JPH04214631A - Method of forming bump - Google Patents

Abstract

PURPOSE:To improve the adhesive strength in the case that a semiconductor element is mounted on a wiring board by a bump and to make electric resistance small. CONSTITUTION:A gourd-shaped or ellipsoidal ball 50 is made at the top 1a of the wire 1 led out to the top of a capillary 9, and this ball 50 is pressure- bonded to the aluminum pad 4 of an IC chip 5, and then the wire 1 extended from this pressure-bonded ball 50 is cut.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming bump electrodes on electrode pads of semiconductor devices.

0002

2. Description of the Related Art Conventionally, as a method for electrically connecting a liquid crystal panel constituting a liquid crystal display device and its driving IC, bump electrodes are formed on the electrode pads of the driving IC, and the bump electrodes are made electrically conductive. A method of adhesively mounting a liquid crystal glass substrate with an adhesive (COG method) has become a desirable method from the viewpoint of miniaturization of a liquid crystal display device and mounting cost. On the other hand, as a method for forming bump electrodes on the electrode pads of the driving IC, there is a method of gold plating through a barrier metal. However, this method requires a special formation process, and when forming bump electrodes on the electrode pads of the driving IC, a wire bonder that is generally used in the manufacture of semiconductor devices is used.

FIGS. 3A and 3B are step-by-step sectional views showing a conventional method for forming bump electrodes. As shown in FIG. 3(a), a discharge phenomenon is generated between the gold (Au) wire 1 drawn out from the tip of the capillary 14 and the discharge electrode 10, and the thermal energy caused by this discharge causes the tip of the gold wire 1 to 1
a is instantly melted. As a result, a ball 2 is formed at the tip 1a of the gold wire 1, as shown in FIG. 3(b).

Next, as shown in FIG. 3(c), as the capillary 14 descends, the ball 2 is pressed onto the aluminum (Al) pad 4 of the IC chip 5, and heat and ultrasonic vibration are applied thereto. As a result, the ball 2 is bonded onto the aluminum pad 4. Note that this process is the same as wire bonding for normal semiconductor devices.

[0005] Then, by raising the capillary 14 to a predetermined position and moving it slightly laterally,
Deals shearing damage to Gold Wire 1. Next, Figure 3(d)
As shown in the figure, the capillary 14 and the wire clamp (
(not shown), the gold wire 1 is torn off from the part where shear damage has been caused. As a result, bump electrodes 13 are formed on aluminum pads 4.

Thereafter, the irregularly shaped portion of the upper portion 13' of the bump electrode 13 is pressed and flattened to complete the formation of the bump electrode 13. The size of the bump electrode 13 formed in this way is approximately 50 [μ] in diameter of the head 13a.
m] and height approximately 25 [μm], and the maximum diameter is approximately 9 [μm].
It is 0 [μm]. Bump electrode 1 formed in this way
A method for mounting an IC chip 5 having a 3.0-inch structure on a liquid crystal glass substrate will be described below with reference to FIGS. 4(a) and 4(b).

As shown in FIG. 4(a), an IC chip 5
is held with the bump electrode 13 facing downward. Then, the conductive adhesive 20 is transferred to the bump electrode 13 by dipping the bump electrode 13 into an extremely thinly spread conductive adhesive (not shown). Next, as shown in FIG. 4(b), the IC chip 5 with the conductive adhesive 20 transferred to the bump electrode 13 and the ITO layer provided on the liquid crystal glass substrate 7 are assembled.
After aligning with the film pattern 8, the bump electrodes 13 are pressed against the ITO film pattern 8 with a predetermined pressure to be bonded. Then, apply the conductive adhesive 6 to a temperature of about 10°C.
The conductive adhesive 20 is cured by heat treatment at 0 [° C.] for one hour, and thereby the IC chip 5 is bonded to the liquid crystal glass substrate 7.

[0008]

However, when bonding the bump electrode 13 formed by such a conventional bump electrode forming method to the ITO film pattern 8 of the liquid crystal glass substrate 7, the viscosity of the conductive adhesive 20, The conductive adhesive transferred to the bump electrode 13 may be caused by variations in properties such as thixotropy and viscosity of the conductive filler, variations in the thickness of the conductive adhesive spread extremely thinly, or variations in the height of the bump electrode 13. There was a problem in that the transferred amount of the agent 20 varied widely.

