JP2001115131A - Flame-retardant resin adhesive and base for flexible printed circuit using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a flame-retardant resin adhesive which yields a base for a flexible printed circuit which is highly reliable and highly heat-resistant using a conventional facility for preparing a base for a three-layered flexible printed circuit via a process similar to that for bases for three-layered flexible printed circuits, and a base for a flexible printed circuit prepared using the same. SOLUTION: A flame-retardant resin adhesive which essentially comprises a maleimide resin having a glass transition temperature of <=400 deg.C and may be thermocompression bonded at <=400 deg.C, is used. Here, the maleimide resin is obtained by mixing 100 pts.wt. composition containing a powder of a maleic acid analogue of formula 1 and a diamine powder in a molar ratio of 1:1 and from 0.1 to 10 pts.wt. layered clay mineral at a solid state and heating this mixture in a solid state at from 80 to 200 deg.C, and contains a repeating unit of formula 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flame-retardant resin adhesive excellent in heat resistance and workability at low temperatures, and to a flexible printed circuit board using the same.

[0002]

2. Description of the Related Art A flexible printed wiring board having a circuit formed on a flexible insulating film is widely used in electronic devices requiring space saving, such as cameras and liquid crystal televisions. In recent years, due to the miniaturization and precision of such electronic devices, the spread of flexible printed wiring boards has tended to increase more and more. On the other hand, the requirements for the material of the flexible printed wiring board itself, such as heat resistance and electrical characteristics, have also become higher.

[0003] A conventional flexible printed wiring board is obtained by laminating a polyimide resin and a copper foil with an ordinary epoxy or acrylic adhesive (three-layer flexible printed circuit board: hereinafter referred to as three-layer flexible). Was used. However, since the characteristics strongly depend on the characteristics of the adhesive, the characteristics of the polyimide resin cannot be fully utilized, and the demand for flame retardancy cannot be sufficiently satisfied.

In order to satisfy these requirements, a so-called two-layer flexible printed circuit board (hereinafter referred to as a two-layer flexible printed circuit) in which a wiring layer is in direct contact with a polyimide resin as a base material without using such an adhesive. Is also used. The two-layer flexible manufacturing method includes a casting method of applying and drying a polyimide precursor varnish on a copper foil, a sputtering method and a plating method of depositing and growing copper on a polyimide film, and a method of depositing a metal on a polyimide film to form a conductor. There are vapor deposition methods for forming layers, and in any case, the production process requires high-performance and large-scale production equipment in each step such as high-temperature drying and vapor deposition after coating. Compared to the three-layer flexible
It has the drawback of becoming expensive.

On the other hand, the use of a thermoplastic polyimide resin as an adhesive is also considered in the case of a three-layer flexible film. However, since a high temperature of 300 ° C. or more is required for the bonding temperature, the manufacturing apparatus is relatively large. Become. Attempts have been made to add an epoxy resin or the like to a silicon-based polyimide resin having a low glass transition temperature in order to impart low-temperature processability to this adhesive. There has been a problem that the flame retardant characteristics of the resin cannot be fully utilized.

Attempts have also been made to use a maleimide resin as an adhesive, but it has not been possible to obtain sufficient flame retardancy using the maleimide resin alone. As described above, there is a need for a low-cost flexible printed circuit board that maintains high reliability and high heat resistance, and is flame-retardant and excellent in productivity.

[0007]

SUMMARY OF THE INVENTION The present invention provides a flexible printed circuit which can be manufactured in the same process as a three-layer flex using conventional three-layer flex manufacturing equipment, and which can maintain high reliability and high heat resistance. It is an object of the present invention to provide a flame-retardant resin adhesive for a circuit board and a flexible printed circuit board using the same.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the above problems, and as a result, low-temperature processing is possible due to the composition comprising a maleimide resin and a layered clay mineral as main components. Found that an adhesive with excellent flame retardancy can be obtained, and further, by using this, obtains a substrate for a flexible printed circuit with good productivity, high reliability, high heat resistance, and flame retardancy. The present invention has been completed.

