JP3223804B2 - Method of forming bump - Google Patents

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 bump on an electrode of a work.

[0002]

2. Description of the Related Art As a method of forming bumps (protruding electrodes) on electrodes of a work such as an IC chip, a method using a wire bonding technique is known. Hereinafter, a conventional bump forming method will be described.

FIGS. 19 (a), (b), (c), (d) and FIG. 20 are explanatory views of a conventional bump forming method.
As shown in FIG. 19A, the lower end of the wire 2 is brought close by bringing the torch 3 closer to the lower end of the wire 2 led out from the capillary tool 1 and generating a spark between the torch 3 and the lower end of the wire 2. The ball 4 is formed. Reference numeral 5 denotes a cut clamper that is located above the capillary tool 1 and clamps the wire 2, and 6 is a tension clamper that is located above the cut clamper 5 and applies tension to the wire 2.

Next, as shown in FIG. 19B, the capillary tool 1 is lowered to press the ball 4 against the electrode of the work 7. Reference numeral 8 denotes a base on which the work 7 is placed. Next, as shown in FIG. 19 (c), the capillary tool 1 is slightly raised to derive a wire 2 (referred to as a tail) having a length necessary for the next ball formation from the lower end of the capillary tool 1. The wire 2 is firmly clamped by the cut clamper 5. Next, as shown in FIG. 19D, by raising the cut clamper 5 and the capillary tool 1 while clamping the wire 2, the wire 2 is cut immediately above the ball 4 to complete a series of operations, and the work 7 is completed. A bump 4 is formed on the electrode.

[0005]

FIG. 20 is a block diagram of FIG.
In the step shown in (c), after bonding the ball 4 to the electrode 7a of the work 7, the wire 2 is clamped by the cut clamper 5, and the wire 2 is pulled up to cut the wire 2 in an enlarged manner. I have. a is a cutting line, 1a is a center hole of the capillary tool 1 through which the wire 2 is inserted. When the wire 2 is lifted, the wire 2 is forcibly cut from the cutting line a immediately above the ball 4. At this time, the ball (bump) 4 and the electrode 7
A large tensile stress is generated at the joint surface a, so that the ball (bump) 4 is easily peeled off from the electrode 7a, and the lower surface of the ball (bump) 4 is easily damaged. In FIG. 20, a black portion on the lower surface of the ball 4 indicates a damaged portion.

Accordingly, it is an object of the present invention to provide a method of forming a bump at which a ball at the lower end of a wire can be firmly bonded to an electrode of a work and the lower surface of the ball (bump) is not damaged.

[0007]

For this purpose, the present invention provides a step of forming a ball by sparking by approaching a torch to a lower end of a wire which is inserted through a center hole of a capillary tool and led out downward, and Lowering the capillary tool while clamping it with the cut clamper brings the ball closer to the workpiece electrode, cutting the wire directly above the ball, and further lowering the capillary tool to press the ball against the workpiece electrode. A method for forming a bump is constituted by a bonding step and a step of pressing the upper surface of the ball bonded to the electrode of the work with a pressing jig.

[0008]

According to the present invention, the wire is cut before bonding the ball at the lower end of the wire to the electrode of the work, and then the ball is pressed against the electrode of the work for bonding. The lower surface of (1) is not damaged, and the bump can be formed by firmly bonding the ball to the electrode of the work.
By pressing the upper surface of the bump with a pressing jig, the tail protruding from the bump is crushed, and the height of the upper surface of the bump can be made uniform.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a side view of a bump forming apparatus according to an embodiment of the present invention, and FIG. 2 is a partial perspective view of the bump forming apparatus. 3 to 16 are process charts for forming the bumps, which are shown in the order of the processes. FIG. 17 is a partially enlarged sectional view of the capillary tool at the time of wire cutting in the bump forming step.

First, the overall structure of a bump forming apparatus will be described with reference to FIGS. In FIG. 1, reference numeral 11 denotes a horn, and a capillary tool 12 is held at the tip of the horn. The capillary tool 12 is a hollow cylindrical body, and a wire 13 is provided in a center hole 12a (see FIG. 17).
Is inserted. An ultrasonic oscillator 34 is attached to the base end of the horn 11. An upward tension is always applied to the wire 13 by a tension mechanism (not shown).

