JPH07179840A - Bonding method with heat-resistant adhesive film - Google Patents

Abstract

PURPOSE:To obtain a bonded article having an excellent heat resistance, a low coefficient of linear thermal expansion, and a good dimensional accuracy by sticking and thermally pressing a heat-resistant adhesive film produced from a polyisoimide resin to an adherend. CONSTITUTION:A heat-resistant adhesive film obtd. from a polyisoimide resin having at least 40mol% isoimide units of the formula is bonded to an adherend by sticking the film to the adherend and pressing the film at the glass transition point of the resin or higher to thereby subject the film to imide rearrangement. In the formula, Ar1 is a tetravalent arom hydrocarbon group; Ar2 is a divalent arom. hydrocarbon group. The film, having isoimide units, thermally adheres well even to a polyimide which is not thermoplastic. Isoimide units in the resin easily undergo imide rearrangement when heated and give a polyimide with an elevated glass transition point, thus giving a cover lay film, a bilayered substrate, a multilayered substrate. etc., excellent in resistances to heat and chemicals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bonding method using a polyisoimide resin film containing an isoimide unit in the molecule as a heat resistant adhesive film.

[0002]

2. Description of the Related Art In recent years, with the development of the electronics industry and the electrical industry, mounting methods for consumer and communication devices are required to be simple, compact, and highly reliable, and use of printed circuit boards is demanded. There is. In particular, it is effective to use a flexible printed circuit board because the printed circuit board can be made smaller and lighter and can be surface-mounted.

A flexible printed circuit board generally uses a heat-resistant film such as a polyimide film and a copper foil with or without an adhesive agent and directly laminates the same as a substrate. In such a case, the heat resistance originally possessed by the heat resistant film cannot be fully utilized, and the heat resistance of the flexible printed board depends on the heat resistance of the adhesive. Therefore, it is becoming mainstream to use a so-called two-layer substrate obtained by directly laminating without using an adhesive.

On the other hand, a coverlay film is generally laminated on the circuit surface in order to protect the circuit of the flexible printed circuit board from external humidity and foreign matter. Also in this cover lay film, when an adhesive is used for laminating and coating, a problem that heat resistance is deteriorated is exhibited as in the above case. In addition, normally, a polyimide film having heat resistance is used for the coverlay film, but many of these films do not have adhesiveness to themselves, and the film surface must be coated with an adhesive during lamination. I have to.

However, the epoxy-based adhesives and the like which are widely used as adhesives have a low working temperature, but they are not sufficient in terms of heat resistance and storage stability. Further, in recent years, those using a thermoplastic polyimide resin as an adhesive layer have also been proposed, but the temperature at the time of adhesion is relatively high although it has excellent heat resistance and storage stability, and it can be said that it is still satisfactory in workability. Absent. Further, since the thermoplastic polyimide resin has a large coefficient of linear expansion, when it is adhered or laminated with a copper foil or a flexible printed circuit board, sufficient dimensional stability cannot be obtained, or the curl due to the difference in the coefficient of linear expansion with the adherend. There is a problem such as occurrence of. Therefore, it is a fact that there is a demand for the development of an adhesive film which does not require an adhesive agent and has excellent workability and also has excellent dimensional accuracy and heat resistance.

[0006]

Therefore, as a result of investigations to solve the problems of the above-mentioned conventional adhesive films, the present inventors have found that by using a polyisoimide resin film having an isoimide unit in the molecule, excellent adhesion can be achieved. A heat resistant film having performance was found.

As a result of further studies on an adhesive method using this film, a polyimide resin obtained by imide conversion of the isoimide unit when a temperature higher than the glass transition temperature is applied during thermocompression bonding of the polyisoimide resin film. It has been found that the glass transition temperature of the film is increased by 20 ° C. or more than that of the polyisoimide resin and the heat resistance is improved, and the linear expansion coefficient is also 50 ppm or less, so that an adhesive having extremely good dimensional accuracy can be obtained.
The present invention has been completed.