That is, according to the present invention, a maleic acid analog powder represented by the general formula (1) and a diamine powder are mixed in a molar ratio of 1:
After mixing in a solid state in Step 1, the mixture is subjected to a heat treatment at 80 to 200 ° C. in a solid state. The mixture contains a repeating unit represented by the general formula (2) and has a glass transition temperature of 400 ° C. or lower. And 100 parts by weight of a maleimide resin (A) that can be thermocompression-bonded with a layered clay mineral (B) 0.1 to 1
A flame-retardant resin adhesive containing 0 part by weight as a main component and capable of being thermocompression-bonded at a temperature of 400 ° C. or lower,
And a single-sided and double-sided flexible printed circuit board characterized in that a metal foil and a heat-resistant resin film are bonded to each other via the metal foil and the heat-resistant resin film.

[0010]

Embedded image

[0011]

Embedded image

[0012] In the formula, each of R _1, R ₂ represents hydrogen, an alkyl group, a phenyl group or substituted phenyl group,, R ₃
Is a non-fused group in which an aliphatic group having 2 or more carbon atoms, a cycloaliphatic group, a monocyclic aromatic group, a condensed polycyclic aromatic group, and an aromatic group are connected to each other directly or by a crosslinking member. Represents a divalent aromatic organic group selected from the group consisting of polycyclic aromatic groups.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The polyimide resin (A) having a glass transition temperature of 400 ° C. or lower and which can be thermocompression-bonded, which is used in the flame-retardant resin adhesive of the present invention, is represented by the general formula (1). It is obtained by mixing a maleic acid analog powder and a diamine powder in a solid state at a molar ratio of 1: 1 and then subjecting the mixture to a heat treatment at 80 to 200 ° C. in a solid state; Maleimide-based resin containing a repeating unit represented by the following, other than the present resin-based, a glass transition temperature is 400 ° C. or less, as long as it is a polyimide resin capable of thermocompression bonding, other silicon-based polyimide resin A polyimide resin such as a thermoplastic polyimide resin or the like can also be used.

As the maleic acid analog used in the present invention, any compound represented by the above general formula (1) can be used, and specific examples thereof include maleic acid and citraconic acid. . Among them, maleic acid is particularly preferred. The reason is that the reactivity at the time of the heating reaction is high and that it is inexpensive. The maleic acid analogs may be used alone or in combination of two or more.

On the other hand, as the diamine, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,6-dimethyl-
m-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, 2,4-diaminomesitylene, 4,4 ′
-Methylenedi-o-toluidine, 4,4'-methylenedi-
2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 2,4-toluenediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylpropane, 3,3 ' -Diaminodiphenylpropane, 4,4'-diaminodiphenylethane, 3,3'-
Diaminodiphenylethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 4,4 '
-Diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfide,
4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether, benzidine, 3,3′-diaminobiphenyl, 3,3′-dimethyl-4,4′-diaminobiphenyl, 3,3′-dimethoxybenzidine, Bis (p-aminocyclohexyl) methane, bis (p-β-amino-t
-Butylphenyl) ether, bis (p-β-methyl-
δ-aminopentyl) benzene, p-bis (2-methyl-4-aminopentyl) benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis (β-amino-t-butyl) Toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine,
p-xylylenediamine, 2,6-diaminopyridine,
2,5-diaminopyridine, 2,5-diamino-1,3,4
-Oxadiazol, 1,4-diaminocyclohexane, piperazine, methylenediamine, ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, 2,5-dimethylhexamethylenediamine, 3-methoxyhexamethylenediamine, heptamethylenediamine 2,5-dimethylheptamethylenediamine, 3-methylheptamethylenediamine, 4,4-dimethylheptamethylenediamine, octamethylenediamine, nonamethylenediamine, 5-methylnonamethylenediamine, decamethylenediamine, 1.3
-Bis (3-aminophenoxy) benzene, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 1,3-bis (4-aminophenoxy) benzene,
Bis-4- (4-aminophenoxy) phenylsulfone, bis-4- (3-aminophenoxy) phenylsulfone and the like can be mentioned.