The horn 11 is mounted on a bearing 16 integrally with a swing arm 15 so as to be swingable up and down around a pin 17. Reference numeral 18 denotes a base for the bearing 16. Swing arm 1
A roller 19 is mounted on the rear end of the roller 5. Roller 1
9 is in contact with the cam 20. Reference numeral 21 denotes an elastic spring for bringing the roller 19 into contact with the cam 20. When the motor 22 is driven to rotate the cam 20, the swing arm 15 and the horn 11 swing vertically about the pin 17 as a unit, whereby the capillary tool 12 performs a vertical movement. That is, the roller 19, the cam 20, the spring 2
1, a motor 22 and the like are a vertical movement mechanism that causes the horn 11 and the capillary tool 12 to perform a vertical movement. The vertical movement mechanism may be a mechanism using a linear motor or a voice coil or a mechanism using a ball screw type feed mechanism.

A bar 23 is pivotally mounted on a pin 24 at the tip of the swing arm 15 so as to be rotatable in the vertical direction. Bar 2
An actuator 25 is attached to the tip of the actuator 3. 2, the actuator 25 holds a pair of left and right tension clampers 26. A clamp 27 is mounted on the inner surface of the tension clamper 26.
When the actuator 25 is driven, the tension clamper 26 opens and closes, but when the tension clamper 26 is closed, the clamp portion 27 lightly clamps the wire 13.
Can slide in its length direction (vertical direction).
The clamp 27 holds the wire 1 in the clamped state.
3 is specially provided so as to be able to slide in the vertical direction, and as a material thereof, for example, an elastic material such as felt or an elastic resin can be used.

In FIG. 1, the rear end of the bar 23 is connected to the upper surface of the swing arm 15 via a piezoelectric element 35. The piezoelectric element 35 has the property of expanding and contracting when a voltage is applied. Therefore, when the piezoelectric element 35 expands and contracts, the bar 23 swings up and down around the pin 24.
That is, the piezoelectric element 35 serves as up / down movement means for vertically moving the bar 23 and the tension clamper 26 independently of the horn 11. By moving the tension clamper 26 up and down independently of the horn 11 in this manner, the tailing of the wire 13 (the operation of leading the lower end of the wire 13 to the predetermined length from the lower end of the capillary tool 12) is performed. When the motor 20 is driven and the swing arm 15 swings up and down, the bar 23 swings integrally with the horn 11 and the tension clamper 26
Moves up and down integrally with the capillary tool 12.

In FIG. 2, a cut clamper 28 is provided above the tension clamper 26. The cut clamper 28 is held by an actuator 29, and opens and closes when the actuator 29 is driven.
The wire 13 is clamped and released. The clamp 30 mounted on the inner surface of the cut clamper 28
The wire 13 is made of a hard material such as stainless steel.
Clamp tightly. The actuator 29 is fixed to the shaft 31. Conventionally, as shown in FIG. 19, the tension clamper is provided above the cut clamper. In contrast, in this bump forming apparatus, the tension clamper 26 is provided below the cut clamper 28,
In addition, the clamp 27 described above is attached to the tension clamper 26.
With such a characteristic configuration, it is possible to perform an operation of fitting and holding a ball 14, which will be described later, at a lower end portion of a center hole 12 a of the capillary tool 12, and an operation of taking out a tail of the wire 13. ing.

Reference numeral 36 denotes a torch. The tip of the torch is brought close to the lower end of the wire 13 extending from the lower end of the capillary tool 12, and a high voltage is applied to the torch 36 in this state to make the torch lower. A spark is generated between the wires 13 to form a ball 14 at the lower end of the wire 13.
Reference numeral 10 denotes a chip as a work, and a receiving table 33 (FIG. 1).
It is placed on. As shown in FIG. 2, a large number of electrodes 10a are formed on the upper surface of the chip 10, and bumps 14 are formed on these electrodes 10a as described later.

