JPS6020978A - Adhesive composition for flexible printed circuit board substrate - Google Patents

Abstract

PURPOSE:To provide the titled adhesive compsn. having high adhesive power and excellent heat resistance, flexibility and electrical insulation, prepd. by dissolving a water-soluble epoxy compd. having two or more epoxy groups in one molecule, in an aqueous soln. of a specified acrylic copolymer. CONSTITUTION:90-98pts.wt. monomer mixt. consisting of acrylonitrile, acrylic ester and styrene, 1-8pts.wt. (meth)acrylic acid and 1-9pts.wt acrylamide are copolymerized and 20-60pts.wt. water-soluble epoxy compd. having at least two epoxy groups in one molecule (e.g. ethylene glycol diglycidyl ether or glycerol polyglycidyl ether) is dissolved in an aqueous soln. contg. 100pts.wt. above copolymer to obtain the aimed adhesive compsn. for flexible printed circuit board substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an adhesive composition suitable for use in flexible printed circuit boards, and more particularly, to an adhesive composition suitable for use in flexible printed circuit boards. Adhesives used to form metal foil laminates made by bonding sheets together, coverlay sheets made of heat-resistant resin films or heat-resistant resin nonwoven sheets, adhesives, and protective sheets with releasable properties. The present invention relates to a water-based acrylic adhesive that has excellent adhesive strength, heat resistance, fusibility, electrical insulation properties, etc. required for metal foil laminates and coverlay sheets, and that enables safe and easy production of the metal foil laminates and coverlay sheets.

BACKGROUND ART In recent years, electronic devices have become smaller, lighter, and more dense, and demands for their performance are becoming increasingly sophisticated. As one of the countermeasures against this problem, flexible circuit boards are being widely used to make it possible to make electronic devices smaller, lighter, and more dense.

Flexible printed circuit boards are basically
Using a non-woven sheet made of a heat-resistant resin film such as polyester Jugetsu, Boliimi Hitachi January, polyamide-imide resin, Borin (lanocic acid resin, etc.) or fiber strength S of these resins, A metal foil-clad laminate is provided by laminating conductive metal foil such as copper or aluminum using two adhesives.

In addition, the coverlay sheet is produced at the final stage of the printed wiring processing process for the above-mentioned metal foil laminate. U)
After a turn is formed using an etching method or the like (two-strand wiring), it is laminated and bonded onto a funkin pull board for the purpose of preventing the formed metal conductor wiring from deteriorating due to oxidation or the like. This strength barley sheet is made of a heat-resistant resin film or a non-woven sheet similar to that used for the exploitation of metal foil-clad laminates. It is provided with a protective sheet such as treated paper attached.

The adhesive for this flexible metal foil laminate and coverlay sheet (hereinafter collectively referred to as flexible substrate except when special distinction is required) has adhesive strength, heat resistance, flexibility, and electrical insulation properties. In addition, coverlay sheets are also required to have various customizations such as resin flow during lamination processing, so-called wiring part embedding ability, and shelf life in a semi-cured state.

Conventionally, adhesives that meet these requirements include acrylonitrile-butadiene rubber, butyral resin, and
Crosslinkable acrylic rubber system, nylon/epoxy system, acrylonitrile-butadiene/phenol resin system, carboquine-containing acrylonitrile-butadiene/epoxy resin system,
Various adhesives such as acrylic rubber/Evogin type adhesives have been proposed, and among these adhesives, the acrylonide 9-19 diene/phenol resin type adhesive is a relatively well-balanced adhesive for all types of customization and customization. It is widely used. And recently, good electrical insulation properties,
Acrylic rubber/Evogin-based adhesives have been attracting attention due to their excellent performance, including ease of embedding and long shelf life when used in coverlay sheets.