Among them, 4,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,4'-
Diaminodiphenylethane, 3,3'-diaminodiphenylethane, 4,4'-diaminodiphenylmethane, 3,3 '
-Diaminodiphenylmethane, 4,4'-diaminodiphenylether, 3,3'-diaminodiphenylether are preferred. Among them, 4,4′-diaminodiphenylmethane is more preferable in terms of reactivity and cost.
The above diamines may be used alone or in combination of two or more.

The method for producing a polyimide resin containing the layered clay mineral (B) according to the present invention is characterized in that the maleic acid analog powder and the diamine powder are mixed in a composition 100 having a molar ratio of 1: 1.
Parts by weight, and after mixing 0.1 to 10 parts by weight of the layered clay mineral in a solid state, heat-treating the solid state at 80 to 200 ° C. to react the maleic acid analog powder and the diamine powder. This is performed to obtain a maleimide-based resin containing a layered clay mineral and having a repeating unit represented by the general formula (2).

When the heat treatment temperature is higher than 200 ° C., the reaction is fast, but the partial gelation due to side reaction becomes remarkable, and contains a part insoluble in the solvent. On the other hand, if the heating temperature is lower than 80 ° C., the reaction rate is low, unreacted substances remain, and a high molecular weight resin cannot be obtained, resulting in poor heat resistance.

The maleimide-based resin obtained here is solvent-soluble, and is pulverized to a particle size of 2 mm or less and dissolved in an aprotic polar solvent to form a flame-retardant resin adhesive solution. At this time, the method of pulverizing the maleimide resin is as follows:
An ordinary pulverizer such as a cutting mill and a ball mill can be used. When the particle size is larger than 2 mm, it is not suitable because undissolved parts are left out upon dissolution in a solvent or a considerable time is required until complete dissolution. Further, in order to facilitate the dissolution of the resin, the solvent may be dissolved by heating the solvent to a temperature equal to or lower than the boiling point of the solvent as long as the resin does not impair the properties.

The organic solvent used for preparing the flame-retardant resin adhesive solution is not particularly limited, but an aprotic polar solvent is preferable, and typical solvents of this type include N, N-
Dimethylformamide, N, N-dimethylacetamide, N, N-diethylformamide, N, N-diethylacetamide, N, N-dimethylmethoxyacetamide, dimethylsulfoxide, hexamethylphosphamide, N-methyl-2-pyrrolidone , Pyridine, dimethylsulfone, tetramethylsulfone, γ-butyllactone and the like. In particular, N, N-
Dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone are more preferred. These aprotic polar solvents may be used alone,
Alternatively, a mixture of two or more solvents may be used. Further, other compatible polar solvents or non-polar solvents may be mixed and used.

The type of the layered clay mineral (B) is not particularly limited, and examples thereof include saponite, montmorillonite, synthetic mica, and the like. Alkali metal ions and alkaline earth metal ions contained between layers of the clay mineral can be used. A layered clay mineral (B ′) obtained by ion-exchange with an onium ion having 10 to 20 carbon atoms to obtain an organoclay is preferable. Further, the content of the layered clay mineral (B) is determined by the polyimide resin (A) 10
0.1 to 10 parts by weight is preferable with respect to 0 parts by weight. 0.
If the amount is less than 1 part by weight, the effect of the layered clay mineral is small,
Sufficient flame retardancy cannot be realized. On the other hand, if the amount exceeds 10 parts by weight, the layered clay mineral tends to agglomerate, is not uniformly dispersed in the polyimide resin, and does not have flexibility.

When alkali metal ions and alkaline earth metal ions contained between layers of the layered clay mineral are not ion-exchanged with onium ions, they are uniformly dispersed in an organic solvent at the stage of forming a flame-retardant resin solution. And layered clay minerals may precipitate.

