JP2000067949A - Anisotropic conductive sheet and joining structure of joining object using the same - Google Patents

Abstract

(57) [Summary] When joining components to be joined using an anisotropic conductive sheet, the electrical connection is improved and the operation can be easily performed. An anisotropic conductive sheet A in which a plurality of columnar conductors 11 extending in a thickness direction of the sheet body 10 are provided in a sheet body 10 having electrical insulation.
At least one or more conductive whisker-like members 11 b are disposed inside each conductor 11, and at least one end of each conductor 11 is connected to the whisker-like member 11 b.
It is formed of a metal softer than b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anisotropic conductive sheet used for bonding a semiconductor chip to a circuit board, for example, and a bonding structure of a bonding object using the sheet.

[0002]

2. Description of the Related Art Conventionally, means for bonding a semiconductor chip on a substrate using an anisotropic conductive sheet is disclosed in
There is a means described in JP-A-86536. This means, as shown in FIG. 12 of the present application, converts an anisotropic conductive sheet 9 interposed between a substrate 7 and a semiconductor chip 8 into a sheet body 90 having a constant thickness and having electrical insulation. A plurality of columnar conductors 91 extending in the thickness direction of the body 90 are provided. The longitudinal intermediate portion 91a of each conductor 91 is C
u, the two ends 91b and 91c in the longitudinal direction.
Is Au. A conductive particle layer 92 is also provided on the surface of the sheet body 90. The conductive particle layer 92 is obtained by uniformly dispersing conductive particles such as metal powder in an insulating adhesive.

According to the above-mentioned means, since the anisotropic conductive sheets 9 have electrical conductivity only in the direction in which the substrate 7 and the semiconductor chip 8 are opposed to each other, an undesired electrical short circuit does not occur and they face each other. The terminal 70 of the substrate 7 and the terminal 80 of the semiconductor chip 8 can be electrically connected. When the terminal 80 is made of aluminum and has an oxide film (not shown) formed on the surface thereof, the oxide film can be broken by the conductive particles of the conductive particle layer 92. Therefore, according to the above-described means, a columnar conductor is simply provided in a sheet having electrical insulation as in the means described in, for example, JP-A-4-363811 and JP-A-63-13287. Compared with the means using an anisotropic conductive sheet having only a simple structure, it is possible to improve the electrical conductivity between the substrate and the electronic component.

[0004]

However, in the above-mentioned conventional means, the oxide film of the terminal 80 is to be broken using the conductive particles of the conductive particle layer 92 provided on the surface of the sheet member 90. There was such a problem.

First, in the prior art, the material is made of Au for the purpose of reducing the connection resistance when the end portion 91b of the conductor 91 is brought into contact with the terminal 80. When the conductive particle layer 92 is provided on the surface, the end portion 91b cannot be brought into direct contact with the surface of the terminal 80 over a wide area. Conventionally, an insulating adhesive or conductive particles of the conductive particle layer 92 was interposed between the end portion 91b and the terminal 80. For this reason, the electrical conductivity between the conductor 91 and the terminal 80 could not be made very good.

Second, the conductive particles contained in the conductive particle layer 92 are simply particles having a small particle size and are merely dispersed in an insulating adhesive. It was not so easy to break through the hard oxide film formed on the surface by the conductive particles.

Third, conventionally, in order to provide the conductive particle layer 92 on the surface of the anisotropic conductive sheet 9, after the anisotropic conductive sheet 9 is mounted on the substrate 7, an insulating adhesive containing conductive particles is used. The agent must be coated. Therefore, this work was troublesome.

The present invention has been conceived in view of the above circumstances, and when joining a component to be joined using an anisotropic conductive sheet, the electrical connection is improved. Further, it is an object of the present invention to make it possible to easily perform the work.

[0009]

Means for Solving the Problems To solve the above problems, the present invention takes the following technical means.