However, all of these adhesives are supplied as solutions of flammable organic solvents such as methyl ethyl ketone, toluene, acetone, and 7x ethanol, so they are difficult to bond with heat-resistant base materials and metal foils and heat-resistant in the production of flexible circuit boards. During processes such as applying and semi-curing the adhesive to the adhesive base material,
The work of volatilizing and removing these organic solvents is inevitable, and this work is highly dangerous and is not good for the health of the workers (both workers), so this work requires special safety and occupational health precautions. It was pointed out that smallpox was necessary.

From this fI perspective, emulsion polymerization type adhesives have finally been developed, and their representative properties include basic performance such as adhesive strength, heat resistance, and flexibility, as well as electrical properties that are unique to acrylic, and cover. An emulsion polymerization type acrylic rubber/evogish adhesive which has excellent embeddability and shelf life when used for reint has now been provided.

However, the solder heat resistance of this emulsion polymerization type adhesive is poor, and this is due to the hygroscopicity of this adhesive. Therefore, it is necessary to appropriately insert a drying process into the printed circuit processing process of the flexible substrate, and in particular, a sufficient drying operation is essential before attaching components to the flexible substrate by soldering. For this reason, the number of work steps is forced to increase, and as a result, productivity and economic efficiency are reduced in terms of work efficiency, so these adhesives are generally not used at present. .

The present invention was developed in view of the above circumstances, and its main purpose is to provide adhesives for flexible substrates that are non-solvent and have properties such as adhesive strength, heat resistance, flexibility, and electrical insulation properties. An object of the present invention is to provide an adhesive assembly for flexible substrates which has excellent properties and which can simplify the manufacturing process of flexible substrates by eliminating the need to appropriately insert a drying process and reducing the number of work steps.

Another object of the present invention is to provide an adhesive composition for flexible substrates that is free from the risk of fire caused by volatile solvents, unlike organic solvent adhesives, and is not harmful to the human body. It is in.

That is, the present invention provides acrylic acid and/or 90 to 98 parts by weight of monomer group (A) consisting of acrylonitrile, acrylic esters, and optionally added styrene.
or an aqueous copolymer (D) consisting of 1-8 parts by weight of methacrylic acid (B) and 1-9 parts of 1-dihydroxyalkyl acrylic acid ester and/or acrylamide (C). A water-soluble epoxy compound (E) having two or more epoxy groups in the molecule is dissolved in the polymerization liquid at a ratio of 20 to 60 parts by weight per 100 parts by weight of the copolymer (D). An adhesive composition for flexible printed circuit boards, characterized by:

The monomer group (A) of the adhesive composition of the present invention includes acrylonitrile, acrylic esters, and optionally styrene.

By using acrylonitrile as a component of the monomer group (A), the adhesive is given resistance and adhesive strength to organic chemicals used for processing printed circuits of flexible substrates, such as acetone, methylene chloride, and trichlene. For that purpose, preferably 10-
It is used in an amount of 60 parts by weight as needed.

A part of this acrylonitrile component can be replaced with styrene if desired, and preferably acrylonitrile. It is used in place of the 70th section and below.

These acrylonitrile and styrene components mainly act as components that give rigidity to the adhesive, in contrast to the flexible properties of the acrylic esters, which are other components that constitute the main components of the copolymer (D). can be changed as desired to adjust properties such as the glass transition temperature of the entire adhesive composition.

As the acrylic esters that are other components of the Nanatsuma group (A) of the present invention, one or more types of general acrylic esters such as ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate can be used. can. This acrylic ester is a component that mainly provides adhesive strength to the adhesive and also provides flexibility, which is one of the other important performance requirements. It is preferable to use the acrylic ester in an amount of 40 to 80 parts by weight.

These seven needles (A) constitute the main component of the adhesive,
The compositions can be appropriately combined within the above-mentioned preferred ranges, but according to extensive practice by the present inventors, adhesive compositions that also include the below-mentioned seven-layer components (B) and (C), etc. The overall glass transition point is -30, which satisfies the above-mentioned performance requirements such as flexibility and chemical resistance.
It is desirable to select the temperature within the range of ”～o℃,
Furthermore, the composition of the monomer group (A) as a whole relative to the copolymer (D) is selected from the range of 90-98 parts by weight.