This bump forming apparatus is configured as described above. Next, a method for forming a bump will be described with reference to FIGS. First, as shown in FIG. 3, with the capillary tool 12 positioned above the tip 10, the torch 3
6 is brought close to the lower end of the wire 13 leading out of the capillary tool 12, and then a spark is generated between the torch 36 and the lower end of the wire 13 as shown in FIG. Ball 14 having an outer diameter larger than the inner diameter of the 12 central holes 12a
To form 3 and 4, the tension clamper 26 and the cut clamper 28 are both closed to clamp the wire 13.

Next, the cut clamper 28 is opened to release the clamped state (FIG. 5), and then the motor 22 is driven to swing the swing arm 15 downward. Then, the capillary tool 12 and the tension clamper 26 descend toward the chip 10 (FIG. 6). At this time, the piezoelectric clamp 35 is driven to raise the tension clamper 26 relatively to the capillary tool 12. The raising operation of the tension clamper 26 is a preparation operation for a tailing step of the wire 13 to be performed later, and enables the tension clamper 26 to hold the wire 13 and approach the capillary tool 12 in the tailing step. Do it for

The wire 13 rises relatively to the capillary tool 12 by the raising operation of the tension clamper 26, and the ball 14 is fitted so that the capillary tool 12 bites into the center hole 12a of the capillary tool 12 ( (FIG. 7).

Next, when the ball 14 approaches the work 10, the cut clamper 28 closes and clamps the wire 13 firmly (FIG. 8). In this state, the capillary tool 1
When the wire 2 is further lowered, the wire 13
8 is tightly clamped, so that the wire 13
Is cut off by the capillary tool 12 (FIG. 9). Of course, this cutting by tearing may be performed by firmly clamping the wire 13 with the cut clamper 28 and pulling it up. In short, the capillary tool 12 is connected to the ball 1 of the wire 13.
It is only necessary to lower relative to 4.

FIG. 17 shows an enlarged cross section near the lower end of the capillary tool 12 at the time of this cutting. In the process shown in FIG. 4, the ball 14 is formed at the lower end of the wire 13 by sparking. At the time of this spark, the vicinity of the lower end of the wire 13 is heated to a high temperature by Joule heat of the internal current. The ball 14 is formed by melting the wire 13 due to the high temperature. Since the vicinity of the lower end of the wire 13 is heated to a high temperature, the structure of the wire 13 is weakened. Therefore, when tension is applied to the wire 13, the wire 13 is placed at a position immediately above the ball 14 shown in FIG. It will be cut. FIG.
7, the ball 14 is fitted and held at the lower end of the center hole 12a.

Next, as shown in FIG. 10, the capillary tool 12 descends to move the ball 14 to the electrode 10a of the chip 10.
And bonding. Next, cut clamper 8
After opening, the capillary tool 12 and the tension clamper 26 rise integrally (FIGS. 11 and 12). Thereby, bumps (balls) are formed on the electrodes 10a of the chip 10.
14 is formed. At this time, since the wire 13 is clamped by the tension clamper 26, it rises together.

Next, with the cut clamper 28 opened,
Only the tension clamper 26 descends independently of the horn 11, so that the lower end of the wire 13 is led out from the lower end of the capillary tool 12, and the tail of the wire 13 is taken out (FIGS. 13 and 14). Cut clamper 2
When 8 is closed, it returns to the initial state of FIG. Thus, the bump forming operation is completed. As shown in FIG. 2, on the upper surface of the chip 10, there are many electrodes 10a,
Therefore, by repeating the above operation for one chip 10, bumps 14 are sequentially formed on all the electrodes 10a. 13 and 14, the ultrasonic oscillator 34 is driven to drive the capillary tool 12
Is ultrasonically vibrated, the wire 13 can be easily led out from the lower end of the capillary tool 12.

Bump 1 bonded to work 10
4 from the top of the tail 13 '(cut off the wire 13)
Tend to protrude (see FIG. 13). Therefore, as shown in FIG. 16, the tail 13 'is crushed to make the bumps 14 uniform in height. In FIG. 16, reference numeral 37 denotes a cylinder as a pressing jig.
Is provided. Accordingly, the tail 13 ′ is crushed by the presser 39 by lowering the presser 39 by projecting the rod 38. In this case, preferably, the work 1
A heater 41 is incorporated in the receiving table 40 on which the workpiece 0 is placed, and the work 10 and the tail 13 ′ are heated by the heat of the heater 41, so that the tail 13 ′ is easily crushed. Of course, in this case, when the tail 13 ′ is crushed by the pressing jig on the receiving table 33, a heater is built in the receiving table 33.

