KR100638199B1 - Heat resistant bonding sheet for flexible printed circuit board - Google Patents

Abstract

Provided is a heat resistant adhesive sheet for a flexible printed circuit board (FPCB) which is excellent in adhesive strength and shows heat resistance and chemical resistance. The heat resistant adhesive sheet(1) comprises a releasing paper(4); an adhesive(3) which comprises a resin mixture comprising 80-90 wt% of a urethane resin and 10-20 wt% of an epoxy resin, 3-30 wt% of an acrylic multifunctional monomer and 5-10 wt% of a potential curing agent and is formed on the releasing paper; and a protective film(1) which is adhered on the adhesive. Preferably the acrylic multifunctional monomer is selected from dipentaerythritol tetraacrylate, dipentaerythritol hexaacrylate and trimethylolpropane triacrylate; and the potential curing agent is dicyandiamide.

Description

Heat resistant adhesive sheet for flexible printed circuit board

1 is a view showing a cross section of the adhesive sheet.

** Explanation of symbols for the main parts of the drawings **

* 1: adhesive sheet 2: protective film

3: adhesive 4: release paper

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat resistant adhesive sheet for a flexible printed circuit board, in which a plurality of flexible printed circuit boards are laminated and bonded to form a multilayer.

As the functions of electronic products are improved in various ways, the base board of the printed circuit board (PCB) used here is made of conventional phenol resin or epoxy resin. Hard sheets have been used, but recently, film-like soft substrates made of polyimide resin have also been used.

Printed circuit boards composed of flexible substrates are called flexible printed circuit boards (hereinafter referred to as FPCBs) because of their flexibility.

FPCBs are thinner than rigid PCBs, making it easier to multilayer substrates and being less constrained in shape.

The configuration of the printed circuit on the substrate is the same as the method of forming a printed circuit on a rigid substrate by the method of forming by etching the copper or aluminum film formed on the substrate.

The FPCB is mainly formed by forming a printed circuit on one side of a polyimide resin on a film. The multilayer FPCB is manufactured by adhering a plurality of polyimide resin films on which a printed circuit is formed with an adhesive.

As an adhesive for bonding a polyimide resin film and a polyimide resin film in which a conventional printed circuit is formed, an adhesive made of a mixture of nitrile-butadien rubber and epoxy resin having excellent heat resistance, or transparency of an acrylic resin and an epoxy resin, if desired Adhesives of a mixture are mainly used, and adhesives of a mixture of a urethane resin and an epoxy resin are also known. (Korean Patent Publication No. 1993-0004427)

 The reason why the adhesive is composed of the two resin mixtures is that the natril-butadiene rubber, the acrylic resin and the urethane resin are used to form a flexible film, and the epoxy resin is to maintain the adhesiveness.

When bonding FPCB and FPCB to form FPCB in multiple layers, the bonding process is generally performed under high temperature (110 ℃ ~ 200 ℃) pressurization (10㎏ ~ 100㎏ / ㎠). The remaining solvent volatilizes, making it difficult to control the process along with the environmental pollution problem, and thus, the productivity is significantly reduced.

For this reason, the adhesive is used in the form of an adhesive sheet (bonging sheet) rather than using a liquid adhesive directly. As shown in FIG. 1, the adhesive sheet is formed by applying an adhesive on a release paper and allowing all the solvent in the applied adhesive to be volatilized so that the adhesive is formed into a film and attaching a protective film.

In use, the protective film is removed and then the adhesive on the film is peeled off from the release paper to be interposed between the FPCB and the FPCB to be bonded and heated and pressurized to bond the FPCB.

Generally, a protective film constituting the adhesive sheet is a polyethylene film having a thickness of 15 to 30 μm, a polypropylene film or a polyester film, and a release paper having a thickness of 50 to 100 μm that is released on one surface is used and the thickness of the adhesive is used. It is configured to about 10 ~ 100㎛.

