JPH11186313A - Bump-forming method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bump-forming method and a device with which bumps, having little irregularities in height, can be formed in a short time by concurrently conducting a bump forming operation and a levelling operation. SOLUTION: A ball 17 is formed at the end of a metal wire 15, and a bump 18 is formed by press-bonding the ball 17 to the electrode part 12 of a bare chip 11. A diameter D of the pressing surface 16 of the end of a capillary 13, which feeds the metal wire 15, is formed twice or more in an electrode pitch P formed by a bump 18, and the adjacent bump 18 levelled by squashing its end by the pressing part 16 at the same time as with the formation of the bump.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method and an apparatus for forming a bump using a metal wire.

[0002]

2. Description of the Related Art Conventionally, when a protruding contact portion (hereinafter, referred to as a bump) is formed on an electrode portion of an electronic circuit, it is difficult to form a protruding contact portion.
As described in Japanese Patent No. 41519, a method of forming a bump using a metal wire is known. In this method, as shown in FIG. 1, a ball 3 is formed at the tip of a metal wire 2 inserted into a capillary 1 (see (a)).
The ball 3 is attached to an electrode portion 4 such as a semiconductor element by pressing or heating or applying ultrasonic waves (see (b)), the capillary 1 is pulled up (see (c)), and the wire 2 is cut by the cut clamper 5. The wire 2 is cut near the ball 3 by being clamped and further raised (see (d)). Thereafter, the ball 3 is formed again at the tip of the wire 2 using the electric torch 6 or the like (see (e)), and the same operation is repeated thereafter.

In this case, a wire 2 having a high hardness and a fine-grained crystal structure is used. After the ball 3 is formed by thermal energy, the portion of the wire 2 adjacent to the ball 3 is recrystallized to form a coarse-grained crystal structure. And the wire 2 is cut off at the weakened portion.

[0004]

In the case of the above-described bump forming method, the cut end 7a of the wire 2 remains at the upper end of the formed bump 7, and the height of the bump 7 cannot be made uniform. When face-down mounting is performed using such irregular bumps 7, there is a possibility that an open defect or a short defect of an electronic circuit may occur due to a variation in the height of the bumps 7. Therefore, conventionally, the semiconductor element 8 having the bumps 7 formed thereon as shown in FIG.
By pressing against, leveling is performed collectively. As described above, since a leveling step is required after the formation of the bumps, the number of steps is increased and the manufacturing time is increased. Further, when the semiconductor element 8 is pressed against the substrate 9, a large load is applied to the semiconductor element 8, so that the semiconductor element 8 may be damaged.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a bump forming method and apparatus capable of forming bumps with little height variation in a short time by simultaneously performing bump formation and leveling. Another object of the present invention is to provide a bump forming method and apparatus which cause less damage to an electronic circuit during bump formation.

[0006]

According to one aspect of the present invention, there is provided a method for forming a bump on an electrode portion of an electronic circuit using a metal wire, the method comprising: Is formed to have a diameter of at least twice the electrode pitch at which the bumps are formed, and the leveling is performed by pressing the tips of adjacent bumps simultaneously with the formation of the bumps on the pressing surface.

First, a ball is formed at the tip of a metal wire inserted through a capillary by thermal energy, and the ball is pressed against the electrode portion by the capillary. Next, the capillary is pulled up and cut at a wire portion near the ball, and a ball is formed again by thermal energy at the end of the wire. Then, the capillary is moved laterally by one pitch, and the ball is pressed against an adjacent electrode portion. . At this time, since a pressing surface having a radius of at least twice the electrode pitch is provided at the tip of the capillary, the pressing surface presses the tip of an adjacent bump to level. That is, the leveling of the adjacent bumps is performed simultaneously with the pressing of the ball, so that it is not necessary to perform the leveling step later. Further, since only the adjacent bumps are leveled when the ball is pressed, the load on the electronic circuit is smaller than in the collective leveling method, and the electronic circuit is less damaged.