The layered clay mineral in the present invention prevents precipitation in the flame-retardant resin solution by the above-mentioned method, and each layer is dispersed in a molecular form in the flame-retardant resin solution, thereby forming a filler having a molecular size. It functions and can impart flame retardancy to the maleimide resin. Further, other resins such as an epoxy resin and an acrylic resin may be mixed as long as the flame retardancy and other characteristics are not impaired.

By using the flame-retardant resin solution thus obtained, a flame-retardant flexible printed circuit board can be prepared in the same manner as in the production of ordinary three-layer flex. That is, a flame-retardant resin solution containing a polyimide-based resin (A) and a layered clay mineral (B) as main components is applied as an adhesive on a heat-resistant resin film or a metal foil, and an adhesive layer is formed and dried. Thereafter, a metal foil is heat-bonded to the heat-resistant resin film and a heat-resistant resin film is heat-pressed to the metal foil to obtain a single-sided flexible printed circuit board. On the heat-resistant resin film surface of the obtained flexible printed circuit board, the flame-retardant resin solution of the present invention is further applied to form an adhesive layer, and then thermocompression-bonded to a metal foil to obtain a double-sided board. Can also. Further, the bonded single-sided and double-sided flexible printed circuit boards can be subjected to after-curing as necessary, so that the flame-retardant resin adhesive can be sufficiently cured.

It is desirable to use a polyimide film as the heat-resistant resin film serving as the base of the substrate for a flexible printed circuit, from the viewpoint of utilizing the heat resistance, reliability and flame retardancy of the adhesive of the present invention. The metal foil is not particularly limited. Copper foil, aluminum foil, stainless steel foil and the like can be mentioned, among which it is preferable to use copper foil,
General. Also, the thickness of the metal foil is not particularly limited, but is preferably 18 to 70 μm from the viewpoint of utilizing flexibility, which is an important characteristic as a substrate for a flexible printed circuit.

The method of casting and coating a flame-retardant resin adhesive solution on a heat-resistant film is performed by a known method such as a rotary coater, knife coater, die coater, comma coater, doctor blade, or flow coater. Is applied by casting so that the thickness of the film becomes a uniform thickness of 20 μm or less. The thickness of the adhesive layer is desirably 20 μm or less from the viewpoint of flexibility and solder heat resistance. When the thickness is 20 μm or more, the flexibility and solder heat resistance, which are important properties as a substrate for a flexible printed circuit, are impaired. Therefore, a thickness that can maintain the adhesiveness between the conductive foil and the heat-resistant film is necessary. Is desirable. In addition, in the removal of the solvent of the flame-retardant resin adhesive solution by heating, if strong heating is performed from the beginning, the surface becomes rough or tight, so it is preferable to gradually increase the temperature from a low temperature. For example, from 60 ° C to 150
Heat continuously to 2 ° C. over 2 minutes.

As a method of heating and pressing the heat-resistant film having the adhesive layer formed thereon and the metal foil, a roll laminator is usually used.
0 ° C., 0.1 to 50 kgf / cm and 0.5 to 20 m / min are appropriate, and the temperature is preferably higher than the drying temperature of the flame-retardant resin adhesive. Although the productivity is low, the heating and pressure bonding can be performed in a press format. Depending on the composition of the adhesive, the conditions are generally
100-250 ° C, 1-100 kgf / cm ² , 5-120 minutes are suitable.

[0028]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to specific examples, but the present invention is not limited to these examples. First, after synthesizing a polyimide resin and dissolving it in a solvent to form an adhesive solution, a flexible printed circuit board was adjusted using the solution, and the obtained circuit board was evaluated for its peel strength, Solder heat resistance,
Folding resistance and flame resistance were measured.

