KR960003294B1 - Adhesive composition for flexible pcb - Google Patents

Abstract

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Description

Adhesive composition for flexible printed circuit board

The present invention relates to an adhesive composition for a flexible printed circuit board having excellent adhesion, flame retardancy, in particular solvent resistance and heat resistance.

In recent years, as the trend of thin, short, high density, and high performance in electric, electronic, and semiconductor fields has been prominent, printed circuit boards have not only become multilayered in the existing rigid single-sided and double-sided centers, but also the share of flexible printed circuit boards is rapidly increasing.

Flexible printed circuit boards have films on both sides of flexible metal foil circuits, and their thickness is very thin (50 ~ 300㎛), so they are mainly used for products requiring thin, small, flexible, and high density that rigid printed circuit boards are difficult to apply. have. Examples of thin and short products are cameras, compact recorders, camcorders, and notebook computers. Typical examples of products requiring flexibility are printheads and tape automated bonds, which are used for semiconductor lead frames. The use of flexible printed circuit boards is expanding day by day.

The substrate of the flexible printed circuit board may be roughly classified into a plastic film (polyimide, polyester, etc.), an adhesive (acrylic, epoxy, polyurethane, polyester, etc.) and metal foil (copper, aluminum, tin, etc.).

In the manufacture of flexible printed circuit boards, a photoresist such as a dry film is laminated on a flexible kappa clad laminate (made by applying an adhesive on a film and laminating), and after exposure is developed on a mask to form a circuit on a copper foil surface, The copper layer is etched with a ferric aqueous solution, the photoresist layer is peeled off with an aqueous alkali solution, the coverlay is laminated, soldered as necessary, and a flexible printed circuit board is manufactured through a series of processes.

As mentioned above, during the manufacturing process of flexible circuit boards, there are chemical treatments such as acid and base, heat lamination, and soldering, so that there is no deterioration of adhesive properties in these processes. The adhesive properties should be maintained, and the solvent resistance of the exposed adhesive surface during copper etching and the heat resistance during soldering are required.

Conventionally, as adhesives for flexible printed circuit boards, epoxy, acrylic, polyurethane, and polyester adhesives are generally widely used. In particular, in manufacturing a flexible disc by adhering a polyimide film and a copper foil among these adhesives, epoxy-based and acrylic rubber / epoxy adhesives are disclosed as described in Japanese Patent Laid-Open No. 63-297483 and Japanese Patent Laid-Open No. 63-120783. It has been used a lot.

However, in the case of epoxy-based adhesives, there are disadvantages in that they have excellent heat resistance, chemical resistance, and dimensional stability, but lack of adhesion and flexibility. Acrylic rubber / epoxy adhesives are solvent type and are dissolved in solvents such as methyl ether ketone, toluene, acetone, and alcohol. As a result, gas is generated during adhesive application and drying and removal of solvents during the manufacturing process of flexible printed circuit boards. This organic solvent gas is not only harmful to workers' health, but also has many risks in terms of workability and economic efficiency. It is relatively disadvantageous, and in the lamination process, residual solvents may cause defects such as bubbles. To solve this problem, Japanese Patent Application Laid-Open No. 61-261307 describes an emulsion adhesive of acrylic / phenol formaldehyde resin. Such an acrylic emulsion adhesive has excellent properties such as adhesion, flexibility, and dimensional stability. It is known that there is a problem in chemical resistance when the adhesive layer is exposed after etching.

Accordingly, an object of the present invention is to provide an adhesive acrylic adhesive composition for flexible printed circuit boards and a method of manufacturing the same, which are free of harmful gases in the manufacturing process and have excellent adhesion, flame retardancy, especially heat resistance and chemical resistance.

In order to achieve the above object as well as another object that can be easily expressed in the present invention, the emulsion type obtained by polymerizing a mixed monomer of alkyl acrylate, acrylonitrile-based, glycidyl methacrylate-based and fluorinated alkyl acrylate By using a curing agent such as phenol resin or melamine resin in the copolymer, it was possible to obtain a flexible printed circuit board adhesive having no harmful gas during manufacture and excellent physical properties.