According to a first aspect of the present invention, there is provided an anisotropic conductive sheet. The anisotropic conductive sheet is an anisotropic conductive sheet in which a plurality of columnar conductors extending in the thickness direction of the sheet body are provided in a sheet body having electrical insulation. At least one or more conductive whisker-like members are disposed inside the conductor, and at least one end of each of the conductors is formed of a metal softer than the whisker-like member. It is characterized by:

Preferably, the whisker-like member is
Any one of W, Mo, and Co, or an alloy or a composite material containing any of these as a main component, and the soft metal is In, Sn, Pb, B
i, or Au, or an alloy containing any of these.

According to a second aspect of the present invention, there is provided a joining structure for joining objects using an anisotropic conductive sheet.
In the joining structure of the joining object, the anisotropic conductive sheet provided by the first aspect of the present invention is interposed between the first joining object and the second joining object, In addition, the respective terminals of the first joining object and the second joining object are electrically connected via the conductor.

[0013]

First, in the present invention, when the end of each conductor of the anisotropic conductive sheet is brought into direct contact with the terminal surface of the object to be joined and pressed, the whisker-like shape is formed from the end of each conductor. The member can be protruded to the outside, and the whisker-shaped member can be cut into the surface of the terminal to establish a conductive connection between the terminal and each conductor. If a coating is formed on the surface of the terminal, the coating can be pierced to conduct the terminal. Unlike the conventional method, it is not necessary to form a conductive particle layer on the surface of the anisotropic conductive sheet by a coating operation as a means for breaking through the coating.

Secondly, since the whisker-shaped member has a relatively sharp end, the present invention uses a relatively thin coating on the terminal surface even if the terminal coating is hard. It is possible to easily break through.

Third, according to the present invention, while the whisker-like member is cut into the terminal surface of the object to be joined,
The end of each conductor softer than the whisker-shaped member,
It can be crushed by directly contacting the terminal surface.
Therefore, the ends of the conductors can be brought into direct contact with the terminal surfaces over a wide area. For example, the end portions and the surfaces of the terminals are alloyed by atomic diffusion so that the connection resistance of the contact portions is reduced. Can be reduced. If an oxide film is formed on the terminal surface,
By performing a process of breaking the oxide film by applying heat and pressure to the terminal surface or the like, alloying between the end of each conductor described above and the terminal surface can be achieved.

Other features and advantages of the present invention will become more apparent from the following description of embodiments of the invention.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a sectional view showing an example of the anisotropic conductive sheet according to the present invention.

The anisotropic conductive sheet 1 is made of a sheet 10
And a plurality of columnar conductors 11 embedded in the sheet body 10. The anisotropic conductive sheet 1 is provided with a plurality of conductors 11 only at locations corresponding to the terminals of two objects to be joined using the anisotropic conductive sheet 1 among the portions of the sheet body 10. Configuration.

The sheet body 10 has a constant thickness at various points, and has a rectangular shape in plan view, for example. The sheet body 10 is made of, for example, polyimide, and has electrical insulation and elasticity. However, in the present invention, as the material of the sheet body 10, a resin such as silicone or epoxy, or rubber can be applied, and a material other than these may be used.

As shown in the enlarged view of the portion A of FIG. 1, each of the conductors 11 has a conductive whisker inside a columnar metal 11a which forms a main part of the conductor 11. A large number of members 11b are arranged. As the metal 11a, a fairly soft metal is used, for example, any of In, Sn, Pb, Bi, and Au, or a soft alloy containing any of these. The diameter of the metal 11a, that is, the diameter of each conductor 11 is, for example, about several hundred μm.

Each of the whisker-like members 11b has a relatively elongated fibrous shape as a whisker (single crystal metal fiber growth), and has a diameter of several μm, for example.
m to several tens of μm. Whiskers themselves can be positively generated by, for example, a metal plating process, etc., but the whisker-like member referred to in the present invention may be formed by such a method, or formed by other methods. May be. The whisker-like member referred to in the present invention is:
The morphology is not limited to the whisker itself, as long as the form is an elongated shape similar to the metal fiber growth.

The plurality of whisker-like members 11b are arranged in the conductors 11 so as to extend in the same direction as the conductors 11. Each of the whisker-shaped members 11b is made of a conductive member that is considerably harder than the metal 11a.
One of o and Co, or an alloy containing any of these, or a composite material containing carbide, boride, silicide, nitride, or the like is used.

Next, a method of manufacturing the anisotropic conductive sheet 1 will be described.

