JPH0575250A - Electrical connecting method - Google Patents

Abstract

PURPOSE:To connect two circuit boards positively and easily so as to obtain high reliability on continuity without generating short circuits even when a large number of terminals to be connected are formed on the circuit boards at short pitches when the two circuit boards are connected electrically. CONSTITUTION:A film 10 for electrical connection, in which conductive particles 3 and spacer particles 4 having heat resistance higher than the conductive particles and the grain size of 20-80% of the grain size of the conductive particles are held on a film 1 in one layer uniformly, is used. The terminal surface of a first circuit board 5 and a surface, on which the conductive particles and the spacer particles are held, in the film 10 for electrical connection are joined, both surfaces are primarily contact-bonded, and peeled, the conductive particles 3 are transferred onto the terminals 5a of the first circuit board, and the terminal surface of the first circuit board 5, on which the conductive particles 3 are transferred, and the terminal surface of the second circuit board 7 are mainly contact-bonded through adhesives 8 as a method, in which the terminals of the first circuit board and the terminals of the second circuit board are bonded electrically by employing the film for electrical connection.

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 an electrical connection film and an electrical connection circuit board 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, one in which conductive particles are embedded near the surface of a sheet-shaped insulating base material made of a thermoplastic resin is also known. 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, and then the second circuit board is heated and pressed on the heat-welded bonding material. The sheet-like insulating base material of the bonding material is melted to bond between the two circuit boards, and at the same time, the conductive particles welded to the terminals of the first circuit board are bonded to the terminals of the second circuit board ( 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 interposed over the entire bonding area of the circuit board including the terminals to be connected. Therefore, the conductive particles are present not only between the terminals to be connected but also between 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.

According to a method of using a bonding material in which conductive particles are embedded near the surface of a sheet-like insulating base material made of a thermoplastic resin (Japanese Patent Laid-Open No. 64-14886), it is possible to improve the conduction reliability to some extent. However, due to the large variation in the particle size of the conductive particles in the bonding material, even if the crimping surface is slightly tilted during heating and pressure bonding of the circuit board and the bonding material, the crimping pressure will not be applied uniformly and conduction failure will occur. There was a problem that it would occur. Also in this method, similar to the method using the conventional anisotropic conductive adhesive, the conductive particles are present on the entire bonding area including the terminals to be connected of the circuit board. The problem that a short pitch is likely to occur when the pitch becomes fine has not been solved.

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 that the number of steps is large and 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 above-mentioned problems of the prior art, and in the case where a large number of terminals to be connected to 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 by uniform pressure bonding so that high conduction reliability can be obtained without causing a short circuit.

[0011]

In order to achieve the above object, the present invention provides a conductive material on a film and a heat-resistant and conductive particle more than the conductive particles as a bonding material used in an electrical connection method. And a spacer particle having a particle diameter of 20 to 80% of the above particle diameter are uniformly held in one layer.

Further, as a circuit board used for the electrical connection method, the terminal surface on the circuit board and the surface of the above-mentioned electrical connection film on which the conductive particles and the spacer particles are held are put together and heated. Provided is a circuit board for electrical connection, in which one layer of conductive particles is fused only on the terminals of the circuit board, which is obtained by transferring the conductive particles onto the terminals of the circuit board by pressure bonding and peeling.

As an electrical connection method of the present invention, the terminal surface of the first circuit board and the surface of the above-mentioned electrical connection film on which the conductive particles and the spacer particles are held are brought into contact with each other by heating and pressure bonding. Then, the conductive particles are transferred onto the terminals of the first circuit board by peeling, and then the terminal surface of the first circuit board on which the conductive particles are transferred and the terminal surface of the second circuit board are bonded with an adhesive. Provided is an electrical connection method characterized by performing thermocompression bonding via.