Acrylic acid and/or methacrylic acid (B) is used as a component of the copolymer (D) component of the adhesive composition of the present invention, and these components are used to adjust the crosslink density of the entire adhesive composition. An appropriate amount is added, and the amount is selected from the range of 1 to 8 parts by weight based on the copolymer (D).

When the amount of acrylic acid and/or methacrylic acid is less than 1 part by weight, it is difficult to obtain a stable aqueous copolymer solution. Also,
Even if an aqueous copolymer solution is obtained and used as an adhesive, a flexible substrate that is satisfactory in peel strength after heat resistance, chemical resistance, etc. cannot be obtained. On the other hand, if the amount exceeds 8 parts by weight, crosslinking will proceed too much and the three-dimensional structure will become excessive, resulting in a significant decrease in the bending strength of the flexible substrate and further a decrease in peel strength after heat resistance. Is recognized.

It is assumed that the crosslinking reaction mentioned here occurs between the carboxyl group of acrylic acid or methacrylic acid and the epoxy group of the epoxy resin described below.

Next, in the present invention, the reason why hydroxyalkyl acrylic acid esters and/or agrilamides are used is that the upper two monomers are hydrophilic monomers, and the first seven monomers (A) in the present invention are used. This is because these components together with (B) are essential components for stable copolymerization in water. The hydroxyalkyl acrylates include 2-hydrogyneethyl acrylate, 2
-hydrogine ethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydrogine propyl meth')
A variety of compounds can be used, such as 3-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, and 3-hydroxypropyl acrylate, and one type or a mixture of two or more of these can be used.

Various acrylamides can be used, such as acrylamide, methacrylamide, and N-methylol acrylamide, and one or more of these may be used.

These hydrophilic monomers, hydroxyalkyl acrylates and acrylamides, may be used alone or in combination, and the amount thereof is selected from the range of 1 to 9 overlapped parts. If this amount is less than 1 part by weight, the hydrophilization of the monomer in the aqueous polymerization system will be insufficient, and the stable state of the monomer during the polymerization operation cannot be determined. When polymerized, the composition of the copolymer becomes uneven and the dispersion of the copolymer in the polymerization solution becomes unstable, so that it cannot be put to practical use as an adhesive for flexible substrates. On the other hand, the amount of this hydrophilic heptamer is 9
If the amount exceeds M, the originally excellent properties of the composition of the present invention, such as adhesiveness, heat resistance, and flexibility, will be impaired, and in particular, the deterioration of heat resistance will be significant.

Copolymer (D) of the present invention comprising the above monomer group
The aqueous copolymerization solution can be manufactured by the following method. That is, a predetermined amount of potassium persulfate as a polymerization initiator, for example, is dissolved in distilled water at 70° C., and the monomer groups (A), (B), and (C) of the present invention prepared separately and distilled water are added. The mixed solution was dropwise polymerized while stirring for about 3 to 4 hours, and then the polymerization was completed over 13 to 4 hours, cooled to room temperature, excessive particles were filtered with a suitable fxp material, and then ammonia Adjust pII to 7-9 with water or the like.

At this time, the resin component (D) in the aqueous copolymerization solution is adjusted to 30 to 70 parts by weight of the total reaction system, that is, within a range in which the copolymerization reaction can be carried out well. The adhesive composition liquid of the present invention can be obtained by directly dissolving a water-soluble epoxy resin in the liquid.

rf, in the copolymerization operation of the polymer, a chain transfer agent or the like may be added according to a conventional method, or a dispersant may be added within a range that does not impair the properties of the produced adhesive composition for use in flexible substrates. can also be used as an auxiliary if necessary.

