JP2000077465A - Electronic unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic unit which can prevent the occurrence of improper conduction or an increase in contact resistance by increasing the mechanical joining strength of a bare IC chip to a printed board. SOLUTION: An electronic unit 1 is constituted by flip-chip mounting a bare IC chip 3 on a printed board 2, formed by directly forming plated silver layers 2M on the surfaces of electrodes 2A which are composed of a copper foil and by making bumps 3B formed on the electrodes 3A of the IC chip 3 bite into the electrodes 2A of the printed board 2. In addition, the unit 1 is also constituted by directly forming the plated silver layers 2M on the newly exposed surfaces of the electrodes 2A, after the newly prepared surfaces are formed by chemically polishing the surfaces of the electrodes 2A composed of the copper foil.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electronic unit in which a bare IC chip is flip-chip mounted on a printed circuit board.

[0002]

2. Description of the Related Art As one method of mounting a bare IC chip on a printed circuit board, there is a flip chip mounting method (a flip chip bonding method) using a bonding material such as an anisotropic conductive film.

FIG. 7 shows an electronic unit A manufactured by a flip chip mounting method. A bare IC chip D is bonded to a printed board B via an anisotropic conductive film C.

The printed board B has electrodes Ba, Ba... Made of copper foil on its mounting surface, and these electrodes Ba, B.
are plated with gold plating Bc with nickel plating Bb as a base.

On the other hand, the bare IC chip D is provided with electrodes Da, Da... On its mounting surface, and bumps Db, D made of a metal material such as Au (gold) are provided on the surfaces of these electrodes Da.
b ... are formed.

In the electronic unit A described above, an anisotropic conductive film C, in which a large number of conductive particles Cb are mixed in a film-like insulating resin Ca, is temporarily bonded to a mounting surface of a printed circuit board B. The bare IC chip D is mounted on the conductive conductive film C, the anisotropic conductive film C is heated while the bare IC chip D is pressed, and the bare IC chip D is fully bonded to the printed circuit board B. .

[0007]

In the conventional electronic unit A, the nickel plating Bb applied to the electrode Ba of the printed circuit board B as a base is harder than the bump Db of the bare IC chip D. When the bare IC chip D is pressurized to be bonded to the substrate B,
The electrode Ba is not deformed, and the bump Db of the bare IC chip D is bonded to the smooth surface of the gold plating Bc on the electrode Ba.

Here, the electrical continuity between the printed circuit board B and the bare IC chip D is determined by the electrode B on the printed circuit board B.
(a) Contact between gold plating Bc and bump Db of bare IC chip D, or conductive particles Cb of anisotropic conductive film C
The bonding strength of the bare IC chip D to the printed board B is mainly obtained by the adhesive component of the insulating resin Ca in the anisotropic conductive film C.

For this reason, after an environmental test (constant temperature / humidity test, temperature cycle test, etc.) is performed, the above-mentioned adhesive component of the insulating resin Ca deteriorates, and the printed circuit board B
The mechanical joining strength between the semiconductor chip and the bare IC chip D is reduced, which causes inconveniences such as poor conduction and increased contact resistance.

The present invention has been made in view of the above circumstances, and has as its object to provide an electronic unit capable of increasing the mechanical bonding strength of a bare IC chip to a printed circuit board, thereby preventing poor conduction and increase in contact resistance. Things.

[0011]

In order to achieve the above object, an electronic unit according to the present invention comprises a bare IC chip mounted on a printed circuit board having a silver plating layer formed directly on the surface of an electrode made of copper foil. It is characterized by being flip-chip mounted.

Further, the electronic unit according to the present invention is an electronic unit in which a bare IC chip is flip-chip mounted on a printed board, and a bump formed on an electrode of the bare IC chip is cut into an electrode of the printed board. It is characterized by comprising.

The electronic unit according to the present invention is an electronic unit in which a bare IC chip is flip-chip mounted on a printed circuit board. The printed circuit board has a new surface formed by chemically polishing the surface of an electrode made of copper foil. After forming,
It is characterized in that a silver plating layer is directly formed on the surface of the electrode on which the new surface is formed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing embodiments. As shown in FIG. 1, an electronic unit 1 according to the present invention includes a printed circuit board 2 and a bare I
C chip 3, using anisotropic conductive film 4,
It is configured by mounting a bare IC chip 3 on a printed circuit board 2 in a flip chip manner.