FIG. 18 is a process chart of forming a bump according to another embodiment of the present invention. In FIG. 16, the tails 13 ′ of the bumps 14 are crushed one by one by the pressers 39, but in FIG. 18, the plurality of bumps 14 bonded to the work 10 are Of the tail 13 'is crushed at once. Of course, also in this case, the work 10 and the tail 13 'are desirably heated by the heater. The step of crushing the tail 13 'shown in FIGS. 16 and 18 may be performed at any time after the step shown in FIG. 15 is completed.

[0025]

According to the present invention, the wire is cut before bonding the ball at the lower end of the wire to the electrode of the work, and then the ball is pressed against the electrode of the work for bonding. The lower surface is not damaged and the ball can be firmly bonded to the electrode of the work. By pressing the upper surface of the bump with a pressing jig, the tail protruding from the bump is crushed, and the height of the upper surface of the bump can be made uniform.

[Brief description of the drawings]

FIG. 1 is a side view of a bump forming apparatus according to an embodiment of the present invention.

FIG. 2 is a partial perspective view of a bump forming apparatus according to an embodiment of the present invention.

FIG. 3 is a process chart of forming a bump according to an embodiment of the present invention;

FIG. 4 is a process diagram of forming a bump according to an embodiment of the present invention;

FIG. 5 is a process diagram of forming a bump according to an embodiment of the present invention;

FIG. 6 is a process chart of forming a bump according to an embodiment of the present invention;

FIG. 7 is a process chart of forming a bump according to an embodiment of the present invention;

FIG. 8 is a process diagram of forming a bump according to an embodiment of the present invention.

FIG. 9 is a process chart of forming a bump according to an embodiment of the present invention;

FIG. 10 is a process chart of forming a bump according to an embodiment of the present invention;

FIG. 11 is a process chart of forming a bump according to an embodiment of the present invention;

FIG. 12 is a process chart of forming a bump according to an embodiment of the present invention;

FIG. 13 is a process chart of forming a bump according to an embodiment of the present invention.

FIG. 14 is a process chart of forming a bump according to an embodiment of the present invention;

FIG. 15 is a process chart of forming a bump according to an embodiment of the present invention;

FIG. 16 is a process chart of forming a bump according to an embodiment of the present invention;

FIG. 17 is a partially enlarged cross-sectional view of a capillary tool at the time of wire cutting in a bump forming step according to an embodiment of the present invention.

FIG. 18 is a process diagram of forming a bump according to another embodiment of the present invention;

FIG. 19A is an explanatory view of a conventional bump forming method. FIG. 19B is an explanatory view of a conventional bump forming method. FIG. 19C is an explanatory view of a conventional bump forming method.

FIG. 20 is an explanatory view of a conventional bump forming method.

[Explanation of symbols]

 Reference Signs List 10 chip (work) 11 horn 12 capillary tool 12a center hole 13 wire 13 'tail 14 ball (bump) 15 swing arm 20 cam 21 spring 22 motor 26 tension clamper 27 clamp unit 28 cut clamper 35 piezoelectric element 36 torch 37 pressing jig Tool (cylinder)

Continuation of the front page (56) References JP-A-9-148381 (JP, A) JP-A-7-122560 (JP, A) JP-A-5-275428 (JP, A) JP-A-62-154648 (JP) , A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01L 21/60

Claims (1)

(57) [Claims] 1. A step of forming a ball by sparking by approaching a torch to a lower end of a wire that is inserted through a center hole of a capillary tool and extends downward, and lowers the capillary tool with the wire clamped by a cut clamper. Causing the ball to approach the electrode of the work by cutting the wire, and cutting the wire directly above the ball; further lowering the capillary tool to press the ball against the electrode of the work for bonding; and Pressing the upper surface of the bonded ball with a pressing jig.