The other 4'14 component of the adhesive composition of the present invention is a water-soluble Evogin compound having two or more epoxy groups in one molecule.

Examples of the water-soluble epoxy compound include dieboglycyl compounds having a hydrophilic ether bond in the main chain of the molecule, such as ethylene glycol diglycidyl ether and polyethylene glycol diglycidyl ether having 9 or less carbon atoms in the main chain; 1, such as polyepoxy compounds having an alcoholic hydroxyl group in addition to an ether bond in the molecule, such as edel, diglycerol polygrindyl ether, melbitol polygrindyl ether, etc.
More than one species is used.

This water-soluble epoxy compound strengthens the adhesive strength of the adhesive, and a part of it reacts with the carboxyl group contained in the copolymer (D) to form a crosslinked structure, giving the adhesive rigidity. It is a component that imparts heat resistance.

The blending amount of this water-soluble epoxy compound is as follows: copolymer (D)
It is selected from the range of 20-60 parts by weight per 100 parts by weight. If the amount is less than this range, the adhesive composition will not have sufficient heat resistance or chemical resistance, and if it exceeds this range, not only will the chemical resistance decrease, but the bending durability will also be insufficient.
Z thing and rx one.

The adhesive composition of the present invention obtained as described above is a general water-based adhesive having a viscosity of 50 to 2000 centipoise. Normally 10 pieces to 80 pieces per woven sheet base
After coating to a film thickness of μ (dry base), the desired flexible substrate is obtained by drying and curing the resin.

The conditions for drying and curing the adhesive are as follows: First, dry and semi-cure using hot air at a temperature of 80°C to 180°C for a residence time of 0.5 to 20 minutes. Then, a releasable polyone fin film or release paper is applied to the semi-cured resin surface to create a product.

This coverlay sheet is laminated onto a board on which wiring has been formed on the user's side, and then the temperature is 160℃ to 180℃.
, the pressure is i 0 Ky/cr! RX Ishi 60 Kf/
cd, the adhesive is completely cured by hot-pressing for 30 to 90 minutes, and the bonding between the wiring board and the coverlay sheet is completed.

On the other hand, in the production of metal foil-clad laminates, after the adhesive has been semi-cured in the same manner as in the case of the coverlay sheet described above, rolled copper foil with a thickness of 5 μm to 80 μm, electrolytic copper foil, etc. After laminating foil, rolled aluminum foil, etc., heat to 160°C.
Contact with a metal roll heated to 180℃ or 180℃, or apply a linear pressure of 3-5o with a heat-resistant rubber roll or cotton roll R or C.
It is crimped at about Kg/cm and laminated and cured. After that, it is usually heated at 3 to 48℃ in an atmosphere of 80℃ to 200℃.
A post-cure process is carried out for a period of time to completely cure the metal foil-clad laminate.

However, the usage conditions shown here are just examples, and it goes without saying that the manufacturing conditions will vary depending on the coating machine used, the structure and specifications of the pressure roll, etc., and the optimal conditions should be determined at the time of manufacturing. In any case, as long as the adhesive of the present invention is used, organic solvents will not volatilize in the above manufacturing process unlike in the case of solvent-based adhesives, and manufacturing workers will not be exposed to the risk of inhalation of volatilized solvents or fire hazards. be freed from

In addition, printed circuit boards using the adhesive of the present invention have improved soldering heat resistance, and the drying process before soldering, which was essential for printed circuit boards using conventional emulsion polymerization type acrylic adhesives, can be omitted. The adhesive of the present invention provides industrially extremely useful effects, such as the ability to

The characteristics were evaluated according to the following method.

1. Peel strength The adhesive strength between the copper foil and the base to heat film was measured based on IPC-FC-240B. In embodiments of the invention:
The adhesion between the copper conductor wiring surface on which the printed circuit was formed and the coverlay sheet was demonstrated. Further, "normal state" means a test after being left at a temperature of 20° C. and a relative temperature of 65° C. for 48 hours, and "after heat resistance" means a test after being left at a temperature of 120° C. for 24 hours.