The measuring device used for measuring the peel strength is as follows:
The measurement conditions and samples are as follows. Measuring device: Tensile tester (STOROGRAPH-M1:
(Manufactured by Toyo Seiki Co., Ltd.) Measurement conditions: peeled by pulling in the direction of 180 degrees at a rate of 50 mm / min. Thickness 2
The sample was fixed on a stainless steel plate having a thickness of 2 mm with a double-sided tape and used for measurement.

Example 1 (1) Ion exchange treatment of layered clay mineral 8.82 g of dodecylamine and 4.8 ml of concentrated hydrochloric acid were added to water 10
0 ml and stirring at an internal temperature of 80 ° C.
The ammonium salt of dodecylamine was obtained. And water 4
To 00 ml, a colloidal solution in which 20 g of saponite (trade name: Smecton SA, manufactured by Kunimine Industries Co., Ltd.) was added, stirred at 80 ° C. for 1 hour, filtered, washed with hot water twice or more, After drying, saponite ion-exchanged with dodecyl ammonium ion was obtained.

(2) Synthesis of polyimide resin in which layered clay mineral is dispersed Powder of maleic acid 116 parts by weight (1 mol), 4,4'-
Powder of 198 parts by weight of diaminodiphenylmethane (1 mol) and 15 parts by weight of saponite ion-exchanged with dodecylammonium ions were uniformly mixed in a mortar, and maleic acid / 4,4′-diaminodiphenylmethane /
A solid mixture of saponite was prepared. This mixture is
The mixture was heated in a dryer at 40 ° C. for 1 hour to obtain a maleimide resin in which saponite was dispersed (synthesized).

(3) Adjustment of adhesive 150 parts by weight of N-methyl-2-pyrrolidone were added to 100 parts by weight of the maleimide resin in which the layered clay mineral synthesized as described above was dispersed, and the mixture was uniformly dissolved. A conductive resin adhesive solution was prepared.

(4) Production of Flexible Printed Circuit Substrate The obtained flame-retardant resin adhesive resin solution was applied on a polyimide film (manufactured by Dupont Toray, Kapton 100H).
It is applied using a die coater so that the thickness after drying becomes 15 μm, and continuously 100 ° C./3 minutes, 150 ° C./3
After being dried for a minute, the rolled laminator was continuously thermocompression-bonded to the roughened surface of the 18 μm rolled copper foil. This was rolled up in a roll and heat-treated at 200 ° C. for 3 hours to obtain a single-sided flexible printed circuit board.

The obtained substrate for a flexible printed circuit had a peel strength of 1.5 kgf / cm, and showed no abnormalities even after dipping in a solder bath at 260 ° C. for 1 minute, showing excellent solder heat resistance. In addition, the folding resistance (MI
(T method, weight: 500 g, R = 0.8 mm) was also excellent in flexibility as 220 times, and the flammability was measured according to UL94, which was equivalent to V-0.

(Example 2) Except for using 15 parts by weight of montmorillonite (trade name: Knipia F, manufactured by Kunimine Industries Co., Ltd.) instead of saponite as the layered clay mineral,
All were operated in the same manner as in Example 1 to obtain a single-sided flexible printed circuit board.

The obtained substrate for a flexible printed circuit had a peel strength of 0.87 kgf / cm, showed no abnormality even after dipping in a solder bath at 260 ° C. for 1 minute, and showed excellent solder heat resistance. Also, the folding resistance of the copper clad board itself,
The flexibility was excellent 190 times, and the flammability was measured in accordance with UL94.

Example 3 The same operation as in Example 1 was carried out except that 15 parts by weight of synthetic mica (manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of saponite as the layered clay mineral.
A single-sided flexible printed circuit board was obtained.

The obtained substrate for a flexible printed circuit had a peel strength of 0.79 kgf / cm, showed no abnormality even after dipping in a solder bath at 260 ° C. for 1 minute, and exhibited excellent solder heat resistance. The folding resistance of the copper clad board itself is 180
It was excellent in flexibility and time, and when it was measured for flammability according to UL94, it was equivalent to V-0.