In the present invention, 20 to 60% by weight of an alkyl acrylate having a glass transition temperature of 5 to 60 ° C. and a weight average molecular weight of 100,000 to 2,000,000 (where the alkyl group has 5 or less carbon atoms), acrylonitrile, methacrylonitrile or a mixture thereof Emulsion type of monomer consisting of ~ 40% by weight, glycidyl acrylate, glycidyl methacrylate or a mixture of 5 to 15% by weight thereof and 1 to 20% by weight of fluorinated alkyl acrylate of the general formula (I) An adhesive for preparing a flexible printed circuit board was prepared using 1 to 10 wt% of phenol resin or melamine resin as a curing agent based on 100 wt% of the mixture of the acrylic copolymer and the viscosity modifier.

Here, R is hydrogen or an alkyl group having 3 or less carbon atoms, and R 'is -CF ₃ , -CH ₂ CF _3, or -CH (CF ₃ ) ₂ .

Polymerization of the emulsion type acrylic copolymer was prepared by emulsion polymerization method by free radical initiation reaction. The monomer content of the fluorinated alkyl acrylate contained in the acrylic copolymer affects heat resistance, chemical resistance and flame retardancy, and as the content thereof increases, the above characteristics are improved. However, when the monomer content of the fluorinated alkyl acrylate is a certain amount or more, the emulsion is unstable, the polymerization yield is lowered, causing a decrease in adhesion. Therefore, the fluorinated alkyl acrylate is preferably 1 to 20% by weight based on 100% by weight of the emulsion type acrylic copolymer. The content of alkyl acrylate + fluorinated alkyl acrylate is suitable 25 to 66% by weight, the content of fluorinated alkyl acrylate should be at least 1% or more can be expected to effect. The content of fluorinated alkyl acrylate is at least 5 in order to have characteristics of heat resistance of 60 seconds or more at 270 ° C., 10% sodium hydroxide, 10% hydrochloric acid solution (room temperature), and chemical resistance of 20 minutes and UL-94 (flame retardant). It should not be less than weight percent. As for the composition ratio of an alkyl acrylate, an acrylonitrile type compound, and a glycidyl acrylate type compound, the above-mentioned range is preferable from a viewpoint of adhesiveness, flexibility, dimensional stability, etc. Solid content of the emulsion type acrylic copolymer was 10 to 60weight% of the range.

In the present invention, a high molecular weight emulsion type acrylic having a weight average molecular weight of 800,000 to 2,000,000 and a low molecular weight emulsion type acrylic of 100,000 to 500,000 were used in order to improve adhesive properties.

At this time, the mixing ratio of high molecular weight and low molecular weight is in the range of 40/60 ~ 80/20% by weight. Low-molecular-weight emulsion-type acrylic improves adhesion but has poor heat resistance, and the fluidity of the adhesive is too high at high temperatures, which is a major cause of defects in terminal bonding due to excessive leakage of adhesive into holes and terminal portions in lamination and heat treatment processes. .

Polyvinyl alcohol having a weight average molecular weight of 100,000 or more was used to adjust the viscosity of the mixed emulsion-type acrylic. At this time, the amount of polyvinyl alcohol added was in the range of 0.2 to 1.0% by weight was adjusted to 100-2,000CPS, which is an appropriate viscosity level for each coating method.

The adhesive of the composition was applied on a polyimide or polyester film having a thickness of 25 to 100 μm using a roll, a reverse, a coma coater, and the like, so that the adhesive was applied to a thickness of 20 to 50 μm, followed by a dryer of 80 to 120 ° C. Residual time 2-7 minutes) was removed to remove moisture, and then, the metal foil, such as copper and aluminum in the heating, pressure roll was bonded at a temperature / pressure of 80 ~ 140 ℃ / 5 ~ 20kg / cm. The following examples and comparative examples further illustrate the present invention, but do not limit the scope of the present invention.

Example 1

A) Preparation of low molecular weight emulsion type acrylic

250 g of deionized distilled water, 2.0 g of sodium lauryl sulfate, and 0.3 g of sodium metabissulfite were added to a reactor and heated to 60 ° C. while stirring under a nitrogen atmosphere.

