JPH10135218A - Bump and forming method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bump well connectable by a flip chip bonding method. SOLUTION: The bump 1 has relations: h/w=1 or h/w≈1, where w is max. overall size of the bump 1 and h is height thereof. If a pressing force is exerted on each bump 1, when being connected by a flip chip bonding method, resultant stress from the pressing force is absorbed because of the height h thereof which is sufficient to prevent the entire shape of the bump 1 from deforming, thus ensuring expected height of the bump, corresponding to the space between the terminal electrode and conductor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a bump for flip chip bonding and a bump forming method.

[0002]

2. Description of the Related Art A flip chip bonding method is known as a method for connecting an electronic circuit element such as an IC or an LSI to a circuit board. In this method, the bumps formed on the terminal electrodes on the bottom surface of the element and the conductors on the circuit board are electrically connected using solder or the like, or the terminal electrodes on the bottom surface of the element and the bumps formed on the conductors on the circuit board are connected. This is a method of electrically connecting using solder or the like. The above-mentioned bump is a known wire bump, and is formed in advance on a terminal electrode of an electronic circuit element or a conductor of a circuit board by a wire bonder.

Here, an example of a conventional bump forming method will be introduced with reference to FIG. Incidentally, in the figure, 101 is a capillary, 102 is a wire, 103 is an electronic circuit element, 10
Reference numeral 4 denotes a terminal electrode provided on the bottom surface of the element.

In forming a bump, first, FIG.
As shown in (1), a ball 102a is formed by applying heat to the tip of a wire 102 inserted into a hole 101a of a capillary 101 by gas flame, electrostatic discharge, or the like.

Next, as shown in FIG. 1B, the capillary 101 is moved downward to press the ball 102a against the terminal electrode 104, and is bonded by thermocompression bonding or ultrasonic waves. By this pressing, the ball 102a is crushed and deformed to be flat.

Next, as shown in FIGS. 1 (c) and 1 (d),
Only the capillary 101 is moved upward, and further moved laterally from the raised position. Capillary 1 at this time
The lateral movement amount of 01 is such that the center of the wire insertion hole 101a does not deviate outside the deformed ball 102a. Also, the capillary 101 is moved by the lateral movement.
The wire 102 is pulled out from the hole 101a by a length corresponding to the amount of movement.

Next, as shown in FIG. 1E, the capillary 101 is moved downward from the lateral movement position, and the pulled-out wire 102 is pushed into the ball 102 with the tip of the capillary 101, thereby causing the ball 102 to move. Absorb.
As a result, the boundary between the wire 102 and the ball 102a is weakened, and the portion is easily cut due to a small diameter or a cut due to the weakening.

Next, as shown in FIG. 1 (f), the capillary 101 is moved upward together with the wire 102, and the wire 102 and the ball 102a are cut off at the weakened portion. As described above, the bump B is formed on the terminal electrode 104.

A wire trace is left on the bump B. The wire trace is crushed and absorbed by the bump B when the electronic circuit element 103 is connected to a circuit board (not shown) by a flip chip bonding method. Therefore, there is no particular problem in connection.

[0010]

When an electronic circuit element having a plurality of bumps formed thereon is connected to a circuit board by a flip chip bonding method, each bump on the bottom face of the element is deformed by being pressed against a conductor of the circuit board. . However, it is difficult to equalize the pressing force applied to each bump due to the relationship of the number and the position of the bumps, and the degree of deformation of each bump tends to vary. In particular, FIG.
When the height dimension h is smaller than the maximum external dimension w, as in the case of the bump B shown in (f), the overall shape of the bump is likely to be greatly collapsed by the above-mentioned pressing, and the bump having a large degree of deformation is expected. It is difficult to secure the height dimension.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a bump which can be connected favorably by a flip chip bonding method and a bump forming method.

[0012]

In order to achieve the above object, the present invention is directed to a flip chip bonding bump formed on a terminal electrode of an electronic circuit element or a conductor of a circuit board. The external dimension w and the height dimension h have a relationship of h / w = 1 or h / w ≒ 1,
The feature is that.