[0008]

That is, according to the present invention, an isoimide unit represented by the following general formula (Formula 2) is incorporated into the molecule in an amount of 40
After heat-resistant adhesive film made of polyisoimide resin containing more than mol% is laminated on the surface of the adherend, it is heat-pressed at a temperature not lower than the glass transition temperature of the polyisoimide resin to convert the film into an imide. An adhesive method using a film is provided.

[0009]

[Chemical 2]

(However, Ar ₁ represents a tetravalent aromatic hydrocarbon residue, and Ar ₂ represents a divalent aromatic hydrocarbon residue.)

The resin layer in the present invention contains the isoimide unit represented by the above general formula (Formula 2) in the molecule in an amount of 40 mol%, preferably 80 mol% or more. When the number of isoimide units is small and, as a result, the number of imide units is large, it is necessary to increase the temperature during thermocompression bonding, so that workability is reduced. In addition, when the resin layer is subjected to laser irradiation for dry etching or chemically wet-etched for processing, the etching property may be poor.

To prepare the above-mentioned isoimide unit, a known monomer for synthesizing a polyimide resin, that is, an aromatic tetracarboxylic dianhydride component and an aromatic diamine component may be reacted. However, in the present invention, after preparing a polyamic acid, dicyclohexylcarbodiimide or trifluoroacetic anhydride, thionyl chloride, phosphorus trichloride, ethyl chloroformate, a ring closure using a dehydration condensation agent such as acetic anhydride as a polyimide precursor. The polyisoimide of is prepared. At this time, a polyimide unit, a polyamic acid unit or the like may be contained within the above range. When a large amount of polyamic acid unit is contained, the degree of dimensional shrinkage due to dehydration condensation at the time of imidization becomes large, so it is necessary to suppress the amount of polyamic acid unit to 10 mol% or less.

Examples of the tetracarboxylic dianhydride component used in the above synthetic reaction include, for example, pyromellitic acid,
3,3 ′, 4,4′-biphenyltetracarboxylic acid,
2,2 ', 3,3'-biphenyltetracarboxylic acid,
4,4'-oxydiphthalic acid, 2,2 ', 3,3'-benzophenonetetracarboxylic acid, 3,3', 4,4'-
Benzophenone tetracarboxylic acid, 2,2-bis (3
4-dicarboxyphenyl) propane, 2,2-bis (3,4-dicarboxyphenyl) sulfone, bis (3,4-dicarboxyphenyl) methane, bis (2,2
3-dicarboxyphenyl) methane, 2,2-bis (2,3-dicarboxyphenyl) hexafluoropropane, 2,2-bis (3,4-dicarboxyphenyl)
Hexafluoropropane, bis (3,4-dicarboxyphenyl) difluoromethane, bis (2,3-dicarboxyphenyl) difluoromethane, 2,3,6,7-naphthalenetetracarboxylic acid, 1,4,5,8 -Naphthalene tetracarboxylic acid, hydroquinone diether, 1,
3-bis (3,4-dicarboxyphenyl) -1,1,
A dianhydride such as 3,3-tetramethyldisiloxane and derivatives thereof can be used alone or in combination of two or more. The tetracarboxylic dianhydride component may be a structural isomer.

On the other hand, as the diamine component, for example, 2,
2-bis (trifluoromethyl) 4,4'-diaminobiphenyl, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,
4'-diaminodiphenyl ether, 2,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone,
3,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,
4'-diaminobenzophenone, 4,4'-diaminodiphenylpropane, 3,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,
4'-diaminodiphenylhexafluoropropane,
3,4'-diaminodiphenylhexafluoropropane, 3,3'-diaminodiphenylhexafluoropropane, bis [4- (3-aminophenoxy) phenyl]
Methane, bis [4- (4-aminophenoxy) phenyl] methane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] Propane, 2,2-bis [4- (3-aminophenoxy) phenyl] hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, 1,3-bis (3- Aminophenoxy) benzene, 4,4'-bis (4-aminophenoxy) biphenyl, bis [4- (3
-Aminophenoxy) phenyl] sulfone, bis [4-
(4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] ether,
Bis [4- (4-aminophenoxy) phenyl] ether, 4,4′-diaminobenzanilide, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4
-Aminophenoxy) benzene, bis [4- (4-aminophenoxy) phenyl] ether and the like can be used alone or in combination of two or more. The diamine component may be a structural isomer.