15.0 g of acrylonitrile, 20.0 g of butyl acrylate, 5.0 g of glycidyl methacrylate, and 5.0 g of 1,1,1,3,3,3-hexafluoro wasopropyl methacrylate were added to emulsify for 20 minutes. Then add 0.8 g of potassium persulfate. After the initial reaction for 30 minutes, 0.5g of n-dodecyl merapton is added and a second monomer is added.

80.0 g of acrylonitrile, 113.0 g of butyl acrylate, 25.0 g of glycidyl methacrylate, and 20.0 g of 1,1,1,3,3,3-hexafluoro isopropyl methacrylate at a constant rate for 3 hours Input. After the addition of the monomer was stirred while maintaining the temperature of 60 ℃ again for 2 hours to complete the reaction. As a result of the reaction, an emulsion-type acrylic having a solid content of 25.0% and a weight average molecular weight of 450,000 was prepared.

The weight average molecular weight of the acrylic resin was measured by using GPC (Gel Permeation Chromatography). At this time, the emulsion type acrylic resin was completely removed from the vacuum dryer at 50 ° C., dissolved in tetrahydrofuran solution to make 0.3% solution, and RI (refractive index) detector was used under tetrahydrofuran developing solution, and the weight average molecular weight was 100,000. The weight average molecular weight of the emulsion type acrylic resin was determined in comparison with the phosphorus polymethmethyl acrylate reference sample.

B) Preparation of high molecular weight emulsion type acrylic

250 g of deionized distilled water, 2.0 g of sodium lauryl sulfate, and 0.1 g of sodium metabissulphite were placed in a reactor and heated to 60 ° C. while stirring under a nitrogen atmosphere.

15.0 g of acrylonitrile, 20.0 g of butyl acrylate, 5.0 g of glycidyl methacrylate, 3.0 g of 1,1,1,3,3,3, -hexafluoro isopropyl methacrylate was added and emulsified for 20 minutes. After adding 0.3 g of potassium persulfate.

80.0 g of acrylonitrile, 125.0 g of butyl acrylate, 25.0 g of glycidyl methacrylate, and 10.0 g of 1,1,1,3,3,3-hexafluoroisopropylmethacrylate at a constant rate for 3 hours Input. After the addition of the monomer was stirred for another 3 hours while maintaining the temperature of 60 ℃ and the reaction was completed. As a result of the reaction, an emulsion-type acrylic having a solid content of 52.0% and a weight average molecular weight of 2,000,000 was prepared.

The weight average molecular weight of the acrylic resin was measured by Gel Permeation Chromatography (GPC). At this time, the emulsion type acrylic resin was completely removed from the vacuum dryer at 50 ° C., dissolved in tetrahydrofuran solution to make 0.3% solution, and RI (refractive index) detector was used under tetrahydrofuran developing solution, and the weight average molecular weight was 1,000,000 The weight average molecular weight of the emulsion-type acrylic resin was determined in comparison with the polymethylmethylacrylate reference sample.

3) Adhesive Manufacturing

The two kinds of emulsion-type acrylic resins having different molecular weights prepared in (A) and (B) were mixed, a polyvinyl alcohol having a weight average molecular weight of 100,000 was added as a viscosity improving agent, and phenolformaldehyde was mixed as a curing agent. It has the same composition as the adhesive was made of viscosity 800CPS.

TABLE 1

The mixed adhesive emulsion (50 wt% solids) of the above composition was coated on a polyimide film having a thickness of 20 μm using a coma coater, dried at 90 ° C. for 2 minutes, and at 110 ° C. for 2 minutes, and then heated to 120 ° C. Laminated a copper foil of 35㎛ at a pressure of 15kg / cm at and heat-treated for 10 hours in a dryer of 110 ℃.

The adhesiveness, chemical resistance, soldering heat resistance, and solvent resistance of the manufactured flexible printed circuit board were evaluated in the same manner as in Table 2, and the results are shown in Table 3.

TABLE 2

Evaluation Standards and Methods of Adhesives for Flexible Printed Circuit Board Adhesives

[Examples 2-3]

Except for changing the amount of low-molecular weight emulsion type acrylic copolymer resin, high molecular weight emulsion type acrylic resin and phenol formaldehyde resin was prepared in the same manner and conditions as in Example 1 to prepare a flexible circuit board and evaluated its characteristics The results are shown in Table 3.