According to the bump of the present invention, the maximum outer dimension w and the height dimension h of the bump are h / w = 1 or h / w.
Since there is a relationship of ≒ 1, even when a pressing force is applied to each bump at the time of connection by the flip chip bonding method, the stress applied to the bump by the pressing force is absorbed by its height dimension, and the overall shape of the bump is largely collapsed. Can be prevented.

According to a second aspect of the present invention, in a flip chip bonding bump formed on a terminal electrode of an electronic circuit element or a conductor of a circuit board, at least a tip portion of the bump has a coarse-grained crystal structure. Features.

According to the bump of the present invention, since at least the tip portion of the bump has a coarse-grained crystal structure, even if a pressing force is applied to each bump at the time of connection by the flip-chip bonding method, the pressing force causes the bump to be pressed. The received stress is relaxed in the coarse-grained crystal structure portion, so that the overall shape of the bump can be prevented from being largely collapsed.

According to a third aspect of the present invention, a ball is formed by applying heat to the tip of a wire inserted into a hole of a capillary, and the ball is pressed against a bump forming partner using a capillary and then separated from the wire. In the bump forming method, a predetermined portion of the wire tip is coarsened by recrystallization, and then heat is applied to the tip to form a ball having a coarse-grained crystal structure at least at the boundary between the wire and the ball. The feature is.

According to the bump forming method of the present invention, the bump according to the second aspect can be formed accurately and stably.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] FIG. 1 shows a first embodiment of the present invention, in which 1 is a bump, 2 is an electronic circuit element such as an IC or LSI, and 3 is a terminal provided on the bottom of the element. Electrodes.

The bump 1 is made of a metal such as copper, aluminum or gold, and has two flat cylindrical portions 1a and 1 having different outer diameters.
The upper and lower portions of the lower flat cylindrical portion 1a are joined to the terminal electrodes 3 by wire traces 1c on the upper surface of the upper flat cylindrical portion 1b. In addition, the maximum outer dimensions of the bump 1 (here, the maximum outer diameter of the lower flat cylindrical portion 1a)
w and the height dimension h have a relationship of h / w = 1 or h / w ≒ 1.

The bump 1 is formed by a known bump forming method,
For example, it is formed on the terminal electrode 3 by the same procedure as the bump forming method illustrated in FIG. Both flat cylindrical portions 1 of the bump 1
a and 1b are pressed and shaped when the capillary tip (see FIGS. 4 and 5) having the same inner surface shape approaches the terminal electrode.

The bumps 1 are formed on each of the terminal electrodes 3 of the electronic circuit element 2, and the electronic circuit element 2 is connected to a circuit board (not shown) by a flip chip bonding method. During this connection, each bump 1 on the bottom surface of the element is deformed by being pressed against the conductor of the circuit board.

Although it is difficult to equalize the pressing force applied to each bump 1 due to the number, position, etc. of the bumps 1,
The maximum external dimension w and the height dimension h of the bump 1 are h / w = 1.
Or h / w ≒ 1, so that even when a pressing force is applied to each bump 1 at the time of connection by the flip chip bonding method, the stress applied to the bump by the pressing force is absorbed by its height dimension h, It is possible to prevent the entire shape of the bumps 1 from being largely collapsed, and it is possible to secure the desired height dimension (corresponding to the distance between the terminal electrode and the conductor) for each bump 1.

FIG. 2 shows typical bump shapes other than those illustrated in FIG. The bump 4 in FIG. 2A has a wire trace 4b on the upper surface of the flat cylindrical portion 4a, and has a maximum outer dimension (here, the maximum outer diameter of the flat cylindrical portion 4a) w
And the height dimension h have a relationship of h / w = 1 or h / w ≒ 1.

The bump 5 shown in FIG. 2B is a drum-shaped portion 5a.
Has a wire trace 5b on its upper surface, and the maximum outer dimension (here, the maximum outer diameter of the drum-shaped portion 5a) w and the height dimension h have a relationship of h / w = 1 or h / w ≒ 1. doing.

The bump 6 shown in FIG. 2C has a hemispherical portion 6a.
Has a wire trace 6b on the upper surface thereof, and the maximum outer dimension (here, the maximum outer diameter of the hemispherical portion 6a) w and the height dimension h have a relationship of h / w = 1 or h / w ≒ 1. doing.