When forming printed circuits on polyimide resin films, chemicals that are highly corrosive to metals are used, and when the multilayer FPCB is manufactured, the bonding process is performed under high pressure, and the FPCB must maintain durability and strong adhesive force. FPCB adhesives are evaluated to have excellent heat resistance, chemical resistance and flexibility.

When constructing a printed circuit on the FPCB is subjected to a soldering process in the manufacturing process, the adhesive is required for heat resistance that does not cause deformation such as melting for 30 to 60 seconds at 300 ~ 330 ℃.

In the conventional soldering process, the solder (melting point 260 ℃) was mainly used, but as lead is defined as a pollutant, a welding alloy containing no lead is used recently, and the melting point of the welding alloy is about 280 ℃.

Therefore, the heat resistance of the adhesive sheet is also required heat resistance that does not melt at 300 ~ 330 ℃ higher than the melting point of the weld alloy.

Conventional adhesives made of a mixture of nitrile-butadiene rubber and an epoxy resin or a mixture of a urethane resin and an epoxy resin have a significant heat resistance when the thickness of the coating film is less than 30 μm or when the adhesive is in a hygroscopic state in which some moisture in the air is absorbed. There is a problem that the production of defective products occurs frequently by causing deformation such as the adhesive flows down during the soldering process.

Therefore, in this field, it is necessary to develop an adhesive sheet having excellent adhesive strength and heat resistance and chemical resistance of 330 ° C. or higher.

An object of the present invention is to provide an adhesive sheet for multilayer FPCB excellent in chemical resistance and heat resistance. The adhesive sheet of the present invention can be used as an adhesive to bond these films by interposing between the polyimide resin film and the polyimide resin film in which a printed circuit is formed.

The present inventors in the construction of the adhesive sheet for FPCB, an acrylic polyfunctional monomer having a urethane resin and an epoxy resin or a mixture of an acrylic resin and an epoxy resin as a main component of the adhesive and having a plurality of acrylic functional groups (acryl fuctional radicals) The adhesive sheet is composed of a mixture of multifuctional acrylic momer and latent curing agent in a small amount, and the adhesive sheet is excellent in chemical resistance and heat resistance compared to the acrylic polyfunctional monomer and latent curing agent. It was confirmed that the obtained to complete the present invention.

The present invention relates to an adhesive sheet for FPCB.

As shown in FIG. 1, the adhesive sheet of the present invention has a structure in which an adhesive 3 is coated on a release paper 4 and a protective film 2 is laminated thereon.

The present invention will be described in detail with reference to the following Examples.

Example

<Manufacture of urethane resin adhesive>

Preparation Example 1

800 g (10.5 mol) of polypropylene glycol, 490 g (5.0 mol) of maleic anhydride, and 740 g (5.0 mol) of phthalic anhydride were dissolved in 20 g of xylene and condensation reaction under an inert atmosphere in which nitrogen gas was injected. Let's do it.

When the condensation reaction is complete, 100 ml of xylene is added to lower the viscosity. 0.3 mole of xylene diisoeyanate is slowly added dropwise to the urethane reaction to form a one-component urethane resin. Solid content of this urethane resin was 40%.

Polyurethane adhesives include one-component (one-component) and two-component (two-component) types depending on their usage. The curing of the end group (-NCO) of the polymer with water in the air or other high molecular material in itself is called a one-part type, and the curing with a polyol or another curing agent is called a two-part type.

To about 100 g of the one-component urethane resin, about 10 g of an epoxy resin was mixed, 15 g of dipentaerythritol tetrahexa acrylate was added thereto, and 5 g of dicyandiamide was added as a latent curing agent. Get

In this embodiment, the dipentaerythritol hexa acrylate is an acrylic polyfunctional monomer containing six acrylic functional groups.

In general, acrylic resins have high heat resistance. In addition, the acrylic monomer has excellent cross ringing properties.