The pressing surface at the tip of the capillary may be flat on the entire surface or may be formed in a step shape as described in the second aspect. That is, the pressing surface has a first pressing surface provided around the wire supply hole and a second pressing surface provided around the first pressing surface via a step.
The bumps may be leveled to a predetermined height by pressing the adjacent bumps on the pressing surface. For example, when the second pressing surface is located behind the first pressing surface, by slightly crushing the tip of the bump, the height of the bump can be leveled higher than the closest distance between the capillary and the electrode portion. .

As the material of the metal wire, gold, solder,
There are copper, aluminum, and the like. Since both are soft materials, leveling can be performed without imposing a large load on the capillary.

[0010]

FIG. 3 shows a first embodiment of the bump forming apparatus according to the present invention. In this embodiment, an example in which a bump is formed on a bare chip will be described. A bare chip 11 such as an IC chip or an LSI chip is mounted on the wire bonding stage 10. This stage 1
0 is heated to, for example, about 150 ° C. in order to enhance the bonding property. Electrode portions 12 are formed on the bare chip 11 at a predetermined pitch P. On the other hand, a capillary 13 is disposed above the bare chip 11 so as to be vertically movable, and a supply hole 14 provided in the center of the capillary 13 is provided.
To gold, solder, copper, aluminum or other metal wire 15
Is supplied. A flat pressing surface 16 is formed at the tip of the capillary 13, and the diameter D of the pressing surface 16 is set to be twice or more the electrode pitch P. That is, D ≧ 2
P

An electrode torch (not shown) or the like is inserted into a gap between the capillary 13 and the bare chip 11, and a wire 15 is provided.
The ball 17 is formed by applying thermal energy to the tip of the ball 17. The bumps 18 are formed by pressing the balls 17 against the heated electrode portions 12 of the bare chip 11.

Next, a method of forming a bump by using the bump forming apparatus having the above-described configuration will be described with reference to FIG. First, as shown in (a), the capillary 13 holding the wire 15 is positioned on the first electrode portion 12, and the wire 1
The ball 17 is formed by applying heat energy to the tip of the ball 5. Next, as shown in (b), the ball 17 is pressed onto the first electrode portion 12, and at the same time, the capillary 13 is pulled up and cut at the portion of the wire 15 near the ball 17, thereby forming the bump 18. However, this bump 18
A cut end 18a of the wire 15 remains at the upper end of the wire 15 as a projection. Next, after the capillary 13 is moved laterally by one pitch as shown in (c), thermal energy is again applied to the tip of the wire 15 to form the ball 17. next,
The ball 17 is crimped to the second electrode portion 12 as shown in FIG. At this time, since the pressing surface 16 having a radius equal to or more than twice the electrode pitch is provided at the tip of the capillary 13, the pressing surface 16 crushes the protrusion of the adjacent bump 18,
Leveling (forming). That is, the leveling of the adjacent bump 18 is performed simultaneously with the pressing of the ball 17. Next, as shown in (e), the capillary 13 is pulled up, and the wire 15 is cut. At this time, the first bump 18 has been leveled to a predetermined height, but the second bump 18 has a cut 18 a of the wire 15 remaining. Thereafter, by repeating operations such as lateral movement of the capillary 13, formation of the ball 17, and pressure-bonding (leveling) of the ball 17, the bumps 18 having a uniform height as shown in FIG.

When the bare chip 11 on which the bumps 18 are formed as described above is mounted face down on an electrode such as a printed circuit board, the bumps 18 have a uniform height, so that an open defect or a short defect can be prevented. . In addition, since one or several bumps 18 are leveled for one bump formation, the burden on the bare chip 11 per one leveling is small, and the bare chip 11 is hardly damaged.

The capillary 13 has alumina,
A heat-resistant material such as ruby or sapphire is used. However, if a capillary having a thin tip is used as in the related art, it is easily broken and has low durability. On the other hand, when the capillary 13 having a wide tip pressing surface 16 is used as in the present invention,
This also helps to improve the strength of the capillary 13 itself, and can improve durability.