The bumps 7 shown in FIG.
a has a wire trace 7b on the upper surface thereof, and the maximum external dimension (here, the maximum outer diameter of the truncated conical portion 7a) w and the height dimension h have a relationship of h / w = 1 or h / w ≒ 1. Have.

The same operations and effects as those of the bump 1 shown in FIG. 1 can be obtained also with each of the bumps 4 to 7 shown in FIG.

[Second Embodiment] FIG. 3 shows a second embodiment of the present invention.
An electronic circuit element 3 such as an LSI is a terminal electrode provided on the bottom of the element.

The bump 8 is made of a metal such as copper, aluminum, or gold, and has two flat cylindrical portions 8a and 8b having different outer diameters at the top and bottom, like the bump 1 of the first embodiment.
A wire trace 8c is provided on the upper surface of the upper flat cylindrical portion 8b, and the lower surface of the lower flat cylindrical portion 8a is joined to the terminal electrode 3. Further, the tip portion A of the bump 8 (the upper part of the upper flat cylindrical portion 8b and the wire trace 8c) has a coarse-grained crystal structure by recrystallization.

Here, a method of forming the bump 8 will be described with reference to FIG. By the way, 9 in the figure is a capillary,
9a is a wire insertion hole, and 10 is a wire.

First, as shown in FIG. 4A, heat is applied by gas flame, electrostatic discharge, or the like to a portion of the wire 9 inserted into the hole 9a of the capillary 9 at a predetermined distance from the tip of the wire 10 to form fine particles. The crystal structure is recrystallized to form a coarse-grained crystal structure portion A1.
To form

Next, as shown in FIG. 4B, a ball 10a is formed by similarly applying heat to the wire tip including a part of the coarse-grained crystal structure portion A1.

Next, the capillary 9 is moved downward, the ball 10a is pressed against the terminal electrode 3 of the electronic circuit element 2, and bonded by thermocompression bonding or ultrasonic waves. Due to this pressing, the ball 10a is pressed and shaped by the tip of the capillary having the same inner surface shape, and has a shape as shown in FIG.

Next, only the capillary 9 is moved upward, and a pulling force is applied to the wire 10. As a result, the ball 10a and the wire 10 joined to the terminal electrode 3 are separated from each other so as to be torn off at the boundary between them. Thus, the bumps 8 shown in FIG. 3 are formed on the terminal electrodes 3. Of course, the bump shape may be a shape as shown in FIGS. 2A to 2D, and the bump forming method illustrated in FIG. 6 and other well-known bump forming methods may be employed.

The bumps 8 are formed on each of the terminal electrodes 3 of the electronic circuit element 2, and the electronic circuit element 2 is connected to a circuit board (not shown) by a flip chip bonding method. During this connection, each bump 8 on the bottom surface of the element is deformed by being pressed against the conductor of the circuit board.

Although it is difficult to equalize the pressing force applied to each bump 8 due to the relationship between the number and position of the bumps 8,
Since the tip portion A of the bump 8 has a coarse-grained crystal structure having low strength and hardness, even when a pressing force is applied to each bump 8 during connection by the flip-chip bonding method, the stress received by the bump due to the pressing force is reduced. It is possible to prevent the entire shape of the bumps 8 from being largely collapsed by relaxing at the granular crystal structure portion A, and it is possible to secure the desired height dimension (corresponding to the distance between the terminal electrode and the conductor) for each bump 8. .

In the above-described embodiment, a bump having a coarse-grained crystal structure only at the tip portion of the bump is exemplified. However, a bump having a coarse-grained crystal structure as a whole can be formed as follows. .

That is, as shown in FIG. 5A, heat is applied by gas flame, electrostatic discharge or the like to a region from the tip of the wire 10 inserted into the hole 9a of the capillary 9 to a position away from the tip by a predetermined length. Then, the fine-grained crystal structure is recrystallized to form a coarse-grained crystal structure portion A2, and then, as shown in FIG. By forming the ball 10a, a bump having a coarse-grained crystal structure as a whole can be easily formed.