EXAMPLES 4-5

In the same polymerization method as in Example 1, emulsion-type acrylic resins having different molecular weights of the following compositions were polymerized. The solids content was 49% by weight and the molecular weight was 1,800,000 for the high molecular weight emulsion type acrylic and 500,000 for the low molecular weight emulsion type acrylic.

Table 2 shows the results of evaluating the characteristics of the high-molecular-weight and low-molecular-weight emulsion-type acrylic copolymer resins prepared in the same proportions as in Example 1 to prepare a disc for flexible circuit board under the same method and conditions as in Example 1. Shown in

[Comparative Examples 1-4]

The high and low molecular weight two types of emulsion-type acrylic copolymer resins of the same composition as in Example 1 were mixed in the following ratios to prepare a flexible circuit board with the same method and conditions as in Example 1 to evaluate the characteristics thereof. Is shown in Table 3.

[Comparative Example 5]

In the same polymerization method as in Example 1, emulsion-type acrylic resins having different molecular weights of the following compositions were polymerized. The solids content was 49% by weight and the molecular weight was 1,800,000 for the high molecular weight emulsion type acrylic and 500,000 for the low molecular weight emulsion type acrylic.

Table 2 shows the results of evaluating the properties of the emulsion-coated acrylic copolymer resin having different molecular weights prepared above by applying an adhesive on a polyimide film, drying, lamination and post-treatment.

TABLE 3

Characteristic evaluation result

As can be seen from the Examples and Comparative Examples, Comparative Examples 1 and 4 (when the low molecular weight emulsion-type acrylic is mixed less than 10%) showed poor adhesion and flame retardancy, and Comparative Examples In the case of Examples 2 and 3 (when the high molecular weight emulsion-type acrylic is mixed less than 15%), the adhesive property was very good but the heat resistance was poor. However, in Comparative Example 5 containing no unsaturated alkyl acrylate, although the adhesiveness and heat resistance were relatively good, there was a problem in flame retardancy and chemical resistance.

However, as shown in the results of the examples, a high molecular weight emulsion-type acrylic having a fluorinated alkyl acrylate of 5% or more and a weight average molecular weight of 1,000,000 to 2,000,000 and a low molecular weight emulsion-type acrylic of 100,000 to 500,000 are 40 /. In the range of 60 to 80/20% by weight and mixed with 1 to 10% by weight of melamine or phenolic resin curing agent, the adhesives, flame retardancy, heat resistance and chemical resistance were excellent in all properties.

Claims (4)

20 to 60% by weight of an alkyl acrylate having a glass transition temperature of 5 to 60 ° C and a weight average molecular weight of 100,000 to 2,000,000, 20 to 40% by weight of acrylonitrile, methacrylonitrile or a mixture thereof, glycidyl acrylate or glyc Emulsion type acrylic copolymer 99.0-99.9 weight% and a viscosity modifier 0.2- of the monomer composition of 5-15 weight% of cyl methacrylate or its mixture, and 1-20 weight% of unsaturated alkyl acrylates of following General formula (I) The adhesive composition for flexible printed circuit boards which added 5 to 10 weight% of hardeners with respect to 100 weight% of the mixture which mixed 1 weight%. Here, R is hydrogen or an alkyl group having 3 or less carbon atoms, and R 'is -CF ₃ , -CH ₂ CF _3, or -CH (CF ₃ ) ₂ . The emulsion-type acrylic copolymer of claim 1, wherein the high molecular weight emulsion-type acrylic copolymer having a weight average molecular weight of 800,000 to 2,000,000 and the low molecular weight emulsion type acrylic copolymer having a median average molecular weight of 100,000 to 500,000 is 40/60 to Adhesive composition for a flexible printed circuit board, characterized in that the mixture in the range of 80/20% by weight. The adhesive composition of claim 1, wherein the viscosity modifier is polyvinyl alcohol. The adhesive composition of claim 1, wherein the curing agent is a phenol resin or melamine resin.