For example, a bump electrode 13 with a small amount of conductive adhesive 20 transferred as shown in FIG. 4(c) is bonded to an ITO film pattern 8 provided on a liquid crystal glass substrate 7 as shown in FIG. 4(d). In this case, the conductive adhesive 20 will not spread sufficiently between the bump electrode 13 and the ITO film pattern 8. As a result, the electrical resistance between the bump electrode 13 and the ITO film pattern 8 increases, and also, because sufficient adhesive strength cannot be obtained between the IC chip 5 and the liquid crystal glass substrate 7, separation occurs between the two. There was a problem.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a method for forming bump electrodes that can obtain sufficient adhesive strength and reduce electrical resistance when a semiconductor element is mounted on a wiring board. It is to provide.

[0011]

A method for forming a bump electrode according to claim 1 is characterized in that a gourd-shaped or slender spherical ball is formed at the tip of a thin metal wire. The method for forming a bump electrode according to claim 2 is the method for forming a bump electrode according to claim 1, in which a spherical ball is formed by heating and melting the tip of the thin metal wire with thermal energy by flame or electric discharge. Thereafter, the fine metal wire on the top of the ball is heated and melted by flame or thermal energy from electric discharge to form a ball, thereby forming a gourd-shaped or elongated spherical ball.

The method for forming a bump electrode according to claim 3 comprises:
In the method for forming a bump electrode according to claim 1, after the thin metal wire between the tip of the thin metal wire and the capillary is heated and melted by thermal energy by flame or electric discharge in the vicinity of the tip of the thin metal wire and then spheroidized. It is characterized by forming a gourd-shaped or elongated spherical ball by heating and melting the tip of a thin metal wire with heat energy from flame or electric discharge to make it spherical.

[0013]

[Operation] According to the structure of the present invention, by forming a gourd-shaped or elongated spherical ball at the tip of the thin metal wire,
The height of the bump electrode formed on the electrode pad of the semiconductor element can be increased. Therefore, in order to mount a semiconductor element on which bump electrodes are formed on a wiring board,
When the conductive adhesive is transferred to the bump electrode, the absolute amount of the conductive adhesive transferred can be significantly increased compared to the conventional method, and the variation in the transferred amount can be reduced.

[0014]

[Example] An example of this invention is shown in Figs. 1(a) to (f).
This will be explained based on FIGS. 2(a) to 2(d). FIGS. 1A to 1F are step-by-step sectional views showing a method for forming a bump electrode according to an embodiment of the present invention.

As shown in FIG. 1(a), the capillary 9
A gold wire 1, which is a fine metal wire, is fed out from a metal wire, and a discharge electrode 10.
A discharge phenomenon is generated between the metal wire 1 and the metal wire 1, and the thermal energy generated by the discharge heats and melts the tip portion 1a of the gold wire 1. As a result, a spherical ball 2 is formed at the tip 1a of the gold wire 1, as shown in FIG. 1(b). Furthermore, this ball 2
The formation process is the same as wire bonding in a normal semiconductor device manufacturing method. Further, the tip portion 1a of the gold wire 1 may be heated using a flame.

Next, as shown in FIG. 1(c), the gold wire 1 on the top of the ball 2 is heated and melted for a very short period of time by the thermal energy of the hydrogen flame 12, thereby making it spherical. As a result, the spherical part 2' partially overlaps the top of the ball 2 formed in the step of FIG. 1(a), and as a result, as shown in FIG. The ball 50 thus formed has a gourd shape with a constricted central portion. The gold wire 1 above the ball 2 may be heated using thermal energy generated by electric discharge.

Next, as shown in FIG. 1(e), the capillary 9 is lowered and the gourd-shaped ball 50 is inserted into the IC chip 5.
By pressing the ball 50 onto the aluminum pad 4 and applying heat and ultrasonic waves, the ball 50 is placed on the aluminum pad 4.
Bond to. Then, as shown in Fig. 1(f), the capillary 9 is raised to a predetermined position and then moved slightly laterally to cause shear damage to the gold wire 1, and then the capillary 9 is moved as shown in Fig. 1(f). As shown, a capillary 9 and a wire clamp (not shown) are operated to tear off the gold wire 1 at the position where shear damage has been caused, thereby forming a bump electrode 3 having a height of about 60 [μm].

A method for mounting the IC chip 5 having the bump electrodes 3 thus formed on a liquid crystal glass substrate serving as a wiring substrate will be described below with reference to FIGS. 2(a) to 2(d). As shown in FIG. 2(a), after transferring the conductive adhesive 6 to the bump electrodes 3 in the same manner as in the conventional method, as shown in FIG. 2(b), the bump electrodes 3 of the IC chip 5 are transferred.
IC chip 5 is mounted on liquid crystal glass substrate 7 by aligning and applying pressure and heating to ITO film pattern 8 of liquid crystal glass substrate 7 .