The film for electrical connection used as a bonding material in the present invention secures conductivity by the conductive particles in the bonding material as in the case of the conventional anisotropic conductive adhesive or a bonding material similar thereto. However, the bonding material of the present invention is characterized in that it contains, in addition to the conductive particles, spacer particles that are more heat resistant than the conductive particles. Then, even if the pressure-bonded surface is inclined during the heat-pressure bonding of the circuit board and the bonding material due to a large variation in the particle diameter of the conductive particles, the presence of the spacer particles enables uniform heat-pressure bonding. To improve the reliability of continuity between circuit boards.

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 the electrical connection film 1 of the present invention.
It is a sectional view of an example of 0. As shown in these figures, the film for electrical connection 10 has conductive particles 3 on the film 1.
And one spacer particle 4 is uniformly held. By holding one layer of the conductive particles 3 and the spacer particles 4 in this manner, the conductive particles can be evenly fused to the terminals of the circuit board at the time of the primary pressure bonding between the electrical connection film and the circuit board, which will be described later. It will be possible.

As a method of forming such a film 10 for electrical connection, for example, the conductive particles 3 and the spacer particles 4 are dispersed in a resin binder solution, and the binder solution is applied onto the film 1 in a thickness of the conductive particles. It may be applied so as to have a particle size of 3 or less. This results in 1
The conductive particles 3 and the spacer particles 4 of the layer are the binder layer 2
As a result, the film 10 for electrical connection held on the film 1 can be obtained.

Further, in this electrical connection film, various modes can be adopted as a form in which one layer of conductive particles and spacer particles is held on the film,
For example, the adhesive tape may have conductive particles or spacer particles attached thereto. As a method for forming such a film for electrical connection, one layer of conductive particles and spacer particles may be electrostatically attached onto a release film, and this may be transferred to a heat-resistant adhesive tape.

As the conductive particles 3 used in the electrical connection film 10, various particles having a metal surface can be used, but it is preferable to select them according to the material of the terminal of the circuit board to be connected. For example, as shown in (a) of FIG. 1, when a gold plating layer or a nickel plating layer 5b is formed on the terminal 5a of the circuit board 5 or when the terminal is treated with glycoat, solder particles, tin Particles, indium particles, other alloy particles thereof, or particles plated with solder, tin, or indium are used. When the terminals of the circuit board are made of aluminum, gold particles or gold plated particles are used. Further, as shown in FIG. 2B, when the solder plating layer or the tin plating layer 5c is formed on the terminals 5a of the circuit board 5, the conductive particles 3 are solderable metal particles or Use metal plated particles.

The shape of the conductive particles 3 is spherical,
Various types such as needle-like, columnar, plate-like, and amorphous can be used, but spherical ones are preferably used. The particle size is preferably 0.5 to 50 μm, and the particle size distribution is preferably as uniform as possible.

As the spacer particles 4, particles that are more heat-resistant than conductive particles are used. That is, when the conductive particles and the terminals of the circuit board are fused with each other during thermocompression bonding of the circuit board and the electrical connection film, those having a hardness sufficient to maintain the original particle shape are used. Therefore, the type of the spacer particles 4 is determined according to the type of the conductive particles and the terminal material of the circuit board, but generally, resin particles such as polystyrene, divinylbenzene, benzoguanamine and the like can be used. When the terminals of the circuit board are plated with gold or nickel, metal particles such as copper or nickel can be used.

The size of the spacer particles 4 is 20 to 80% of the particle size of the conductive particles, preferably 3 μm or more. If the particle size of the spacer particles 4 is out of this range, it becomes difficult to perform uniform pressure bonding when the pressure bonding surface is inclined during heat pressure bonding of the circuit board and the bonding material.

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 film 10 as described above. That is,
As shown in FIG. 1B or FIG. 2B, the terminals 5 a of the first circuit board 5 and the electrical connection film 10 are formed.
The conductive particles 3 and the surface on which the spacer particles 4 are held are combined, and both are thermocompression bonded (primary compression 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 10 for electrical connection holding the solder particles as the conductive particles 3 is first pressure-bonded to the gold-plated terminal 5a, solder is used. 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 10 for electrical connection is first pressure-bonded, the solder layer 5c on the terminal 5a may be melted and the terminal 5a and the conductive particles 3 may be fused.