As shown in FIGS. 1 and 2, a printed circuit board 2 has an electrode 2 formed by patterning a copper foil on a mounting surface thereof.
A, 2A... Are provided, and these electrodes 2A, 2A.
Are formed with silver plating layers 2M, 2M... Respectively.

On the surfaces of the silver plating layers 2M, organic films 2a are formed for the purpose of preventing oxidation, sulfurization or migration of the silver plating layers 2M. Needless to say, the organic film 2a is not an essential requirement of the present invention.

On the other hand, the bare IC chip 3 is provided with electrodes 3A, 3A... On a mounting surface thereof, and these electrodes 3A, 3A.
Are formed on the surface of each of the bumps 3B, 3B,... Made of a metal material such as gold (Au).

Further, the anisotropic conductive film 4 is formed by adding a large number of conductive particles 4b and 4 to a film-like insulating resin 4a.
.. are mixed.

In the electronic unit 1 having the above-described configuration, first, the anisotropic conductive film 4 is supplied to the mounting surface of the printed board 2, and the bare IC chip 3 And then thermocompression bonding the bare IC chip 3 to the printed circuit board 2.

Here, as is clear from FIG. 1, the bump 3B of the bare IC chip 3 breaks the organic film 2a on the printed circuit board 2 and cuts into and joins the silver plating layer 2M and the electrode 2A. The conductive particles 4b of the anisotropic conductive film 4 are formed by the bumps 3B and the silver plating layer 2M.
And the electrode 2A.

As described above, the bumps 3 of the bare IC chip 3
B is the silver plating layer 2M of the printed circuit board 2 and the electrode 2A
In this case, the mechanical bonding strength of the bare IC chip 3 to the printed circuit board 2 is increased.

Therefore, even if the adhesive component of the anisotropic conductive film 4 deteriorates after the environmental test, the printed circuit board 2 and the bare I
Sufficient bonding strength with the C chip 3 can be secured,
Therefore, poor conduction and increase in contact resistance due to a decrease in bonding strength can be prevented.

The bumps 3B of the bare IC chip 3
The contact between the bump 3B and the electrode 2A is increased by biting into and joining the silver plating layer 2M and the electrode 2A of the printed circuit board 2, and thus the electrical connection between the printed circuit board 2 and the bare IC chip 3 is increased. It is possible to reduce the connection resistance at the junction.

The silver plating layer 2M on the printed circuit board 2 is formed on the surface of the electrode 2A through the steps S1 to S8 shown in FIG. That is, first, the degreasing process (S1) is performed on the patterned printed circuit board.
In the cleaning step (S2), oil and dirt on the surface are removed.
In, cleaning is performed by removing the degreasing agent and the like from the surface.

Next, in the etching step (S3), chemical polishing is performed to remove oxides from the surface of the electrode 2A, and a new surface is formed on the surface of the electrode 2A.

Thereafter, after the cleaning step (S4), in the conditioning step (S5), the surface of the electrode 2A is conditioned so that silver plating can be easily applied.

Next, in a silver plating step (S6), the silver plating layer 2 is formed on the surface of the electrode 2A by a substitution reaction between copper and silver.
M is formed, followed by a washing step (S7) and a drying step
Through (S8), the printed circuit board 2 is completed.

As described above, the operation of removing the oxide from the surface of the electrode 2A is performed not by mechanical polishing but by chemical polishing, and the silver plating layer 2M is formed directly on the surface of the electrode 2A on which a new surface is formed. In addition, the adhesion strength between the electrode 2A and the silver plating layer 2M can be improved, and the silver plating layer 2M having a uniform thickness and good smoothness can be obtained.

In the electronic unit 1 shown in FIG. 1, an anisotropic conductive paste or an adhesive may be used instead of the anisotropic conductive film 4. Further, an adhesive may be supplied around the bare IC chip 3 for the purpose of increasing the bonding strength between the printed circuit board 2 and the bare IC chip 3. Further, the method of joining the printed circuit board 2 and the bare IC chip 3 is not limited to thermocompression bonding, but may be implemented by pressure, heat, ultrasonic waves, ultraviolet rays, or a combination of each.

The electronic unit 10 shown in FIG. 4 has a spacer 15 interposed between the printed circuit board 12 and the bare IC chip 13 for defining the distance between the printed circuit board 12 and the bare IC chip 13. This spacer 15
Is for preventing a short circuit caused by contact between the conductor portion of the printed circuit board 12 and the bare IC chip 13, and is made of an insulating material.

