JPH07300577A - Adhesive composition for flexible printed circuit substrate - Google Patents

Abstract

(57) [Summary] [Purpose] A flexible flame-retardant adhesive for printed circuit boards, which has excellent flame retardancy (UL 94-Vo), heat resistance, adhesiveness and flexibility. To provide an adhesive composition for a flexible printed circuit board. An acrylic copolymer polymerized with 10 to 45% by weight of acrylonitrile, 40 to 70% by weight of an alkyl acrylate having 8 or less carbon atoms, and 3 to 15% by weight of an olefin compound having at least one functional group capable of reacting with epoxy. 100 to 100% by weight of polymerized resin (based on solid content)
10 to 30% by weight of a polyfunctional epoxy resin having an epoxy equivalent of 300 and 20 to 90% by weight of a brominated epoxy resin having an epoxy equivalent of 200 to 900 and a bromine content of 30 to 70% by weight. It is a mixed adhesive composition for flexible printed circuit boards.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adhesive composition for flexible printed circuit boards, which has excellent adhesiveness and heat resistance, and particularly excellent flame retardancy.

[0002]

2. Description of the Related Art Recently, there has been a remarkable trend toward light, thin, short, compact, high density and high performance in the fields of electricity, electronics and semiconductors. Even in the case of a multilayer printed circuit board, existing rigid single layer or double sided center The specific gravity of a flexible printed circuit board from an object is rapidly increasing. The flexible printed circuit board has a film attached to both sides of a flexible metal foil circuit, and the thickness is about 50 to 300 μm, which is very thin and difficult to apply to the rigid printed circuit board. It is mainly used for products that require densification. Examples of light, thin, short and small products are cameras, small recorders, camcorders,
There is a notebook computer etc., an example applied to products requiring flexibility is a printer head etc.An example applied to high density products is tape automated bonding used as a substitute for semiconductor lead frame etc. , Flexible printed circuit board applications are expanding day by day.

The base material of the flexible printed circuit board is mainly a plastic film such as polyimide or polyester,
It consists of acrylic, epoxy, polyurethane, polyester, and other adhesives and copper, aluminum, tin, and other metal foils. In the production of flexible printed circuit boards, a photoresist such as a dry film is laminated on a flexible copper clad laminate (produced by coating an adhesive on a film and laminating copper), and then exposed on a mask and developed. After forming the circuit on the copper foil surface, the copper layer is etched with ferric chloride aqueous solution etc., the photoresist layer is peeled off with alkaline aqueous solution, the coverlay is laminated, and soldering etc. is performed as necessary. Manufacture flexible printed circuit boards.

As described above, in the manufacturing process of the flexible circuit board, chemical treatment of acid, base, etc., heat lamination,
Since there are heat treatment steps such as soldering, it is required that the characteristics of the adhesive are not deteriorated in these steps. Adhesives must maintain adhesive properties above a specified value in any environment during the process, and the solvent resistance of the adhesive surface exposed during copper foil etching and the heat resistance during soldering are required. Since it is mainly used for electronic products, flame retardancy is often required in the original plate or circuit board component state.

However, among the materials of the flexible printed circuit board, the copper foil and the polyimide film have flame retardancy by themselves, so that imparting flame retardancy to the adhesive directly affects the flame retardancy of the product. As conventional adhesives for flexible printed circuit boards, epoxy-based, acrylic-based, polyurethane-based, polyester-based adhesives and the like are generally widely used.
In particular, among the adhesives, a polyimide film and a copper foil are bonded to each other to manufacture a flexible substrate.
JP-A-3-2974843 and JP-A-63-120783.
Epoxy and acrylic rubber / epoxy adhesives were often used, such as those described in the publication.

Further, Japanese Patent Application Laid-Open No. 56-81382 describes an adhesive which imparts flame retardancy by mixing a brominated epoxy resin, a brominated vinylphenol resin and an acrylic copolymer resin.