The present inventors can add an acrylic polyfunctional monomer to a mixture of a urethane resin and an epoxy resin or an adhesive mainly composed of an acrylic resin and an epoxy resin to crosslink the resin mixture into a network structure and improve heat resistance. It is anticipated to complete the present invention.

As a result, chemical resistance was greatly improved by crosslinking.

In the present invention, the acrylic polyfunctional monomer is dipenta erythritol hexa acrylate (acrylic functional group 6) pentaerythritol tetraacrylate (pertaerythritol tetraacrylate: acrylic functional group 4) trimethylol propane triacrylate (trimethylol propano triacrylate: acrylic functional group 3) A monomer containing three or more acrylic functional groups as mentioned above is said.

Generally, when a hardening agent for a synthetic resin is mixed with a synthetic resin, the synthetic resin is cured in a short time. After curing, the processing to change the shape of the synthetic resin cannot be performed. Therefore, the curing agent is stored separately from the synthetic resin and mixed with the synthetic resin immediately before curing. Therefore, after mixing the curing agent in the synthetic resin, the time to process the synthetic resin is limited and the time that can be treated is called pot life (可使 時間).

In the present invention, the latent curing agent has a function as a curing agent, but does not immediately cause a curing reaction when added to the synthetic resin, and refers to a curing agent that can cause the curing reaction only under specific conditions such as high temperature or ultraviolet irradiation.

Suitable latent curing agents for use in the present invention include dicyanide and melamine.

In the mixture of the urethane resin and the epoxy resin or the mixture of the acrylic resin and the epoxy resin, dicyanide is cured at 160 ° C. or higher and melamine is cured at 110 ° C. or higher.

Preparation Example 2

In the following Production Example, the one-component urethane resin obtained in Production Example 1 was used as the urethane resin.

100 g of urethane resin

15 g of epoxy resin

Dicydian diamide 5g

20 g of trimethylol furophane

Triacrylate

Preparation Example 3

100 g of urethane resin

15 g of epoxy resin

Dicydian diamide 5g

Pentaerythritol 20g

Tetra acrylate

<Acrylic resin adhesive manufacturing>

Preparation Example 4

100 g of acrylic resin

15 g of epoxy resin

Dicydian diamide 5g

Defenta erythritol 20g

Hexaacrylate

Preparation Example 5

100 g of acrylic resin

15 g of epoxy resin

Dicydian diamide 5g

20 g of trimethylol furophane

Triacrylate

Comparative Example 1

100 g of acrylic resin

15 g of epoxy resin

5 g of ethylene diamine

In the present invention, the adhesive is preferably used in a ratio of 80 to 90% by weight of urethane resin and 10 to 20% by weight of epoxy resin when comprehensively evaluating flexibility, chemical resistance, and heat resistance.

In addition, the acrylic polyfunctional monomer and the latent curing agent added to the resin mixture are suitably used in the range of 5 to 30% by weight of the acrylic polyfunctional monomer and 3 to 10% by weight of the latent curing agent with respect to the resin mixture.

<Production of Adhesive Sheet>

After drying the adhesive obtained in the production example on a release paper and dried to a thickness of 50㎛ and then as shown in Figure 1 to adhere a protective film thereon.

As the protective film, a polypropylene film was used.

<Property Test of Adhesive Sheet>

An adhesive sheet was prepared using the adhesive obtained in the above production examples, and the adhesive sheet was interposed between the polyimide film and the polyimide film and adhered by pressing at 170 ° C. and 30 kg / cm 2, and then peeling strength, chemical resistance, and heat resistance. The test was performed and the results are shown in Table 1 below. In the above heating and pressing bonding step, the curing reaction of the latent curing agent in the adhesive sheet occurs. Test Example 1 in Table 1 below shows the physical properties of the adhesive sheet using the adhesive obtained in Preparation Example 1.