To manufacture the anisotropic conductive sheet 1,
First, the conductor 11 is manufactured. The production of the conductor 11
For example, as shown in FIG. 2A, a pair of molds 2a and 2b
Is filled with a molten metal 11a ', and a number of whisker-like members 11b are mixed into the molten metal 11a'. The cavity 20 is formed as shown in FIG.
As shown in FIG. In such a state, a pair of electrodes 21a and 21b are arranged near both ends in the longitudinal direction of the cavity 20, and a magnetic field is generated between the pair of electrodes 21a and 21b. Then, each of the many whisker-shaped members 11b is arranged in the molten metal 11a 'in a direction extending in the direction of the line of magnetic force of the magnetic field, that is, in the longitudinal direction of the cavity 20. In this state, if the metal 11a is cooled and solidified, a bar-shaped conductor 11 'having a predetermined length can be formed as shown in FIG.
By cutting 1 ′ to an appropriate length, the plurality of conductors 11 can be obtained.

Next, as shown in FIG.
The raw material 10 ′ of the sheet body 10 is filled in the cavity 23 of the 2 a and 22 b in a molten state, and the raw material 1 ′ is
The plurality of conductors 11 are arranged in 0 '. In such a state, an appropriate number of pairs of electrodes 24a and 24b are provided at the upper and lower positions of the dies 22a and 22b, and a magnetic field is generated between the pair of electrodes 24a and 24b. The body 11 can be arranged in a posture extending in the vertical direction of the dies 22a and 22b along the lines of magnetic force of the magnetic field. Therefore, if the raw material 10 'is solidified in this state, the above-described anisotropic conductive sheet 1 is obtained.

Further, instead of the means shown in FIG. 5, for example, means shown in FIGS. 6 (a) and 6 (b) can be applied. That is, first, as shown in FIG. 6A, a plurality of holes 25 are provided in a relatively thick sheet body 10 ″, and each of the plurality of holes 25 is provided with the conductor 11 ′ shown in FIG. The plurality of holes 25 can be provided, for example, by irradiating the sheet body 10 ″ with a laser. Next, as shown in FIG. 6B, the sheet body 10 ″ is sliced in a direction crossing the thickness direction. Then, the above-described anisotropic conductive sheet having an appropriate thickness from the sheet body 10 ″ is sliced. A plurality of 1s can be obtained.

Next, a case where an electronic component is mounted on a circuit board using the anisotropic conductive sheet 1 will be described.

First, as shown in FIG. 7, when the semiconductor chip 4 is mounted on the circuit board 3 by the flip chip method, the anisotropic conductive sheet 1 is placed on the circuit board 3, The semiconductor chip 4 is mounted thereon. in this case,
As shown in FIG. 8, the plurality of terminals 30 of the circuit board 3 and the plurality of terminals 40 (electrodes) of the semiconductor chip 4 are positioned so as to face each other via the plurality of conductors 11. Next, the anisotropic conductive sheet 1 is heated while pressing the semiconductor chip 4 downward from above.
This operation may be performed, for example, by pressing the upper surface of the semiconductor chip 4 using a jig with a built-in heater. The material of the sheet body 10 is heat-fusible (adhesive) by heating.
For example, in the case of a polyolefin or a polyamide resin, the circuit board 3 and the semiconductor chip 4 can be bonded to each other via the anisotropic conductive sheet 1 by the above-described working process. However, in the present invention, the above three members may be bonded using an adhesive instead of such means.

When the semiconductor chip 4 is pressed downward,
As shown in FIG. 9, the upper end of each of the conductors 11 is crushed, and a plurality of whisker-like members 11b protrude from the top. In particular, since each of the conductors 11 is made of the above-described soft metal, the upper end thereof is easily crushed, and a plurality of whisker-shaped members 11b can largely protrude above each of the conductors 11. Therefore, the tips of the plurality of whisker-like members 11b can be deeply cut into the surface of the terminal 40. Since each of the whisker-like members 11b is made of the above-described hard material and has a sharp tip, the terminal 40 is made of, for example, aluminum having a hard oxide film (not shown) on its surface. Even if it is a terminal made of, the oxide film can be relatively easily pierced by the plurality of whisker-like members 11b. Therefore, the conductive connection between the terminal 40 and the conductor 11 can be ensured.