FIG. 5 shows a second embodiment of the present invention. In this embodiment, two pressing surfaces 20,
In this case, the capillary 13 in which 22 is formed is used. That is, a flat first pressing surface 20 is formed around the wire supply hole 14 of the capillary 13, and a flat second pressing surface 22 that is lowered by one step through the step 21 around the first pressing surface 20. Are formed. The outer diameter D ₂ of the second pressing surface 22 is equal to ₂ of the electrode pitch P so that the adjacent bumps can be pressed.
Is set to at least doubled, the outer diameter D ₁ of the first pressing surface 20 is set below the electrode pitch P so as not to press the adjacent bumps.

Also in this case, when the ball 17 is pressed against the second electrode portion 12 as shown in FIG. 5B, the protruding portion 18a of the adjacent first bump 18 is pressed to perform leveling (forming). be able to. At this time, since the step 21 having the predetermined height H is provided between the first pressing surface 20 and the second pressing surface 22, the bump 18 is not crushed more than necessary, Can be adjusted arbitrarily.

In this embodiment, since the height of the bump 18 can be arbitrarily adjusted, the connection resistance due to the bump bonding can be adjusted to a predetermined value, which is effective when the connection resistance of a high-frequency module or the like affects the module characteristics. is there.

In the above embodiment, the case where the bumps 18 are formed on the bare chip 11 has been described. However, the present invention can be applied to the case where the bumps are formed on a wiring board for mounting the bare chip face down. Of course. Also, as a method of forming a bump, a method of cutting a wire by pulling up a capillary after forming a bump by pressing a ball on an electrode portion has been described. The present invention can also be applied. Furthermore, the diameter of the pressing surface of the capillary is not limited to a size that allows one adjacent bump to be leveled, and may be a size that allows two or more bumps to be simultaneously leveled.

[0019]

As is apparent from the above description, according to the present invention, the diameter of the pressing surface at the tip of the capillary is twice or more the electrode pitch at which the bump is formed, and the tip of the adjacent bump is simultaneously pressed with the ball. Is pressed to perform leveling, so that bumps having a uniform height can be formed, and it is not necessary to separately perform a leveling step, so that the efficiency of the bump forming operation can be increased. Further, since only the adjacent bumps are leveled when the ball is pressed, the load applied to the electronic circuit is smaller than in the collective leveling method, and the electronic circuit is less damaged.

[Brief description of the drawings]

FIG. 1 is a process chart of an example of a conventional bump forming method.

FIG. 2 is a cross-sectional view of an example of a conventional bump leveling method.

FIG. 3 is a partial cross-sectional view of an example of a bump forming apparatus according to the present invention.

FIG. 4 is a process chart of a method of forming a bump using the bump forming apparatus of FIG. 3;

FIG. 5 is a process chart of another example of the bump forming method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Bare chip 12 Electrode part 13 Capillary 15 Metal wire 16 Pressing surface 17 Ball 18 Bump 20 First pressing surface 21 Step 22 Second pressing surface

Claims (5)

[Claims] 1. A method for forming a bump on an electrode portion of an electronic circuit using a metal wire, wherein a diameter of a pressing surface at a tip of a capillary is at least twice as large as an electrode pitch on which a bump is formed. A method for forming a bump, comprising pressing the tip of an adjacent bump at the same time as forming the bump to perform leveling. The pressing surface has a first pressing surface provided around the wire supply hole and a second pressing surface provided around the first pressing surface via a step. 2. The bump forming method according to claim 1, wherein the bump is leveled to a predetermined height by pressing an adjacent bump on the second pressing surface. 3. The material of the metal wire is gold, solder, copper,
2. The method according to claim 1, wherein the material is one of aluminum.
Or the bump forming method according to 2. 4. An apparatus for forming a bump on an electrode portion of an electronic circuit using a metal wire, wherein a tip of the capillary has an electrode pitch of 2 at which the bump is formed.
A bump forming apparatus provided with a pressing surface having a diameter twice or more. 5. The pressing surface has a first pressing surface provided around the wire supply hole and a second pressing surface provided around the first pressing surface via a step. 5. The bump forming apparatus according to claim 4, wherein the second pressing surface is configured to press adjacent bumps.