Comparative Example 1 A single-sided flexible printed circuit board was obtained in the same manner as in Example 1, except that no layered clay mineral was used. The obtained flexible printed circuit board has a peel strength of 1.4 kgf / cm.
The copper-clad plate itself was excellent in flexibility as 210 times, but when it was dipped in a solder bath at 260 ° C. for 1 minute, foaming was observed. Further, when the flammability was measured in accordance with UL94, the combustion of all the samples reached the support clamp.

Comparative Example 2 A single-sided flexible printed circuit board was obtained in the same manner as in Example 1, except that 40 parts by weight of saponite was used as the layered clay mineral. The obtained flexible printed circuit board has 26
No abnormality was observed even when dipped in a solder bath at 0 ° C. for 1 minute, and the flammability measured in accordance with UL94 was equivalent to V-0, but the peel strength was significantly reduced to 0.22 kgf / cm. The folding resistance of the copper-clad plate itself was low at 20 times, and the flexibility was reduced.

[0041]

According to the method of the present invention, it is possible to manufacture a substrate for a flexible printed circuit by using the conventional three-layer flexible manufacturing apparatus in the same process as the conventional three-layer flexible. Flexibility and flame retardant compatibility
It is possible to manufacture a highly reliable flexible printed circuit board.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05K 1/03 670 H05K 1/03 670Z F term (Reference) 4H028 AA10 AA12 AA44 4J040 EH031 HA316 HA356 JB02 LA08 MA02 MA10 NA19 NA20 4J043 PA02 PB03 PB08 PC016 PC116 QC02 RA08 RA34 SA06 SB01 TA12 TA72 TB01 UA041 UA121 UA131 UA141 UA261 UA321 UA361 UA761 UA762 UA771 UB011 UB021 UB121 UB131 UB301 UB401 Z02AVAA XA14A06A041

Claims (8)

[Claims] 1. A resin composition comprising 100 parts by weight of a thermocompression-bondable polyimide resin (A) having a glass transition temperature of 400 ° C. or lower and 0.1 to 10 parts by weight of a layered clay mineral (B) as main components. A flame-retardant resin adhesive characterized by being capable of thermocompression bonding at a temperature of 2. The thermocompression-bondable polyimide resin (A) comprises:
After mixing the maleic acid analog powder represented by the general formula (1) and the diamine powder in a solid state at a molar ratio of 1: 1,
The maleimide-based resin containing a repeating unit represented by the general formula (2), which is obtained by heat-treating the mixture in a solid state at 80 to 200 ° C, characterized in that it is a maleimide-based resin. Flame retardant resin adhesive. Embedded image Embedded image In the formula, R ₁ and R ₂ each represent hydrogen, an alkyl group, a phenyl group, or a substituted phenyl group, and R ₃ has 2 carbon atoms.
Non-condensed polycyclic aromatic groups in which the above aliphatic groups, cycloaliphatic groups, monocyclic aromatic groups, condensed polycyclic aromatic groups, and aromatic groups are interconnected directly or by a bridge member Represents a divalent aromatic organic group selected from the group consisting of groups; 3. The layered clay mineral (B ′) obtained by ion-exchanging an alkali metal ion and an alkaline earth metal ion contained between layers of the clay mineral with onium ions (B ′). 2. The method according to claim 1, wherein
Or the flame-retardant resin adhesive according to claim 2. 4. The flame-retardant resin adhesive according to claim 1, wherein the layered clay mineral (B) is saponite. 5. The flame-retardant resin adhesive according to claim 1, wherein the layered clay mineral (B) is montmorillonite. 6. The flame-retardant resin adhesive according to claim 1, wherein the layered clay mineral (B) is synthetic mica. 7. A flexible structure comprising a metal foil and a heat-resistant resin film bonded to each other via the flame-retardant resin adhesive according to any one of claims 1 to 6. Printed circuit board. 8. The flexible printed circuit board according to claim 7, wherein the heat-resistant resin film is a polyimide film.