2. Solder heat resistance The wiring surface (coverlay sheet laminated side) was brought into contact with solder and floated in a solder bath at 260° C. for 60 seconds, and then the appearance was observed. Here, "after water immersion" refers to water resistance and moisture resistance. After soaking the circuit board in water for one hour at room temperature, take it out, wipe off the moisture with gauze, etc., and then float it in the solder bath as described above. and observed the appearance.

3. Chemical resistance In accordance with JISC6481, the test piece was immersed in trichlene, acetone, and methylene chloride for 15 minutes at room temperature, and then taken out and observed for appearance.

4. Folding strength Using an MIT type repeated bending tester, the test piece was
The number of times the conductor was bent until it stopped conducting was measured under a load of 1.

5. Insulation Resistance In accordance with JISC6481, the volume solid resistance under normal conditions (after being left at a temperature of 20° C. and a relative humidity of 65% for 96 hours) was measured.

Example 1 30 parts by weight of acrylonitrile, 10 parts by weight of ethyl acrylate
50 parts by weight of butyl acrylate, 5 parts by weight of methacrylic acid, and 5 parts by weight of hydroxyethyl acrylate were mixed with distilled water to prepare a monomer group mixture.

Next, a predetermined amount of potassium persulfate as a polymerization initiator was added at 70%
3. Prepare an aqueous solution dissolved in distilled water at ℃, and add the previously prepared monomer group mixture to this aqueous solution while stirring.
The mixture was added dropwise over a period of 5 hours, and after the completion of the addition, polymerization was continued for an additional 4.5 hours to complete the reaction. Then, the reaction solution was heated to room temperature by %, >
On the other hand, excessive particles were removed by p-filtering to obtain an aqueous copolymer solution containing 500 parts by weight of the resin component. The obtained aqueous copolymerization liquid had a pH of 7.6 and a viscosity of 1050 centiboise,
Separately, the glass transition point of the resin component was measured by DSC method and was found to be -8°C. Copolymer 10 in this aqueous copolymer solution
0 parts by weight of diethylene glycol diglycidyl ether (product name: Denacol EX-851, manufactured by Nagase Sangyo Co., Ltd.) o) 20 parts by weight were mixed into the aqueous copolymerization solution;
An adhesive composition liquid of the present invention was obtained by electrolysis. This adhesive composition liquid was applied to a 50μ thick polyimide film (E.I. DuPont product: trade name, Kapton) using a reverse roll coater to a thickness of approximately 40μ (Tribase). , dry, semi-cure (temperature 120°C1)
After a residence time of 7 minutes), electrolytic copper foil with a thickness of 35 μm (manufactured by Fukuyama Metal Co., Ltd., trade name Nie 7) was laminated, and a linear pressure of 5 Kg/c was applied.
It was pressed at a temperature of 170° C. and then post-cured at 150″C for 15 hours to obtain a Funxipur copper-clad laminate.

Furthermore, the adhesive composition liquid of the present invention obtained in this example was applied to a polyimide film (E.I.
DuPont product (trade name, Kapton) was coated with a reverse roll coater to a thickness of approximately 50 μm (Tribase), dried and semi-cured (temperature 120°C, residence time 7 minutes), and coated with a 25 μm thick Polyester films were laminated to create a rain root.

Using this coverlay sheet and the previously produced flexible copper-clad laminate, printed circuit processing of a test pattern was carried out by the subtract method to obtain a flexible printed circuit board. The characteristics of this circuit board were evaluated for each of the above items, and the results are shown in Table 1.

The press conditions for the coverlay sheet are press pressure: 3.
The temperature was 160° C. and the pressing time was 30 minutes.