When the terminal 40 is made of aluminum,
When the surface of the terminal 40 and the upper end of each conductor 11 are pressed together while heating, the oxide film on the surface of the terminal 40 can be peeled off by the conductor 11. Therefore, when the oxide film is peeled off from the surface of the terminal 40 in this manner, the metal surface at the upper end of the conductor 11 can be brought into direct contact with the metal surface of the terminal 40. Moreover, as described above, the upper end of the conductor 11 is in a crushed state,
The contact area between the terminal 40 and the conductor 11 becomes large. As a result, it is possible to achieve alloying by atomic diffusion of the metal in a wide contact portion between the metal surfaces of the terminal 40 and each conductor 11, thereby reducing the connection resistance between the terminal 40 and the conductor 11. You can also.

When each terminal 30 of the circuit board 3 is made of aluminum, the connection between each terminal 30 and the lower end of each conductor 11 is also determined by the connection between each terminal 40 and the upper end of each conductor 11. The same operation as described for the connection with is obtained. Of course, if the terminals 30 are made of, for example, copper other than aluminum and a hard coating is not formed on the surface, the lower end of the conductor 11 contacts the surface of the terminal 30 over a wide area. The whisker-shaped member 11b can be directly cut into the surface of the terminal 30 while the terminal 30 is being moved. Therefore, these conductive connections can be surely achieved, and their connection resistance can be reduced.

In the mounting structure of the semiconductor chip shown in FIG.
If the circuit board 3, the anisotropic conductive sheet 1, and the semiconductor chip 4 are made of different materials and have different linear expansion coefficients, and a temperature change occurs in a mounting portion of the semiconductor chip, for example, the plurality of terminals 30 And the terminal 40 may be relatively displaced in the direction of the arrow N1 (the direction crossing the thickness direction of the anisotropic conductive sheet 1). On the other hand, since each of the conductors 11 is made of a soft metal and the sheet body 10 is elastically deformable, the arrow N1
It can be bent and deformed in the direction. Therefore, the plurality of terminals 30
When the terminal and the terminal 40 are displaced in the direction of the arrow N1, the respective conductors 11 are flexed and deformed in the same direction. Can be kept in contact with each other. Therefore, the semiconductor chip 4 and the circuit board 3
Also, the effect of appropriately maintaining the electrical connection with the device can be obtained.

FIGS. 10 and 11 are cross-sectional views of main parts showing other examples of the anisotropic conductive sheet according to the present invention. The same parts as those in the previous embodiment are denoted by the same reference numerals.

In the anisotropic conductive sheet 1A shown in FIG. 10, the upper and lower ends 11c and 11d of each conductor 11 are, for example, I
A soft metal which is n, Sn, Pb, Bi, Au, or an alloy containing any of them is used, and the intermediate portion 11e is made of a harder metal, for example, Cu. Even with such a configuration, as in the case of the anisotropic conductive sheet 1 of the previous embodiment, both ends 11c,
The whisker-like member 11b can be made to protrude outside from 11d and cut into a predetermined terminal surface. In addition, both ends 11c and 11d of each conductor 11 can be brought into direct contact with a predetermined terminal surface in a wide area in a crushed state.

In the anisotropic conductive sheet 1B shown in FIG. 11, only one end 11f of each conductor 11 is made of, for example, In or S.
The soft metal is n, Pb, Bi, Au, or an alloy containing any of these, and the other portions are harder metals. In the anisotropic conductive sheet 1B, the one end portion 11f is brought into contact with a terminal (for example, an aluminum terminal having an oxide film) which is difficult to make a conductive connection, while the other end portion 11g of each conductor 11 is made conductive. C that can be connected relatively easily
What is necessary is just to use it so that it may contact the terminal of u or Au.

The specific structure of the anisotropic conductive sheet and the joining structure of the object to be joined according to the present invention is not limited to the above-described embodiment, and various design changes can be made.