In addition, Test Example 2 is the adhesive of Preparation Example 2, Test Example 3 is the adhesive of Preparation Example 3, Test Example 4 is the adhesive of Preparation Example 4, Test Example 5 is the adhesive of Preparation Example 5, Comparative Example 1 is the arc It shows the physical properties of the adhesive sheet using a conventional adhesive without using a reel-based polyfunctional monomer and a latent curing agent.

[Table 1] Property Test Table of Adhesive Sheet

 Result  Test Example 1  Test Example 2  Test Example 3  Test Example 4  Test Example 5  Comparative Example 1 Adhesive thickness㎛  25  25  25  25  25  25 Peel Strength PI / PI 13 kg / 10 mm 13.5 kg / 10 mm 13 kg / 10 mm 13.7 kg / 10 mm 14 kg / 10 mm 14.5kg / 10mm Peel Strength CU / PI 20 kg / 10 mm 21 kg / 10 mm 20 kg / 10 mm 22 kg / 10 mm 23 kg / 10 mm 25 kg / 10 mm Chemical resistance (23 ℃ for 1 hour in acetone)  pass  pass  pass  pass  pass  pass Soldering heat resistance (soaked for 30 seconds) Room temperature  350 ℃  330 ℃  337 ℃  340 ℃  336 ℃  310 ℃ Soldering heat resistance (soak for 30 seconds)  330 ℃  310 ℃  325 ℃  325 ℃  310 ℃  280 ℃  Housework time  4 months  3 months  4 months  4 months  3 months  1 month

※ Test Methods

-Peel strength (PI / PI): After bonding polyimide (PI) film and polyimide (PI) film with an adhesive sheet, it was tested according to the peel strength test method described in Japanese Standard JISC 6471.

-Peel strength (CU / PI): After bonding copper foil (CU) and polyimide (PI) film with an adhesive sheet, it was tested according to the peel strength test method described in Japanese Standard JC 6471.

-Chemical resistance: After the adhesive sheet was immersed in acetone (23 ℃, 1 hour), the adhesive did not appear peeling phenomenon was passed.

-Soldering heat resistance room temperature: It shows the maximum temperature of molten lead that the adhesive sheet does not cause melting or peeling by immersing the adhesive sheet for 25 seconds in molten lead after storing it for 12 hours at 25 ℃ and 80% relative humidity.

-Soldering heat-absorbing moisture absorption: It shows the maximum temperature of molten lead that the adhesive sheet does not cause melting or peeling by immersing the adhesive sheet for 12 seconds in molten lead after storing it for 12 hours at 25 ℃ and 80% relative humidity.

Pot life: Shows pot life when the adhesive sheet of this example is stored at 5 ° C.

In this example, the adhesive sheet of the present invention was confirmed that the solder heat resistance is increased by at least 20 to 40 ° C. as compared with the conventional adhesive sheet without the acrylic polyfunctional monomer and the latent curing agent.

The adhesive sheet of the present invention is excellent in adhesiveness and has an effect of showing heat resistance and chemical resistance.

Claims (3)

To the resin mixture composed of 80 to 90% by weight of urethane resin and 10 to 20% by weight of epoxy resin on the release paper (4), an acrylic polyfunctional monomer, 3 to 30% by weight, latent curing agent, and 5 to 10% by weight were used. A heat-resistant adhesive sheet for a flexible printed circuit board, wherein an adhesive (3) formed by mixing is applied and a protective film (1) is attached on the adhesive (3). The flexible printed circuit board of claim 1, wherein the acrylic polyfunctional monomer is selected from dipentaerythritol tetra acrylate, dipentaerythritol hexa acrylate, or trimethylol furopan triacrylate, and the latent curing agent is dicyane diamide. Heat-resistant adhesive sheet for. The heat-resistant adhesive sheet for flexible printed circuit board according to claim 1, wherein the protective film (1) is selected from polyethylene film, polypropylene film or polyester film.

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