[0007]

However, in the former two patents, in the case of the epoxy adhesive, the heat resistance, chemical resistance, and dimensional stability are excellent, but the adhesive strength and flexibility are insufficient. However, there is a problem that the acrylic rubber / epoxy adhesive has insufficient flame retardancy.

It is known that the adhesive described in the latter patent has excellent flame retardancy but has problems of adhesive strength and flexibility. Therefore, an object of the present invention is a flame-retardant adhesive for flexible printed boards, which is flame-retardant (UL 94-Vo), heat-resistant,
It is an object of the present invention to provide an adhesive composition for a flexible printed circuit board, which is very excellent in various properties such as adhesive and flexibility.

[0009]

In order to achieve not only the above-mentioned object but also other objects that can be easily expressed, the present invention provides a polyfunctional resin based on 100% by weight of acrylic copolymer resin (based on solid content). Provided is a flexible printed circuit board adhesive having excellent adhesiveness, heat resistance and flame retardancy by blending about 10 to 30% by weight of a base epoxy resin and 20 to 90% by weight of a brominated epoxy resin. .

The present invention will be described in more detail as follows. The acrylic copolymer resin used in the present invention includes acrylonitrile, an alkyl acrylate having 8 or less carbon atoms such as ethyl acrylate, methyl methacrylate, methacrylate and butyl acrylate, and a functional group (carboxyl group) capable of reacting with epoxy. , A hydroxyl group, an amide group, etc.).

The acrylic copolymer affects heat resistance, flexibility, stability and the like depending on the content of each component. The content of acrylonitrile is 1 with respect to the total weight of the acrylic copolymer.
It is preferably from 0 to 45% by weight. If the acrylonitrile content is less than 10% by weight, the heat resistance of the solder is deteriorated, and if it exceeds 45% by weight, the flexibility and the stability of the adhesive may be deteriorated and the color may change at a high temperature.

The acrylic acrylate having 8 or less carbon atoms is preferably 40 to 70% by weight based on the total weight of the acrylic copolymer. The olefin compound having at least one functional group is preferably 3 to 15% by weight based on the total weight of the acrylic copolymer. When the content of the olefin compound having a functional group is less than 3%, the crosslink density with the epoxy is low, and the heat resistance of the finally obtained adhesive composition decreases, and when it exceeds 15% by weight, the unreacted functional group is flexible. The electrical characteristics of the flexible printed circuit board may be degraded.

The acrylic copolymer resin having a glass transition temperature (Tg) of 5 to 35 ° C. is preferably used. This is manufactured by controlling the composition of each component appropriately. The acrylic copolymer resin used in the adhesive composition of the present invention includes α, α′-azobisisobutyronitrile (hereinafter abbreviated as AIBN), bezoyl peroxide (hereinafter abbreviated as BPO), and the like. Solution polymerization is performed using an initiator, and polymerization is performed using a solvent such as methyl ethyl ketone, ethyl acetate, toluene or a mixed solvent as a solvent.
The molecular weight of the produced copolymer can be measured by gel permeation chromatography, and in the present invention, the one having a number average molecular weight of 100,000 to 800,000 is used.

Examples of the polyfunctional epoxy resin used in the adhesive composition of the present invention include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, triglycidyl tris (2-hydroxyethyl) isocyanurate, and epoxycresol novolac resin. Mention may be made of resins having an epoxy equivalent of 100-300. These serve to improve heat resistance and adhesion.

As the brominated epoxy resin, dibrom neopentyl glycol diglycidyl ether represented by the following structural formula (I), dibromophenyl glycidyl ether represented by the following formula (II), or the following structural formula (II
A flame retardant resin or resin mixture selected from the group consisting of bisphenol brominated epoxy resins represented by I) is selected.