The electronic unit 10 having the above-described configuration includes:
First, the anisotropic conductive film 1 is mounted on the mounting surface of the printed circuit board 12.
4 and supply the anisotropic conductive film 14 to the printed circuit board 1.
2, the bare IC chip 13 and the spacer 1
5 is supplied, and then the printed circuit board 12, the bare IC chip 13, and the spacer 15 are joined by thermocompression bonding.

The structure of the electronic unit 10 described above is the same as that of the electronic unit 1 shown in FIG. 1 except for the spacer 15, and the operation and effect are the same as those of the electronic unit 1. , Having the same function as the components of the electronic unit 1 include:
In FIG. 4, a detailed description is omitted by attaching a number obtained by adding 10 to the reference numeral in FIG.

The electronic unit 20 shown in FIG.
The bump 23B of the chip 23 breaks the organic film 22a on the printed circuit board 22 via the conductive paste 26,
It is joined to the silver plating layer 22M and the electrode 22A.

The above-described electronic unit 20 first supplies the conductive paste 26 to the printed circuit board 22 and then supplies the bare IC chip 23, and the printed circuit board 22, the conductive paste 26 and the bare IC chip 23 are thermocompressed. After bonding, the adhesive 27 is supplied to the gap between the printed circuit board 22 and the bare IC chip 23, and then the adhesive 27 is cured by heat.

The configuration of the printed circuit board 22 and the bare IC chip 23 in the electronic unit 20 is the same as that of the printed circuit board 2 and the bare IC chip 3 shown in FIG. Elements having the same functions as those of the constituent elements are given the same reference numerals as those in FIG.

In the electronic unit 20 having the above-described configuration, similarly to the electronic unit 1 described above, the bump 23B of the bare IC chip 23 cuts into the silver plating layer 22M and the electrode 22A of the printed circuit board 22 and is joined. Therefore, it is possible to prevent a conduction failure and an increase in contact resistance due to a decrease in bonding strength, and to prevent the printed circuit board 2
It is possible to reduce the connection resistance at the electrical junction between the second IC and the bare IC chip 23.

In the above-described electronic unit 20, a conductive film may be used instead of the conductive paste 26. Also, the printed circuit board 22 and the bare I
The joining method with the C chip 23 is not limited to the thermocompression bonding, but may be carried out by pressure, heat, ultrasonic waves, ultraviolet rays, or a combination thereof. The adhesive 27 increases the bonding strength between the printed circuit board 22 and the bare IC chip 23, but is not always necessary. Further, the spacer (15) disclosed in FIG. 4 can be interposed between the printed board 22 and the bare IC chip 23.
And the bare IC chip 23 can be effectively prevented.

The electronic unit 30 shown in FIG.
The bump 33B of the chip 33 breaks the organic film 32a on the printed circuit board 32, cuts into the silver plating layer 32M and the electrode 32A, and is joined.

The electronic unit 30 supplies the bare IC chip 33 to the printed circuit board 32 and
2 and the bare IC chip 33 are joined by pressure.

The configurations of the printed circuit board 32 and the bare IC chip 33 in the electronic unit 30 are the same as those of the printed circuit board 2 and the bare IC chip 3 shown in FIG. In FIG. 6, those having the same functions as those of the components are denoted by the same reference numerals as those in FIG.

In the electronic unit 30 having the above-described configuration, similarly to the electronic unit 1 described above, the bump 33B of the bare IC chip 33 cuts into the silver plating layer 32M and the electrode 32A of the printed circuit board 32 and is joined. Thus, it is possible to prevent a poor conduction and an increase in contact resistance due to a decrease in bonding strength, and to prevent the printed circuit board 3
It is possible to reduce the connection resistance at the electrical junction between the semiconductor chip 2 and the bare IC chip 33.

Here, the method of joining the printed circuit board 32 and the bare IC chip 33 in the above-described electronic unit 30 is not limited to pressurization, but may be pressure, heat, ultrasonic waves, ultraviolet rays, or a combination thereof. Can also be implemented. In order to increase the bonding strength, a gap between the printed circuit board 32 and the bare IC chip 33 or a bare IC
An adhesive may be supplied around the chip 33. further,
4 between the printed circuit board 32 and the bare IC chip 33.
Can be interposed, and the above-described configuration can effectively prevent a short circuit between the printed circuit board 32 and the bare IC chip 33.