For example, as the specific material of each part of the metal or whisker-like member constituting the sheet body or the conductor of the anisotropic conductive sheet, materials other than the above-mentioned materials can be used. Further, in the structure shown in FIG. 8, a plurality of conductors 11 are in contact with one terminal 30 or terminal 40, but the present invention is not limited to this, and one terminal 30 or one terminal A configuration in which a conductor is brought into contact may be employed. Furthermore, the plurality of conductors are preferably provided only at locations corresponding to the terminals of the object to be joined,
For example, a configuration may be adopted in which a large number of conductors are evenly scattered over substantially the entire area of the sheet member. The bonding structure according to the present invention is not limited to a structure in which a semiconductor chip is mounted on a circuit board, and is not particularly limited to a specific type of a bonding target according to the present invention.

[0039]

As described above, according to the present invention, when electrical connection between objects to be joined is made by using an anisotropic conductive sheet, they are formed on the terminal surfaces of the objects to be joined. As a means for breaking through the coating, unlike the related art, there is no need to separately coat the conductive particle layer on the surface of the anisotropic conductive sheet. Also, in the present invention, since the whisker-shaped member is used, even if the terminal surface has a hard coating, it can be broken through relatively easily. Therefore, the operation of conducting the connection of the terminal having the coating formed on the surface becomes easier than before, and the conduction can be surely established. Further, in the present invention, by alloying by atomic diffusion between the end of the conductor and the terminal surface by directly contacting and crushing the end of the conductor to the terminal surface of the object to be joined, The connection resistance of those contact portions can be reduced, and the electrical conductivity can be further improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of an anisotropic conductive sheet according to the present invention.

FIG. 2A is a cross-sectional view showing a first step in manufacturing a conductor, and FIG. 2B is a cross-sectional view taken along the line II-II of FIG.

FIG. 3 is a fragmentary plan cross-sectional view showing a second step in manufacturing a conductor.

FIG. 4 is a perspective view of a conductor manufactured through the steps shown in FIGS. 2 and 3;

FIG. 5 is a fragmentary cross-sectional view showing one example of a process for manufacturing an anisotropic conductive sheet.

FIGS. 6A and 6B are cross-sectional views of main parts showing another example of a manufacturing process of the anisotropic conductive sheet.

FIG. 7 is a cross-sectional view showing an example of an operation for mounting a semiconductor chip on a circuit board.

FIG. 8 is a sectional view showing a structure in which a semiconductor chip is mounted on a circuit board.

FIG. 9 is an enlarged sectional view of a main part of FIG.

FIG. 10 is a sectional view of a main part showing another example of the anisotropic conductive sheet according to the present invention.

FIG. 11 is a sectional view of a main part showing another example of the anisotropic conductive sheet according to the present invention.

FIG. 12 is a sectional view of a main part showing a conventional example.

[Explanation of symbols]

 1, 1A, 1B Anisotropic conductive sheet 3 Circuit board (object to be joined) 4 Semiconductor chip (object to be joined) 10 Sheet 11 Conductor 11a Metal 11b Whisker-shaped member 30 Terminal 40 Terminal

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Makoto Sasaki 4-1-1 Kagamidanaka, Nakahara-ku, Kawasaki-shi, Kanagawa F-term in Fujitsu Limited (reference) 5G307 HA02 HB03 HC01 HC02

Claims (3)

[Claims] 1. An anisotropic conductive sheet, wherein a plurality of columnar conductors extending in the thickness direction of the sheet body are provided in a sheet body having electrical insulation properties, At least one or more conductive whisker-like members are disposed inside, and at least one end of each of the conductors is formed of a metal softer than the whisker-like members. Characterized by an anisotropic conductive sheet. 2. The whisker-like member is any of W, Mo, and Co, or an alloy or a composite material containing any of these, and the soft metal is In, Sn, Pb. , Bi, and A
The anisotropic conductive sheet according to claim 1, wherein the conductive sheet is any one of u and an alloy containing any of these. 3. The anisotropic conductive sheet according to claim 1, which is interposed between a first joining object and a second joining object, and wherein the first joining object is provided. A joining structure of an object to be joined using an anisotropic conductive sheet, wherein respective terminals of the object and a second object to be joined are electrically connected to each other via the conductor.