The coarse-grained crystal structure portion A of the wire 10
Ball 2 having a coarse-grained crystal structure by heating
Since 0a is formed, the ball 10a can be formed into a beautiful spherical shape without unevenness or distortion as compared with a case where a ball is formed at the tip of a wire not having the same portion. This avoids stress concentration when the ball 10a is pressed against the terminal electrode 3 of the electronic circuit element 2 and is pressed and shaped by the tip of the capillary, so that ball bonding to the terminal electrode 3 and ball shaping can be performed accurately and stably. Can be.

Since the bumps thus formed have a coarse-grained crystal structure with low strength and hardness as a whole, even if a pressing force is applied to each bump at the time of connection by the flip chip bonding method, the pressing force is not changed. The stress received by the bumps is reduced by the coarse-grained crystal structure,
It is possible to prevent the entire shape of the bumps from being largely collapsed, and it is possible to ensure the desired height dimension (corresponding to the distance between the terminal electrode and the conductor) for each bump.

As described above, in each of the first and second embodiments, an example in which a bump is formed on a terminal electrode of an electronic circuit element has been described. The effect can be obtained.

[0042]

As described above in detail, according to the first aspect of the present invention, the maximum external dimension w and the height dimension h of the bump are h / h.
Since w = 1 or h / w ≒ 1, even when a pressing force is applied to each bump at the time of connection by the flip chip bonding method, the stress applied to the bump by the pressing force is absorbed by the height dimension h. Therefore, it is possible to prevent the entire shape of the bump from being largely collapsed, and it is possible to secure an expected height dimension (corresponding to the distance between the terminal electrode and the conductor) for each bump.

According to the second aspect of the present invention, at least the tip portion of the bump has a coarse-grained crystal structure having low strength and hardness. The stress applied to the bumps by the pressing force is relieved in the coarse-grained crystal structure part, preventing the overall shape of the bumps from being significantly deformed. Each bump has the expected height (equivalent to the distance between the terminal electrode and conductor). ) Can be secured.

According to the third aspect of the present invention, the bump according to the second aspect can be formed accurately and stably. In addition, applying heat to the coarse-grained crystal structure portion of the wire to form a ball having a coarse-grained crystal structure as a whole causes the ball to be uneven or distorted, compared to forming a ball at the tip of the wire without the same portion It can be a beautiful spherical shape without
This avoids stress concentration when the ball is pressed against the bump forming partner and is pressed and shaped by the tip of the capillary, so that ball bonding and ball shaping to the bump forming partner can be performed accurately and stably.

[Brief description of the drawings]

FIG. 1 is a side view of a bump according to a first embodiment of the present invention.

FIG. 2 is a view showing another bump shape;

FIG. 3 is a side view of a bump according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a bump forming method.

FIG. 5 is a view showing another bump forming method.

FIG. 6 is a diagram showing a conventional bump forming method and a bump shape;

[Description of Signs] 1 ... Bump, 2 ... Electronic circuit element, 3 ... Terminal electrode, 4,
5, 6, 7: bump, 8: bump, A: coarse-grained crystal structure portion, 9: capillary, 9a: wire insertion hole, 10: wire, 10a: ball, A1, A2: coarse-grained crystal structure portion.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Ichitaka Suzuki 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Denki Co., Ltd.

Claims (3)

[Claims] In a flip chip bonding bump formed on a terminal electrode of an electronic circuit element, a conductor of a circuit board, or the like, a maximum external dimension w and a height dimension h of the bump are h / w = 1 or h / w /. A bump having a relationship of w ≒ 1. 2. A bump for flip-chip bonding formed on a terminal electrode of an electronic circuit element, a conductor of a circuit board, or the like, wherein at least a tip portion of the bump has a coarse-grained crystal structure. 3. A method of forming a ball by applying heat to a tip of a wire inserted into a hole of a capillary to form a ball, pressing the ball against a bump forming partner using a capillary, and then separating the ball from the wire. Bumps comprising: forming a ball having a coarse-grained crystal structure at least at a boundary between the wire and the ball by applying heat to the predetermined end of the wire to form coarse particles by recrystallization; Forming method.