In each of the above embodiments, the bear I
The bump in the C chip has a flat spherical shape. However, depending on various conditions related to flip chip mounting, such as the magnitude of the pressure of the bare IC chip on the printed circuit board, the bump shape may be a sphere, a cylinder, a cone, a polygonal pillar, or the like. Needless to say, the shape can be set to an appropriate shape such as a polygonal pyramid or a part of the above-described embodiment made into a plane.

[0044]

As described in detail above, the electronic unit according to the first aspect of the present invention includes a bare IC on a printed circuit board in which a silver plating layer is formed directly on the surface of an electrode made of copper foil.
The chip is flip-chip mounted. According to the above configuration, by pressing the bare IC chip against the printed circuit board, the bumps of the bare IC chip can be cut into the electrodes of the printed circuit board. The bonding strength is increased, and it is possible to prevent poor conduction and increase in contact resistance.

An electronic unit according to a third aspect of the present invention is an electronic unit in which a bare IC chip is flip-chip mounted on a printed circuit board. It is made to bite into. According to the above configuration, the bumps of the bare IC chip are cut into the electrodes of the printed board, so that the mechanical bonding strength between the printed board and the bare IC chip is increased,
As a result, it is possible to prevent poor conduction and increase in contact resistance.

Further, the electronic unit according to the invention of claim 6 is an electronic unit in which a bare IC chip is flip-chip mounted on a printed board, and the printed board is formed by chemically polishing the surface of an electrode made of copper foil. After the formation of the new surface, a silver plating layer is formed directly on the surface of the electrode on which the new surface is formed. According to the above configuration, since the silver plating layer is formed directly on the surface of the electrode, the bare IC chip is pressed against the printed circuit board, and the bare IC chip is pressed.
The bumps of the C chip can be cut into the electrodes of the printed circuit board, thereby increasing the mechanical bonding strength between the printed circuit board and the bare IC chip, preventing conduction failure and increasing contact resistance. Becomes

[Brief description of the drawings]

FIG. 1 is a conceptual cross-sectional side view showing an electronic unit according to the present invention.

FIG. 2 is a conceptual cross-sectional side view showing components of an electronic unit according to the present invention.

FIG. 3 is a flowchart showing a manufacturing process of a printed circuit board constituting the electronic unit of the present invention.

FIG. 4 is a conceptual cross-sectional side view showing an electronic unit according to the present invention.

FIG. 5 is a conceptual cross-sectional side view showing an electronic unit according to the present invention.

FIG. 6 is a conceptual cross-sectional side view showing an electronic unit according to the present invention.

FIG. 7 is a conceptual cross-sectional side view showing a conventional electronic unit.

[Explanation of symbols]

 1, 10, 20, 30: electronic unit, 2, 12, 22, 32: printed circuit board, 2A, 12A, 22A, 32A: electrode, 2M, 12M, 22M, 32M: silver plating layer, 3, 13, 23, 33: bare IC chip, 3A, 13A, 23A, 33A: electrode, 3B, 13B, 23B, 33B: bump, 15: spacer.

Claims (6)

[Claims] An electronic unit comprising a bare IC chip flip-chip mounted on a printed circuit board having a silver plating layer formed directly on the surface of an electrode made of copper foil. 2. The electronic unit according to claim 1, further comprising a spacer interposed between the printed circuit board and the bare IC chip for defining an interval between the printed circuit board and the bare IC chip. 3. An electronic unit in which a bare IC chip is flip-chip mounted on a printed circuit board, wherein the bumps formed on the electrodes of the bare IC chip are cut into the electrodes of the printed circuit board. Electronic unit. 4. The electronic unit according to claim 3, wherein the printed board has a silver plating layer formed directly on a surface of an electrode made of copper foil. 5. The electronic unit according to claim 3, further comprising a spacer interposed between the printed circuit board and the bare IC chip for defining an interval between the printed circuit board and the bare IC chip. 6. An electronic unit in which a bare IC chip is flip-chip mounted on a printed circuit board, wherein the printed circuit board is formed by chemically polishing a surface of an electrode made of copper foil to form a new surface, and then forming the new surface. An electronic unit comprising a silver plating layer formed directly on the surface of the electrode.