[0016]

[Chemical 1]

[0017]

[Chemical 2]

[0018]

[Chemical 3]

In the adhesive composition of the present invention, the mixing ratio of the three types of acrylic copolymer resin, polyfunctional epoxy resin and brominated epoxy resin is 100% by weight of acrylic copolymer resin (based on solid content). 10 to 30% by weight of a polyfunctional epoxy resin, and a brominated epoxy resin 20 to
Good properties can be expected at 90% by weight. When the content of the polyfunctional epoxy resin is less than 10%, the adhesiveness is insufficient, and when it exceeds 30%, the flame retardancy is lowered. If the content of brominated epoxy is less than 20%, the flame retardancy is insufficient, and if it exceeds 90%, the heat resistance and the adhesive strength are reduced.

Desirably, the total content of the polyfunctional epoxy resin and the brominated epoxy resin is in the range of 40 to 100% by weight based on 100% by weight of the acrylic copolymer resin. With such a range, flame resistance, heat resistance,
Excellent adhesion can be obtained. The brominated epoxy resin has an epoxy equivalent of 200-900,
The bromine content is preferably 30 to 70% by weight.

In producing the adhesive composition of the present invention by preparing these liquids, a tertiary amine or an imidazole is used as a curing reaction catalyst, and an epoxy curing agent such as diamine or dianhydride is used if necessary. You can Flexibility A flexible printed circuit board can be manufactured as follows. After applying an adhesive having the above composition on a polyimide or polyester film having a thickness of 20 to 100 μm using a roll, a reverse roll, a comma coater or the like so that the adhesive application thickness after drying becomes 20 to 50 μm, ~ 1
After passing through a dryer (retention time: 1 to 5 minutes) at 00 ° C. to remove volatile components such as a solvent, a metal foil such as copper and aluminum is heated to 80 to 140 ° C. at a pressure roll with a pressure of 5 to 20 kg /
Bond at a temperature / pressure of cm ² . In the case of a coverlay, an adhesive is applied and dried under the same conditions as described above, and then an adhesive layer protective film or release paper is bonded at room temperature (20 ° C) to 100 ° C.

The flexible printed circuit board thus manufactured was heat-treated at 120 ° C. for 12 hours, and then, in the case of a coverlay, 1
After drying at 00 ℃ for 20 minutes, or at 178 ℃, 30k
The physical properties after processing for 60 minutes at g / cm ² were evaluated. The following examples and comparative examples illustrate the invention in more detail, but do not limit the scope of the invention.

[0023]

【Example】

Example 1 (1) Polymerization of Acrylic Copolymer Resin Under a nitrogen atmosphere, 1 liter equipped with a reflux condenser and a stirrer
In a three-necked flask, the monomer 100 having the composition shown in Table 1
After adding g, a solution in which 0.1 g of AIBN (azobisisobutyronitrile) was dissolved in 50 g of ethyl acetate was added, and then the temperature was raised to 70 ° C. to proceed the polymerization initiation reaction.

Again, 0.5 g of a 5% by weight solution of AIBN in ethyl acetate was divided into 4 portions every 2 hours and charged.
After stirring for 10 hours and again adding 5 g of 5% by weight AIBN in ethyl acetate and 345 g of ethyl acetate solvent, the polymerization reaction was allowed to proceed for another 4 hours and Tg was 28 ° C.
An acrylic copolymer resin having a number average molecular weight (Mn) of 250,000 and a solid content of 20% by weight was produced.

(2) Preparation of Adhesive Preparation Liquid and Copper Clad Laminate (CCL) Sorbitol polyglycidyl ether type epoxy resin (molecular weight: 100,000) 20 g and dibromoneopentyl glycol glycidyl ether 15 g
Then, 15 g of bisphenol type brominated epoxy resin (number average molecular weight: 120,000) was added, 0.01 g of a curing accelerator was added, and the mixture was stirred for 15 minutes and filtered through a 1000 mesh filter. After filtration, it was coated on a polyimide film (25 μm) using a Mayer bar, dried at 100 ° C. for 3 minutes, laminated with a 35 μm copper foil with a 130 ° C./15 kg / cm ² laminator, and dried again at 120 ° C. Heated for 12 hours in a machine. The properties of the obtained copper clad laminate were evaluated.