After the primary pressure bonding, FIG. 1 (c) or FIG.
(C), the first circuit board 5 and the electrical connection film 10 are separated from each other to separate the first circuit board 5 from each other.
The conductive particles 3 are transferred onto the terminals 5a, and the circuit board 6 for electrical connection in which the conductive particles 3 are present only on the terminals 5a is obtained. In this case, the spacer particles 4 remain on the film 1 of the electrical connection film 10.

Next, 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 terminal surfaces 5a, 7a thereof 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.

[0028]

The electrical connection film provided by the present invention as a bonding material has spacer particles in addition to the conductive particles, and therefore, the particle size of the conductive particles varies greatly. Even if the crimping surface is inclined during the heating and crimping, the crimping is performed uniformly, and the conduction reliability is improved. The effect of improving the conduction reliability by blending the spacer particles is that when the circuit board terminals are treated with a soft metal such as solder plating or tin plating, the conductive particles are composed of a soft metal such as solder particles. Demonstrate prominently when being. This is because when the terminals of the circuit board are treated with soft metal and the conductive particles are composed of hard particles, the metal of the terminals of the circuit board serves as a cushioning material to absorb the inclination of the crimping surface, This is because when the conductive particles are also composed of soft particles, the metal of the terminals of the circuit board does not serve as a buffer material, and the action of the spacer particles is considered to be large.

The electrical connection film of the present invention is a conventional bonding material in which conductive particles are embedded near the surface of a sheet-like insulating base material made of a thermoplastic resin (Japanese Patent Laid-Open No. 64-14).
No. 886), which makes it possible to improve the continuity reliability as compared with the electrical connection method using the conventional anisotropic conductive adhesive. Even if a large number of terminals are formed at a fine pitch on the circuit board, the connection can be made without causing a short circuit by using the electrical connection method described in (1). That is, according to the electrical connection method of the present invention, the conductive particles of the electrical connection film in which the conductive particles and the spacer particles are held in one layer on the film are provided only on the terminals to be connected of the first circuit board. Since the first circuit board and the second circuit board are adhered to each other via the transfer after the transfer, the conductive particles do not exist in the portions other than the terminals to be connected to the circuit board. Therefore,
Short circuit will not occur. Moreover, since the number of the conductive particles connecting the terminals of the two circuit boards can be increased by increasing the density of the conductive particles of the electrical connection film, it is possible to further improve the conduction reliability. ..

Further, according to the electrical connection method of the present invention, unlike the conventional transfer bump method, it is not necessary to form bumps on the IC chip or to align the bumps and the circuit board. The process of electrically connecting the two circuit boards is facilitated.

[0031]

EXAMPLES The present invention will be specifically described below based on examples. Examples 1 to 3 and Comparative Examples 1 to 3 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.),
6 parts by weight of solder particles (average particle diameter 12 μm, F1-635M, made by Senju Metal), various spacer particles 1 shown in Table 1
By weight, the dispersion was uniformly dispersed, and this dispersion was applied to a polyimide film having a thickness of 25 μm so that the average thickness was 5 μm to prepare an electrical connection film similar to that shown in FIG.

Next, this electrical connection film was cut to 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 = 8: 2) terminal is 0.1mm
Placed on the pitch), 190 ℃,
Primary compression bonding was performed at 5 Kg / cm ² for 5 seconds. In this case,
As shown in, a press machine consisting of a press head 31, a pedestal 32, and a micro jack 33 is used, and the flatness is made uniform by using a prescale (made by Fuji Chemical Paper Co., Ltd.). Is increased by 3 μm,
The crimp surface is tilted.

After cooling, the electrical connection film was peeled from the TAB, and the solder particles were transferred to the TAB terminals.