The above-mentioned monomers (acid dianhydride component and diamine component) are blended in approximately equimolar amounts, for example, N-methyl-
2-pyrrolidone, N, N-dimethylacetamide, N,
N-dimethylformamide, 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, dimethyl sulfide, dimethyl sulfone, pyridine, tetramethylurea, diglyme, triglyme, tetrahydrofuran, dioxane, dichloroethane, dichloromethane, acetonitrile, methyl ethyl ketone, methyl isobutyl Solution polymerization is carried out using an organic solvent such as ketone, toluene or xylene to prepare a polyamic acid, and then polyisoimidization is carried out under the above conditions.

The polyisoimide-containing resin solution obtained as described above has a thickness of 2 after dried using a roll coater, comma coater, knife coater, doctor blade or the like on a flexible support. ~ 200μ
The solution is applied by casting so as to be about m, and the organic solvent used in the reaction is dried and removed at a temperature of 50 to 200 ° C. In addition,
If the drying temperature is too high (for example, 300 ° C. or higher), the polyisoimide will undergo imide transfer, so care must be taken when adjusting the temperature. The heating is preferably performed in the absence of oxygen, usually under an inert gas atmosphere or under reduced pressure.
The resin layer may be a single layer or a multilayer of two or more layers, and may have a polyisoimide composition distribution in the thickness direction.

In the present invention, a plastic film, a metal foil or the like is used as the support for coating the resin solution to form the heat-adhesive resin layer. When a plastic film is used as the support, it can be used as a coverlay film for covering and protecting the circuit surface of a flexible printed circuit board or a rigid circuit board. As such a plastic film, one having electrical insulation is preferable, and for example, a film made of polyester resin or polyimide resin can be used. From the viewpoint of heat resistance, it is preferable to use a polyimide resin.

On the other hand, when a metal foil made of a metal such as copper, aluminum, nickel or stainless steel is used as the support, a flexible multi-layer substrate having thermal adhesiveness can be obtained. For example, a double-sided substrate can be produced by adhering the two adhesive films of the two-layered substrates to each other, or a multilayer substrate can be produced by laminating a plurality of substrates. In the case of such a two-layer board or a multilayer board, a metal foil can be patterned to form a circuit and used. Furthermore, the obtained multilayer substrate is an excimer laser, a carbon dioxide gas laser, a YAG laser,
Dry etching by laser irradiation of argon ion laser, semiconductor laser, etc., or a layer of commercially available negative or positive resist is formed on the resin layer, and if necessary, ultraviolet rays are irradiated through a mask to expose the unexposed area. By performing a wet etching process for dissolving and removing the, it is possible to perform opening (opening) processing as a flexible printed circuit board. Polyisoimide dissolves in an organic solvent or an inorganic alkaline aqueous solution such as sodium hydroxide or potassium hydroxide, or a mixed solution of an organic alkaline aqueous solution such as tetramethylammonium hydroxide and an alcohol, so that it can be used to dissolve the resin layer during wet etching. Is suitable to use such a solution.

In the adhesive film thus obtained, the isoimide unit easily undergoes imide transfer by heating. At the time of this transition, shrinkage due to dehydration condensation as seen during imidation from polyamic acid does not occur, so that it is extremely excellent in dimensional stability.

For example, when a laminated adhesive film using a plastic film as a support is used as a cover lay film, it is superposed on the circuit of a flexible printed circuit board as an adherend and then heated by a hot molding machine such as a hot press. 100-400 ° C, preferably 250-
It is preferable to perform thermocompression bonding under heating at 350 ° C. at a pressure of 1-250 kg / cm ² , preferably 5-100 kg / cm ² . If the temperature is low or the pressure is low, sufficient adhesive strength cannot be obtained, and if the temperature is too high, the embrittlement temperature or decomposition temperature of the film may be reached. The circuit may peel from the base film. Note that it is preferable to perform thermocompression bonding for 1 second or more in order to ensure thermal adhesion.

