JPH10135217A - Method of forming bumps - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably form bumps of a specified shape, by depositing a conductor paste on bump forming regions and radiating a laser beam on the paste. SOLUTION: For forming bumps a conductor paste P is deposited in a specified shape on terminal electrodes 2; the shape depending on a paste depositing means is pref. circular columnar, drum-like, truncated circular conical, or semi- spherical in approximately fixed size. A laser beam LB is radiated through an optical system on the paste P deposited on the electrodes 2 to apply a thermal energy on the entire deposited paste P enough to evaporate solvents in the paste and thermally decompose a binder, thus baking the paste P and hence forming bumps 3 of a shape corresponding to the deposited paste P on the electrodes 2. Thus, bumps are formed in a simple procedure and stably in the shape corresponding to the paste deposition shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bump forming method for forming a connecting bump (projecting conductor) on an electronic circuit element or a circuit board.

[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 FIG. 1C, only the capillary 101 is moved upward, and further moved laterally from the raised position. At this time, the amount of movement of the capillary 101 in the lateral direction is set so that the center of the wire insertion hole 101a does not move outside the deformed ball 102a. Further, the horizontal movement causes the hole 1 of the capillary 101 to move.
01a is pulled out by a length corresponding to the amount of movement.

Next, as shown in FIG. 1D, the capillary 101 is moved downward from the lateral movement position, and the pulled-out wire 102 is pushed into the ball 102 by 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. 1E, 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.

[0009]

In the conventional bump forming method, not only the method illustrated in FIG. 2 but also a considerable amount of pulling force is applied to the wire to separate the wire from the ball.
Variations are likely to occur in the wire cutting position, and if the cutting position is too close to the ball, problems such as formation of a dent in the ball and distortion of the overall shape will occur.

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 forming method capable of stably forming a bump having a predetermined shape.

[0011]

In order to achieve the above object, a bump forming method according to the present invention includes a step of attaching a conductive paste to a bump forming partner and a step of irradiating the attached paste with a laser beam. That is its main feature.

According to this bump forming method, the conductive paste adhered to the bump forming partner is irradiated with a laser beam to apply heat energy to the adhered paste and sinter the paste to form a shape corresponding to the shape of the adhered paste. A bump can be formed on a bump forming partner.

[0013]

FIG. 1 shows an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an electronic circuit element such as an IC or LSI, and FIG.
Denotes a terminal electrode provided on the bottom surface of the element, 3 denotes a bump, P denotes a conductive paste, and LB denotes a laser beam.

In forming a bump, first, FIG.
As shown in (2), a conductive paste P is adhered to the terminal electrode 2 in a predetermined shape. The shape of the conductive paste P to be applied varies depending on the means of applying the paste. However, the conductive paste P should be formed in a substantially constant size such as a cylinder, a drum, a truncated cone, or a hemisphere.

The conductor paste includes Au, Ag, Cu, A
Examples thereof include those prepared by mixing an organic solvent and a binder such as a cellulose derivative with a metal powder selected from g-Pt, Ag-pd, and the like, and those prepared by adding a glass frit such as lead borosilicate to this. The glass frit is used to increase the adhesion between the bump 3 and the terminal electrode 2. Preferably, a glass frit having a softening point of 400 to 700 ° C. is added to the metal powder in an amount of 5 to 20 vol%.

In addition, a known thick film printing method typified by screen printing can be used for attaching the conductive paste P, and a method of extruding the conductive paste from the tip of a small-diameter nozzle and attaching it can be used.

Next, as shown in FIG. 1B, the conductor paste P attached to the terminal electrode 2 is irradiated with a laser beam LB via an optical system (not shown).

The laser beam LB is a YAG laser beam, more specifically, a continuous pulse wave having a wavelength of 1064.1 nm and an output of 0.4.
A YAG laser beam having a frequency of 3 to 7 KHz is used. The laser light irradiation conditions are appropriately changed depending on the paste components, but are basically set so that heat energy for firing can be applied to the adhered paste P.

By this laser beam irradiation, thermal energy is applied to the entirety of the paste P, the solvent in the paste evaporates, the binder is thermally decomposed, and the paste P is baked. The bump 3 is formed on the terminal electrode 2.

In the case of the conductor paste P containing glass frit, the glass frit is softened by thermal energy at the time of laser beam irradiation, and a glass-excess layer is generated near the interface with the terminal electrode 2, and the terminal electrode 2 and the bump are bumped. 3 improves the adhesion.

Although the desired bump 3 can be formed by the above procedure, in order to further improve the adhesion of the bump 3 to the terminal electrode 2, as shown in FIG.
It is preferable to further heat-treat the bumps 3.

For the heat treatment, a heating furnace, more specifically, a heating furnace equipped with a heater and a conveyor belt and maintained at a temperature of 400 to 600 ° C. is used. The heat treatment conditions are appropriately changed depending on the paste components, but are basically set so that heat energy for improving adhesion can be applied to the baked paste 3.

By this heat treatment, heat energy is applied to the entire baked paste 3, and the bonding force between the metal particles in the paste and the bonding force between the metal particles and the terminal electrode 2 are increased.
The bump 3 firmly adheres to the terminal electrode 2.

As described above, according to the above-described bump forming method, the bumps 3 can be formed on the terminal electrodes 2 by a simple procedure of simply irradiating the adhesive paste P with the laser beam LB, and the conductive paste can be formed. The bump 3 having a shape corresponding to the shape of the P can be stably obtained.

Moreover, if the conductor paste P containing glass frit is used, the adhesion between the terminal electrode 2 and the bump 3 can be improved by the excess glass layer generated near the interface between the terminal electrode 2 and the bump 3. it can.

Further, by further applying a heat treatment to the bumps 3, the adhesion of the bumps 3 to the terminal electrodes 2 can be further increased, and the bonding between the bumps 3 and the terminal electrodes 2 can be strengthened.

In the above-described embodiment, an example in which a bump is formed on a terminal electrode of an electronic circuit element is illustrated. However, a bump can be formed on a conductor of a circuit board by the same procedure.

Further, if a laser light absorption promoter such as carbon, an organic dye, and a low melting point metal powder is added to the conductive paste, the laser light absorption of the adhered paste is increased, thereby improving the processing efficiency by laser light irradiation. Can be.

[0029]

As described in detail above, according to the present invention,
A bump can be formed on the bump forming partner by a simple procedure of simply irradiating the adhesive paste with laser light, and a bump having a shape corresponding to the shape of the conductive paste can be stably obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a bump forming method according to the present invention.

FIG. 2 is a view showing a conventional bump forming method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electronic circuit element, 2 ... Terminal electrode, 3 ... Bump, P ... Conductor paste, LB ... Laser light.

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

Claims (4)

[Claims] 1. A method for forming a bump, comprising: attaching a conductive paste to a bump forming partner; and irradiating the attached paste with laser light. 2. The bump forming method according to claim 1, further comprising a step of applying heat to the paste after the laser beam irradiation. 3. The bump forming method according to claim 1, wherein the conductive paste contains glass frit. 4. The bump forming method according to claim 1, wherein the conductive paste contains a laser light absorbing agent.