will be performed at the time of curing treatment (aging treatment) after bonding. The curing treatment can be performed, for example, by leaving it to stand for a predetermined time (for example, 24 to 168 hours) in a heated state of 23 to 60°C.

In the case of epoxy curing, melamine curing, metal curing, oxazoline curing, free radical curing via heat and initiators, curing occurs simultaneously with solvent drying. In the case of ultraviolet curing and electron beam curing, curing is performed by irradiating ultraviolet rays or electron beams before or after bonding. The ultraviolet ray is irradiated with, for example, 50 to 2000 mJ/cm ² , and the electron beam is irradiated with, for example, 10 to 300 kGry.

The release film 11 constructed as above will be used to produce a printed circuit board which will be described later.

FIG. 2 shows an example in which the release film 11 is used in the production of a flexible printed circuit board. Fig. 2(a) is an example of producing a flexible printed circuit board using a single-sided copper foil substrate (CCL) 21a; Fig. 2(b) is an example of producing a flexible printed circuit board using a double-sided copper foil substrate (CCL) 21b. Numeral 22 in FIG. 2 is a cover film (CL). As shown in FIG. 3 , the copper foil substrate is covered up and down with the release film 11, and then sandwiched by the heating plate 23, and then heated and press-molded.

At this time, since the release resin layers 12 located on the upper and lower layers of the release film 11 have the same structure, the release film 11 has no surface or inner surface, and it is not necessary to care about the surface and the inner surface of the release film 11 during use.

Heating and pressing are carried out at a predetermined temperature and a predetermined time, for example, at a temperature above 150°C and below 300°C, for a time of 15 minutes or more and 120 minutes or less; after cooling to room temperature, the flexible printed circuit board is produced.

Because the buffer layer 13 of the release film 11 is formed of a viscoelastic body, it has a cross-linked structure without a melting point, so even if it is heated and compressed at a high temperature, it can prevent dissolution and prevent the mold or product from being polluted due to resin dissolution. Inhibit the occurrence of adverse events.

Furthermore, since the buffer layer 13 is formed by curing an adhesive with a low elastic storage rate, it can still maintain its conformability to the uneven surface of the product or the like. In particular, if polyetheretherketone (PEEK) is used for the release resin layer 12, the melting point can be as high as 334°C, which not only has high mechanical properties such as tensile strength, but also has better heat resistance, so a high-performance release film can be produced. 11.

In addition, in the prior art, the contact surface between the release film and the heating plate is made of paper or buffer film as an intermediary, but this intermediary can be omitted in the present invention.

Other examples of the release film will be described below.

FIG. 4 is a cross-sectional view of another embodiment of the release film 11 . In this embodiment, the buffer layers 13 are stacked in plural. As shown in the figure, the buffer layer 13 is not limited to only one layer, and may be formed into a plurality of layers depending on the actual conditions of processing.

FIG. 5 is a cross-sectional view of another embodiment of the release film 11 . In this embodiment, the surface of the release resin layer 12 is further provided with a release coating 14 . The release coating 14 is coated with substances such as silicon or fluorine, which can improve or supplement the function of the release resin layer 12 .

FIG. 6 is a cross-sectional view of another embodiment of the release film 11 . In this embodiment, a resin layer 15 is provided between the release resin layer 12 and the buffer layer 13 of one layer. The resin layer 15 can be made of resin with or without mold release properties according to the conditions of use.

The use of the release film 11 with the structure of FIG. 6 has the following advantages: if the synthetic resin used in the release resin layer 12 is expensive, such as polyetheretherketone (PEEK), the amount of the resin used can be reduced.

FIG. 7 is a cross-sectional view of another embodiment of the release film 11 . In this embodiment, the release film 11 has a buffer layer between two resin layers. One of the two resin layers is a release resin layer 12 composed of thermoplastic resin, and the other layer is composed of a resin layer 16 without release properties.

11: Release film

12: Release resin layer

13: Buffer layer

Claims (4)

A release film for manufacturing a printed circuit board, comprising a buffer layer between two resin layers, wherein at least one of the two resin layers is a release resin layer composed of thermoplastic resin, the melting point of which is above 200° C. ; The buffer layer is composed of an adhesive with a cross-linked structure or a curable resin composed of a viscoelastic body, and the elastic storage rate after curing is 0.1 MPa or more and 10 MPa or less at 23 ° C and 10 Hz. The release film for manufacturing a printed circuit board according to claim 1, wherein the curable resin is made of a heat-resistant adhesive having heat resistance. The release film for manufacturing a printed circuit board according to claim 1 or 2, wherein the elastic storage rate after curing of the curable resin is 0.6 MPa or more and 6 MPa or less at 23° C. and 10 Hz. The release film for manufacturing a printed circuit board according to claim 1 or 2, wherein the elastic storage rate of the curable resin after curing is 0.012 MPa or more and 0.6 MPa or less at 300° C. and 10 Hz.

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