JP2660943B2 - Circuit board bonding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for bonding circuit boards, and more particularly, to a method for bonding fine pattern electrodes to each other by using a photosensitive adhesive exhibiting adhesiveness by heat treatment. Related to the bonding method.

[0002]

2. Description of the Related Art Circuit boards formed by connecting circuit boards are conventionally manufactured by soldering electrodes of each circuit board. Since this method heats and melts the solder to connect the electrodes, if the pitch between the electrodes on the circuit board is very small, there is a problem that short-circuiting easily occurs between the electrodes. In order to avoid the above-mentioned thermal problem, a method of bonding circuit boards to each other using an anisotropic conductive adhesive has recently been used.

The anisotropic conductive adhesive disperses conductive particles in the adhesive and presses the conductive particles to coagulate and fix.
It shows conductivity only in its thickness direction, and shows non-conductivity in other directions. Utilizing this anisotropic conductivity, this anisotropic conductive adhesive layer is formed on the surface of the electrode to be bonded, and the anisotropic conductive adhesive layer interposed between the electrodes is pressed in the thickness direction to form the conductive particles. The electrical connection between the two electrodes is established.

However, in the method using an anisotropic conductive adhesive, when the pitch between the electrodes to be connected is as wide as 150 μm or more, the interconnections can be well connected to each other. In the case of having the conductive particles, a conductive state occurs due to the conductive particles dispersed in the adhesive, which causes a short circuit.

Further, in order to cope with the miniaturization of electrodes, a photocurable adhesive is applied onto a circuit board, and photocuring is performed on portions other than the electrode portions, thereby leaving adhesiveness only on the electrodes, and allowing the conductive particles to move there. There is also known a method in which a photocurable adhesive is applied thereon, and the circuit boards are bonded by superimposing the circuit boards and irradiating the circuit boards with light while applying pressure (Japanese Unexamined Patent Publication (Kokai) No. 3-131089). ). However, even this method cannot sufficiently cope with recent miniaturization. In particular, when the pitch between electrodes is 50 μm or less, a short circuit is likely to occur, which is not a practical method, and a circuit that can sufficiently cope with miniaturization between electrodes. There is a strong demand for the development of a method for bonding substrates.

[0006]

SUMMARY OF THE INVENTION In view of the above demand, the present inventors have conducted intensive studies to develop an effective method for bonding circuit boards having a fine pitch between electrodes. A photosensitive adhesive indicating the connection between circuit boards,
In particular, the present inventors have found that the object can be achieved by applying the present invention to bonding between electrodes of a circuit board, and have accomplished the present invention.

[0007]

According to the present invention, a first circuit board having a first electrode formed thereon is overlapped with a second circuit board having a second electrode formed at a position corresponding to the first electrode. In a method of bonding a circuit board for connecting a first electrode and the second electrode, a photosensitive adhesive is applied on the first electrode of the first circuit board and on a portion where the first electrode is not formed, and dried. Forming a photosensitive adhesive layer by irradiating the photosensitive adhesive layer with actinic rays selectively, and then performing a development process to remove only the photosensitive adhesive layer on the first electrode. And
Next, a heating process is performed to impart adhesiveness to the photosensitive adhesive layer remaining between the first electrodes, the first circuit board and the second circuit board are overlapped, and heat-pressed, 1
Electrically connecting the electrode and the second electrode;
Applying a heat treatment and / or an actinic ray irradiation treatment to a circuit board composed of the first circuit board and the second circuit board to which an electrode and the second electrode are connected. Is a bonding method.

Hereinafter, the present invention will be described in detail. As shown in FIG. 1, the method for bonding a circuit board according to the present invention comprises the steps of:
On an insulating substrate 1 such as a printed circuit board, a glass substrate, a ceramic substrate, etc., ITO (indium, tin oxide), Ti,
As shown in FIG. 2, a photosensitive adhesive is applied on a first circuit board on which a first electrode 2 made of a conductor such as Ta, Mo, Ni, Al, Cu, Au, Sn, or Pb or an alloy thereof is formed. The photosensitive adhesive layer 3 was formed by applying a roll coater, a curtain flow coater, a screen printing, a spray coater, a spin coater, or the like on the first electrode 2 and a portion where the first electrode 2 was not formed, and then drying. Later
As shown in FIG. 3, a portion corresponding to the first electrode 2 is selectively irradiated with actinic rays such as ultraviolet rays through a mask 4 in which light is shielded, or when a transparent substrate such as a glass substrate is used, the back surface of the substrate is used. Irradiating with actinic light from above, and removing the unirradiated portion using a developing solution as shown in FIG. 4 so that the photosensitive adhesive layer 3 ′ is left only between the first electrodes 2 and then subjected to heat treatment. To give the photosensitive adhesive layer 3 an adhesive property, and then, as shown in FIG. 5, Ti, T
The second circuit board on which the second electrode 6 corresponding to the first electrode 2 made of a conductor such as a, Mo, Ni, or Al, or an alloy thereof is formed, and the first circuit board 2 is bonded to the first circuit board 2 by heating and pressing. After the second electrode 6 is connected, the whole is subjected to heat treatment and / or irradiation treatment with actinic rays such as ultraviolet rays,
By completely bonding the first circuit board and the second circuit board with a photosensitive adhesive, it is possible to bond a circuit board which is excellent in adhesiveness and free from problems such as a short circuit even in a circuit board having fine electrodes. .