In the bonding method of the present invention, the heating temperature during the above-mentioned thermocompression bonding is carried out at a temperature higher than the glass transition temperature of the polyisoimide resin in order to surely transfer the imide of the polyisoimide and to improve workability. The glass transition temperature of the resulting polyimide resin film is adjusted to 20 ° C. or higher than that of the polyisoimide resin before heating.
As a result, the heat resistance of the adhesive film after heating becomes good, and the linear expansion coefficient becomes 50 ppm or less, so that an adhesive product with extremely good dimensional accuracy can be obtained.

In order to completely imidize polyisoimide, an organic base such as pyridine or triethylamine, or an organic acid such as trifluoroacetic acid or paratoluenesulfonic acid can be used as an imidization promoting catalyst.

[0023]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Synthesis Example 1 64 g (0.2 mol) of 2,2-bis (trifluoromethyl) -4,4-diaminobiphenyl was dissolved in 1149 g of N-methyl-pyrrolidone, and 3,3 ', 4 was added thereto. ，
58.8 g of 4'-biphenyltetracarboxylic dianhydride
(0.2 mol) was added at room temperature and reacted for 12 hours to obtain a solution of polyamic acid (A).

Next, 56 ml (0.4 mol) of trifluoroacetic anhydride was added to the obtained solution and triethylamine 56.
ml (0.4 mol) was added, and the mixture was reacted at room temperature for 4 hours. After the reaction, the polyisoimide precipitated by pouring into excess isopropanol was separated by filtration, washed with isopropanol, and dried under reduced pressure at 40 ° C. to obtain a polyisoimide powder. The glass transition temperature (by differential scanning calorimeter) of this powder was 280 ° C. The obtained polyisoimide powder was mixed with N, N- so that the polymer content was 20% by weight.
It was dissolved in dimethylacetamide to obtain a polyisoimide solution (A).

Synthesis Example 2 11.5 g of pyromellitic dianhydride as an acid anhydride
(0.06 mol) and 4,4'-oxydiphthalic acid dianhydride 43.4 g (0.14 mol) were used, and N-methyl-pyrrolidone was used as a reaction solvent in the same manner as in Synthesis Example 1 except that 1070 g was used. A solution of polyamic acid (B) was obtained.

Then, the same operation as in Synthesis Example 1 was performed using the obtained solution to obtain a polyisoimide powder. The glass transition temperature (by differential scanning calorimeter) of this powder is 240.
It was ℃. The obtained polyisoimide powder was dissolved in N, N-dimethylacetamide so that the polymer content was 20% by weight to obtain a polyisoimide solution (B).

Example 1 The polyisoimide solution (A) obtained in Synthesis Example 1 was uniformly applied onto a copper foil (thickness 35 μm) as a support so as to have a thickness after drying of 25 μm using a comma coater. It was applied by casting and continuously heated at 100 ° C. to remove the solvent.
Subsequently, nitrogen replacement was performed, and after heating at 200 ° C in a continuous heating furnace with an oxygen concentration of 1.5% or less, it was cut to an appropriate size and dried under reduced pressure at 200 ° C for 4 hours to consist of polyisoimide / copper foil. A heat resistant adhesive film was produced.

Two polyisoimide layers of the heat-resistant adhesive film were opposed to each other and thermocompression bonded (370 ° C., 80 kg / cm ² , 15 minutes) using a hot press to prepare a double-sided substrate. When the copper foil of the obtained double-sided board was etched and the infrared absorption spectrum of the polyisoimide layer was measured, the imidization was completely completed. The linear expansion coefficient was measured and found to be 30 ppm. The changes in the adhesion state and the glass transition temperature are shown in Table 1.

Example 2 A heat resistant adhesive film was prepared in the same manner as in Example 1 except that a polyimide film (thickness: 25 μm) was used as the support instead of the copper foil.

