JPH0574846A - Electrically connecting method - Google Patents

Abstract

PURPOSE:To surely and easily connect two circuit boards with high continuity reliability without causing a short circuit even when many terminals to be connected are formed on the circuit boards at fine and dense pitches when the two circuit boards are connected electrically. CONSTITUTION:In a method, terminals on a first circuit board are connected electrically to terminals on a second circuit board. In the method, a transfer film 1, for electrical connection use, wherein conductive particles 3 have been held as one layer on a film 2 is first formed, the face where the conductive particles on the transfer film 1 have been held is overlapped with the terminal face of the first circuit board 5, both are pressure-bonded primarily, they are stripped, the conductive particles 3 are transferred onto the terminals 5a on the first circuit board, the terminal face of the first circuit board 5 onto which the conductive particles 3 have been transferred is pressure-bonded formally to the terminal face of the second circuit board 7 via an adhesive 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for electrically connecting terminals between two circuit boards. More specifically, the present invention reliably and easily connects the terminals between the two circuit boards without causing a short circuit between the terminals even when a large number of terminals to be connected to the circuit board are formed at a fine pitch. The present invention relates to an electrical connection method that enables connection, and a transfer film for electrical connection and a circuit board for electrical connection used in such an electrical connection method.

[0002]

2. Description of the Related Art As a method of electrically connecting terminals between two circuit boards, such as a case of connecting a liquid crystal panel and a TAB, a method using an anisotropic conductive adhesive has hitherto been used. Are known. In this method, an anisotropic conductive adhesive is used in which conductive particles such as solder particles, metal particles such as nickel particles or resin particles plated with gold are dispersed in a thermosetting or thermoplastic adhesive. Then, such an anisotropic conductive adhesive is interposed between the two circuit boards,
By heating and pressurizing, electrical connection between two opposing terminals can be obtained (JP-A-51-114439).

As a bonding material similar to such an anisotropic conductive adhesive, conductive particles are brought into contact with one surface of the base material in a sheet-like insulating base material made of a thermoplastic resin or one of the base materials. It is also known that it is buried so as to be exposed from the surface. As a method of using this bonding material, first, the terminal surface of the first circuit board and the conductive particles of the bonding material are heat-welded. Next, the second circuit board is heated and pressed on the heat-welded bonding material to melt the sheet-shaped insulating base material of the bonding material,
The two circuit boards are joined together, and the conductive particles welded to the terminals of the first circuit board and the terminals of the second circuit board are joined together (JP-A-64-14886).

As a method of connecting the IC chip to the TAB, there is known a transfer bump method in which a gold pillar is formed on a bump forming substrate by plating, the gold pillar is aligned with the TAB and transferred, and then connected. There is.

Further, a method is known in which a conductive adhesive is placed only on a pattern to be connected on a circuit board by printing or dipping.

[0006]

However, in the conventional method using the anisotropic conductive adhesive, the anisotropic conductive adhesive is applied over the entire bonding area including the terminals to be connected of the two circuit boards. Since they are interposed, the conductive particles are present not only between the terminals to be connected but also between the other adjacent terminals. Therefore, there is a problem that short-circuiting is likely to occur when the pitch of the terminals is fine. For such a problem, it has been considered to reduce the amount of conductive particles blended in the anisotropic conductive adhesive, but if the amount of conductive particles blended is reduced, it exists between terminals to be connected. Since the conductive particles are also reduced, there is a problem that conduction reliability is lowered.

Further, the transfer bump method requires a step of forming a gold pillar by plating and a step of aligning this with the TAB, so that there is a problem in that the number of steps is large and the workability is poor.

Further, in the method of placing the conductive adhesive only on the pattern to be connected to the circuit board by printing, dipping or the like, there is a problem that the technique of placing the conductive adhesive only on a predetermined pattern is difficult. .. Also, 2
Since the two circuit boards are joined only by adhering the terminal patterns to each other, there is a problem that the adhesive strength and the reliability are lowered.

The present invention is intended to solve the problems of the prior art as described above, and in the case where a large number of terminals to be connected between the two circuit boards are formed on the circuit board at a fine pitch. However, it is an object of the present invention to ensure reliable and easy connection so that high conduction reliability can be obtained without causing a short circuit.

[0010]

In order to achieve the above object, the present invention is characterized in that a conductive particle is held in one layer on a film as a bonding material used in an electrical connection method. A transfer film for electrical connection is provided.