(3) Preparation of adhesive solution and coverlay: 500 g of acrylic copolymer resin (solid content 20% by weight), 15 g of sorbitol polyglycidyl ether epoxy resin (molecular weight: 100,000) and dibrom neopentyl glycol diglycidyl. 30 g of ether type epoxy resin and bisphenol type brominated epoxy resin (number average molecular weight: 12
35 g and 0.01 g of the curing accelerator are added, and the mixture is stirred for 15 minutes, filtered through a 1000 mesh filter, and a polyimide film (25 μm) is applied using a Mayer bar.
m) and dried at 100 ° C. for 4 minutes to obtain a film having an adhesive layer of 30 μm. A 35 μm polyester film was laminated on this polyimide film at room temperature to produce a coverlay film.

(4) Item-Specific Evaluation Standards and Methods for Adhesives for Flexible Printed Circuit Boards The copper clad laminate and coverlay thus produced were evaluated by the items and methods shown in Table 1.

[0028]

[Table 1]

The results of the characteristic evaluation are summarized in Tables 2 and 3.

[0030]

[Table 2]

[0031]

[Table 3]

In the table, HEMA is hydroxyethyl methacrylate, SPGE is sorbitol polyglycidyl ether type epoxy, ECN is epoxycresol novolac resin, DNGDE is dibromoneopentyl glycol diglycidyl ether, and BPBE is bisphenol type. Brominated epoxy and DEMI represent 1-dicyanoethyl-2-ethyl-4-methylimidazole. Examples 2-5 and Comparative Examples 1-5 A copper clad laminate and a copper clad laminate were prepared in the same manner as in Example 1 except that the composition of the acrylic copolymer and the compounding ratio of the adhesive were changed to those shown in Tables 2 and 3. Manufacture cabaret,
Its characteristics were evaluated.

[0033]

As can be seen from the above Examples and Comparative Examples, the presence of an appropriate amount of a carboxyl group, a hydroxy group, an amide group, etc. capable of undergoing a crosslinking reaction with an epoxy functional group of an acrylic copolymer resin is important, Acrylonitrile also plays an important role in heat resistance, polyfunctional epoxy resin plays a role in improving the adhesive strength and heat resistance of the adhesive, and in order to impart flame retardancy, a certain amount or more of brominated epoxy resin is used. Must be added. Acrylic copolymer resin 10
The content of the polyfunctional epoxy resin is 10% with respect to 0% by weight.
~ 30 wt%, brominated epoxy resin content 20 ~ 9
A flexible printed circuit board adhesive having good properties can be produced at 0% by weight.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jang Kyun Ho Unification of 2 Arai, Yangcheon, Yangcheon, Seoul, Republic of Korea 3 203

Claims (4)

[Claims] 1. A polyfunctional epoxy resin of 10 to 30% by weight and a brominated epoxy resin of 20 to 90% by weight are mixed with 100% by weight of acrylic copolymer resin (based on solid content). An adhesive composition for flexible printed circuit boards. 2. The acrylic copolymer resin comprises 10 to 45% by weight of acrylonitrile, 40 to 70% by weight of alkyl acrylate having a carbon number of 8 or less, and an olefin compound having 2 or more functional groups capable of reacting with epoxy. 15% by weight
The adhesive composition according to claim 1, which is polymerized by: 3. The acrylic copolymer resin comprises 10 to 45% by weight of acrylonitrile, 40 to 70% by weight of alkyl acrylate having 8 or less carbon atoms, and 3 to 6 of an olefin compound having at least one functional group capable of reacting with epoxy. 15% by weight
The adhesive composition according to claim 1, which is polymerized by: 4. The polyfunctional epoxy resin is 100 to 30.
The adhesive composition according to claim 1, wherein the epoxy resin has an epoxy equivalent of 0, the brominated epoxy resin has an epoxy equivalent of 200 to 900, and the content of bromine is 30 to 70% by weight.