The photosensitive adhesive used in the above-described bonding method of the present invention may be any as long as it is cured by irradiation with actinic rays such as ultraviolet rays and the cured product shows adhesiveness by heat treatment. Is esterification obtained by reacting at least one selected from cresol novolak type epoxy resin, phenol novolak type epoxy resin, glycidylamine type epoxy resin, biphenyl type epoxy resin and bromine adduct thereof with an unsaturated basic acid. Those containing a resin and a photopolymerization initiator can be used,
In particular, those containing a photopolymerization initiator and an esterified resin obtained by a reaction of at least one selected from a cresol novolak type epoxy resin and a phenol novolak type epoxy resin with an unsaturated basic acid can be preferably used. In this case, the cresol novolak type epoxy resin is obtained by reacting epichlorohydrin or methyl epichlorohydrin with a cresol novolak resin obtained from cresol and formaldehyde. Alternatively, it can be obtained by reacting methyl epichlorohydrin.

The unsaturated basic acid which reacts with the cresol novolak type epoxy resin and / or phenol novolak type epoxy resin includes acrylic acid, methacrylic acid, crotonic acid, monomethyl maleate, monopropyl maleate, monobutyl maleate, sorbin There are acids and the like, which may be used alone or in combination of two or more.

The esterification catalyst used in the reaction between the epoxy resin and the unsaturated basic acid includes diethylamine hydrochloride, diethylamine acetate, triethylamine and the like.
Primary and tertiary amines can be used.

Examples of the photopolymerization initiator include benzophenone, 4,4'-dimethylaminobenzophenone,
Benzophenones such as 4,4'-diethylaminobenzophenone, anthraquinones such as 2-ethylanthraquinone and tert-butylanthraquinone, benzoin alkyl ethers such as benzoin ethyl ether and benzoin isopropyl ether, and 2,2-dimethoxy-2-phenylacetophenone 2,2-diethoxyacetophenone, 2-chlorothioxanthone, diethylthioxanthone, 2-hydroxy-2-methylpropiophenone, 4'-isopropyl-2-hydroxy-2-
And methylpropiophenone, one of these.
2 to 10 or more kinds of the esterified resin
It is preferable to mix in the range of weight%.

The above-mentioned photosensitive adhesive is cured by actinic rays such as ultraviolet rays, and the cured product is subjected to heat treatment.
Although it must show adhesiveness, the heat treatment temperature in this case is 50 to 100 ° C., preferably 65 to 90 ° C.
Range. If the temperature is lower than 50 ° C., it is not preferable because good adhesiveness cannot be provided.
When the temperature exceeds ℃, a pattern having a good shape cannot be obtained, which is not preferable.

The above-mentioned photosensitive adhesive used in the bonding method of the present invention is practically used in the form of a coating solution dissolved in an organic solvent.
Ethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, methyl isobutyl ketone, 1,1,1-trichloroethane, trichloroethylene Or a mixture of two or more.

The above photosensitive adhesive is selectively irradiated with actinic rays such as ultraviolet rays, and then the unirradiated portions of the actinic rays are removed by a developing treatment. Examples thereof include aqueous inorganic alkali solutions such as sodium carbonate and sodium hydroxide, aqueous organic alkali solutions such as quaternary ammonium salts and amines, and organic solvents such as trichloroethane, butyl acetate, xylene, and ethylene glycol monobutyl ether acetate.

If necessary, a compatible resin, a coloring agent such as a dye or a pigment, a surfactant, or the like may be added to the photosensitive adhesive.

According to the bonding method of the present invention, the first circuit board and the second
After the circuit board is overlaid and heated and pressed to connect the first electrode and the second electrode, the whole is subjected to heat treatment and / or irradiation treatment with actinic rays such as ultraviolet rays to form a photosensitive adhesive layer. The first circuit board and the second circuit board are completely cured, and the heat treatment in this case is preferably performed at a temperature in the range of 140 to 180 ° C. If the heating temperature is lower than 140 ° C., it is not preferable because complete adhesion cannot be achieved, and if it is higher than 180 ° C., there is no problem in the adhesiveness, but it is not preferable because it adversely affects the substrate and the electrodes.

As a means for thermocompression bonding, a constant heat method is effectively used.