Example 2 15 parts by weight of acrylonitrile, 15 parts by weight of tin, 60 parts by weight of butyl acrylate, 5 parts by weight of methacrylic acid, 3 parts by weight of hydroxyethyl azilylate and 2 parts by weight of acrylamide were mixed in distilled water, and the method of Example 1 was carried out. An aqueous copolymerization solution containing 600 parts by weight of the resin component was obtained by polymerizing according to the following procedure.

This aqueous copolymer solution has a pH of 7.8 and a viscosity of 120 centiboise, and the glass transition point of the resin component was separately determined by DSC.
When measured by the method, the temperature was -15°C. In this aqueous copolymerization solution, 30 parts by weight of sorbitol tetraglyndyl ether (manufactured by Nagase Sangyo Co., Ltd., trade name, Bunacol EX-611) is mixed with 1 part by weight of 100ml of the copolymer in this solution, and the mixture is electrolyzed. An adhesive composition liquid was obtained.

This adhesive composition liquid was coated on a polyamide-imide film with a thickness of about 50μ (a film made of a polymer obtained by the method described in @' Publication No. 56-44891) using a reverse roll coater to a thickness of about 30μ (tribase). After drying and semi-curing at a temperature of 130°C and a residence time of 5 minutes, a rolled copper foil with a thickness of 30μ (manufactured by Nikko Gould Co., Ltd., trade name, AN21) was laminated, and a linear pressure of 10% was applied. The material was pressed at a roll temperature of 165° C. and then post-carried at 130° C. to obtain a flexible silk-clad laminate.

Furthermore, adhesive composition 1 of the present invention obtained in this example
The gas-liquid was applied to a polyamide-imide film similar to that used for the above-mentioned copper-clad laminate using a reverse roll coater to a thickness of 70μ (dry base) at a temperature of 130°C and a residence time. After drying and semi-curing for 5 minutes, a release paper (manufactured by Fujimori Industries Co., Ltd., trade name, Pine Sheet) was attached to obtain a coverlay sheet.

Using this coverlay sheet and the previously produced flexible silk-clad laminate, printed circuit processing of a test pattern was carried out by the subtract method to obtain a flexible printed circuit board. The characteristics of this circuit board were evaluated for each of the above items, and the results are shown in Table 1.

The pressing conditions for the coverlay sheet were a pressing pressure of 50°C, a temperature of 170°C, and a pressing time of 20 minutes.

Comparative Examples 1 to 7 A flexible printed circuit board was prepared in the same manner as in Example 2, except that the composition of the aqueous copolymerization liquid and the blending ratio of the epoxy resin were changed as shown in the composition section of the table. The characteristics were evaluated and the results are shown in Table 1.

Reference Example 1 A flexible copper-clad laminate made of polyimide and a cover 74769 were prepared using a commercially available acrylic adhesive, and a printed circuit was processed using these in the same manner as in Example 1, thereby producing a Fregimple circuit board. We evaluated the characteristics of The results are shown in Table 1.

Claims (3)

[Claims] (1) A group of seven twigs consisting of acrylonitrile, acrylic esters and optionally added styrene (
A combination consisting of 90-98 parts by weight of A), 1-8 parts by weight of acrylic acid and/or methacrylic acid CB) and 1-9 parts by weight of hydroxyalkyl acrylates and/or acrylamides (C). A water-soluble epoxy compound (E) having two or more epoxy groups in the molecule is added to the aqueous copolymerization solution of the polymer (D).
An adhesive composition for a flexible printed circuit board, characterized in that it is prepared by dissolving 20-60 parts by weight to 0.00 parts by weight. (2) The adhesive composition for flexible signs and circuit boards according to claim 1, wherein the monomer group (A) comprises acrylonitrile, styrene, and acrylic esters. (3) The adhesive composition for a flexible printed circuit board according to claim 1, wherein the monomer group (A) comprises acrylonitrile and an acrylic ester.