Further, as a circuit board used in the electrical connection method, there is provided an electrical connection circuit board in which one layer of conductive particles is fused only on the terminals of the circuit board.

As the electrical connection method of the present invention for electrically connecting the terminals of the first circuit board and the terminals of the second circuit board, the terminal surface of the first circuit board and the transfer film The surface of the first circuit board on which the conductive particles are held is joined, and both are heat-pressed and separated to transfer the conductive particles onto the terminals of the first circuit board, and then the first circuit board on which the conductive particles are transferred. Provided is a method characterized in that the terminal surface and the terminal surface of the second circuit board are thermocompression bonded via an adhesive.

The electrical connection method of the present invention will be specifically described below with reference to the drawings. In the drawings, the same reference numerals represent the same or equivalent constituent elements.

FIGS. 1 and 2 are explanatory views of the steps of the electrical connection method of the present invention, and FIG. 1 (a) and FIG. 2 (a) are both electrical connections used in the method of the present invention. It is a cross-sectional view of an example of a transfer film for use. As shown in the figure, the transfer film 1 for electrical connection of the present invention is one in which one layer of conductive particles 3 is held on the film 2. By holding one layer of conductive particles in this way,
As will be described later, when the transfer film is first pressure-bonded to the circuit board, the conductive particles can be uniformly fused to the terminals of the circuit board.

As a method for forming such a transfer film 1 for electrical connection, for example, the conductive particles 3 are dispersed in a resin binder liquid, and the binder liquid is applied onto the film 2 so that the conductive particles 3 have a particle diameter of It may be applied in the following manner. As a result, as shown in the drawing, the transfer film 1 for electrical connection in a form in which one layer of the conductive particles 3 is held on the film 2 by the binder layer 4 can be obtained.

In the transfer film for electrical connection of the present invention, various modes can be adopted as a form in which one layer of conductive particles is held on the film. For example, the conductive tape is adhered to the adhesive tape. May be As a method of forming such a transfer film for electrical connection, one layer of conductive particles is electrostatically attached onto a release film,
This may be transferred to a heat resistant adhesive tape.

The film 2 used for the transfer film 1 for electrical connection is preferably a heat resistant one, and for example, a polyimide film, Teflon or the like can be used.

As the conductive particles 3 used in the transfer film 1 for electrical connection, various particles having a metal surface can be used, but they should be selected according to the material of the terminal of the circuit board to be connected. Is preferred. For example, as shown in FIG. 1B, when a gold-plated layer or a nickel-plated layer 5b is formed on the terminal 5a of the circuit board 5 or when the terminal is treated with glycoat, conductive particles are generated. Is solder particles, tin particles, indium particles, other alloy particles thereof, or solder plating, tin plating,
Particles plated with indium are used. When the terminals of the circuit board are made of aluminum, gold particles or gold plated particles are used. Further, FIG. 2 (b)
As shown in, when the solder plating layer or the tin plating layer 5c is formed on the terminal 5a of the circuit board 5, solderable metal particles or metal plating particles are used as the conductive particles 3.

The shape of the conductive particles 3 is spherical, needle-like,
Various shapes such as columnar shape, plate shape, and amorphous shape can be used, but spherical shape is preferable. Also, as the particle size,
It is preferable to use one having a particle size of 0.5 to 50 μm, and the particle size distribution is preferably as uniform as possible.

In the electrical connection method of the present invention, first, the electrical connection circuit board of the present invention is prepared by using the electrical connection transfer film 1 as described above. That is, as shown in FIG. 1B or FIG. 2B, the terminals 5a to be connected to the first circuit board 5 and the conductive particles 3 of the transfer film 1 for electrical connection are held. The surfaces are aligned with each other, and both are heated and pressure bonded (primary pressure bonding). The heating and pressurizing conditions of the primary pressure bonding may be appropriately set depending on the types of the terminals 5a and the conductive particles 3 of the circuit board 5 so that the terminals 5a and the conductive particles 3 are fused. For example, as shown in FIG. 1B, when the transfer film 1 for electrical connection holding the solder particles as the conductive particles 3 is first pressure-bonded to the terminal 5a subjected to gold plating, It suffices that the conductive particles 3 made of particles are melted and the terminals 5a and the conductive particles 3 are fused together. Further, as shown in FIG. On the other hand, when the transfer film 1 for electrical connection is first pressure-bonded, the solder layer 5c on the terminal 5a is melted and the terminal 5a and the conductive particles 3 are melted.
It suffices to fuse and.