Here, using an image processing apparatus (manufactured by Nippon PC System Co., Ltd.), the area ratio of the solder particles in 200 μm square of the initial electrical connection film and the solder particles transferred to the TAB were measured. 200μm of film for electrical connection
The area ratio of the solder particles in the corner was measured, and the transfer ratio was measured by the following formula (i). The results are shown in Table 1.

[0035] The shape of solder particles before transfer to TAB is 12 μm in diameter.
Assuming that the shape is a sphere and that after transfer, it is a cylinder, the diameter (d) of the solder particles after transfer was measured with a microscope, and the height of the cylinder was determined by the following equation (ii). The results are shown in Table 1.

Height = volume of solder particles / (d / 2) ² · π (ii) Next, an epoxy adhesive film having the following composition is temporarily pressure-bonded to this TAB, and then an ITO pattern with a pitch of 0.1 mm is formed. Glass substrate formed and 170 ℃, 40Kg
The main press-bonding was performed at / cm ² for 20 seconds.

[0037]Epoxy adhesive film composition  Phenoxy resin (YP50, manufactured by Tohto Kasei) 42.5 parts Bis-A type epoxy (Ep828, manufactured by Yuka Shell) 42.5 parts Curing agent (Hx3748, manufactured by Asahi Kasei) 15.0 parts After that, TAB and ITO pattern Initial conduction resistance and MI
1000 hours of energy with L STD 202F106E
Conduction resistance after insulation and insulation resistance are digitally
It was measured using a chymeter. The results are shown in Table 1.

From the results shown in Table 1, the solder particle size of 20 to
In the example using the spacer particles having a particle size of 80%, although the pressure-bonded surface was inclined during the primary pressure-bonding,
The heights of the transfer particles on the left and right were almost the same, and it was confirmed that the transfer particles were pressed uniformly. It was also confirmed that the conduction resistance after 1000 hours of MIL was low and the conduction reliability was high.

[0039]

[Table 1] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Spacer particles M ^{* 1} M Copper powder-MM Particle size (μm) 3 5 3 2 10 Transfer rate (%) 42 38 41 43 39 13 Particle height (μm) Left 5.1 4.8 5.2 6.5 6.0 9.5 Right 3.8 4.3 3.9 2 2.5 2.2 Conduction resistance Max (Ω) Initial 6 6.5 5.8 1.1 10.5 8 After MIL1000hr 17 15.8 16.3 1.2k 0.8k 0.4k Insulation resistance ○ ^{* 2} ○ ○ ○ ○ ○ Note * 1 Benzoguanamine resin particles (Micropearl, manufactured by Catalysis) * 2 10 ¹⁰ Ω or more

[0040]

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.

FIG. 3 is a schematic configuration diagram of a press used for primary pressure bonding.

[Explanation of symbols]

 1 Film 2 Binder Layer 3 Conductive Particles 4 Spacer Particles 5 First Circuit Board 5a Terminals of First Circuit Board 6 Circuit Board for Electrical Connection 7 Second Circuit Board 7a Terminals of Second Circuit Board 8 Adhesive Film 10 Film for electrical connection

Claims (3)

[Claims] 1. A single layer of conductive particles and spacer particles having a heat resistance higher than that of the conductive particles and having a particle size of 20 to 80% of the particle size of the conductive particles are uniformly held on the film. Film for electrical connection. 2. The circuit board by aligning the terminal surface on the circuit board with the surface of the electrical connection film according to claim 1 on which the conductive particles and the spacer particles are held, and by thermocompression bonding and peeling. The circuit board for electrical connection, obtained by transferring the conductive particles onto the terminals, and in which one layer of the 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 film for electrical connection according to claim 1. The conductive particles and the surface on which the spacer particles are held are brought together, and both are heat-pressed and peeled off to transfer the conductive particles onto the terminals of the first circuit board, and then to transfer the conductive particles to the first An electrical connection method, characterized in that the terminal surface of the circuit board and the terminal surface of the second circuit board are thermocompression bonded via an adhesive.