This heat-resistant adhesive film was used as a cover lay film, which was superposed on an adhesiveless flexible printed circuit board having a line and space pattern of 300 μm, and hot-pressed by hot pressing (370 ° C., 100 ° C.).
(kg / cm ² , 20 minutes) to prepare a substrate with a cover lay. The polyisoimide layer is completely imidized,
When the linear expansion coefficient was measured, it was 30 ppm. The changes in the adhesion state and the glass transition temperature are shown in Table 1.

Example 3 A heat resistant adhesive film was prepared in the same manner as in Example 1 except that the polyisoimide solution (B) obtained in Synthesis Example 2 was used to obtain a double-sided substrate (thermocompression bonding condition: 380 ° C., 100 kg
/ Cm ² , 15 minutes). The polyisoimide layer is completely imidized, and the linear expansion coefficient was measured to be 16 ppm.
Met. Table 1 shows the changes in adhesion state and glass transition temperature.
It was the street.

Comparative Example 1 Using the polyamic acid solution (A) obtained in Synthesis Example 1, copper foil (thickness 35 μm) was cast-coated as a support in the same manner as in Example 1 and continuously heated at 100 ° C. Then, the solvent was removed. Subsequently, nitrogen replacement was carried out, and after heating at 400 ° C. in a continuous heating furnace having an oxygen concentration of 1.5% or less, it was cut into an appropriate size to prepare a heat resistant film made of polyimide / copper foil.

The polyimide layers of the two heat-resistant films are made to face each other, and thermocompression bonding (39
An attempt was made to prepare a double-sided substrate at 0 ° C., 120 kg / cm ² , for 20 minutes), but no double-sided substrate could be prepared because of no adhesion. Moreover, when the linear expansion coefficient was measured, it was 30
It was ppm. The changes in the adhesion state and the glass transition temperature are shown in Table 1.

Comparative Example 2 Using the polyamic acid solution (B) obtained in Synthesis Example 2, one side of a polyimide film (thickness: 25 μm) as a support was cast and imidized in the same manner as in Comparative Example 1 to form a polyimide. / A polyimide heat resistant film was prepared.

This heat-resistant film was used as a coverlay film in the same manner as in Example 2, and was superposed on an adhesiveless flexible printed circuit board having a line and space pattern of 300 μm, and heat-pressed by hot pressing (390 ° C., 150 kg / cm ² , 30 minutes). However, it did not adhere completely and was partially peeled off. The linear expansion coefficient was measured and found to be 16 ppm. The changes in the adhesion state and the glass transition temperature are shown in Table 1.

[0037]

[Table 1]

[0038]

As described above, the bonding method of the present invention uses a resin film composed of a specific isoimide unit having a heat bonding property, so that it has excellent heat resistant adhesion, a small coefficient of linear expansion, and good dimensional accuracy. An adhesive can be obtained. Furthermore, since the resin film has an isoimide unit, good thermal adhesiveness can be obtained even for a polyimide structure that does not exhibit thermoplasticity. Further, the isoimide unit in the resin layer in the present invention becomes a polyimide having an intramolecular imide transition easily caused by heating to raise the glass transition temperature, and thus a coverlay film or a two-layer substrate having excellent heat resistance and chemical resistance. Thus, a multilayer substrate can be obtained.

Claims (3)

[Claims] 1. A heat resistant adhesive film made of a polyisoimide resin containing 40 mol% or more of an isoimide unit represented by the following general formula (Formula 1) in the molecule is laminated on the surface of an adherend, and then the polyisoimide resin is obtained. The method of bonding using a heat-resistant adhesive film, which comprises subjecting the film to imide conversion by heating under pressure at a temperature not lower than the glass transition temperature. [Chemical 1] (However, Ar ₁ represents a tetravalent aromatic hydrocarbon residue, and Ar ₂ represents a divalent aromatic hydrocarbon residue.) 2. The bonding method using the heat resistant adhesive film according to claim 1, wherein a support made of a plastic film or a metal foil is laminated on one surface of the heat resistant adhesive film made of polyisoimide resin. 3. The bonding method using a heat resistant adhesive film according to claim 1, wherein the adherend is a flexible printed circuit board.