After the primary pressure bonding, FIG. 1 (c) or FIG.
(C), the first circuit board 5 and the electrical connection transfer film 1 are separated from each other to transfer the conductive particles 3 onto the terminals 5a of the first circuit board 5, and the terminals 5a Circuit board 6 for electrical connection in which conductive particles 3 are present only on the top
To get

Then, as shown in FIG. 1D or FIG. 2D, the electrical connection circuit board 6 and the second circuit board 6 in which the conductive particles 3 are present only on the terminals 5a. 7 and the terminals 5a, 7a are placed inside, an adhesive film 8 is placed as an adhesive between them, and they are superposed and thermocompression bonded (main compression bonding). As a result, the first circuit board 5 and the second circuit board 5
Since the entire surface of the circuit board 7 is adhered by an adhesive film, it is connected with a strong adhesive strength. Moreover, since the conductive particles 3 are present only on the terminals 5a of the first circuit board 5, the terminals 5a of the first circuit board 5 and the terminals 7a of the second circuit board 7 may be short-circuited or the like. Securely connected without causing conduction failure.

Here, a thermosetting or thermoplastic resin film can be used as the adhesive film 8. Further, the thermosetting or thermoplastic resin liquid used in the conventional anisotropic conductive adhesive may be applied between two circuit boards without using such a film as the adhesive. ..

The heating and pressurizing conditions for the main pressure bonding may be appropriately set depending on the terminal materials of both circuit boards, the type of conductive particles 3, the type of adhesive, and the like.

[0025]

The transfer film for electrical connection of the present invention is similar to the conventional bonding material (Japanese Patent Laid-Open No. 64-14886) in which conductive particles are embedded near the surface of a sheet-shaped insulating base material made of a thermoplastic resin. It can be used, thereby making it possible to improve the conduction reliability as compared with the electrical connection method using the conventional anisotropic conductive adhesive, but according to the electrical connection method of the present invention By using
Even when a large number of terminals are formed on the circuit board at a fine pitch, it is possible to connect without causing a short circuit. That is, according to the electrical connection method of the present invention, a transfer film for electrical connection in which one layer of conductive particles is held on the film is used, and the conductive particles of the transfer film for electrical connection are used in the first circuit. Since the first circuit board and the second circuit board are adhered to each other via an adhesive agent, the conductive particles are transferred onto only the terminals to be connected to the board, so that the conductive particles are applied to portions other than the terminals to be connected to the circuit board. Will not exist. Therefore, the short circuit does not occur. Further, by increasing the density of the conductive particles in the transfer film for electrical connection, it is possible to increase the number of conductive particles connecting the terminals of the two circuit boards, so that it is possible to improve the conduction reliability. ..

Further, unlike the conventional transfer bump method,
Since it is not necessary to form bumps on the IC chip or to align the bumps with the circuit board, the process of electrically connecting the two circuit boards is facilitated.

[0027]

EXAMPLES The present invention will be specifically described below based on examples.

Example 1 ME of polyester resin (VE3220, made by Unitika)
To 100 parts by weight of K15% solution, 0.15 parts by weight of isocyanate (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.),
Conductive particles obtained by plating nickel and gold on benzoguanamine particles (Bright 20GNR10EH, diameter 10 μm,
1.5 parts by weight of Nippon Kagaku Kogyo Co., Ltd. are evenly dispersed,
This dispersion was applied to a polyimide film having a thickness of 25 μm so that the average thickness was 5 μm to prepare a transfer film for electrical connection (area ratio of conductive particles, about 21%).

Next, this transfer film for electrical connection was cut into an appropriate size, and TAB (on a polyimide film substrate having a thickness of 75 μm, copper having a thickness of 35 μm and solder plating having a thickness of 1 μm (tin: lead) was used. = 8: 2) the terminal is 0.1m
(formed with m pitches), 190
Primary pressure bonding was performed at 5 ° C., 5 Kg / cm ² , and 5 seconds. After cooling, T
The transfer film for electrical connection was peeled off from AB. When this state was observed with an image processing apparatus, about 70% of the conductive particles of the transfer film for electrical connection were transferred to the TAB, and the area ratio of the conductive particles on the terminal was 15%.