At this time, the conductive adhesive 6 is attached to the bump electrode 3.
The amount of transfer varies, as shown in FIGS. 2(a) and 2(c). This may be due to variations in the characteristics of the conductive adhesive 6, variations in the thickness of the conductive adhesive (not shown) spread extremely thinly for transfer to the bump electrodes 3, or variations in the height of the bump electrodes 3. It is caused by However, since the height of the bump electrode 3 is high, the absolute amount of the conductive adhesive 6 transferred to the bump electrode 3 due to the surface tension of the conductive adhesive 6 becomes significantly larger than that in the past. Therefore, as shown in FIG. 2(c), even if the amount of conductive adhesive 6 transferred to the bump electrode 3 is smaller than that in FIG. 2(a), as shown in FIG. 2(d), Bump electrode 3 and I
The bonding area of the conductive adhesive 6 with the TO film pattern 8 is almost the same as the bonding area of the standard conductive adhesive 6 shown in FIG. 2(c), and a sufficient bonding area can be obtained. .

As a result, sufficient adhesive strength can be obtained between the bump electrode 3 and the ITO film pattern 8, and electrical resistance can also be reduced. In the embodiment, the ball 50 formed at the tip 1a of the gold wire 1 has a gourd shape with a constricted central portion, but it may also have an elongated spherical shape. In addition, in the example, after forming the spherical ball 2 on the tip 1a of the gold wire 1, the gourd-shaped ball 50 was formed by sphericalizing the gold wire 1 on the top of the ball 2. After the gold wire 1 between the tip 1a of the gold wire 1 and the capillary 9 is heated and melted near the tip 1a of the wire 1 by heat energy from flame or electric discharge to form a sphere, the tip of the gold wire 1 is heated and melted. A gourd-shaped or elongated spherical ball may be formed by heating and melting 1a with thermal energy from flame or electric discharge to make it spherical.

[0021]

[Effects of the Invention] According to this method for forming a bump electrode, a gourd-shaped or slender spherical ball is formed at the tip of a thin metal wire, thereby forming a tall bump electrode on an electrode pad of a semiconductor element. be able to. Therefore, when the conductive adhesive is transferred to this bump electrode, the absolute amount of the conductive adhesive transferred can be significantly increased compared to the conventional method, and the variation in the transferred amount can be reduced.

As a result, when the semiconductor element on which the bump electrodes are formed is mounted on a wiring board, it is possible to increase the bonding area between the bump electrodes and the wiring board using the conductive adhesive. Thereby, sufficient adhesive strength can be ensured between the semiconductor element and the wiring board, electrical resistance can be reduced, and reliability of the device can be improved.

[Brief explanation of the drawing]

FIG. 1 is a step-by-step sectional view showing a method for forming a bump electrode according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view for explaining how an IC chip having bump electrodes to which the bump electrode forming method of one embodiment of the present invention is applied is mounted on a liquid crystal glass substrate.

FIG. 3 is a step-by-step sectional view showing a conventional method for forming a bump electrode.

FIG. 4 is a partial cross-sectional view for explaining how an IC chip having bump electrodes is mounted on a liquid crystal glass substrate using a conventional bump electrode forming method.

[Explanation of symbols]

1 Thin metal wire (gold wire) 1a Tip 2 Ball 9 Capillary 50 balls

Claims (3)

[Claims] Claim 1: A step of forming a ball at the tip of a thin metal wire led out to the tip of a capillary, a step of crimping the ball onto an electrode pad of a semiconductor element, and cutting the thin metal wire extending from the crimped ball. A method for forming a bump electrode, the method comprising: forming a gourd-shaped or elongated spherical ball at the tip of the thin metal wire. 2. After forming a spherical ball by heating and melting the tip of the thin metal wire using thermal energy generated by flame or electric discharge, the thin metal wire above the ball is heated by thermal energy generated by flame or electric discharge. 2. The method for forming a bump electrode according to claim 1, wherein the gourd-shaped or elongated spherical ball is formed by melting and spheroidizing the ball. 3. After the thin metal wire between the tip of the thin metal wire and the capillary is heated and melted near the tip of the thin metal wire by flame or thermal energy from electric discharge to make it spheroidized, the thin metal wire is spheroidized. 2. The method of forming a bump electrode according to claim 1, wherein the gourd-shaped or slender spherical ball is formed by heating and melting the tip of the bump electrode using thermal energy generated by flame or electric discharge to make the ball spherical.