In the bonding method of the present invention, when connecting the first electrode and the second electrode, the connection between the first electrode and the second electrode is set to A.
A conductor such as u, Sn, or In alloy may be attached to the first electrode or the second electrode, and connected via those conductors.

[0020]

According to the circuit board bonding method of the present invention, by using a photosensitive adhesive exhibiting adhesiveness by heat treatment,
Since the photosensitive adhesive is selectively formed only between the electrodes and the electrodes can be directly connected to each other, the connection between circuit boards having an electrode pattern of, for example, 50 μm or less is also possible regardless of the width between the electrodes. This is extremely practical because it can be easily and reliably performed and problems such as short circuits can be eliminated.

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto.

[0022]

Example 1 Phenol novolak type epoxy acrylate resin to which tetrahydrophthalic anhydride was added 7.5 g Cresol novolak type epoxy acrylate resin to which tetrahydrophthalic anhydride was added 17.9 g Cresol novolak type epoxy resin 14.4 g (Epiclon N-673) Dainippon Ink and Chemicals, Inc.) Urethane oligomer 8.3 g 2-Methyl- [4- (methylthio) phenyl] -2-morpholino-1-propane 1.8 g Diethylthioxanthone 1.1 g 49.0 g of propylene glycol monomethyl ether acetate The mixture was dissolved to prepare a photosensitive adhesive solution.

Next, the second electrode having a pitch between electrodes of 40 μm
A solution of the above photosensitive adhesive was applied on a glass substrate on which an ITO film pattern having a width of 5 μm and a thickness of 0.5 μm was formed by a spinner, dried at 90 ° C. for 5 minutes on a hot plate, and dried to a thickness of 10 μm. A photosensitive adhesive layer was obtained.

Next, after selectively irradiating with an actinic ray through a mask having a light-shielding portion corresponding to the ITO film pattern on the glass substrate, it is immersed in a 5% by weight aqueous solution of triethanolamine at 25 ° C. for 3 minutes. As a result, only the photosensitive adhesive layer on the ITO film pattern was selectively dissolved and removed.

Next, a silicon wafer on which an Au pattern was formed in a form corresponding to the ITO
The u pattern and the ITO film pattern on the glass substrate were aligned so as to be connected, and the glass substrate and the silicon wafer were heated and pressed at a heating temperature of 80 ° C. and a pressure of 2.5 kg / cm ² .

Thereafter, ultraviolet rays were applied at 3 J / from the glass substrate side.
By irradiating the entire surface with an intensity of 1 cm ² for 1 minute, the photosensitive adhesive layer was completely cured, and the glass substrate and the silicon wafer were completely adhered to each other, whereby a circuit board having well-connected electrodes was obtained. .

[0027]

Example 2 In Example 1, instead of performing the entire surface irradiation of ultraviolet rays from the glass substrate side for completely curing the photosensitive adhesive layer, a heat treatment at 150 ° C. for 30 minutes was performed in an oven. Except for the above, a circuit board was obtained in the same manner as in Example 1. It was confirmed that the electrodes of this circuit board were also well connected.

[Brief description of the drawings]

FIG. 1 shows the steps of the bonding method of the present invention.

FIG. 2 shows the steps of the bonding method of the present invention.

FIG. 3 shows the steps of the bonding method of the present invention.

FIG. 4 shows the steps of the bonding method of the present invention.

FIG. 5 shows the steps of the bonding method of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 insulating substrate 2 first electrode 3 photosensitive adhesive layer 3 ′ photosensitive adhesive layer after irradiation with active light 4 mask 5 insulating substrate 6 second electrode

Continuation of the front page (72) Inventor Toshimi Aoyama 150 Nakamaruko, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Within Tokyo Ohka Kogyo Co., Ltd. (56) References JP-A-3-131089 (JP, A) Jpn. JP, U)

Claims (1)

(57) [Claims] 1. A first circuit board on which a first electrode is formed and a second circuit board on which a second electrode is formed at a position corresponding to the first electrode, and the first electrode and the second electrode are overlapped. And (b) applying a photosensitive adhesive on the first electrode of the first circuit board and on a portion where the first electrode is not formed, and drying and applying the photosensitive adhesive. Forming a layer; (b) selectively irradiating the photosensitive adhesive layer with actinic rays, and then subjecting the photosensitive adhesive layer to a development treatment to remove only the photosensitive adhesive layer on the first electrode; Next, heat treatment is performed,
(C) superimposing the first circuit board and the second circuit board, and pressing them by heating and pressing, so that the first electrode and the first electrode are bonded to each other. Electrically connecting the second electrode with the second electrode; and (d) heat-treating and / or heating the circuit board including the first circuit board and the second circuit board to which the first electrode and the second electrode are connected. A method for bonding a circuit board, comprising a step of irradiating an actinic ray.