Next, an epoxy-based adhesive film having the following composition was temporarily press-bonded to this TAB, and then a glass substrate on which an ITO pattern of 0.1 mm pitch was formed and 170
The main press-bonding was performed at 40 ° C., 40 Kg / cm ² , and 20 seconds.

[0031]Epoxy adhesive film composition  Bisphenol A-type epoxy 36.02 parts (Ep1007, manufactured by Yuka Shell) Bisphenol A-type epoxy 36.02 parts (Ep828, manufactured by Yuka Shell) Epoxy silane coupling agent (A187, Nihon Unica) 1.95 parts Modified imidazole ( Hx3748, Asahi Kasei Kogyo Co., Ltd.) 26.00 parts As a result, the initial resistance of the TAB and ITO patterns is a maximum of 9
Ω, 1 according to MIL STD 202F106E
Stable with a maximum of 15Ω even after aging for 000 hours
It was Also, no short circuit occurred.

Example 2 A transfer film for electrical connection was prepared in the same manner as in Example 1 except that 6 parts of solder particles having a diameter of 10 μm (Sparklumilon No. 1635MF, manufactured by Senju Metal Co., Ltd.) were used as conductive particles. did.

This transfer film for electrical connection was used in Example 1.
In the same manner as above, the TAB was first pressure-bonded and peeled. As a result TA
The area ratio of the conductive particles on the B terminal was 18%.

Next, as in the first embodiment, TAB and I
The glass substrate on which the TO pattern was formed was permanently pressure-bonded. As a result, the initial resistance is 8Ω at maximum, and the MIL S
It was stable at 19Ω at maximum even after aging for 1000 hours with TD202F106E. Also, no short circuit occurred.

Example 3 After rubbing a polyester release film with a cloth to charge it,
The same solder particles as in Example 2 were placed, excess solder particles were removed, and one layer of solder particles was attached onto the polyester release film. This solder particle is used as a heat resistant adhesive tape (P
ET8083 (manufactured by Sony Chemical Co., Ltd.) was transferred using a hand roller to prepare a transfer film for electrical connection.

Next, as in the first embodiment, TAB and I
The glass substrate on which the TO pattern was formed was permanently pressure-bonded. As a result, the initial resistance is 5Ω at maximum and the MIL S
Even after aging for 1000 hours with TD202F106E, it was stable at a maximum of 15Ω. Also, no short circuit occurred.

Comparative Example 1 The same solder particles as in Example 2 were added to a resin binder having the same composition as that of the epoxy adhesive film used in Example 1.
phr was added to prepare an anisotropic conductive film. The particle area ratio of this anisotropic conductive film was 20%.

Next, this anisotropic conductive film was sandwiched between the TAB and the glass substrate on which the ITO pattern was formed as in Example 1, and pressure-bonded at 170 ° C., 40 Kg / cm ² , and 20 seconds. .. As a result, the particle area ratio on the pattern is 17
%Met. In addition, the initial resistance is 7Ω at maximum, and the MIL
It was stable at a maximum of 19Ω even after aging for 1000 hours with STD 202F106E, but particles were continuous between patterns, and shorts occurred at 4 points out of 120 pins.

[0039]

According to the present invention, when connecting terminals between two circuit boards, even when a large number of terminals to be connected are formed on the circuit board at a fine pitch, a short circuit is not generated. It is possible to connect reliably and easily so as to obtain high conduction reliability.

[Brief description of drawings]

FIG. 1 is a process explanatory diagram of an electrical connection method of the present invention.

FIG. 2 is a process explanatory diagram of the electrical connection method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transfer film for electrical connection 2 Film 3 Conductive particles 4 Binder layer 5 First circuit board 5a Terminal of first circuit board 6 Circuit board for electrical connection 7 Second circuit board 7a Terminal of second circuit board 8 Adhesive film

Claims (3)

[Claims] 1. A transfer film for electrical connection, comprising one layer of conductive particles held on the film. 2. A circuit board for electrical connection in which one layer of conductive particles is fused only on the terminals of the circuit board. 3. A method for electrically connecting a terminal of a first circuit board and a terminal of a second circuit board, wherein the terminal surface of the first circuit board and the conductive particles of the transfer film according to claim 1. Align with the held surface, heat and pressure bond both, peel off to transfer the conductive particles onto the terminals of the first circuit board,
Next, an electrical connection method characterized in that the terminal surface of the first circuit board to which the conductive particles are transferred and the terminal surface of the second circuit board are thermocompression bonded via an adhesive.